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Pressure-controlled versus volume-controlled ventilation: Does it matter?
Abstract
Volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) are not different ventilatory modes, but are different control variables within a mode. Just as the debate over the optimal ventilatory mode continues, so too does the debate over the optimal control variable. VCV offers the safety of a pre-set tidal volume and minute ventilation but requires the clinician to appropriately set the inspiratory flow, flow waveform, and inspiratory time. During VCV, airway pressure increases in response to reduced compliance, increased resistance, or active exhalation and may increase the risk of ventilator-induced lung injury. PCV, by design, limits the maximum airway pressure delivered to the lung, but may result in variable tidal and minute volume. During PCV the clinician should titrate the inspiratory pressure to the measured tidal volume, but the inspiratory flow and flow waveform are determined by the ventilator as it attempts to maintain a square inspiratory pressure profile. Most studies comparing the effects of VCV and PCV were not well controlled or designed and offer little to our understanding of when and how to use each control variable. Any benefit associated with PCV with respect to ventilatory variables and gas exchange probably results from the associated decelerating-flow waveform available during VCV on many ventilators. Further, the beneficial characteristics of both VCV and PCV may be combined in so-called dual-control modes, which are volume-targeted, pressure-limited, and time-cycled. PCV offers no advantage over VCV in patients who are not breathing spontaneously, especially when decelerating flow is available during VCV. PCV may offer lower work of breathing and improved comfort for patients with increased and variable respiratory demand.
... Controlled ventilation can be divided into volume controlled ventilation (VCV) and pressure controlled ventilation (PCV) [17] . In the VCV mode, the parameters such as the tidal volume, respiratory rate and respiratory ratio are controlled by the ventilator [18] . As shown in Figure 5, the flow rate waveform is square waves and the inspiratory flow rate is constant. ...
... In the PCV mode, we set the airway pressure and frequency, and use deceleration flow to maintain the airway pressure at the pre-set level. As shown in Figure 6, the flow rate waveform is of decreasing wave and the inspiratory flow rate is decreasing [18] . The single breath cycle time is 3 s, and the maximum tidal volume reaches 1000mL at 1.5 s. ...
... person's health and lung condition. 2 Artificial airway connected as part of the ventilation enable interventions such as suctioning for the removal of secreted mucus and delivery of aerosolized medications deep within the lung airways. ...
We advanced a novel model to calculate viscoelastic lung compliance and airflow resistance in presence of mucus, accounting for the quasi-linear viscoelastic stress-strain response of the parenchyma (alveoli) tissue. We adapted a continuum-based numerical modeling approach for the lung, integrating the fluid mechanics of the airflow within individual generations of the bronchi and alveoli. The model accounts for elasticity of the deformable bronchioles, resistance to airflow due to the presence of mucus within the bronchioles, and subsequent mucus flow. Simulated quasi-dynamic inhalation and expiration cycles were used to characterize the net compliance and resistance of the lung, considering the rheology of the mucus and viscoelastic properties of the parenchyma tissue. The structure and material properties of the lung were identified to have an important contribution to the lung compliance and airflow resistance. The secondary objective of this work was to assess whether a higher frequency and smaller volume of harmonic air flow rate compared to a normal ventilator breathing cycle enhanced mucus outflow. Results predict, lower mucus viscosity and higher excitation frequency of breathing are favorable for the flow of mucus up the bronchi tree, towards the trachea.
... To avoid hyperventilation during CPR, the ventilator needs to follow a standard compression to ventilation ratio that usually sets at 30:2 [10,11]. Multiple parameters of ventilator, including the tidal volume (VT), ventilation frequency (VF), positive end expiratory pressure (PEEP), inspiratory flowrate (IF), expiratory time (ET) and inspiratory time (IT) are usually specified for working mode [12]. Volume controlled intermittent positive pressure ventilation (V-IPPV), which requires VT as default parameters and VF as controlled parameters, is the most common mode for CPR ventilation [13,14]. ...
... Perioperative PCV is a commonly applied mode of invasive ventilation and is preferred to volume-controlled ventilation for some reasons like better patient comfort and lower work of ventilation [16]. Especially for postoperative ventilatory care and ICU patients in need of invasive ventilation, PCV modes like "biphasic positive airway pressure" (BIPAP, Draeger Medical GmbH, Lübeck, Germany) are commonly utilized. ...
Background In on-pump cardiac surgery, lungs are at high risk of periprocedural organ impairment because of
atelectasis formation, ventilator-induced lung injury, and hyperinflammation due to the cardiopulmonary bypass
which results in postoperative pulmonary complications in half of this patient population. The new ventilation
mode flow-controlled ventilation (FCV) uniquely allows full control of ins- and expiratory airway flows. This approach
reduces the mechanical power of invasive ventilation as a possible cause of ventilator-induced lung injury. The scope
of FLOWVENTIN HEARTSURG is to compare perioperative individualized FCV with best clinical practice pressure-controlled
ventilation (PVC) modes in patients with elective on-pump cardiac surgery procedures. We hypothesize that
the postoperative inflammatory response can be reduced by the perioperative application of FCV compared to PCV.
Methods FLOWVENTIN HEARTSURG is a single-center, randomized, parallel-group trial with two intervention arms:
perioperative PCV modes (n = 70, PCV group) with an individualized positive end-expiratory pressure (PEEP) and a
tidal volume of 6–8 ml/kg predicted bodyweight compared to perioperative FCV (n = 70, FCV group) with an individualized
PEEP and driving pressure, resulting in a liberal tidal volume. As the primary study endpoint interleukin
8 plasma level is assessed 6 h after cardiopulmonary bypass as a surrogate biomarker of systemic and pulmonary
inflammation. As secondary aims clinically relevant patient outcomes are analyzed, e.g., perioperative lung function
regarding oxygenation indices, postoperative pulmonary and extra-pulmonary complications, SIRS-free days as well
as ICU and total inpatient stays. As additional sub-studies with an exploratory approach perioperative right ventricular
function parameters are assessed by echocardiography and perioperative lung aeration by electrical impedance
tomography.
Discussion Current paradigms regarding protective low tidal volume ventilation are consciously left in the FCV
intervention group in order to reduce mechanical power as a determinant of ventilator-induced lung injury in this
high-risk patient population and procedures. This approach will be compared in a randomized controlled trial with
current best clinical practice PCV in FLOWVENTIN HEARTSURG.
... Therefore, some investigators suggested that PCV might provide a lower respiratory work and a better comfort. 10 The superiority of the PCV on VCV was demonstrated for the supply of the sufficient oxygenation and normocapnia in obese patients, who were diagnosed with ARDS in intensive care units. In addition, it was emphasized that hemodynamics might proceed more stable in PCV as a result of the limitation of the pressure. ...
Mechanical ventilators are used in intensive care units and in operating rooms. It consists of filtering, air compression, and humidifying control board units. A mechanical ventilator is a device that combines the patient’s respiratory tract to assist the respiratory system in conditions where the patient has difficulty in breathing or after operations. The device supplies controlled air to the patient by the inner compressor. The breakdown of the oxygen sensor and the heating of the circuit boards (if the filter is not cleaned) are the most common problems in mechanical ventilators. They may not stabilize with required values over time and the tester is used to maintain stability. The device must be calibrated regularly or if the gauge of the test device does not match the standard values of gas flow, volume, pressure and oxygen parameters. The anaesthesia machine delivers pressurised medical gases like air, oxygen, nitrous oxide, heliox etc. and controls the gas flow individually. It composes a known and controlled gas mixture at a known flow rate and then delivers it to the gas outlet of the machine. Therefore, the fresh gas flow is serviced to the anaesthesia circle breathing system in order to make artificial respiration in the patient and monitor vital functions closely. For patient safety, the most important thing is to check out the system regularly and in pre-use and to ensure that there exists a ready and functioning alternative solution for ventilating the patient’s lungs. Standards and regulations for the production and post-market surveillance of medical devices, including anaesthesia devices, have been examined. Given the lack of proposed methodology for post-market surveillance of both devices, a new validated method is introduced.
Volume-controlled ventilation is a form of controlled ventilation. A targeted tidal volume is set and administered to the patient. The set flow determines the speed at which the air is administered. The breathing cycle depends on the settings of the ventilation rate and respiratory time ratio. Volume-controlled ventilation appears to be the classic form of ventilation. It has the advantage of ensuring safe and reliable ventilation for the patient. Disadvantages include unknown high ventilation pressures, pendulum air, shear forces and emphysema formation.Volume-controlled ventilation is a form of controlled ventilation. The work of breathing is performed by the respirator. Unlike pressure-controlled ventilation, where ventilation pressures are set, a tidal volume is set and administered to the patient. Volume-controlled ventilation appears to be the classic form of ventilation. It has the advantage of providing safe and reliable ventilation for the patient with a secured inspiratory volume.
Introduction:
Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated.
Methods:
Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmH2O until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured.
Results:
The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmH2O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH2O) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min).
Discussion:
We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.
Envenomation by snakes in Elapidae and Viperidae families have been associated with respiratory failure in dogs and cats. Mechanical ventilation may be required for hypoventilation due to neuromuscular paralysis or hypoxemia due to pulmonary hemorrhage or aspiration pneumonia. Median incidence of dogs and cats with snake envenomation that require mechanical ventilation is 13% (0.06–40%). Standard treatment of snake envenomation in dogs and cats includes prompt administration of appropriate antivenom and management of envenomation complications such as coagulopathy, rhabdomyolysis and acute kidney injury. When mechanical ventilation is required, overall prognosis is good with appropriate treatment. Standard anesthetic protocols and mechanical ventilator settings are generally appropriate, with lung protective ventilation strategies typically reserved for patients with pulmonary disease. Median survival to discharge for cats and dogs with elapid envenomation is 72% (76–84%) with 33 h (19.5–58 h) median duration of mechanical ventilation and 140 h (84–196 h) median hospitalization. This article reviews indications for mechanical ventilation in cats and dogs with snake envenomation, and discusses ventilator settings, anesthetic and nursing considerations, complications and outcomes specific to this disease.
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