[Show abstract][Hide abstract] ABSTRACT: Background
The anaesthetic conserving device AnaConDa® (ACD) reflects exhaled anaesthetic agents thereby facilitating the use of inhaled anaesthetic agents outside operating theatres. Expired CO2 is, however, also reflected causing a dead space effect in excess of the ACD internal volume. CO2 reflection from the ACD is attenuated by humidity. This study tests the hypothesis that sevoflurane further attenuates reflection of CO2. An analysis of clinical implications of our findings was performed.
Twelve postoperative patients received mechanical ventilation using a conventional heat and moisture exchanger (HME, internal volume 50 ml) and an ACD (100 ml), the latter with or without administration of sevoflurane. The ACD was also studied with a test lung at high sevoflurane concentrations. Reflection of CO2 and dead space effects were evaluated with the single-breath test for CO2.
Sevoflurane reduced but did not abolish CO2 reflection. In patients, the mean dead space effect with 0.8% sevoflurane was 88 ml larger using the ACD compared with the HME (P
Preview · Article · May 2014 · BJA British Journal of Anaesthesia
[Show abstract][Hide abstract] ABSTRACT: The anesthetic conserving device (ACD) reduces consumption of volatile anesthetic drug by a conserving medium adsorbing exhaled drug during expiration and releasing it during inspiration. Elevated arterial CO2 tension (PaCO2) has been observed in patients using the ACD, despite tidal volume increase to compensate for larger apparatus dead space. In a test lung using room temperature dry gas, this was shown to be due to adsorption of CO2 in the ACD during expiration and release of CO2 during the following inspiration. The effect in the test lung was higher than in patients. We tested the hypothesis that a lesser dead space effect in patients is due to higher temperature and/or moisture attenuating rebreathing of CO2.
The lungs of 6 postoperative cardiac surgery patients were ventilated using a conventional heat and moisture exchanger (HME) or an ACD. The ACD was studied with a test lung at varying temperatures and moistures. Infrared spectrometry was used to measure apparent dead space by the single-breath test for CO2 as well as rebreathing of CO2.
In patients, the median apparent dead space was 136 mL (95% confidence interval [CI,] 120-167) larger using the ACD compared with an HME (after correction for difference in internal volume 100 and 50 mL, respectively). Median rebreathing of CO2 using the ACD was 53% (range 48-58) of exhaled CO2 compared with 29% (range 27-32) with an HME. The median difference in CO2 rebreathing was 23% (95% CI, 18-27). In the test lung apparent dead space using ACD was unaffected by body temperature but decreased from 360 to 260 mL when moisture was added. This decreased rebreathing of CO2 from 62% to 48%.
The use of an ACD increases apparent dead space to a greater extent than can be explained by its internal volume. This is caused by adsorption of CO2 in the ACD during expiration and release of CO2 during inspiration. Rebreathing of CO2 was attenuated by moisture. The dead space effect of the ACD could be clinically relevant in acute respiratory distress syndrome and other diseases associated with ventilation difficulties, but investigations with larger sample sizes would be needed to determine the clinical importance.
Full-text · Article · Dec 2013 · Anesthesia and analgesia
[Show abstract][Hide abstract] ABSTRACT: /st> Low tidal volume (V(T)), PEEP, and low plateau pressure (P(PLAT)) are lung protective during acute respiratory distress syndrome (ARDS). This study tested the hypothesis that the aspiration of dead space (ASPIDS) together with computer simulation can help maintain gas exchange at these settings, thus promoting protection of the lungs.
/st> ARDS was induced in pigs using surfactant perturbation plus an injurious ventilation strategy. One group then underwent 24 h protective ventilation, while control groups were ventilated using a conventional ventilation strategy at either high or low pressure. Pressure-volume curves (P(el)/V), blood gases, and haemodynamics were studied at 0, 4, 8, 16, and 24 h after the induction of ARDS and lung histology was evaluated.
/st> The P(el)/V curves showed improvements in the protective strategy group and deterioration in both control groups. In the protective group, when respiratory rate (RR) was ≈60 bpm, better oxygenation and reduced shunt were found. Histological damage was significantly more severe in the high-pressure group. There were no differences in venous oxygen saturation and pulmonary vascular resistance between the groups.
/st> The protective ventilation strategy of adequate pH or with minimal V(T), and high/safe P(PLAT) resulting in high PEEP was based on the avoidance of known lung-damaging phenomena. The approach is based upon the optimization of V(T), RR, PEEP, I/E, and dead space. This study does not lend itself to conclusions about the independent role of each of these features. However, dead space reduction is fundamental for achieving minimal V(T) at high RR. Classical physiology is applicable at high RR. Computer simulation optimizes ventilation and limiting of dead space using ASPIDS. Inspiratory P(el)/V curves recorded from PEEP or, even better, expiratory P(el)/V curves allow monitoring in ARDS.
Full-text · Article · Jul 2012 · BJA British Journal of Anaesthesia
[Show abstract][Hide abstract] ABSTRACT: The anaesthetic conserving device (ACD) AnaConDa(®) was developed to allow the reduced use of inhaled agents by conserving exhaled agent and allowing rebreathing. Elevated has been observed in patients when using this ACD, despite tidal volume compensation for the larger apparatus dead space. The aim of the present study was to determine whether CO(2), like inhaled anaesthetics, adsorbs to the ACD during expiration and returns to a test lung during the following inspiration.
The ACD was attached to an experimental test lung. Apparent dead space by the single-breath test for CO(2) and the amount of CO(2) adsorbed to the carbon filter of the ACD was measured with infrared spectrometry.
Apparent dead space was 230 ml larger using the ACD compared with a conventional heat and moisture exchanger (internal volumes 100 and 50 ml, respectively). Varying CO(2) flux to the test lung (85-375 ml min(-1)) did not change the measured dead space nor did varying respiratory rate (12-24 bpm). The ACD contained 3.3 times more CO(2) than the predicted amount present in its internal volume of 100 ml.
Our measurements show a CO(2) reservoir effect of 180 ml in excess of the ACD internal volume. This is due to adsorption of CO(2) in the ACD during expiration and return of CO(2) during the following inspiration.
Preview · Article · Apr 2012 · BJA British Journal of Anaesthesia
[Show abstract][Hide abstract] ABSTRACT: Introduction
The inspiratory flow pattern influences CO2 elimination by affecting the time the tidal volume remains resident in alveoli. This time is expressed in terms of mean distribution time (MDT), which is the time available for distribution and diffusion of inspired tidal gas within resident alveolar gas. In healthy and sick pigs, abrupt cessation of inspiratory flow (that is, high end-inspiratory flow (EIF)), enhances CO2 elimination. The objective was to test the hypothesis that effects of inspiratory gas delivery pattern on CO2 exchange can be comprehensively described from the effects of MDT and EIF in patients with acute respiratory distress syndrome (ARDS).
In a medical intensive care unit of a university hospital, ARDS patients were studied during sequences of breaths with varying inspiratory flow patterns. Patients were ventilated with a computer-controlled ventilator allowing single breaths to be modified with respect to durations of inspiratory flow and postinspiratory pause (TP), as well as the shape of the inspiratory flow wave. From the single-breath test for CO2, the volume of CO2 eliminated by each tidal breath was derived.
A long MDT, caused primarily by a long TP, led to importantly enhanced CO2 elimination. So did a high EIF. Effects of MDT and EIF were comprehensively described with a simple equation. Typically, an efficient and a less-efficient pattern of inspiration could result in ± 10% variation of CO2 elimination, and in individuals, up to 35%.
In ARDS, CO2 elimination is importantly enhanced by an inspiratory flow pattern with long MDT and high EIF. An optimal inspiratory pattern allows a reduction of tidal volume and may be part of lung-protective ventilation.
Preview · Article · Mar 2012 · Critical care (London, England)
[Show abstract][Hide abstract] ABSTRACT: Purpose Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation which is not fully reversible. Despite the heterogeneity of COPD, its diagnosis and staging is currently based solely on forced expiratory volume in 1 s (FEV1). FEV1 does not explain the underlying pathophysiology of airflow limitation. The relationship between FEV1, symptoms and emphysema extent is weak. Better diagnostic tools are needed to define COPD. Tomographic lung scintigraphy [ventilation/perfusion single photon emission tomography (V/P SPECT)] visualizes regional V and P. In COPD, relations between V/P SPECT, spirometry, high-resolution computed tomography (HRCT) and symptoms have been insufficiently studied. The aim of this study was to investigate how lung function imaging and obstructive disease grading undertaken using V/P SPECT correlate with symptoms, spirometric lung function and degree of emphysema assessed with HRCT in patients with COPD. Methods Thirty patients with stable COPD were evaluated with the Medical Research Council dyspnoea questionnaire (MRC) and the clinical COPD questionnaire (CCQ). Spirometry was performed. The extent of emphysema was assessed using HRCT. V/P SPECT was used to assess V/P patterns, total reduction in lung function and degree of obstructive disease. Results The total reduction in lung function and degree of obstructive disease, assessed with V/P SPECT, significantly correlated with emphysema extent (r = 0.66–0.69, p r = 0.62–0.74, p Conclusion V/P SPECT is sensitive to early changes in COPD. V/P SPECT also has the possibility to identify comorbid disease. V/P SPECT findings show a significant correlation with emphysema extent and spirometric lung function. We therefore recommend that scintigraphic signs of COPD, whenever found, should be reported. V/P SPECT can also be used to categorize the severity of functional changes in COPD as mild, moderate or severe.
No preview · Article · Mar 2011 · European Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: V/PSPECT has the potential to become a first hand tool for diagnosis of pulmonary embolism based on standardized technology and new holistic interpretation criteria. Pretest
probability helps clinicians choose the most appropriate objective test for diagnosis or exclusion of PE. Interpretation should also take into account all ventilation and perfusion patterns allowing diagnosis of other cardiopulmonary diseases than PE. In such contexts, V/PSPECT has excellent sensitivity and specificity. Nondiagnostic reports are ≤3%. V/PSPECT has no contraindication; it is noninvasive and has very low radiation exposure. Moreover, acquisition time for V/PSPECT is only 20 minutes. It allows quantification of PE extension which has an impact on individual treatment. It is uniquely useful for followup and research.
[Show abstract][Hide abstract] ABSTRACT: Ventilation/perfusion single-photon emission computed tomography (V/Q SPECT) is the scintigraphic technique of choice for the diagnosis of pulmonary embolism and many other disorders that affect lung function. Data from recent ventilation studies show that the theoretic advantages of Technegas over radiolabeled liquid aerosols are not restricted to the presence of obstructive lung disease. Radiolabeled macroaggregated human albumin is the imaging agent of choice for perfusion scintigraphy. An optimal combination of nuclide activities and acquisition times for ventilation and perfusion, collimators, and imaging matrix yields an adequate V/Q SPECT study in approximately 20 minutes of imaging time. The recommended protocol based on the patient remaining in an unchanged position during the initial ventilation study and the perfusion study allows presentation of matching ventilation and perfusion slices in all projections as well as in rotating volume images based upon maximum intensity projections. Probabilistic interpretation of V/Q SPECT should be replaced by a holistic interpretation strategy on the basis of all relevant information about the patient and all ventilation/perfusion patterns. PE is diagnosed when there is more than one subsegment showing a V/Q mismatch representing an anatomic lung unit. Apart from pulmonary embolism, other pathologies should be identified and reported, for example, obstructive disease, heart failure, and pneumonia. Pitfalls exist both with respect to imaging technique and scan interpretation.
Full-text · Article · Nov 2010 · Seminars in nuclear medicine
[Show abstract][Hide abstract] ABSTRACT: Elastic pressure/volume (P(el) /V) and elastic pressure/resistance (P(el) /R) diagrams reflect parenchymal and bronchial properties, respectively. The objective was to develop a method for determination and mathematical characterization of P(el) /V and P(el) /R relationships, simultaneously studied at sinusoidal flow-modulated vital capacity expirations in a body plethysmograph. Analysis was carried out by iterative parameter estimation based on a composite mathematical model describing a three-segment P(el) /V curve and a hyperbolic P(el) /R curve. The hypothesis was tested that the sigmoid P(el) /V curve is non-symmetric. Thirty healthy subjects were studied. The hypothesis of a non-symmetric P(el) /V curve was verified. Its upper volume asymptote was nearly equal to total lung capacity (TLC), indicating lung stiffness increasing at high lung volume as the main factor limiting TLC at health. The asymptotic minimal resistance of the hyperbolic P(el) /R relationship reflected lung size. A detailed description of both P(el) /V and P(el) /R relationships was simultaneously derived from sinusoidal flow-modulated vital capacity expirations. The nature of the P(el) /V curve merits the use of a non-symmetric P(el) /V model.
No preview · Article · Nov 2010 · Clinical Physiology and Functional Imaging
[Show abstract][Hide abstract] ABSTRACT: Lung scintigraphy is primarily used to diagnose pulmonary embolism. Ventilation imaging is often performed using (99m)Tc-DTPA or Technegas, an ultrafine dispersion of (99m)Tc-labeled carbon. Despite the common use of these radioaerosols, they have not been compared in an intraindividual study, and not with ventilation-perfusion (V/P) SPECT. The aim of the present head-to-head study was to systematically investigate differences in ventilation studies performed with (99m)Tc-diethylenetriaminepentaacetate (DTPA) and Technegas.
Sixty-three patients, 28 without and 35 with obstructive lung disease, were examined with V/P SPECT using both (99m)Tc-DTPA and Technegas. V/P SPECT images were randomized and assessed independently by 2 masked physicians according to a predefined scoring system. A paired comparison was performed using the Wilcoxon signed-rank test.
In both obstructive and nonobstructive disease, the overall unevenness of radiotracer deposition and the degree of central deposition were more pronounced in (99m)Tc-DTPA than Technegas studies. Because of better peripheral penetration, the extent of reverse mismatch was less when Technegas was used. Additionally, in obstructive disease, the degree of focal deposition in distal airways was more pronounced with (99m)Tc-DTPA. Mismatched perfusion defects were more frequently found with Technegas in obstructive disease.
This intraindividual comparative study shows that Technegas is the preferred radioaerosol, particularly in obstructive disease.
Full-text · Article · May 2010 · Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: Dead space negatively influences carbon dioxide (CO(2)) elimination, particularly at high respiratory rates (RR) used at low tidal volume ventilation in acute respiratory distress syndrome (ARDS). Aspiration of dead space (ASPIDS), a known method for dead space reduction, comprises two mechanisms activated during late expiration: aspiration of gas from the tip of the tracheal tube and gas injection through the inspiratory line - circuit flushing. The objective was to study the efficiency of circuit flushing alone and of ASPIDS at wide combinations of RR and tidal volume (V(T)) in anaesthetized pigs. The hypothesis was tested that circuit flushing and ASPIDS are particularly efficient at high RR.
In Part 1 of the study, RR and V(T) were, with a computer-controlled ventilator, modified for one breath at a time without changing minute ventilation. Proximal dead space in a y-piece and ventilator tubing (VD(aw, prox)) was measured. In part two, changes in CO(2) partial pressure (PaCO(2)) during prolonged periods of circuit flushing and ASPIDS were studied at RR 20, 40 and 60 minutes(-1).
In Part 1, VDaw, prox was 7.6 +/- 0.5% of V(T) at RR 10 minutes(-1) and 16 +/- 2.5% at RR 60 minutes(-1). In Part 2, circuit flushing reduced PaCO(2) by 20% at RR 40 minutes(-1) and by 26% at RR 60 minutes(-1). ASPIDS reduced PaCO(2) by 33% at RR 40 minutes(-1) and by 41% at RR 60 minutes(-1).
At high RR, re-breathing of CO(2) from the y-piece and tubing becomes important. Circuit flushing and ASPIDS, which significantly reduce tubing dead space and PaCO2, merit further clinical studies.
[Show abstract][Hide abstract] ABSTRACT: As emphasized in Part 1 of these guidelines, the diagnosis of pulmonary embolism (PE) is confirmed or refuted using ventilation/perfusion scintigraphy (V/P(SCAN)) or multidetector computed tomography of the pulmonary arteries (MDCT). To reduce the costs, the risks associated with false-negative and false-positive diagnoses, and unnecessary radiation exposure, preimaging assessment of clinical probability is recommended. Diagnostic accuracy is approximately equal for MDCT and planar V/P(SCAN) and better for tomography (V/P(SPECT)). V/P(SPECT) is feasible in about 99% of patients, while MDCT is often contraindicated. As MDCT is more readily available, access to both techniques is vital for the diagnosis of PE. V/P(SPECT) gives an effective radiation dose of 1.2-2 mSv. For V/P(SPECT), the effective dose is about 35-40% and the absorbed dose to the female breast 4% of the dose from MDCT performed with a dose-saving protocol. V/P(SPECT) is recommended as a first-line procedure in patients with suspected PE. It is particularly favoured in young patients, especially females, during pregnancy, and for follow-up and research.
Full-text · Article · Aug 2009 · European Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: Ventilation/perfusion scintigraphy, a first hand method for diagnosis of pulmonary embolism, PE, is challenged by tomography of the pulmonary arteries, CT. An additional method is based upon dead space analysis. Tomographic ventilation/perfusion scintigraphy, V/PSPECT is superior to planar technique. Important is interpretation criteria based upon pattern recognition and clinical information. With optimal strategy, the rate of non-diagnostic findings is only about 1%. The sensitivity of CT is too low to exclude subsegmental PE,. The radiation dose is for CT is several times higher than for V/PSPECT. Quantification of PE, only offered by V/PSPECT has impact on therapy and is vital for follow up. Limited availability of V/PSPECT makes CT an essential element in a strategy for diagnosis of PE. The single breath test for CO2 offers an alternative when imaging techniques are not available or when radiation is a particular problem in early pregnancy.
No preview · Article · Jul 2009 · Journal of Organ Dysfunction
[Show abstract][Hide abstract] ABSTRACT: Pulmonary embolism (PE) can only be diagnosed with imaging techniques, which in practice is performed using ventilation/perfusion scintigraphy (V/P(SCAN)) or multidetector computed tomography of the pulmonary arteries (MDCT). The epidemiology, natural history, pathophysiology and clinical presentation of PE are briefly reviewed. The primary objective of Part 1 of the Task Group's report was to develop a methodological approach to and interpretation criteria for PE. The basic principle for the diagnosis of PE based upon V/P(SCAN) is to recognize lung segments or subsegments without perfusion but preserved ventilation, i.e. mismatch. Ventilation studies are in general performed after inhalation of Krypton or technetium-labelled aerosol of diethylene triamine pentaacetic acid (DTPA) or Technegas. Perfusion studies are performed after intravenous injection of macroaggregated human albumin. Radiation exposure using documented isotope doses is 1.2-2 mSv. Planar and tomographic techniques (V/P(PLANAR) and V/P(SPECT)) are analysed. V/P(SPECT) has higher sensitivity and specificity than V/P(PLANAR). The interpretation of either V/P(PLANAR) or V/P(SPECT) should follow holistic principles rather than obsolete probabilistic rules. PE should be reported when mismatch of more than one subsegment is found. For the diagnosis of chronic PE, V/P(SCAN) is of value. The additional diagnostic yield from V/P(SCAN) includes chronic obstructive lung disease (COPD), heart failure and pneumonia. Pitfalls in V/P(SCAN) interpretation are considered. V/P(SPECT) is strongly preferred to V/P(PLANAR) as the former permits the accurate diagnosis of PE even in the presence of comorbid diseases such as COPD and pneumonia. Technegas is preferred to DTPA in patients with COPD.
Full-text · Article · Jul 2009 · European Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: Cyclofenil was evaluated versus placebo in the treatment of progressive systemic sclerosis (PSS, scleroderma) in a 2times6-month double-blind crossover study. The mean duration of disease was six years. Of 38 patients entering the study, 27 completed both periods. Reasons for drop-outs were very high liver transaminases in three cases, cardiac death in two, and drug allergy, alcoholic problems, suspected congestive heart failure, reactivation of tuberculosis, arteriosclerotic heart disease, and lethal progression of PSS in one case each. No fatality was attributed to cyclofenil. Liver enzyme abnormalities were seen in 13 of 35 active drug periods and in 5 of 30 placebo periods. Cutaneous and visceral involvement were assessed by a large battery of subjective parameters and objective tests. Overall improvement was seen during 17 drug periods and nine placebo periods (N.S.), but a paired comparison of the status at the end of each treatment period resulted in the following distribution: 15 were improved at the end of the drug period, four at the end of placebo period (p<0.01) and eight were unchanged. In patients with a disease duration of five years or less, joint stiffness and pain were less on drug than on placebo treatment (p<0.05). In the whole group, oesophageal peristalsis improved (p<0.05). Blood folate increased (p<0.01). Working capacity was lower after the drug period than after the placebo period (p<0.05). Several other parameters, however, did not change significantly. Cyclofenil appears to be a promising drug in the treatment of PSS and should be tested further in controlled long-term studies.
No preview · Article · Apr 2009 · Journal of Internal Medicine
[Show abstract][Hide abstract] ABSTRACT: The aim of this retrospective study is to illustrate clinical utility and impact of pulmonary embolism (PE) diagnostics of up to date Ventilation/Perfusion SPECT (V/P (SPECT)) applying holistic interpretation criteria.
During a 2-year period 2328 consecutive patients referred to V/P(SPECT) for clinically suspected PE were examined. Final diagnosis was established by physicians clinically responsible for patient care. To establish the performance of V/P(SPECT) negative for PE, patients were followed up by medical records for 6 months.
Ventilation/Perfusion SPECT was feasible in 99% of the patients. Data for follow-up were available in 1785 patients (77%). PE was reported in 607 patients (34%). Normal pattern was described in 420 patients (25%). Pathology other than PE such as a pneumonia, left heart failure, obstructive lung disease, tumour was described in 724 patients (41%). Report was nondiagnostic in 19 patients (1%). Six cases were classified as falsely negative because PE was diagnosed at follow-up and was fatal in one case. Six cases were classified as falsely positive because the clinician decided not to treat. In 608 patients with final PE diagnosis, 601 patients had positive V/P(SPECT) (99%). In 1177 patients without final PE diagnosis 1153 patients had negative V/P(SPECT) (98%).
Holistic interpretation of V/P(SPECT,) yields high negative and positive predictive values and only 1% of nondiagnostic findings and was feasible in 99% of patients. It is a responsibility and a challenge of nuclear medicine to provide optimal care of patients with suspected PE by making V/P(SPECT) available.
Full-text · Article · Nov 2008 · Journal of Internal Medicine
[Show abstract][Hide abstract] ABSTRACT: A high respiratory rate associated with the use of small tidal volumes, recommended for acute lung injury (ALI), shortens time for gas diffusion in the alveoli. This may decrease CO(2) elimination. We hypothesized that a postinspiratory pause could enhance CO(2) elimination and reduce Pa(CO(2)) by reducing dead space in ALI. In 15 mechanically ventilated patients with ALI and hypercapnia, a 20% postinspiratory pause (Tp20) was applied during a period of 30 min between two ventilation periods without postinspiratory pause (Tp0). Other parameters were kept unchanged. The single breath test for CO(2) was recorded every 5 min to measure tidal CO(2) elimination (VtCO(2)), airway dead space (V(Daw)), and slope of the alveolar plateau. Pa(O(2)), Pa(CO(2)), and physiological and alveolar dead space (V(Dphys), V(Dalv)) were determined at the end of each 30-min period. The postinspiratory pause, 0.7 +/- 0.2 s, induced on average <0.5 cmH(2)O of intrinsic positive end-expiratory pressure (PEEP). During Tp20, VtCO(2) increased immediately by 28 +/- 10% (14 +/- 5 ml per breath compared with 11 +/- 4 for Tp0) and then decreased without reaching the initial value within 30 min. The addition of a postinspiratory pause significantly decreased V(Daw) by 14% and V(Dphys) by 11% with no change in V(Dalv). During Tp20, the slope of the alveolar plateau initially fell to 65 +/- 10% of baseline value and continued to decrease. Tp20 induced a 10 +/- 3% decrease in Pa(CO(2)) at 30 min (from 55 +/- 10 to 49 +/- 9 mmHg, P < 0.001) with no significant variation in Pa(O(2)). Postinspiratory pause has a significant influence on CO(2) elimination when small tidal volumes are used during mechanical ventilation for ALI.
Preview · Article · Oct 2008 · Journal of Applied Physiology