ArticleLiterature Review

Consequences of Under- and Over-humidification

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Abstract

Respiratory mucosal and lung structures and functions may be severely impaired in mechanically ventilated patients when delivered gases are not adequately conditioned. Although under- and over-humidification of respiratory gases have not been defined clearly, a safe range of temperature and humidity may be suggested. During mechanical ventilation, gas entering the trachea should reach at least physiologic conditions (32 degrees C-34 degrees C and 100%relative humidity) to keep the ISB at its normal location. Clinicians must keep in mind that relative humidity is more important than absolute humidity: the warmer the gas, the higher the risk of tracheal mucosa dehydration and proximal airway obstruction. Practical assessment of the adequacy of the humidification system in use is not easy. The consistency (thin, moderate, or thick) of the patient's sputum should be evaluated regularly [47]. Full saturation of inspiratory gases is likely when water condensation is observed in the flex tube [91,92]. Nevertheless, no clinical parameter is accurate enough to detect all the effects of inadequate conditioning [45]. When mechanical ventilation is extended beyond several days, adequate conditioning of respiratory gases becomes increasingly crucial to prevent retention of secretions and to maximize mucociliary function; a requirement that respiratory gases reach at least physiologic conditions is appropriate.

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... For mechanically ventilated patients, respiratory gases need to be appropriately heated and humidified to avoid complications, such as endotracheal tube obstruction and atelectasis (Restrepo and Walsh 2012;Williams et al 1996). Excessive humidification may also cause loss of mucosal function, airway oedema, and bronchial spasm (Pillow et al 2009;Sottiaux 2006;Williams et al 1996). The International Organization for Standardization recommends preparation of respiratory gases close to 100% humidity at 37°C (44mg/L), or at least to 75% of this level (33mg/L) during mechanical ventilation (ISO 8185:2007 Respiratory tract humidifiers for medical use. ...
... These patients are generally under unstable cardiopulmonary conditions, most of whom require mechanical ventilation. Because saturated vapour is temperature-dependent, it reduces under hypothermic conditions (e.g., to 36.6mg/L at 33.5°C) (Sottiaux 2006). However, currently, a humidifier setting for normothermic conditions is recommended, even during therapeutic hypothermia (Lellouche et al 2006). ...
... When a hypothermic patient of 3.5kg is ventilated using the 37.0-default setting, approximately 8mL of water is delivered to the airway per day, assuming that the tidal volume is 8mL/kg and the respiratory rate is 50 breaths/minute. Unlike isotonic fluids, distilled water of this volume may cause airway oedema, bronchial spasms, and mucosal dysfunction (Pillow et al 2009;Sottiaux 2006;Williams et al 1996;Williams 1998). Improved humidification of respiratory gases may significantly ameliorate respiratory complications of patients who undergo therapeutic hypothermia. ...
Article
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Adult patients frequently suffer from serious respiratory complications during therapeutic hypothermia. During therapeutic hypothermia, respiratory gases are humidified close to saturated vapor at 37°C (44 mg/L) despite that saturated vapor reduces considerably depending on temperature reduction. Condensation may cause serious adverse events, such as bronchial edema, mucosal dysfunction, and ventilator-associated pneumonia during cooling. To determine clinical variables associated with inadequate humidification of respiratory gases during cooling, humidity of inspiratory gases was measured in 42 cumulative newborn infants who underwent therapeutic hypothermia. Three humidifier settings of 37-default (chamber outlet, 37°C; distal circuit, 40°C), 33.5-theoretical (chamber outlet, 33.5°C; distal circuit, 36.5°C), and 33.5-adjusted (optimized setting to achieve 36.6 mg/L using feedback from a hygrometer) were tested to identify independent variables of excessively high humidity >40.7 mg/L and low humidity <32.9 mg/L. The mean (SD) humidity at the Y-piece was 39.2 (5.2), 33.3 (4.1), and 36.7 (1.2) mg/L for 37-default, 33.5-theoretical, and 33.5-adjusted, respectively. The incidence of excessive high humidity was 10.3% (37-default, 31.0%; 33.5-theoretical, 0.0%; 33.5-adjusted, 0.0%), which was positively associated with the use of a counter-flow humidifier (p < 0.001), 37-default (compared with 33.5-theoretical and 33.5-adjusted, both p < 0.001) and higher fraction of inspired oxygen (p = 0.003). The incidence of excessively low humidity was 17.5% (37-default, 7.1%; 33.5-theoretical, 45.2%; 33.5-adjusted, 0.0%), which was positively associated with the use of a pass-over humidifier and 33.5-theoretical (both p < 0.001). All patients who used a counter-flow humidifier achieved the target gas humidity at the Y-piece (36.6 ± 0.5 mg/L) required for 33.5-adjusted with 33.5-theoretical. During cooling, 37-default is associated with excessively high humidity, whereas 33.5-theoretical leads to excessively low humidity. Future studies are needed to assess whether a new regimen with optimized Y-piece temperature and humidity control reduces serious respiratory adverse events during cooling.
... The use of cold dry gas may adversely affect lung function and increase the risk of hypothermia, which is an independent risk factor for mortality in preterm infants [4] . The use of dry ventilator gases has been shown to have a detrimental effect on airway epithelium, ciliary function, mucous viscosity and lung inflammation [5,6] . However, there are no recommendations for conditioning gases during newborn stabilisation. ...
... In adults, unconditioned ventilator gases reduce ciliary function and mucociliary clearance whilst increasing mucous viscosity [5,6] . In premature infants, a study from the pre-surfactant, pre-antenatal steroid era found that in infants of <1,500 g ventilated with low-humidity gases of <36.5°C in temperature, respiratory morbidity was greater than in those ventilated with warmer, highhumidity gases [18] . ...
... In premature infants, a study from the pre-surfactant, pre-antenatal steroid era found that in infants of <1,500 g ventilated with low-humidity gases of <36.5°C in temperature, respiratory morbidity was greater than in those ventilated with warmer, highhumidity gases [18] . Although the lower airway adds to gas conditioning [6] , adult studies suggest that gases for endotracheal ventilation should be conditioned to 37°C and 100% RH to minimise the workload [19] . The ISO (International Organisation for Standardisation) specifies that for all patients with an artificial airway, humidifiers must deliver an absolute humidity of ≥ 33 mg H 2 O/l [7] . ...
Article
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Background: Gases for respiratory support at birth are typically 'cold and dry', which may increase the risk of hypothermia and lung injury. Objectives: To determine the feasibility of using heated humidification from birth. Method: A humidifier targeting 37°C, a manual-fill chamber and a Neopuff Infant T-piece resuscitator and circuit were attached to a face mask and a manikin. Recordings using 20 ml H2O for humidification and a flow of 10 l/min were undertaken. Temperature and relative humidity (RH) were recorded. Additional recordings were made, each with one alteration to baseline (50 ml H2O for humidification, auto-fill chamber, a flow of 8 l/min, addition of circuit extension piece, warmed humidification H2O, increased ambient temperature and targeting 31°C). The duration of heated humidification and the response to disconnecting the power were investigated. Results: The baseline circuit achieved 95% RH and 31°C in 3 min, >99% RH in 7 min and ≥35°C in 9 min. No circuit alterations resulted in faster gas conditioning. The extended length circuit and targeting 31°C reduced the maximum temperature achieved. A flow of 8 l/min resulted in slower heating and humidification. The baseline circuit delivered heated humidification for 39 min. Without power, the temperature and humidity fell below international standards in 3 min. Conclusion: Rapid gas conditioning for newborn stabilisation is feasible using the experimental set-up, ≥20 ml H2O and a flow of 10 l/min. The circuit could be used immediately once switched on. Without power, conditioning is quickly lost. Investigation of the clinical effects of gas conditioning is warranted.
... However, under hypothermic conditions, absolute humidity at saturation decreases in a temperature-dependent manner. Therefore, the default humidifier setting for normothermic condition may provide excessive humidity and condensation in hypothermic patients [8][9][10]. Indeed, our previous study demonstrated that the default humidifier setting provided excessive gas heating and humidity in patients cooled at neonatal intensive care units [11]. ...
... Even during therapeutic hypothermia, where absolute humidity at saturation considerably reduces, the default humidifier setting for the normothermic condition is currently recommended. We initially anticipated that the use of this setting in cooled patients may lead to excessive humidification and condensation, which may theoretically cause adverse events, such as mucosal dysfunction and airway oedema [9,14]. Indeed, our previous study in cooled newborn infants highlighted the common incidence of excessive Ypiece gas humidification when this default humidifier setting Y-piece, 36.5 ∘ C), and 33.5-adjusted (optimised setting to achieve saturated vapour at 33.5 ∘ C, or 36.6 mg/L, using feedback from a thermohygrometer), were tested. ...
Article
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For cooled newborn infants, humidifier settings for normothermic condition provide excessive gas humidity because absolute humidity at saturation is temperature-dependent. To assess humidification of respiratory gases in patients who underwent moderate therapeutic hypothermia at a paediatric/adult intensive care unit, 6 patients were studied over 9 times. Three humidifier settings, 37-default (chamber-outlet, 37°C; Y-piece, 40°C), 33.5-theoretical (chamber-outlet, 33.5°C; Y-piece, 36.5°C), and 33.5-adjusted (optimised setting to achieve saturated vapour at 33.5°C using feedback from a thermohygrometer), were tested. Y-piece gas temperature/humidity and the incidence of high (>40.6 mg/L) and low (<32.9 mg/L) humidity relative to the target level (36.6 mg/L) were assessed. Y-piece gas humidity was 32.0 (26.8–37.3), 22.7 (16.9–28.6), and 36.9 (35.5–38.3) mg/L { mean (95% confidence interval) } for 37-default setting, 33.5-theoretical setting, and 33.5-adjusted setting, respectively. High humidity was observed in 1 patient with 37-default setting, whereas low humidity was seen in 5 patients with 37-default setting and 8 patients with 33.5-theoretical setting. With 33.5-adjusted setting, inadequate Y-piece humidity was not observed. Potential risks of the default humidifier setting for insufficient respiratory gas humidification were highlighted in patients cooled at a paediatric/adult intensive care unit. Y-piece gas conditions can be controlled to the theoretically optimal level by adjusting the setting guided by Y-piece gas temperature/humidity.
... They found that Cstat decreases when dry gas is administered. Our results are also in agreement with those of Sottiaux [23], who showed that changes in Cstat, Raw, and FRC could occur due to dry gas as well as to over-humidified gas. ...
... This method for measuring FRC was validated by Olegård et al. [33], who showed that highly precise measurements could be obtained by using the nitrogen elimination method and changing the flow of oxygen/air, and by Dellamonica et al. [34], who found acceptable accuracy and precision for lung-volume measurement at different PEEP levels in patients with ARDS. Our results show that the use of dry gases during short-term MV causes a decrease in FRC values, in agreement with the findings of Sottiaux [23]. The latter author showed that FRC values change due to the use of dry and over-humidified gas. ...
Article
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The use of dry gases during mechanical ventilation has been associated with the risk of serious airway complications. The goal of the present study was to quantify the plasma levels of TNF-alpha and IL-6 and to determine the radiological, hemodynamic, gasometric, and microscopic changes in lung mechanics in dogs subjected to short-term mechanical ventilation with and without humidification of the inhaled gas. The experiment was conducted for 24 hours in 10 dogs divided into two groups: Group I (n = 5), mechanical ventilation with dry oxygen dispensation, and Group II (n = 5), mechanical ventilation with oxygen dispensation using a moisture chamber. Variance analysis was used. No changes in physiological, hemodynamic, or gasometric, and radiographic constants were observed. Plasma TNF-alpha levels increased in group I, reaching a maximum 24 hours after mechanical ventilation was initiated (ANOVA p = 0.77). This increase was correlated to changes in mechanical ventilation. Plasma IL-6 levels decreased at 12 hours and increased again towards the end of the study (ANOVA p>0.05). Both groups exhibited a decrease in lung compliance and functional residual capacity values, but this was more pronounced in group I. Pplat increased in group I (ANOVA p = 0.02). Inhalation of dry gas caused histological lesions in the entire respiratory tract, including pulmonary parenchyma, to a greater extent than humidified gas. Humidification of inspired gases can attenuate damage associated with mechanical ventilation.
... These include secretion volume and consistency, incidence of ETT occlusion, changes in ETT effective diameter and/or resistance, suction frequency, and requirement for normal saline instillation. [25][26][27][28][29] Measurements of secretion volume are subjective and inherently flawed. Secretion volume may change with the number of suction attempts, patient position, use of aerosolized medications, hyperinflation, and saline installation. ...
... Excessive humidification may cause an increase in secretion volume, whereas insufficient hu-midification may result in a decrease in secretion volume as mucus becomes encrusted in the airways. 25 In our experience, these surrogates are poorly reproducible and more likely reflect the individual practice of the clinician instead of the condition of the patient. Measures such as secretion volume and mucus volume are not reliable for comparisons of humidification adequacy. ...
Article
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Management of the artificial airway includes securing the tube to prevent dislodgement or migration as well as removal of secretions. Preventive measures include adequate humidification and appropriate airway suctioning. Monitoring airway patency and removing obstruction are potentially life-saving components of airway management. Cuff pressure management is important for preventing aspiration and mucosal damage as well as assuring adequate ventilation. A number of new monitoring techniques have been introduced, and automated cuff pressure control is becoming more common. The respiratory therapist should be adept with all these devices and understand the appropriate application and management.
... 9 In adults the use of unconditioned gases has been shown to cause airway obstruction due to increased mucous viscosity and reduced mucociliary clearance, and cause cessation of ciliary beating, within 10 min. 10 There is evidence that heated, humidified gases may be beneficial, particularly in low birthweight and preterm neonates, as they have larger surface areas, higher insensible losses and are more likely to receive assisted ventilation in the delivery room. The UK Project 27/28, studying outcomes in infants of 27 and 28 weeks' gestation, earmarked poor initial thermal care as a major cause of mortality in this age group. ...
... We calculate that the energy used to heat and humidify dry resuscitation gases to these levels is about 40 kJ/kg/day (85% of which is used in humidification). 10 If unconditioned gases were applied for 1 h this would represent 1-2% of the energy delivered to a newborn infant on the first day of life (based on an intake of 60 mL/kg of either breast or standard formula milk, or intravenous parental nutrition or dextrose solutions). In addition we know that oxygen consumption increases with increased temperature gradient between the infant and the environment (roughly doubling between an ambient temperature of 35 and 23°C 12 ), to which using unconditioned gas would contribute, placing additional stress on infants. ...
The gases used to stabilise infants during resuscitation are usually unconditioned air and oxygen, often described as 'cold and dry', in comparison with the heated, humidified gases used for ongoing ventilation in neonatal intensive care units. The aim of this study was to determine exactly how 'cold and dry' these unconditioned gases are. Multiple measurements of temperature and relative humidity (RH) of piped gases were recorded at different sites, and at different times of day, across The Royal Women's Hospital, Melbourne. Ambient temperature and relative humidities were also recorded. Eighty paired air and oxygen measurements of temperature and RH were recorded. Mean temperatures of piped oxygen and air were 23.3 (0.9) and 23.4 (0.9) °C respectively. Mean RH of piped air was 5.4 (0.7) %; piped oxygen was significantly drier, mean RH 2.1 (1.1) %. Piped gases were delivered at room temperature and were extremely dry. This highlights the importance of research assessing the practicality of heating and humidifying resuscitation gases, and assessing the impact of their use on clinically important neonatal outcomes.
... A schematic representation of this cyclic inter-play occurring between anatomical features regulating the heat and water mass convective coefficients, as well as cellular water and vasculature supplies, is given in Although the nose provides about 90% of respiratory system air-conditioning requirements [50, 51], further humidification and heating of the inhaled air occurs as it travels through the pharynx and trachea. The ASL lining the conducting airway provides both heat and moisture until the air becomes fully saturated at core body temperature at a position termed as the isothermic saturation boundary (ISB) [70,71]. ...
... On the other hand, progressive over humidification through excessive supplementary humidification causes over-hydration of the ASL and a slowing of MTV due to a reduced cilia driving force [70,125]. If prolonged, over humidification leads to the cessation of ASL transport and the risk of ASL draining into the lungs [70,71,125]. ...
Thesis
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The human nose not only is the main portal through which air passes to and from our respiratory system, it also plays an important role in maintaining airway health. This function takes the form of heating and humidifying inhaled air to prevent airway drying, as well as trapping and disposing of inhaled particles and pathogens within the mucus lining. The ability of the nose to perform these duties appears compromised during the nasal breathing of pressurised air, with many users reporting symptoms associated with nasal airway drying. The cause of this drying is currently debated, but is typically relieved through the use of supplementary humidification. This investigation examines the role air-pressure has on nasal airway drying by the development of a dynamic nasal air-conditioning model to predict nasal airway hydration throughout the breathing cycle, and during ambient and pressurised breathing. Using the model, it was found that the air pressure influenced the mucosal water supply. Implementing previously unknown behaviours into this model provides new insight into the actual function of the nose and its pathophysiology during pressurised air breathing.
... Whether AH or RH is more important for physiological function is unknown. 18 Overhumidification can cause copious secretions and overwhelm the ciliary transport, and may also cause pyrexia and fluid overload by eliminating normal respiratory heat and water loss. 18 Whether temperature or humidity is better for neonatal resuscitation is unknown. ...
... 18 Overhumidification can cause copious secretions and overwhelm the ciliary transport, and may also cause pyrexia and fluid overload by eliminating normal respiratory heat and water loss. 18 Whether temperature or humidity is better for neonatal resuscitation is unknown. Studies have shown that the use of dry cold gas in ventilated infants for just 5 min results in a significant decrease in both pulmonary compliance and conductance. ...
Article
Aim: Dry, cold gas is used for neonatal resuscitation, contributing to low admission temperatures and exacerbation of lung injury. Recently, a method of heating and humidifying neonatal resuscitation gases has become available. We aimed to determine the optimal flow rate, humidifier chamber and water volume needed to reach 36°C, and near 100% humidity at the patient T-piece in the shortest possible time. Method: A T-piece resuscitator was connected via a heated patient circuit to a humidifier chamber. Trials were performed using different gas flow rates (6, 8 and 10L/min), humidification chambers (MR290, MR225) and water volumes (30g, 108g). Temperature was recorded at the humidifier chamber (T1), distal temperature probe (T2) and the T-piece (T3) over a 20min period at 30s intervals. A test lung was added during one trial. Results: No significant difference existed between flow rates 8L/min and 10L/min (p=0.091, p=0.631). T3 reached 36°C and remained stable at 360s (8L/min, MR225, 30mL); near 100% RH was reached at 107s (10L/min, MR225, 30mL). T3 and humidity reached and remained stable at 480s (10L/min, MR290, 30mL). Target temperature and humidity was not reached with the test lung. Conclusions: It is possible to deliver heated, humidified gases in neonatal resuscitation in a clinically acceptable timeframe. We suggest the set-up to achieve optimal temperature and humidity for resuscitation purposes is 10L/min of gas flow, a MR290 humidification chamber, and 30mL of water.
... These results would be of great interest in clinical practice because under-humidification (worsening patients' comfort) could impair the function of the ciliary epithelium and secretion clearance, even favoring secretion retention. 8,9,19 Although this phenomenon of under-humidification caused by decreasing the contact time of the gas with the air-liquid interface of the heated humidifier chamber for equipment that, even in the invasive mode, does not reach 33 mg/L absolute humidity could be mitigated, the way to achieve this in clinical practice could be difficult. 20 Two of the three heated humidifiers managed to deliver absolute humidity > 33 mg/L, even at a high flow, of 100 L/min; however, the different combinations did not always achieve these results. ...
Article
Background: Oxygen therapy via high-flow nasal cannula generates physiologic changes that impact ventilatory variables of patients. However, we know that there are detrimental effects on airway mucosa related to inhalation of gases. The objective of this study was to evaluate the performance in terms of absolute humidity, relative humidity, and temperature of different brands of heated humidifiers and circuits in the invasive mode during the use of high-flow oxygen therapy in flows between 30 and 100 L/min. Methods: A prospective observational study conducted at the Sanatorio Anchorena equipment analysis laboratory; September 5 to October 20, 2019. Results: A statistically significant interaction was found among the programmed flows and the different combinations of devices and circuits for the delivery of absolute humidity (P < .001). An effect of flow on delivered absolute humidity was found, regardless of the equipment and circuit combination (P < .001). However, in the invasive mode, the combination of the Fisher&Paykel MR850 heated humidifier with the Medtronic-Dar circuit, the Intersurgical circuit, and the AquaVENT circuit always reached or achieved absolute humidity values > 33 mg/L, even at flows up to 100 L/min. The combination of the Flexicare FL9000 heated humidifier with the Fisher&Paykel RT202 circuit, the Fisher&Paykel Evaqua 2 circuit, the Flexicare circuit, the AquaVENT circuit, and the GGM circuit achieved similar results. The mean (SD) of absolute humidity delivered in the invasive mode (36.2 ± 5.9 mg/L) was higher compared with the noninvasive mode (26.8 ± 7.2 mg/L) (P < .001), regardless of circuit and programmed flows. Conclusions: When heated humidifiers were used in the invasive mode for high-flow oxygen therapy, absolute humidity depended not only on the heated humidifiers and the combination of circuits but also on the programmed flow, especially at flows > 50 L/min. Moreover, the heated humidifiers exhibited different behaviors, in some cases inefficient, in delivering adequate humidification. However, some equipment improved performance when set to the invasive mode.
... Humidity is expressed as absolute humidity (total mass of water vapor present in a given volume of mass of air; g/m 3 ) or specific humidity (mass of water vapor in a unit mass of air; g/kg), and also as relative humidity (RH), which is the amount (saturation) of water vapor that the atmosphere withstands at a given temperature. Low humidity levels contribute to the dry-out of airway mucosa, compromising the functioning of the mucocilliary barrier as well as the fluidity of the mucus [72]. A low specific humidity (3e6 g/kg) and a low absolute humidity (4e7 g/m 3 ) likely contribute with a cold temperature (between 5 and 11 C) to a higher community transmission and infection, as seen in Paris, Madrid or Milan from January to March 2020 [7,73]. ...
Article
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COVID-19 pandemic has been characterized by a pattern of consecutive declines and regrowth in European countries in 2020. After being partially regressed during the summer, the reappearance of the infection during fall 2020 in many temperate countries strongly suggests that temperature and cold may play a role in influencing the infectivity and virulence of SARS-CoV-2. While promoting medicine as an art, Hippocrates interpreted with logical reasoning the occurrence of diseases such as epidemics, as a consequence of environmental factors, in particular climatic variations. During the Renaissance, Sanctorius was one of the first to perform quantitative measurements, and Harvey discovered the circulation of blood by performing experimental procedures in animals. We think that a reasoning mixing various observations, measurements and experiments is fundamental to understand how cold increases infectivity and virulence of SARS-CoV-2. By this review, we provide evidence linking cold, angiotensin-II, vasoconstriction, hypoxia and aerobic glycolysis (the Warburg effect) to explain how cold affects the epidemiology of COVID-19. Also, a low humidity increases virus transmissibility, while a warm atmosphere, a moderate airway humidity, and the production of vasodilator angiotensin 1-7 by ACE2 are less favorable to the virus entry and/or its development. The meteorological and environmental parameters impacting COVID-19 pandemic should be reintegrated into a whole perspective by taking into account the different factors influencing transmissibility, infectivity and virulence of SARS-CoV-2. To understand the modern enigma represented by COVID-19, an interdisciplinary approach is surely essential.
... For patients who require mechanical ventilation, the inspired gas is heated and humidified to reduce drying of the respiratory mucosa, airway ulceration and impaired secretion clearance [1][2][3] . Insufficient and excessive humidification of respiratory gases are associated with serious complications, such as endotracheal tube obstruction and ventilator-associated pneumonia (VAP) 1,2,4,5 . The incidence rate of VAP is 0.0-4.4 per 1000 days of mechanical ventilation 6 , which increases the mortality rate by 13% compared to those who do not develop VAP 7 . ...
Article
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Inappropriate preparation of respiratory gases is associated with serious complications during mechanical ventilation. To develop a temperature monitoring system of respiratory gases within the endotracheal tube, four newborn piglets were studied using an ultra-rapid-response thermometer attached to the closed endotracheal tube suction system. Respiratory gas temperatures were monitored at the mouth-corner level of the endotracheal tube using three thermocouples (Tairway, inserted into the endotracheal tube via the closed suction system; Ttube_centre and Ttube_wall, embedded within the endotracheal tube 0.5 mm and 1.6 mm from the tube wall, respectively). Univariate analysis showed that inspiratory Ttube_centre and inspiratory Ttube_wall were positively correlated with inspiratory Tairway (both p < 0.001). Multivariate analysis showed the dependence of inspiratory Tairway on inspiratory Ttube_centre and Ttube_wall and deflation of endotracheal tube cuff (p < 0.001, p = 0.001 and p = 0.046, respectively). Inspiratory gas temperature within the endotracheal tube can be monitored using a thermometer attached to the closed endotracheal tube suction system. Our system, with further validation, might help optimise respiratory gas humidification during mechanical ventilation.
... 55 The use of heated humidified gas in the delivery room also has been shown to reduce hypothermia 56 and may reduce alveolar and distal airway damage. 57 This intervention, not currently recommended for the delivery room, deserves further research. Specific data on the optimal means for reducing hypothermia in infants £23 weeks are limited; however, an exploratory trial has demonstrated the feasibility of studying optimal thermal management techniques in this unique population. ...
... § 1º Equipara-se à majoração do tributo a modificação da sua base de cálculo, que importe em torná-lo mais oneroso. § 2º Não constitui majoração de tributo, para os fins do disposto no inciso II deste artigo, a atualização do valor monetário da respectiva base de cálculo 15 O artigo citado anteriormente proíbe os entes federativos de estabelecer tratamento diferente entre contribuintes que se achem em situação equivalente, impedindo qualquer distinção em pretexto de ocupação profissional ou função por eles desempenhada 41 . ...
... § 1º Equipara-se à majoração do tributo a modificação da sua base de cálculo, que importe em torná-lo mais oneroso. § 2º Não constitui majoração de tributo, para os fins do disposto no inciso II deste artigo, a atualização do valor monetário da respectiva base de cálculo 15 O artigo citado anteriormente proíbe os entes federativos de estabelecer tratamento diferente entre contribuintes que se achem em situação equivalente, impedindo qualquer distinção em pretexto de ocupação profissional ou função por eles desempenhada 41 . ...
... The latter, in addition to negatively affecting patient comfort, could impair the function of ciliary epithelium and clearance of secretions, even causing some retention of secretions. 15,16 In general, the combinations evaluated at the different flows implemented kept the delivery of the temperature stable but not the RH, which could be attributed to 2 phenomena. First, the circuit used could have influenced the RH because the HH managed to keep the temperature stable and thus allowed variation in the RH, and therefore the AH could be due to technical issues related to the circuit. ...
Article
BACKGROUND: We sought to evaluate the performance in terms of absolute humidity (AH), relative humidity (RH), and temperature of different heated humidifiers (HH) and circuits that are commonly used to deliver high-flow oxygen therapy in conventional ranges (30–60 L/min) and unconventional ranges (70–100 L/min). METHODS: In this prospective, observational study, an electronic thermohygrometer was used to obtain the required measurements. A mechanical ventilator was used as a source for high-flow nasal cannula oxygen therapy. For active humidifi-cation, the following equipment was used: a HH with standard disposable water trap circuit, 3 servo-controlled HH, and 7 circuits with a heated wire. Data on environmental conditions (ie, temperature, RH, AH) were collected from the laboratory during each measurement; the tem-perature, RH, and AH resulting from the application of 8 flows (30–100 L/min) were also recorded. Variables were compared with analysis of variance for repeated measurements with Tukey post hoc tests. A value of P <.05 was assumed to be significant. RESULTS: During the study, a statistically significant difference was found in the average AH for each flow for the different devices (P <.005). The highest AH values were recorded with the Fisher & Paykel MR850 and the Medtronic-DAR circuit (AH = 40.8 mg/L with flow of 50 L/min, P <.005), and the lowest AH values were recorded with the Flexicare FL9000 HH and the Flexicare circuit (AH = 11.4 mg/L with 100 L/min flow, P <.005). For flows > 50 L/min, the best performance for all flows in terms of AH was found with the Fisher & Paykel MR850 HH, regardless of the circuit used. CONCLUSIONS: During oxygen therapy with very high gas flows, HH devices behave differently and in many cases are inefficient in delivering adequate humidification, even at conventional flows. Caution is therefore recommended when selecting the device and flow settings for the implementa-tion of high-flow nasal cannula oxygen therapy.
... [13][14][15] It is important that the administered oxygen that reaches the trachea should be at physiologic conditions (32-34°C and 100% relative humidity). [16] The cause for development of pneumonia or atelectasis as a side effect of oxygen therapy is multifactorial. Severe hypoxemia should be treated promptly but slowly with stepwise increases in oxygen concentration, avoiding arterial hyperoxemia. ...
Article
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Background: Although oxygen is one of the oldest drugs available, it is still one of the most inappropriately administered drugs leading to over utilization of this very expensive resource. Materials and methods: This prospective observational study was done in a large emergency department (ED) in India. The pattern of oxygen usage was studied before and after the strict implementation of an oxygen treatment algorithm. The algorithm was taught to all doctors and nurses and its implementation was monitored regularly. The main outcome measures were proportion of patients receiving oxygen therapy, inappropriate usage, and avoidable direct medical cost to the patient. Results: The 3-week pre-protocol observation phase in April 2016 included 3769 patients and the 3-week post-protocol observation phase in April 2017 included 4608 patients. The baseline demographic pattern was similar in both the pre-protocol and post-protocol groups. After the strict implementation of the algorithm, the number of patients receiving oxygen therapy decreased from 9.63% to 4.82%, a relative decrease of 51.4%. The average amount of total oxygen used decreased from 55.4 liters per person in pre-protocol group to 42.1 liters per person in the post-protocol group with a mean difference of 13.28 (95% CI 5.30-21.26; P = 0.001). Inappropriate oxygen usage decreased from 37.2% to 8.6%. There was a significant decrease in inappropriate oxygen use for indications like low sensorium (60.8% vs 21.7%) and trauma (88.5% vs 15.8%). The mortality rate in the pre-protocol phase was 2.7% as compared with 3.2% in the post-protocol phase. The total duration of inappropriate oxygen usage significantly decreased from 987 h to 89 h over the 21-day study period. Conclusion: The implementation of an oxygen therapy algorithm significantly reduces inappropriate oxygen use and decreases treatment cost to the patient with no additional mortality risk.
... The administration of cold and dry gases directly into the lower respiratory tract can cause lung damage. [1][2][3][4] Mechanically ventilated neonates are particularly sensitive to lung injury. Furthermore, the use of unconditioned inspired gases has been associated with an increased severity of bronchopulmonary dysplasia. ...
Article
Background: There are many proven benefits of the use of conditioned gases in mechanically ventilated patients. In spite of this, its use in the delivery room is limited, perhaps because of known difficulties with heated humidifiers (HH); moreover, there is no evidence regarding the use of heat-and-moisture exchangers (HME) in a delivery room setting. We sought to asess the airway's absolute humidity level using three diferents strategies: HH, HME and unconditioned gases. Methods: We conducted an experimental study in 12 intubated rabbits ventilated with a T-piece resuscitator. Absolute humidity levels in inspired gases were measured at baseline and at 5, 10, 15, and 20 min while using HH, HME, or no conditioning method (ie, unconditioned). The animals were initially randomized to one of the 3 interventions, and each animal underwent the other methods with at least 24 h between each test. Results: There were no differences in vital signs at baseline or at the end of the procedures. Mean absolute humidity at the end of the tests was 38.2 ± 1.7 g/m3 for HH, 28.9 ± 4.7 g/m3 for HME, and 13.9 ± 5.1 g/m3 for unconditioned gas (P = .003). Conclusions: During ventilation with a T-piece resuscitator, the absolute humidity was the highest with HH. The absolute humidity with HME was lower, but it was still significantly more than that with unconditioned gas. Therefore, the use of a T-piece resuscitator with HME could be a good alternative to HH given that positive-pressure ventilation is used ideally for short periods of time in the delivery room.
... Humidification during invasive mechanical ventilation is currently an accepted standard of care [1] . It is imperative for the proper function of the mucociliary escalator that inspired gases are fully saturated with water vapour and warmed to body temperature [2,3] . Active humidifiers are devices that act by allowing air passage across or through a heated water reservoir and are placed in the inspiratory limb of the ventilator circuit, proximal to the ventilator [4] . ...
Conference Paper
Full-text available
Humidification during invasive mechanical ventilation is currently an accepted standard of care. It is imperative for the proper function of the mucociliary escalator that inspired gases are fully saturated with water vapour and warmed to body temperature. Active humidifiers are devices that act by allowing air passage across or through a heated water reservoir and are placed in the inspiratory limb of the ventilator circuit, proximal to the ventilator. During aerosol therapy, liquid droplets or particles are generated and delivered to the patient’s airway suspended in the inspired gas. Heretofore, aerosol delivery performance across different humidification systems during simulated mechanical ventilation has not been reported. The objective of this study was to evaluate aerosol delivery across two market leading humidification systems during simulated adult and paediatric mechanical ventilation.
... Le kinésithérapeute doit veiller à maintenir des conditions physiologiques d'humidification au niveau des voies aériennes (32 à 34 • C, humidité relative de 100 %) tant en respiration spontanée qu'en ventilation mécanique. Une humidification inadéquate altère la clairance mucociliaire [22,23] . Une sécheresse de la sphère oto-rhino-laryngée due à une respiration exclusivement buccale est souvent observée chez les patients hypoxémiques, entravant l'expectoration des sécrétions. ...
Article
En colaboración con el conjunto del equipo del servicio de reanimación, el kinesiterapeuta participa en la evaluación clínica para garantizar el tratamiento respiratorio y la movilización precoz del paciente. La kinesiterapia se inicia con la evaluación de los signos de dificultad respiratoria para descubrir su causa y orientar el tratamiento. Trata la congestión bronquial del paciente mediante el uso de técnicas de descongestión manual (modulación del flujo espiratorio, rehabilitación con la tos) e instrumentales (ventilación con percusiones intrapulmonares, insuflación/exuflación mecánica, aspiración endotraqueal). Además, participa en el tratamiento del paciente hipoxémico y/o hipercápnico mediante la instauración de la oxigenoterapia y el reglaje adecuado de los parámetros ventilatorios tanto en ventilación mecánica invasiva como en la no invasiva. El confort respiratorio del paciente y la retirada de la ventilación mecánica y de la oxigenoterapia son dos objetivos clave de la kinesiterapia respiratoria en reanimación. El kinesiterapeuta inicia precozmente la movilización del paciente. Se dirige al refuerzo muscular global y analítico (por ejemplo, los músculos respiratorios) para promover la autonomía funcional y la autonomía respiratoria del paciente. Para ello son indispensables un tratamiento multidisciplinario, una limitación de la sedación y una nutrición óptima. Son conocidos los beneficios musculoesqueléticos, respiratorios y psicológicos de la movilización precoz del paciente en reanimación. Realizada en la mayoría de los pacientes en respiración espontánea o intubados y ventilados, las técnicas de movilización van desde la movilización pasiva en la cama a la deambulación del paciente fuera de su habitación.
... 2 Dry nonhumidified and cold inspired gases can cause distal airway and alveolar damage. 3 In infants, even short exposure to dry cold respiratory gases decreased lung compliance and increased work of breathing. 4 However, it is possible that the transient use of dry cold gases during resuscitation does not cause a measurable degree of lung injury that would result in easily detectable respiratory morbidities. ...
... The use of unconditioned ventilator gases has been shown to have a detrimental effect on mucociliary clearance, respiratory function, mucous viscosity, and ciliary function. 23,24 Injury is proportional to the duration of ventilation with unconditioned gases. 23 Animal studies have shown that, as early as after 1 hour of ventilation with unconditioned gases, structural and functional damage of the airway is evident 25 ; with 3 or more hours exposure further injury is seen, with inflammation, necrosis, and blistering of the trachea. ...
Article
Objective To determine whether the use of heated-humidified gases for respiratory support during the stabilization of infants <30 weeks of gestational age (GA) in the delivery room reduces rates of hypothermia on admission to the neonatal intensive care unit (NICU). Study design A multicenter, unblinded, randomized trial was conducted in Melbourne, Australia, between February 2013 and June 2015. Infants <30 weeks of GA were randomly assigned to receive either heated-humidified gases or unconditioned gases during stabilization in the delivery room and during transport to NICU. Infants born to mothers with pyrexia >38°C were excluded. Primary outcome was rate of hypothermia on NICU admission (rectal temperature <36.5°C). Results A total of 273 infants were enrolled. Fewer infants in the heated-humidified group were hypothermic on admission to NICU (36/132 [27%]) compared with controls (61/141 [43%], P < .01). There was no difference in rates of hyperthermia (>37.5°C); 20% (27/132) in the heated-humidified group compared with 16% (22/141) in the controls (P = .30). There were no differences in mortality or respiratory outcomes. Conclusions The use of heated-humidified gases in the delivery room significantly reduces hypothermia on admission to NICU in preterm infants, without increased risk of hyperthermia. Clinical Trial Registration Australian and New Zealand Clinical Trials Register (www.anzctr.org.au) ACTRN12613000093785.
... Humidification helps to maintain normal mucociliary function, clearance of secretions, and normal temperature. [7][8][9][10][11] Inspired gas humidification is typically achieved during anesthesia care by using passive, in-line heat and moisture exchangers (HMEs) or active humidifiers. Because of their effectiveness, low cost, ease of use, portability, and bacterial filtering capabilities, HMEs are more convenient solutions for humidification than active humidifiers. ...
Article
Full-text available
Mechanical ventilation of the anesthetized infant requires careful attention to equipment and ventilator settings to assure optimal gas exchange and minimize the potential for lung injury. Apparatus dead space, defined as dead space resulting from devices placed between the endotracheal tube and the Y-piece of the breathing circuit, is the primary source of dead space controlled by the clinician. Due to the small tidal volumes required by infants and neonates, it is easy to create excessive apparatus dead space resulting in unintended hypercarbia or increased minute ventilation in an effort to achieve a desirable PCO2. The goal of this review was to evaluate the apparatus that are commonly added to the breathing circuit during anesthesia care, and develop recommendations to guide the clinician in selecting apparatus that are best matched to the clinical goals and the patient's size. We include specific recommendations for apparatus that are best suited for different size pediatric patients, with a particular focus on patients <5 kg.
... Delivery of unconditioned gases can have a number of adverse effects on respiratory function, including impaired mucociliary function and thickening of secretions, damage to the airway mucosa, [30][31][32] and a reduction in pulmonary compliance and functional residual capacity [33]. Furthermore, heating and humidification of environmental gas by the upper airway mucosa is associated with both caloric and evaporative heat loss, [34] and can result in hypothermia, factors that are all specifically important to preterm infants [35][36][37]. Therefore, appropriate gas conditioning has been postulated as a potential benefit resulting from HF treatment [15]. ...
Article
Full-text available
Nasal High Flow (HF) is a mode of ‘non-invasive’ respiratory support for preterm infants, with several potential modes of action, including generation of distending airway pressure, washout of the nasopharyngeal dead space, reduction of work of breathing, and heating and humidification of inspired gas. HF has several potential advantages over continuous positive airway pressure (CPAP), the most commonly applied form of non-invasive support, such as reduced nasal trauma, ease of use, and infant comfort, which has led to its rapid adoption into neonatal care. In recent years, HF has become a well-established and commonly applied treatment in neonatal care. Recent trials comparing HF and CPAP as primary support have had differing results. Meta-analyses suggest that primary HF results in an increased risk of treatment failure, but that ‘rescue’ CPAP use in those infants with HF failure results in no greater risk of mechanical ventilation. Even in studies with higher rates of HF failure, the majority of infants were successfully treated with HF, and rates of important neonatal morbidities did not differ between treatment groups. Importantly, these studies have included only infants born at ≥28 weeks’ gestational age (GA). The decision whether to apply primary HF will depend on the value placed on its advantages over CPAP by clinicians, the approach to surfactant treatment, and the severity of respiratory disease in the relevant population of preterm infants. Post-extubation HF use results in similar rates of treatment failure, mechanical ventilation, and adverse events compared to CPAP. Post-extubation HF appears most suited to infants ≥28 weeks; there are few published data for infants below this gestation, and available evidence suggests that these infants are at high risk of HF failure, although rates of intubation and other morbidities are similar to those seen with CPAP. There is no evidence that using HF to ‘wean’ off CPAP allows for respiratory support to be ceased more quickly, but given its advantages it would appear to be a suitable alternative in infants who require ongoing non-invasive support. Safety data from randomised trials are reassuring, although more evidence in extremely preterm infants (<28 weeks’ GA) is required.
... The humidity of inhaled air decreases in case of the use of a high oxygen flow 4 , increased ventilation, the use of dried inhaled gases and the use of tracheal tube. The reduction of the moisture content of the inhaled gas leads to the dryness of airway, increased concentration and the viscosity of airway secretions 6 , the dysfunction of cilia 8,7 , the inflammation and the scarring of airways caused by cellular level destruction 13,9 , the destruction of pulmonary tissue 10 , bronchospasm, atelectasis, which results in hypoxia 14 and an increased risk of pulmonary infection 10 . The dried and sticky secretions enter into the tracheal tube and cause the formation of a layer in its wall 11 . ...
Article
Full-text available
Provision of inspiratory humidity in patients connected to ventilator prevents drying and increasing the density of airway secretions, airway obstruction and following complications. Nursing stuff plays an important role at the correct application of ventilator‘s humidifiers. In this study we evaluate the effect of nursing education on the correct application of ventilator‘s humidifiers in intensive care units. This research was done as a randomized double blind study at two stages: At first step, 327 connected ventilators to patient were investigated according to the presence of humidifier, distilled water in the humidifier‘s container, connection tubes, connectors and connection of humidifier system to inspiratory arm. Then nursing education was done for correct application of ventilator‘s humidifiers in intensive care units, without previous information about research proposal. At second step, after the nursing education, all stages similar to first step were repeated and the data were recorded in questionnaire. Data were analyzed by SPSS software, Chi- square and fisher tests. According to analysis of data statically, before and after nursing education: The %91.40 and %82.60 of ventilators had humidifier system, respectively, which the reduction was statically significant (P= 0.001). The %49.80 and % 65.20 of humidifier systems had connectors and connective tubes, which the increase was statically significant (P= 0.00). The %39.10 and %47.80 of humidifiers had distilled water in their containers, respectively, which was statically significant (P= 0.04). Active and connected ventilators to patient that had humidifier system, connective tubes connected to inspiratory arm and humidifier‘s container with distilled water simultaneously were formed %26.60 and %23.50 of ventilators, the difference was not statically significant (P= 0.37). Nursing education for proper and complete usage of humidifiers in patients under ventilators had a few effect that could be caused by: the lack of the supply of humidifier system, the high amount of duties, the personnel shortages, the low motivation of nurses, the lack of personnel attention to the learning and employing their own knowledge and the lack of the knowledge of nurses about the research. Keywords: Ventilator, Humidifier System, Nursing Education and Inspiratory Humidity.
... El enlentecimiento de la actividad ciliar es la consecuencia de la alteración funcional de la mucosa y aparece antes de las tres horas de ventilación mecánica con gases que transportan una HA inferior a 25 mg/l. 2,3 La Asociación Americana de Cuidados Respiratorios sugiere que el gas entregado en una vía aérea artificial debe estar entre 31º y 35°C de Tº, HR 100% y con un mínimo de HA de 30 mg/l. 4,5 Introducción En el sistema respiratorio la vía aérea superior, sobre todo a nivel de la nasofaringe, es la principal encargada del acondicionamiento del gas inspirado: humidificación, calentamiento y filtración. ...
... Under-humidified gas can result in impaired ciliary function, reduced clearance of secretions, damage to the airway mucosa [2][3][4] and may impair lung function by reducing compliance and functional residual capacity. 5 During normal breathing, air is humidified during inspiration by the nasal mucosa, a process associated with both caloric and evaporative heat loss. 6 Hypothermia has been reported in both adults and infants undergoing surgery who were ventilated with unconditioned gas-an effect that can be corrected with adequate heating and humidification. [7][8][9] While most of this research has been conducted in the context of patients receiving endotracheal ventilation, humidification during non-invasive ventilation is also likely to be beneficial. ...
Article
Full-text available
Objective: Heating and humidification of inspired gases is routine during neonatal non-invasive respiratory support. However, little is known about the temperature and humidity delivered to the upper airway. The International Standards Organization (ISO) specifies that for all patients with an artificial airway humidifiers should deliver ≥33 g/m(3) absolute humidity (AH). We assessed the oropharyngeal temperature and humidity during different non-invasive support modes in a neonatal manikin study. Methods: Six different modes of non-invasive respiratory support were applied at clinically relevant settings to a neonatal manikin, placed in a warmed and humidified neonatal incubator. Oropharyngeal temperature and relative humidity (RH) were assessed using a thermohygrometer. AH was subsequently calculated. Results: Measured temperature and RH varied between devices. Bubble and ventilator continuous positive airway pressure (CPAP) produced temperatures >34°C and AH >38 g/m(3). Variable flow CPAP resulted in lower levels of AH than bubble or ventilator CPAP, and AH decreased with higher gas flow. High-flow (HF) therapy delivered by Optiflow Junior produced higher AH with higher gas flow, whereas with Vapotherm HF the converse was true. Conclusions: Different non-invasive devices deliver inspiratory gases of variable temperature and humidity. Most AH levels were above the ISO recommendation; however, with some HF and variable flow CPAP devices at higher gas flow this was not achieved. Clinicians should be aware of differences in the efficacy of heating and humidification when choosing modes of non-invasive respiratory support.
... In normal conditions the upper airways provide 75 % of the heat and moisture supply to the alveoli [1]. When these airways are by-passed, proper conditioning of the inhaled gases becomes essential to prevent serious damage to the patient's tracheobronchial system [2][3][4]. ...
Article
This paper presents a new test apparatus for the evaluation of the humidification efficiency of heat and moisture exchangers (HMEs). These devices are widely used in invasive ventilation conditions to humidify and to heat medical gases inhaled by the patients. The new custom-made test apparatus allows simultaneous measurements with the two most common methods for in vitro tests: gravimetric, which is considered the reference method by the international standard ISO 9360, and hygrometric. In the reference method, the absolute humidity of the inhaled gas (HME moisture output) is determined by subtracting, from the absolute humidity of the exhaled gas (AHexh), the moisture loss measured with a precision balance. Consequently, AHexh is supposed to be stable throughout the test. In addition, ISO 9360 does not set a limit for the maximum value of AHexh in the measuring process. In the new experimental test apparatus, AHexh is constantly monitored and the humidification efficiency of an HME is expressed as the ratio of the HME moisture output with respect to AHexh, the so-called relative efficiency. Results show that average values of AHexh and of the relative efficiency are very similar with both methods, confirming the reliability of the new test apparatus.
... In normal conditions, these airways provide 75% of the heat and moisture supply to the alveoli [1]. Consequently, it is of primary importance to properly humidify medical gases in order to prevent serious damage to the patient's tracheobronchial system [2][3][4]. ...
Article
Full-text available
In recent decades, Heat and Moisture Exchange (HME) devices have been employed increasingly for short-term use in anaesthesia and long-term use in intensive care units. These devices work as heat exchangers, accumulating the patient’s expired heat and moisture and returning them to the patient during the inhalation phase. Porous matrices obtained from freeze-drying of blends of natural polymers exhibit high open and interconnected porosity and water vapour intake characteristics which make them possible candidates for HME devices. Preliminary tests were conducted on specimens made of gelatine blended with chitosan and treated with a non-toxic cross-linking agent. The tests were carried out in cyclic flow conditions with saturated and dried air. Results show water vapour retention comparable with accepted standards for HME devices.
... Inadequate humidification of inhaled gas increases the risk of atelectasis, enhances the airway resistance, and promotes a greater incidence of infections, a harder respiratory load, and thickening of airway secretions and destruction of airway epithelium. The slowing down of ciliary activity is a consequence of mucous membrane functional disturbance, and it appears within three hours of mechanical ventilation with gases carrying an AH lower than 25 mg/L [2,3]. ...
Article
Full-text available
The effectiveness of the active humidification systems (AHS) in patients already weaned from mechanical ventilation and with an artificial airway has not been very well described. The objective of this study was to evaluate the performance of an AHS in chronically tracheostomized and spontaneously breathing patients. Measurements were quantified at three levels of temperature (T°) of the AHS: level I, low; level II, middle; and level III, high and at different flow levels (20 to 60 L/minute). Statistical analysis of repeated measurements was performed using analysis of variance and significance was set at a P<0.05. While the lowest temperature setting (level I) did not condition gas to the minimum recommended values for any of the flows that were used, the medium temperature setting (level II) only conditioned gas with flows of 20 and 30 L/minute. Finally, at the highest temperature setting (level III), every flow reached the minimum absolute humidity (AH) recommended of 30 mg/L. According to our results, to obtain appropiate relative humidity, AH and T° of gas one should have a device that maintains water T° at least at 53℃ for flows between 20 and 30 L/m, or at T° of 61℃ at any flow rate.
... In general, the volume of secretions is directly proportional to degree of humidification. Excessive humidification will increase secretion volume, and suboptimal humidification will lead to crusting, inspissation of secretions, and a decrease in their volume [46]. Nevertheless, this relationship assumes that humidity is the only factor that influences secretion volume. ...
Article
Full-text available
Humidification of inhaled gases has been standard of care in mechanical ventilation for a long period of time. More than a century ago, a variety of reports described important airway damage by applying dry gases during artificial ventilation. Consequently, respiratory care providers have been utilizing external humidifiers to compensate for the lack of natural humidification mechanisms when the upper airway is bypassed. Particularly, active and passive humidification devices have rapidly evolved. Sophisticated systems composed of reservoirs, wires, heating devices, and other elements have become part of our usual armamentarium in the intensive care unit. Therefore, basic knowledge of the mechanisms of action of each of these devices, as well as their advantages and disadvantages, becomes a necessity for the respiratory care and intensive care practitioner. In this paper, we review current methods of airway humidification during invasive mechanical ventilation of adult patients. We describe a variety of devices and describe the eventual applications according to specific clinical conditions.
... [13][14][15] It is important that the administered oxygen that reaches the trachea should be at physiologic conditions (32-34°C and 100% relative humidity). [16] The cause for development of pneumonia or atelectasis as a side effect of oxygen therapy is multifactorial. Severe hypoxemia should be treated promptly but slowly with stepwise increases in oxygen concentration, avoiding arterial hyperoxemia. ...
... 21 When compared with previous studies, the Humid-Heat device outperformed HHs in the case of high ambient temperature, 10 but important issues with existing passive HMEs (ie, dead space) are still present with active HMEs. Finally, due to the possible condensation in the small airways, there is a risk of overhumidification when inspiratory gases are Ͼ 44 mg H 2 O/L, 30,31 or even below that level if core temperature is Ͻ 37°C. 9 We do not have clinical experience with humidification devices that really provide Ն 40 mg H 2 O/L, such as the Humid-Heat device. ...
Article
During invasive mechanical ventilation, inspired gases must be humidified. We previously showed that high ambient temperature greatly impaired hygrometric performances of heated wire heated humidifiers. The aim of this bench and clinical study was to assess the humidification performances of passive and active heat and moisture exchangers (HME) and the impact of ambient temperature and ventilator settings. We first tested on bench a device with passive and active humidification properties (Humid-Heat, Hudson), and two passive hydrophobic/hygroscopic HMEs (Hygrobac and Hygrobac-S, Mallinkrodt). The devices were tested at three different ambient temperature (from 22 to 30°C), and at two minute ventilations (10 and 20L/min). Inspired gas hygrometry was measured at Y-piece with the psychrometric method. In addition to the bench study, we measured hygrometry of inspired gases in two different clinical studies. In 15 mechanically ventilated patients, we evaluated Humid-Heat at different settings. Additionnaly, we evaluated Humid-Heat and compared it with Hygrobac in a cross-over study in 10 patients. On bench, with the Hygrobac and Hygrobac S, inspired absolute humidity was around 30 mgH2O/L and with the Humid-Heat, slightly below 35 mgH2O/L. Ambient temperature and minute ventilation did not have a clinically significant difference on the performances of the tested devices. During the clinical evaluation, Humid-Heat provided inspired humidity in a range from 28.5 mgH2O/L to 42.0 mgH2O/L, depending on settings, and was only weakly influenced by patient's body temperature. in this study, both passive and active HME had stable humidification performances with negligible influence of ambient temperature and minute ventilation. This contrasts with previous findings with heated wire heated humidifiers. Although there is no clear data demonstrating that higher humidification impact outcomes, it is worth noting that humidity was significantly higher with the active HME.
... In some reports, it has been sug-gested that over humidification occurs when tracheal gas is fully saturated above around 32 °C, a point where water vapor content is higher during inspiration than expiration and exchanges of heat and water are reversed during a respiratory cycle. 3 Others suggest over-humidification occurs when delivered inspired gas is above BTPS. 4 Overhumidification reduces mucus viscosity, increases the pericillary layer, dilutes surfactant and causes neutrophilic infiltration of lungs and bronchioles. ...
Article
Full-text available
Humidification of inspired gas is mandatory for all mechanically ventilated patients to prevent secretion retention, tracheal tube blockage and adverse changes occurring to the respiratory tract epithelium. However, the debate over "ideal" humidification continues. Several devices are available that include active and passive heat and moisture exchangers and hot water humidifiers Each have their advantages and disadvantages in mechanically ventilated patients. This review explores each device in turn and defines their role in clinical practice.
... 3,4 Conversely, animal studies (which used an ultrasonic nebulizer) showed that over-humidification can also cause injuries and alter respiratory function. 1,5 In our opinion, an optimal humidification system has the following properties: adequate heat and humidification, irrespective of the ambient temperature, the patient's temperature, or minute volume (V E ); the lowest possible dead space and flow resistance; no condensate; ease of use; low cost. ...
Article
Full-text available
To improve the heat and humidification that can be achieved with a heat-and-moisture exchanger (HME), a hybrid active (ie, adds heat and water) HME, the Hygrovent Gold, was developed. We evaluated in vitro the performance of the Hygrovent Gold. We tested the Hygrovent Gold (with and without its supplemental heat and moisture options activated), the Hygrobac, and the Hygrovent S. We measured the absolute humidity, using a test lung ventilated at minute volumes of 5, 10, and 15 L/min, in normothermic (expired temperature 34 degrees C) and hypothermic (expired temperature 28 degrees C) conditions. We also measured the HMEs' flow resistance and weight after 24 h and 48 h. In its active mode the Hygrovent Gold provided the highest absolute humidity, independent of minute volume, in both normothermia and hypothermia. The respective normothermia and hypothermia absolute humidity values at 10 L/min were 36.3 + 1.3 mg/L and 27.1 + 1.0 mg/L with the active Hygrovent Gold, 33.9 + 0.5 mg/L and 24.2 + 0.8 mg/L with the passive Hygrovent Gold, 33.8 + 0.56 mg/L and 24.4 + 0.4 mg/L with the Hygrobac, and 33.9 + 0.8 mg/L and 24.6 + 0.6 mg/L with the Hygrovent S. The efficiency of the tested HMEs did not change over time. At 24 h and 48 h the increase in weight and flow resistance was highest in the active Hygrovent Gold. The passive Hygrovent Gold provided adequate heat and moisture in normothermia, but the active Hygrovent Gold provided the highest humidity, in both normothermia and hypothermia.
Article
Aims and objectives To evaluate the necessity of oxygen humidification for low‐flow oxygen therapy in children with Pierre‐Robin syndrome. Background Whether to carry out humidification or not in the low‐flow oxygen delivery remains unclear, and currently there is no published study on this issue in the population of children. Therefore, it's necessary to conduct more studies to elucidate this issue. Design A randomized controlled trial (RCT). Methods We attempt to report this RCT in comply with the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT). 188 children with Pierre‐Robin syndrome will be expected to inclusion. The participants will be randomly divided into the humidified group (n = 94) and non‐humidified group (n = 94) at a ratio of 1:1. For humidified group, the oxygen will be routinely humidified with disposable bottle containing sterile water, whereas for non‐humidified group, the oxygen will not be humidified. Average arterial oxygen partial pressure (PaO2) and carbon dioxide partial pressure (PaCO2), incidence of ventilator‐associated pneumonia (VAP), nasal cavity dryness, nasal mucosal bleeding and bacterial contamination of the humidified bottle, the cost of nasal oxygen therapy and duration of ICU stay are collected and analyzed. Results The study is planned to start in May 2019, and the results will be expected in July 2020. Conclusions This study is expected to provide a credible evidence on the necessity of routine oxygen humidification in low‐flow oxygen delivery. Relevance to Clinical Practice Understanding the role of oxygen humidification and no humidification for low‐flow oxygen therapy in the population of children is beneficial to the nursing care of health care providers in clinical setting. This article is protected by copyright. All rights reserved.
Article
Nasal high flow (nHF) therapy is a commonly used method of providing non‐invasive respiratory support for neonates. It has several potential mechanisms of action: continuous distending pressure, nasopharyngeal dead space washout, provision of heated and humidified gases and reduction of work of breathing. nHF is used in a number of clinical scenarios for preterm and term infants, including primary respiratory and post‐extubation support. In recent years, large trials have generated evidence pertinent to these indications. Novel applications for nHF in neonates warrant further research: during endotracheal intubation, for initial delivery room stabilisation of preterm infants and in conjunction with minimally invasive surfactant therapy.
Chapter
The administration of unconditioned medical gases disrupts respiratory function and results in the loss of heat and body water. Airway humidification can be performed using passive techniques, such as heat and moisture exchangers (HMEs), coaxial circuits, low fresh‐gas flow rates, and maintaining fresh (non‐desiccated) CO2 absorbent. Active airway heating and humidification devices are more effective than passive techniques and include heated humidifiers, nebulizers and heated breathing circuits. Positive airway pressure devices, such as positive end‐expiratory pressure (PEEP) valves, can also be applied to the anesthetic machine to assist with ventilatory management in veterinary patients during general anesthesia.
Article
Aims: To determine the effects of low-flow oxygen therapy with humidified or non-humidified oxygen in adult patients. Background: Although non-humidified oxygen in low-flow oxygen therapy is recommended by many guidelines, humidifying oxygen regardless of oxygen flow has been routinely performed in China and Japan and further studies are needed to evaluate the evidence. Design: A systematic review and meta-analysis that comply with the recommendations of the Cochrane Collaboration were conducted. Data sources: Studies (1980-2016) were identified by searching PUBMED, EMBASE, Science Direct, Cochrane library, CNKI and Wanfang Database. Methods: We performed a comprehensive, systematic meta-analysis of randomized controlled trials on the efficacy of humidified and non-humidified low-flow oxygen therapy. Summary risk ratios or weighted mean differences with 95% confidence intervals were calculated using a fixed- or random-effects model. Results: Twenty-seven randomized controlled trials with a total number of 8876 patients were included. Non-humidified oxygen offers more benefits in reducing the bacterial contamination of humidifier bottles, as shown by the mean operating time for oxygen administration and the respiratory infections compared with humidified oxygen therapy. No significant differences were found in dry nose, dry nose and throat, nosebleed, chest discomfort, the smell of oxygen and SpO2 changes. Conclusions: The routine humidification of oxygen in low-flow oxygen therapy is not justifiable and non-humidified oxygen tend to be more beneficial. However, considering that the quality of most included studies is poor, rigorously designed, large-scale randomized controlled trials are still needed to identify the role of non-humidified oxygen therapy. This article is protected by copyright. All rights reserved.
Chapter
When the tracheal mucosa is bypassed via endotracheal tube (ETT) intubation or from a surgically placed tracheostomy, humidification is essential to preserve tracheobronchial mucosal integrity [1]. Without humidification, the tracheal mucosa will lose ciliary function, develop inspissated secretions, and the underlying connective tissue will undergo structural changes [2–5]. Williams et al. performed a meta-analysis evaluating the relationship between the humidity and temperature of inspired gas and airway mucosal function [6]. They developed a model suggesting above or below optimal temperature, and humidity conditions can lead to impaired airway mucosal dysfunction, or, vice versa, that adequate mucociliary function is an indicator of ideal humidification. Oostdam et al. showed animals that inspired dried air demonstrated a significant reduction of extravascular water of the loose connective tissue of the airways and an increase in airways resistance to histamine [2]. ETT occlusion secondary to thickened or dried secretions is also strongly linked to suboptimal humidification [5, 7]. The most common way to avoid these and other potential complications (Box 1) is accomplished by applying humidification from non-­heated-wire humidifiers, heated-wire humidifiers, or a heat and moisture exchanger (HME) [4, 8]. The goal of each of these humidification devices is to provide tracheal humidification consisting of heat and moisture to the inspired gas with a minimum of 30 mgH2O/l or 100% relative humidity with a delivered gas at 30°C [4, 5].
Chapter
The upper airway extends from the nose to the major bronchi. It fulfils two major functions; firstly it humidifies and heats inspired gas. Secondly it filters and expels particles via the muco-ciliary elevator. The upper airway provides the alveoli with relatively warm, moist, particle-free gas.
Article
Objective This work aims to investigate the incidence rate and possible influencing factors of sputum crust obstruction in cannula of patients with artificial airway. Methods 427 patients with different critical illness were established artificial airway by tracheal intubation or tracheotomy. Occurrence and possible influencing factors of sputum crust obstruction in cannula were recorded when all patients were given clinical criteria care for ventilated patients, such as wetting and heating of artificial airway, sputum suction and dilution, turning shot sputum and exhaustive treatment for their primary disease. Results Sputum crust obstruction in cannula occurred in 69 patients, the incidence rate was 16.2%, and it was highest in patients with severe traumatic brain injury, reached 20.4%. Sputum crust obstruction in cannula was more likely to happen to patients with lung infection, sticky sputum, long intubated time and no cough reflex. Conclusions Even after the adequate prevention and care, sputum crust obstruction in cannula is still a common clinical complication of artificial airway. Especially in patients with gravis type craniocerebral injury, lung infection, sticky sputum, long intubated time and no cough reflex, who need to get close attention. At the same time, new method to prevention sputum crust obstruction in cannula is clinically required.
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Heat-moisture exchanger (HME) is an inexpensive and effective device used to prevent respiratory complications that can be caused by endotracheal tube insertion during general anesthesia. But, HME can increase airway resistance and be occluded by the patient's secretions. Whether a HME could be occluded by clear fluids such as condensate in the airway circuit is not certain yet. In vitro, a case of HME occlusion by normal saline was reported. We report a case of HME obstruction by distilled water came from the heated wire circuit which was unintentionally connected to the HME.
Article
Inhaled air is cold and dry. The highly vascularized nasal mucosa warms and humidifies it, and makes it suitable for breathing. The surface area of the nasal mucosa is enlarged by the three nasal turbinates. As the air is drawn around these, the laminar airflow becomes turbulent. Eddy currents allow better contact of the inspired air with the mucosa and facilitate the transfer of heat and humidity.
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It has been reported that continuous positive airway pressure therapy introduces negative nasal side-effects including sneezing, itching, nasal dryness, nasal congestion and/or a runny nose. As these symptoms are suggestive of nasal dysfunction, heated humidification is often used to fully saturate and heat the inhaled air to core body temperature. It is expected that this relieves the nasal mucosa from having to supply, or recover, heat and moisture from inspired and expired air. This review summarizes the current in vitro and in vivo knowledge relevant to nasal air-conditioning, and identifies further investigations necessary to improve our understanding the changes that occur during nasal continuous positive airway pressure therapy. Investigations into nasal airway fluid transportation, airflow regulation and heat and fluid supply may lead to a therapy temperature/pressure/humidification algorithm that optimizes these parameters for a prescribed therapy pressure. Optimization could lead to a reduction in titration pressure and improved treatment compliance.
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Bronchiolitis, a respiratory illness, is the leading cause of hospitalization for infants. The authors examined whether environmental factors contributed to the severity of the bronchiolitis illness. They compiled environmental data (temperature, dew point, wind speed, precipitation, altitude, and barometric pressure) to augment clinical data from a 30-center prospective cohort study of emergency department patients with bronchiolitis. They analyzed these data using multivariable logistic regression. Higher altitude was modestly associated with increased retractions (odds ratio [OR] = 1.6; 95% confidence interval [CI] = 1.1-2.1; p < .001) and decreased air entry (OR = 2.0; 95% CI = 1.6-2.6; p < .001). Increasing wind speed had a minor association with more severe retractions (OR = 1.3; 95% CI = 1.1-1.7; p = .02). Higher dew points had a minor association with lower admission rates (OR = 0.9; 95% CI = 0.8-0.996; p = .04). Altitude and environmental climate variables appear to have modest associations with the severity of bronchiolitis in the emergency department. Further studies need to be conducted, however, on limiting exposure to these environmental variables or increasing humidity before making broad recommendations.
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We searched the MEDLINE, CINAHL, and Cochrane Library databases for articles published between January 1990 and December 2011. The update of this clinical practice guideline is based on 184 clinical trials and systematic reviews, and 10 articles investigating humidification during invasive and noninvasive mechanical ventilation. The following recommendations are made following the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) scoring system: 1. Humidification is recommended on every patient receiving invasive mechanical ventilation. 2. Active humidification is suggested for noninvasive mechanical ventilation, as it may improve adherence and comfort. 3. When providing active humidification to patients who are invasively ventilated, it is suggested that the device provide a humidity level between 33 mg H(2)O/L and 44 mg H(2)O/L and gas temperature between 34°C and 41°C at the circuit Y-piece, with a relative humidity of 100%. 4. When providing passive humidification to patients undergoing invasive mechanical ventilation, it is suggested that the HME provide a minimum of 30 mg H(2)O/L. 5. Passive humidification is not recommended for noninvasive mechanical ventilation. 6. When providing humidification to patients with low tidal volumes, such as when lung-protective ventilation strategies are used, HMEs are not recommended because they contribute additional dead space, which can increase the ventilation requirement and P(aCO(2)). 7. It is suggested that HMEs are not used as a prevention strategy for ventilator-associated pneumonia.
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Standard practice within the neonatal unit is to use heated humidified gas as it decreases respiratory complications in neonates requiring respiratory support. Using cold unhumidified gases during resuscitation could potentially cool the baby as well as exacerbate potential lung injury. We aimed to study the temperature and humidity aspects of using heated, humidified gas for neonatal resuscitation. A heated patient circuit was connected to a T-piece resuscitator via a humidifier. An oxygen flowmeter was set at 10 L/min. Temperature recordings at the humidifier chamber (T1), distal temperature probe (T2) and T-piece (T3) were taken over 20 min at 30s intervals. A humidity sensor was placed at T3. Target temperatures were not reached. Time to 36°C (mean (sd)): T1 11.1 min (1.71); T3 11.6 min (1.77). T2 took 13.6 min (1.07) to reach 39°C. T1 and T3 were within ±1°C at 5.1 min (0.6). A biphasic relationship demonstrated the time lag between the temperatures of the heated patient circuit and the humidifier chamber. T3 strongly correlated to T1 when T1 is ≥28°C (r(2)=0.85). Humidity was difficult to measure and results were inferred from temperature recordings. This in vitro test showed that heated, humidified gas is possible during neonatal resuscitation. Adequate time must be allowed for the humidifier chamber to warm to near optimal temperature. The patient circuit is initially heated faster than the humidifier chamber. The displayed T1 temperature correlates to the temperature at T3 at ≥28°C.
Article
Heat and moisture exchangers (HMEs) are used for airway humidification in mechanically ventilated patients and have been evaluated only under hospital conditions. U.S. Air Force aeromedical evacuation transports are performed under rugged conditions further complicated by the cold and dry environment in military aircrafts, and HMEs are used to provide airway humidification for patients. This study evaluated 10 commercial HMEs using a test system that simulated aeromedical evacuation conditions. Although the American National Standards Institute recommends inspired air to be at an absolute humidity value of > or = 30 mg/L for mechanically ventilated patients, the highest absolute humidity by any HME was approximately 20 mg/L. Although none of the HMEs were able to maintain a temperature high enough to achieve the humidity standard of the American National Standards Institute, the clinical significance of this standard may be less important than the relative humidity maintained in the respired air, especially on evacuation flights of short duration.
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The objectives of this study were to evaluate a method for measuring BTV in ventilated patients and to study the short-term effect of general anesthesia with midazolam, Fentanyl, pancuronium and O2:N2O on BTV. The study included phantom measurements on a bronchoscopy model and the determination of BTV in patients in a convenience sample trial. The study took place in a university hospital. Fourteen patients undergoing major abdominal surgery with planned postoperative mechanical ventilation were included in the study. All patients gave their written informed consent to participate in the study. Bronchial mucus transport velocity was measured with a small volume (0.05 to 0.08 ml) of technetium 99m-labeled albumin microspheres with an activity of 3 MBq. The radiolabeled bolus was deposited on the dorsal mucosal surface at the distal end of the right and left main bronchus via flexible bronchoscopy. The movement of the microspheres toward the trachea was visualized and recorded using a scintillation camera; quantitative evaluation utilized the condensed image. The technique was validated in a bronchoscopy model and in an intubated patient by moving a radioactive drop in a catheter through the main bronchi at velocities from 0 to 20 mm/min. The velocities determined by the image processing technique correlated well with the data by the model and patient determination (right bronchus, r = 1.0; left bronchus, r = 1.0). In seven ventilated patients, mechanical irritation by the fiberscope produced no significant effect on BTV. The BTV was measured preoperatively in seven conscious patients one day before surgery while they received local anesthesia with 10 ml of 1 percent lidocaine and postoperatively while they received intubation anesthesia. The preoperative and postoperative BTV values showed no significant differences (10.5; 5.7 to 13.7 mm/min; vs 9.7 (3.7 to 15.3) (median with range). By this method, bronchial transport velocity can be determined in a relatively short time in ventilated patients. General anesthesia with midazolam, Fentanyl, pancuronium and O2:N2O does not influence BTV.
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The airway response to inhaled histamine is known to be influenced by various stimuli (e.g., infection, ozone). Temperature (T) has been shown to affect it in vitro. We studied whether T and humidity (H) modify airway response to inhaled histamine in normal subjects. Twelve normal subjects 21 to 46 yr of age (mean age, 29 yr) performed two similar histamine inhalation tests, the only difference being the conditions of the inspired air. One test was done while breathing cold dry air (mean T +/- SEM, -17.3 +/- 1.8 degrees C; relative H, 0%), and the other while breathing warm humid air (mean T +/- SEM, 33.9 +/- 0.5 degrees C; relative H, 100%). Whereas the geometric mean histamine concentration required to produce a 15% fall in FEV1 in the warm humid tests was 22.7 mg/ml, it was 11.9 mg/ml in the cold dry test (p less than 0.01). It is concluded that the T and H of inspired air modify the airway response to inhaled histamine in normal subjects.
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The variation in respiratory water loss (RWL) over time, expressed as the mass of water vapor lost per liter (body temperature and pressure, saturated) of ventilation (MH2O), was investigated in two groups: (1) children with exercise-induced asthma; and (2) healthy children. Children were matched for age and sex and went without medication for at least 12 hours before each experiment. The children breathed dry warm air (TI = 28.4 degrees C +/- 0.3 degree C) for 15 minutes while bicycling at constant and moderate work load (50 W). The MH2O was measured by collecting and weighing the expired water vapor (1) at rest breathing in warm conditions of inspired gas (control values), (2) every five minutes during exercise while breathing dry warm air, and (3) four minutes after the end of exercise. Pulmonary function tests were performed before and six minutes after exercise. The results were abnormal only in children with exercise-induced asthma. During exercise, RWL significantly fell (compared to control value) at the tenth and 15th minute in both groups. Whereas normal subjects recovered their initial values for MH2O four minutes after stopping exercise, asthmatic children still had a reduction in respiratory water loss. During exercise, MH2O decreased a little more in healthy than in asthmatic children. The decrease in MH2O in both groups suggests that the means to fully humidify expired gas are overwhelmed by thermal stress. The lack of increase in MH2O in asthmatic children on stopping exercise suggests that the airway mucosa is unable to produce enough water vapor and is thus dehydrated and probably hyperosmotic.
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Determine the utility of a proposed algorithm in allowing safe, efficient humidification in mechanically ventilated patients using both a hygroscopic condenser humidifier (HCH) and heated humidifier (HH). A prospective study using an algorithm to chose humidification devices based on physical examination and sputum characteristics. All patients admitted to the surgical ICU. One hundred twenty consecutive patients requiring mechanical ventilation (MV) were studied. Patients were examined by the attending respiratory care practitioner and given either an HCH or HH. If patients demonstrated any of the following--thick or tenacious secretions, core temperature < 32 degrees C, or bloody secretions--they were given an HH. All others used an HCH. If any of the above conditions occurred during HCH use, the patient was given an HH. Duration of ventilation, incidence of nosocomial pneumonia, ventilator circuit colonization, and mortality were determined for patients in each group. Cost of humidification devices, number of suctioning procedures per day, and volume of saline solution instilled were also recorded. Initially, 27 percent (32/120) of patients used an HH and 73 percent (88/120) used an HCH. During the study, ten patients required changing to an HH during HCH use. Patients in the HH group were more likely to have preexisting lung disease and had a longer duration of ventilation (83 +/- 21 h) and higher mortality (21 percent). Patients in the HCH group were more likely to be postoperative, had shorter durations of ventilation (38 +/- 14 h), and lower mortality (9 percent). There was no difference in the incidence of nosocomial pneumonia between the two groups (9 percent vs 6 percent) and endotracheal tube occlusion did not occur in either group. Circuit colonization was common in the HH group (64 percent) but rate in the HCH group (5 percent). Cost per day was significantly less for the HCH group ($4 vs $19.80). Patients who required a change from HCH to HH did so at a mean of 5 days. The proposed algorithm resulted in cost-efficient and safe application of humidification devices in patients in the surgical ICU.
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We postulated that water condensate in endotracheal tubes (ETTs) transports bacteria in the ETTs into the lungs during mechanical ventilation. Thirty-two ETTs obtained from freshly extubated patients were studied under wet and dry conditions using a physiologic lung model. All bacteria expelled from the ETTs were collected on culture plates positioned beneath the ETT. The lung model was ventilated with saturated air at 37 degrees C over two time periods (60 min each), one in which condensation formation was prevented and the second in which condensation formed within the ETT. A mean of 457.6 colony-forming units (CFU)/h were expelled with condensation compared to a mean of 2.4 CFU/h without condensation. We concluded that bacteria were continuously transported from the ETT into the lungs during mechanical ventilation in water droplets. Prevention of water condensation abolishes this constant bacterial inoculation in a lung model.
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We compared the effects of humidity delivered by the circle system at low fresh gas flows (FGF) with a conventional two-limb and coaxial circuit on the structure and function of the tracheobronchial epithelium in dogs. Animals were anaesthetized and mechanically ventilated using an anaesthesia ventilator to maintain normocarbia. Group I (control) animals received a FGF equal to the required minute ventilation mimicking an open circuit technique. Group II and III animals had FGF set at 20% of the required minute ventilation. Group II used a two-limb circuit and Group III used a coaxial circuit. Relative humidity and temperature of inspired gases were measured at baseline and hourly afterwards. In the first experiment, biopsies of the tracheobronchial tree were obtained bronchoscopically at baseline and then hourly for six hours. Microscopic examination of these samples allowed calculation of mean ciliary length. In the second experiment, tracheal mucus flow velocity (TMFV) was measured at baseline and hourly afterward, using a cinebroncho-fibrescopic method. Delivered absolute humidity was greatest with low FGF and the coaxial circuit, followed by low FGF and a conventional circuit, and high FGF (15±1.4 vs 9±0.8 vs 5±0.4 mg H 2 O, P<0.01) after two hours. Mean cilia length (μ m) and TMFV (mm/min) fell during the first hour in all three groups. At hour two TMFV returned to baseline in Group III and was significantly greater than Groups I and II (0.8±0.4 vs 8.6±1.1 vs 15.4±2.1, P<0.001). Mean ciliary length demonstrated a similar pattern with reductions from baseline in all three groups for the first two hours. Groups II and III had an increase in cilia length beginning at hour three and were both significantly greater than Group I at hours 3 through 6 (1.3±0.5 vs 3.2±1.1 vs 4.2±0.8, P <0.001). Alterations in tracheobronchial structure and function result from exposure to dry gases and are amplified by the duration of exposure. Our findings suggest a minimum of 12 to 15 mg H 2 O/l is necessary to prevent these alterations. In this study, the combination of low FGF and a coaxial anaesthesia circuit reached this minimum threshold more quickly than a conventional two-limb circuit.
Article
BACKGROUND: The use of humidifiers with a heating wire incorporated into the inspiratory limb of the ventilator circuit has become commonplace in mechanical ventilatory support. The heating wire in the circuit, however, may represent a potential hazard with regard to inspissation of secretions in the upper airway, especially in an artificial airway, due to reduced relative humidity. The current International Standard for airway humidification specifies only absolute humidity (AH) without regard for relative humidity (RH) or temperature. We studied whether either RH or the temperature range and AH should be specified in the Standard to maintain adequate RH. METHODS and MATERIALS: Five kinds of gases with various humidities were passed through an endotracheal-tube model, in which a brown water-soluble gel on dry filter paper was used as a substitute for secretions. Because the gel was hydrated by moisture from the delivered gas, the gel melted and a brown stain spread over the dry filter paper to the extent that the gas could hydrate the gel. The stains were measured and the stained area calculated by computer. The extent of each stained area was assessed with respect to RH, AH, and temperature of the gas. RESULTS: Gases satisfying the recommendations of the International Standard (ie, AH > 30 mg H2O/U), but with low RH, were no more advantageous for hydrating the gel than a gas (AH < 30 mg H2O/L) saturated with water vapor (ie, RH = 100%). The extent to which the brown water- soluble gel stained an increasing area of filter paper, which we assessed as the ability to provide humidification, was almost directly proportional to RH rather than AH or temperature. CONCLUSION: The current International Standard for humidification of bypassed airways should specify either RH or the temperature range with AH of the delivered gas.
Article
Twenty-four cases were studied to establish the relationship between spontaneous hypothermia occurring during surgical operations and the energy expenditure in the early postoperative period. The average maximum increase in oxygen consumption was 68 percent above resting preoperative values when the temperature had fallen by more than 0.2 °C. A fall in body temperature of 0.3 to 1.2 °C. resulted in an average increase in oxygen consumption of 92 percent, but reductions in temperature of more than 1.2 °C. were associated with only a 40 percent rise in oxygen consumption. Penthrane, nitrous oxide, cyclopropane, and fluothane, in that order, were associated with increasingly high postoperative oxygen consumption. The various sources of excessive heat loss under operating room conditions are enumerated, and methods of prevention are discussed.
Article
Experimental data have been presented which suggest that bypassing the nose with artificial airways is well compensated by the ability of these airways to imitate the heat and moisture exchange normally occurring in the nose. The lower airway can also carry on during anaesthesia the same heating, moistening, and recondensing functions that it apparently performs during normal life. Our results, obtained during clinical anaesthesia with the semi-closed circle absorption, indicate that the heat and moisture patterns disclosed along the airway are similar, in practice, to those found in the conscious subject breathing through his nose. This is so mainly for the following reasons: (1) inspired gas mixtures enter the airway with a water vapour tension higher than that usually found in ambient air; ( 2 ) moisture from expired air is conserved by condensation all along the airway and is recaptured during the next inspiratory phase. The high concentrations of water made available through these processes reduce the burden laid upon the respiratory mucosa to transudate further amounts of water. Wide temperature oscillations between inspiration and expiration occur in the respiratory tract until the lower airway is reached. These variations are important features in the physiological mechanisms of water condensation in expiration and water recapture in inspiration. Through these temperature changes, the respiratory tract mucosa, the endotracheal tube, and the swivel valve adjust the amount of water conserved during expiration and contribute significantly to water economy and balance during the anaesthesia with the semi-closed circle.
Article
The effect of breathing warm humidified air upon bronchoconstriction induced with body cooling or inhalation of methacholine was studied in two groups of eight asthmatic subjects. One group had the body cooled using one-minute exposures, first to a cold shower at 15 degrees C and then to a current of wind. The other group received methacholine by inhalation until a decrease of 20 percent or more occurred in the forced expiratory volume in one second. Both groups of asthmatic subjects were tested when breathing room air and warm humidified air. Pulmonary functions were assessed before and after cooling of the body and during inhalation of methacholine. Breathing warm humidified air substantially reduced bronchoconstriction induced by body cooling, but not that induced by inhalation of methacholine. Thus, bronchoconstriction induced by cooling of the body appears to be related to cooling of the airways, which may be compensated by breathing warm humidified air.
Article
Damage to the ciliated cells of the tracheobronchial tree and incidence of postoperative pulmonary complications were measured by point-scoring systems in 202 patients who breathed dry and humidified anesthetic gases for 225 +/- 78 min. The incidence of postoperative pulmonary complications decreased as the humidity of administered anesthetic gases increased from 0 to 32.5 mg H2O/l. A similar relationship was found between the amount of inhaled moisture and the damage to the ciliated epithelium of the tracheobronchial tree. These results appear to indicate that a high inspired humidity is beneficial for operations on normothermic patients, and that cellular damage caused by dryness is a possible contributory factor in the production of the pulmonary atelectasis that follows stoppage of the mucociliary transport system in the immmediate postoperative period.
Article
The effect of the inhalation of dried (less than 40% water-saturation) or humidified air (100% water-saturation at 25, 30, 35 and 40 degrees C) was studied in dogs in which a tracheostomy had been performed to determine the optimal humidity. After inhalation for various periods, the dogs were killed and pieces of lung tissue were excised for analysis of surfactant. Sections of the trachea and the primary to tertiary bronchi were taken for scanning electron microscopic examination. Structural changes were observed in the trachea of dogs inhaling dried at and in the tertiary bronchi of dogs inhaling 100% water-saturated air at 35 degrees C. No changes was observed after 24 h in dogs which had inhaled 100% water-saturated air at 25 degrees C under anaesthesia or at 30 degrees C without anaesthesia. Consequently, the optimal range of humidity was determined to be 100% water-saturation between 25 and 30 degrees C.
Article
The influence of varying humidity levels in the air surrounding the mucous membrane of rabbit tracheae has been investigated in vitro at 34 degrees C, 37 degrees C and 40 degrees C. The following results were obtained: (1) The average mucociliary wave frequency was linearly reduced following decreasing levels of relative humidity (r.h.) from 90% to 20%. (2) A temperature of 40 degrees C was more detrimental to the mucociliary function than that of 34 degrees C and 37 degrees C (body temperature) at decreasing levels of r.h. (3) At decreasing levels of r.h. the duration of experiments with preservation in recordable activity ("mucociliary survival time") was significantly shorter (p smaller than 0.05) between 50% and 40% r.h. than between 60% and 50% r.h.
Article
To compare the effects on canine ciliary and bronchial mucosal function of varying periods of ventilation with dry vs. humidified gas mixtures, 29 anesthetized dogs underwent 2, 4, and 6 hours of ventilation through a Carlen's double-lumen tube. Six dogs were evaluated by clearance studies, nine by differential bronchospirometry, six by surfactant studies, six by electron microscopy, and two by ventilation scanning. By means of two separate respiratory systems, dry gas (DG) was used to ventilate the right lung, and humidified gas (HG) ventilated the left lung in each dog. Serial chest roentgenograms showed more rapid clearance of inspired tantalum dust from the HG-ventilated lung in each of the six dogs, the disparity in clearance between the two lungs being more pronounced after longer periods of ventilation. The surface tension in DG-ventilated lungs increased fourfold, whereas in HG-ventilated lungs it increased only twofold as compared to preoperative values. Longer periods of ventilation did not change the surface tension appreciably in either DG- or HG-ventilated lungs. Scanning electron micrographs of bronchial mucosa from DG-ventilated lungs showed tangling and matting of cilia with a granular and stringy material attached to most cilia; these changes were much less pronounced in HG-ventilated lungs. Bronchospirometric studies showed an increase in ventilatory function in each of the lungs ventilated with the HG mixture (percent Vo2 on 100 percent oxygen increased 27.7 percent) to compensate for the decreased gas exchange provided by the contralateral DG-ventilated lung. Function in each of the lungs returned to normal within 24 hours. Ventilation scans with Xenon133 showed no apparent change in isotope uptake in the HG-ventilated lungs as compared to the DG lungs during the first 24 hours after ventilation. The observations from the present study suggest that ventilation of canine lungs with DG for 4 or more hours dries mucus and transiently retards mucociliary clearance and gas exchange. These changes may be minimized by ventilation with a humidified gas mixture. Application of these findings to patients undergoing prolonged general anesthesia and to lung preservation studies is suggested.
The intrathoracic airways of humans play a prominent part in conditioning inspired air. During inspiration the air is warmed and humidified by the movement of heat and water from the mucosa as a direct function of the temperature and vapor pressure gradients that exist. In this process, the mucosa is cooled. During expiration, the gradients are reversed, and heat and water are given back into the airways. At low levels of ventilation, most of the conditioning process takes place in the upper air passages; however, as ventilation rises, more and more of the tracheobronchial tree becomes involved, and incompletely conditioned air penetrates deeply into the distal airways before it is brought to equilibrium with body conditions. It is likely that the heat required to condition the inspired air is derived from the bronchial circulation, but this has not yet been definitely proved. In normal persons, the thermal events associated with the conditioning of inspired air do not produce any changes in pulmonary mechanics. In contrast, in asthmatics, the airway cooling of hyperpnea and the rapid rewarming that develops when hyperpnea is terminated evoke bronchoconstriction.
Article
Since the introduction of a humidifier with a heating wire, we have frequently experienced severe upper airway obstruction from consolidation of secretions, previously unencountered when a humidifier without a heating wire was used. Such problems led to the suspicion that the heating wire incorporated into the breathing circuit of the heated humidifier might be the cause. Therefore, we scheduled an experiment to assess the hypothesis that relative humidity, rather than absolute humidity, is a dominant factor in the case of drying secretions in the upper airway when using such a humidifier. Three clinical case reports and an experiment with a tracheal model. Intensive care units at Saitama Medical Center, Saitama Medical School, Saitama, Japan. Three intubated patients. An experiment with a tracheal model showed that gas with a higher temperature and lower relative humidity (35 degrees C, 48%) deprived the tracheal model of significantly more water (5.9 +/- 0.2 [SD] g) than gas with a lower temperature and higher relative humidity (24 degrees C, 87%) (2.9 +/- 0.4 g; p less than .01), even though the gases contained the same amount of water vapor (19 mg H2O/L) minus the same absolute humidity. A heated humidifier with a heating wire incorporated into the breathing circuit may be dangerous when only temperature is monitored and controlled. Relative humidity, rather than absolute humidity, is a dominant factor in the case of drying secretions in the upper airway when using such a humidifier.
Article
To compare the degree of tracheobronchial damage in newborn lambs ventilated for 6 hrs with relative humidities of 30% or 90% and continuous positive airway pressure breathing, conventional mechanical ventilation of 25 and 60 breaths/min, or high frequency flow-interrupted ventilation at 600 breaths/min. Tracheobronchial damage secondary to mechanical ventilation remains a major iatrogenic lesion of the newborn despite substantial advances in both mechanical design and ventilatory techniques. A histologic scoring system was used to compare the damage noted in the tracheobronchial epithelium of newborn lambs after 6 hrs of conventional mechanical ventilation or high-frequency flow-interrupted ventilation at two relative humidities. Three groups of animals were ventilated for 6 hrs with an FIO2 of 0.21 at 36.0 degrees C and relative humidity of 90%. The first group received continuous positive airway pressure of 4 cm H2O, the second group received slow rate, conventional mechanical ventilation at 25 breaths/min, and the third group received fast rate, conventional mechanical ventilation at 60 breaths/min. Two other groups of animals were ventilated for 6 hrs with an FIO2 of 0.21 at 36.0 degrees C and relative humidity of 30%. The first group was ventilated with high-frequency flow-interrupted ventilation at 600 breaths/min and the second group with slow rate, conventional mechanical ventilation at 25 breaths/min. Two additional groups served as nonintubated controls; one group was killed immediately after sedation and the other group was killed after 6 hrs of sedation. The damage was mild but significantly different from controls when 90% humidity was used and there was no difference in the histology score between continuous positive airway pressure breathing and conventional mechanical ventilation at 25 or 60 breaths/min. Significant inflammation, erosion, necrosis, and blistering occurred with both conventional mechanical ventilation at 25 breaths/min and high-frequency flow-interrupted ventilation at 600 breaths/min when 30% humidity was used. The damage was only found 5 mm below the tip of the endotracheal tube and not at 3.5 cm beyond the endotrachea tube in the trachea nor in the right main bronchus. These data indicate that endotracheal intubation and mechanical ventilation, regardless of the method of ventilation, cause damage to the tracheal mucosa, but that poorly humidified inspired gases cause significantly greater damage.
Article
Adequate humidification of inspired gases with HMEs during long-term MV remains controversial. In this study, a comparison is made between tracheal secretions during long-term MV either with HME or conventional HH. Both the HME and HH groups were similar with respect to age, sex, diagnosis, duration of MV, SAPS and mortality. Temperature of gases in the tracheal tube was lower and the amount of tracheal instillations was greater in the HME group than in the HH group. Tracheal secretions became thicker between day 1 (control) and day 5, in the HME group than in the HH group. Four and two tube occlusions occurred in HME and HH groups, respectively. Tracheal bacterial colonization was similar in the two groups. Given the advantages of HME (reduced nurses' work and financial cost), HME could be routinely used under cautious surveillance and replaced by HH if difficulty in suctioning occurs.
Article
The efficiencies of airway heat and moisture exchanging filters in reducing respiratory water losses and increasing airway temperatures during general anesthesia were studied in five tracheally intubated patients given isoflurane, nitrous oxide, and oxygen anesthesia during controlled ventilation. Filters (Humid-Vent Filter, Humid-Vent 1, Pall Conserve, Siemens 150, and ThermoVent 600) were placed between the Y-piece of the anesthesia circle system and the endotracheal tube for 40 min each. Airway temperature, esophageal temperature, and water loss (determined by weighing expired water collected in CaSO4) were measured every 10 min. All of the filters reached near-maximum efficiency in reducing water losses within 10 min. The Humid-Vent Filter and Siemens 150 filters were most efficient, the Pall Conserve and ThermoVent 600 less efficient. Airway temperature rapidly increased 2 degrees-8 degrees C during each trial. The more efficient the filter in conserving water, the greater the airway temperature. The respiratory heat conserved by these filters represents 5.5%-7.2% of the estimated total metabolic heat production during anesthesia in adults.
Article
A 75-year-old man with obstructive sleep apnea and secondary right heart failure was started on nasal CPAP therapy. Shortly thereafter he experienced massive life-threatening epistaxis requiring nasal packing and hospitalization. The epistaxis was thought to be due to the drying effect of nasal CPAP.
Article
The hypothesis that both active and passive airway humidification prevents hypothermia in infants and children, but that neither decreases the duration of postoperative recovery was tested. Twenty-seven ASA physical status 1 or 2 patients were studied who weighed between 5 and 30 kg, underwent superficial operations, were anesthetized with halothane and 70% N2O, and whose lungs were ventilated via a Rees modification of an Ayre's t-piece. The children were randomly assigned to receive active airway humidification and warming using an MR450 Servo airway heater and humidifier set at 37 degrees C (n = 10), passive airway humidification using the Humid-Vent 1 heat and moisture exchanger placed between the Ayre's t-piece and the endotracheal tube (n = 8), or no airway humidification and heating (control, n = 9). Distal tracheal and tympanic membrane temperatures and airway humidity were recorded during the first 90 min of surgery. Rectal temperature was measured during the postanesthetic recovery period. Relative humidity of inspired respiratory gases was approximately 30% in the control group and approximately 90% in the group given active airway humidification. Initial inspired humidity in the passive humidification group (50%) increased to approximately 80%, a level not significantly different from that in the active group after 80 min of anesthesia. Central body temperature increased 0.25 degrees C during active active airway humidification and heating, whereas temperature decreased 0.25 degrees C during passive humidification and 0.75 degrees C without airway humidification. Distal tracheal temperature was significantly higher in the groups given passive and active humidification than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
This study compares the thermal transfer and rewarming characteristics of heated aerosol inhalation (HAI) alone and combined with peritoneal lavage (PEL) or pleural lavage (PLL). Closed-system PEL and PLL are equally efficient at rewarming hypothermic dogs and do so at a rate approximating 6 degrees C/h/m2. Cardiovascular responses to PEL and PLL were similar. Serum electrolytes, protein, Hct, and arterial blood gases were comparable and little changed when compared in prehypothermia and postrewarming periods. HAI alone provides little heat for rewarming; more heat is realized from endogenous metabolism. Nevertheless, HAI's ease of use and possible selective cardiac rewarming characteristics argue for its inclusion with other methods of active rewarming. The use of PEL or PLL is governed by clinical circumstances.
Article
We compared the effect of breathing dry air (0.70 mg H2O/l) with that of breathing room air (8.62 mg H2O/l) in guinea pigs anesthetized with urethane. The data showed that breathing dry air caused a reduction of extravascular water (EVW) in the trachea (P less than 0.01) but not the lung. Structural analysis showed that this water loss occurred from the loose connective tissue of the submucosa. Histamine dose response curves performed on the animals showed that breathing dry air caused an increase in the maximum response (delta max RL) (P less than 0.01) without changing either the dose required to produce 50% of the delta max RL or the ratio of delta max RL to this dose. We conclude that breathing dry air produces an acute reduction of EVW of the loose connective tissue of the airways and an increase in the maximum response to histamine.
The tussive and bronchoconstrictive effects of hyperpnea with cold air (HCA) are described in 3 patients with exercise-induced cough, 7 volunteers with exercise-induced cough, and 7 asymptomatic volunteers. Cough associated with HCA exceeded baseline cough in each of the patients and volunteers with exercise-induced cough and in all but one of the asymptomatic volunteers. The time course of cough was similar in each group. Maximal cough frequency occurred during the first 5 min after HCA and persisted to a much lesser degree during the ensuing 26 min. The time course of bronchoconstriction was similar to that of cough, with maximal decrements in specific airway conductance measured 5 min after HCA. Pretreatment with albuterol blocked HCA-induced bronchoconstriction but had no effect on HCA-induced cough. No subject in any of the 3 groups was hyperreactive to methacholine aerosols. In subjects who are nonhyperreactive to methacholine aerosols, HCA has a characteristic, reproducible, and predictable tussive effect. Thus, HCA may be a useful tool for investigating the mechanism of cough and for evaluation of antitussive drugs.
Article
Eleven hypothermic patients were treated by heat supplied via the airway. Three patients died during rewarming, three died of unrelated causes several days after successful rewarming and five survived. Core temperatures were measured by a low reading mercury rectal thermometer and by a thermistor probe inserted into the rectum or mid-oesophagus. In every patient the core temperature rose without any initial after-drop. The problems of the method are discussed and the suggestion made that it might be applicable in rescue work, in the treatment of elderly hypothermic patients, and in combating accidental hypothermia in the operating theatre.
Article
A controlled double-blind study was undertaken to ascertain whether humidification of the anaesthetic gas altered the pulmonary complication rate as compared with dry gas, when administered in a non-rebreathing system to adult patients undergoing abdominal and/or transthoracic operations. Eighty-four patients, anaesthetized on an average for 5 hours, were studied. Sequential analysis showed that there was no significant difference in complication rate between the humidified and the non-humidified groups. The complications in both groups were all transient and harmless. Under the conditions of the study, no reason was found to add the potential risks associated with routine use of humidifiers during anaesthesia.
Article
Airway heat and humidity were investigated in patients whose anaesthesia involved endotracheal intubation. When delivered gases were saturated with water vapour, inspiratory moisture gain kept pace with temperature increase, and all relative humidities remained high. This occurred even when the supplied gas was saturated at room temperature, and the inspiratory temperatures rose more than 5°C en route to the trachea through the artificial airway. The findings are related to possible effects on the respiratory mucosa, and to alterations in total body heat balance.
Article
Observations of mucus flow in the trachea were made on greyhounds under barbiturate anesthesia breathing air at 37° C, at various levels of relative humidity, through an endotracheal tube. The distance travelled by a marker, lycopodium powder, in the mucus was measured at 5 min intervals through a right angled telescope passed down the endotracheal tube. Mucus flow at an inspired relative humidity of 100% was comparable to published values. No difference between flows at inspired relative humidities of 100% and 75% was found. A significant reduction in flows at 50% and 25% relative humidity was found, followed by cessation of flow in 5 of the 7 dogs at 50% relative humidity, and in all 7 at 25%. This would suggest that gas introduced at the top of an endotracheal tube at 37° C should have a relative humidity of over 50%, and preferably 75%, to maintain tracheal mucus flow. This would correspond to 100% relative humidity at 32° C but it remains to be seen within what temperature range mucus flow is maintained.
Article
Mucus flow rates were measured in the intact trachea of anaesthetized dogs, using a radioactive tracer technique. Measurements were made before intubation, and after intubation at inspired air temperatures of 32, 37 and 42°C, with a constant inspired water vapour content of 33 mg/l.; and again at each temperature with a relative humidity of 75%. No significant difference in mucus flow rate was found under any of these conditions.
Article
In a retrospective study of 100 patients treated with prolonged mechanical ventilation, water retention without evidence of cardiac failure developed in 19. This was associated with radiologic evidence of pulmonary edema and with the following significant changes: a mean gain in weight of 2.6 kg; a mean increase in the alveolar-arterial oxygen tension gradient of 127 mm of mercury; a decrease in vital capacity of 29 per cent; a reduction in estimated compliance of 31 per cent; a fall in hematocrit of.13 percent; and a decrease in serum sodium of 5.80 mEq per liter. These changes were reversed after the institution of a negative water balance by restriction of water intake and by diuretic therapy. Radiologic improvement was usually prompt. The appearance of pulmonary edema may be related to a relative water overload, a rise in antidiuretic hormone production or subclinical cardiac failure.
Article
Apparatus is described which can provide a certain amount of heat for the central rewarming of a hypothermic patient. This equipment is portable and cheap and can be used by non-medical people. Examples are given of the quantities of heat involved which can amount to 30 per cent of the heat production of a hypothermic patient.
Article
Ultrasonically nebulized distilled water was administered to healthy individuals, children with cystic fibrosis, and patients with asthma. Changes in airway resistance and expiratory flow volume curves (EFVC) were measured following a 15 minute exposure to the mist. Only in asthmatic children were significant decreases in FVC, FEV1, Vmax, V50, V25 and increases in sRaw noted. No consistent improvement or deterioration was detected in the healthy subjects or in the children with cystic fibrosis. Such a mist may be contraindicated in children with asthma but may be relatively innocuous in children with cystic fibrosis.