Effects of recruitment/derecruitment dynamics on the efficacy of variable ventilation

Vermont Lung Center, Department of Medicine, University of Vermont College of Medicine, Burlington, VT 05405, USA.
Journal of Applied Physiology (Impact Factor: 3.06). 03/2011; 110(5):1319-26. DOI: 10.1152/japplphysiol.01364.2010
Source: PubMed


Variable (or noisy) ventilation (VV) has been demonstrated in animal models of acute lung injury to be superior to constant (or conventional) ventilation (CV), in terms of improved gas exchange and mitigation of lung injury, for reasons that are not entirely clear. We hypothesized that the efficacy of VV is related to the fact that recruitment and derecruitment of lung units are dynamic processes. To test this hypothesis, we modeled the lung computationally as a symmetrically bifurcating airway tree terminating in elastic units. Each airway was fully open or completely closed, at any point in time, according to its pressure history. The model is able to accurately mimic previous experimental measurements showing that the lungs of mice injured by acid aspiration are better recruited after 60 min of VV than CV. The model also shows that recruitment/derecruitment dynamics contribute to the relative efficacy of VV, provided lung units open more rapidly than they close once a critical opening or closing pressure threshold has been crossed. We conclude that the dynamics of recruitment and derecruitment in the lung may be important factors responsible for the benefits of VV compared with CV.

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    • "PROVAR is an investigator-initiated, single center, randomized controlled, two-arm trial comparing CV and VV in patients receiving mechanical ventilation during general anesthesia for open abdominal surgery. The study protocol is approved by the institutional review board of the Medical Faculty and the University Hospital Dresden, Germany (EK 174052011) and has been registered at (NCT01683578). "
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    ABSTRACT: Background General anesthesia usually requires mechanical ventilation, which is traditionally accomplished with constant tidal volumes in volume- or pressure-controlled modes. Experimental studies suggest that the use of variable tidal volumes (variable ventilation) recruits lung tissue, improves pulmonary function and reduces systemic inflammatory response. However, it is currently not known whether patients undergoing open abdominal surgery might benefit from intraoperative variable ventilation. Methods/Design The PROtective VARiable ventilation trial (‘PROVAR’) is a single center, randomized controlled trial enrolling 50 patients who are planning for open abdominal surgery expected to last longer than 3 hours. PROVAR compares conventional (non-variable) lung protective ventilation (CV) with variable lung protective ventilation (VV) regarding pulmonary function and inflammatory response. The primary endpoint of the study is the forced vital capacity on the first postoperative day. Secondary endpoints include further lung function tests, plasma cytokine levels, spatial distribution of ventilation assessed by means of electrical impedance tomography and postoperative pulmonary complications. Discussion We hypothesize that VV improves lung function and reduces systemic inflammatory response compared to CV in patients receiving mechanical ventilation during general anesthesia for open abdominal surgery longer than 3 hours. PROVAR is the first randomized controlled trial aiming at intra- and postoperative effects of VV on lung function. This study may help to define the role of VV during general anesthesia requiring mechanical ventilation. Trial registration NCT01683578 (registered on September 3 3012).
    Trials 05/2014; 15(1):155. DOI:10.1186/1745-6215-15-155 · 1.73 Impact Factor
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    • "Also, variable controlled mechanical ventilation has the potential to reduce histologic lung damage and pulmonary inflammation [18]. The exact mechanisms behind such effects have not been elucidated so far, but release of a lung surfactant [16,20], lung recruitment [21,22] and stochastic resonance [15,19,23] have been suggested. In addition, one randomized controlled trial suggested that intraoperative variable controlled mechanical ventilation improves oxygenation and respiratory system compliance in patients submitted for surgical repair of an aortic aneurysm [24]. "
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    ABSTRACT: In pressure support ventilation (PSV), a non-variable level of pressure support is delivered by the ventilator when triggered by the patient. In contrast, variable PSV delivers a level of pressure support that varies in a random fashion, introducing more physiological variability to the respiratory pattern. Experimental studies show that variable PSV improves gas exchange, reduces lung inflammation and the mean pressure support, compared to non-variable PSV. Thus, it can theoretically shorten weaning from the mechanical ventilator.Methods/design: The ViPS (variable pressure support) trial is an international investigator-initiated multicenter randomized controlled open trial comparing variable vs. non-variable PSV. Adult patients on controlled mechanical ventilation for more than 24 hours who are ready to be weaned are eligible for the study. The randomization sequence is blocked per center and performed using a web-based platform. Patients are randomly assigned to one of the two groups: variable PSV or non-variable PSV. In non-variable PSV, breath-by-breath pressure support is kept constant and targeted to achieve a tidal volume of 6 to 8 ml/kg. In variable PSV, the mean pressure support level over a specific time period is targeted at the same mean tidal volume as non-variable PSV, but individual levels vary randomly breath-by-breath. The primary endpoint of the trial is the time to successful weaning, defined as the time from randomization to successful extubation. ViPS is the first randomized controlled trial investigating whether variable, compared to non-variable PSV, shortens the duration of weaning from mechanical ventilation in a mixed population of critically ill patients. This trial aims to determine the role of variable PSV in the intensive care unit.Trial registration: NCT01769053.
    Trials 10/2013; 14(1):363. DOI:10.1186/1745-6215-14-363 · 1.73 Impact Factor
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    ABSTRACT: Purpose of review: Mechanical ventilation is one of the most important life support tools in the ICU, but it may also be harmful by causing ventilator-induced lung injury (VILI) and other deleterious effects. Advances in ventilator technology have allowed the introduction of numerous ventilator modes in an effort to improve gas exchange, reduce the risk of VILI, and finally improve outcome. In this review, we will summarize the studies evaluating some of the nonconventional ventilation techniques and discuss their possible use in clinical practice. Recent findings: Proportional assist ventilation and neurally adjusted ventilator assist are able to improve patient-ventilator synchrony, possibly sleep, and may be better tolerated than pressure support ventilation; both integrate the physiological concept of respiratory variability like noisy ventilation. Experimental or short-term clinical studies have shown physiological benefits with the application of biphasic pressure modes. Some of the automated weaning algorithms may reduce time spent on ventilator and decrease ICU stay, especially in a busy environment. Summary: Apart from the physiological and clinical attractiveness demonstrated in animals and small human studies, most of the nonconventional ventilator modes must prove their clinical benefits in large prospective trials before being applied in daily clinical practice.
    Current opinion in critical care 12/2012; 19(1). DOI:10.1097/MCC.0b013e32835c517d · 2.62 Impact Factor
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