Abstract
BackgroundA recent prospective trial using porcine models of severe acute respiratory distress syndrome (ARDS) indicated that positive-pressure ventilation delivered by a conventional intensive care ventilator at a moderately high frequency allows safe reduction of tidal volume below 6 ml/kg, leading to more protective ventilation. We aimed to explore whether these results would be replicated when implementing similar ventilation strategies in a high-fidelity computational simulator, tuned to match data on the responses of a number of human ARDS patients to different ventilator inputs.MethodsWe evaluated three different strategies for managing the trade-off between increasing respiratory rate and reducing tidal volume while attempting to maintain the partial pressure of carbon dioxide in arterial blood (PaCO2) constant on a computational simulator configured with ARDS patient datasets.ResultsFor a fixed sequence of stepwise increases in the respiratory rate, corresponding decreases in tidal volume to keep the alveolar minute ventilation and inspiratory flow constant were calculated according to standard formulae. When applied on the simulator, however, these sequences of ventilator settings failed to maintain PaCO2 adequately in the virtual patients considered. In contrast, an approach based on combining numerical optimisation methods with computational simulation allowed a sequence of tidal volume reductions to be computed for each virtual patient that maintained PaCO2 levels while significantly reducing peak airway pressures and dynamic alveolar strain in all patients.ConclusionsOur study supports the proposition that moderately high-frequency respiratory rates can allow more protective ventilation of ARDS patients and highlights the potential role of high-fidelity simulators in computing optimised and personalised ventilator settings for individual patients using this approach.Electronic supplementary materialThe online version of this article (doi:10.1186/s40635-015-0068-8) contains supplementary material, which is available to authorized users.
Highlights
A recent prospective trial using porcine models of severe acute respiratory distress syndrome (ARDS) indicated that positive-pressure ventilation delivered by a conventional intensive care ventilator at a moderately high frequency allows safe reduction of tidal volume below 6 ml/kg, leading to more protective ventilation
Model matching to ARDS patient data The model was configured to match data from individual ARDS patients reported by Nirmalan and colleagues [23], which listed arterial and mixed venous blood gas values and cardiac output measurements taken from patients treated for ARDS
Why do strategies 1 and 2 result in large changes in PaCO2 when they are predicated on maintaining constant alveolar minute ventilation and inspiratory flow? The answer is provided by Fig. 6, which plots the relationship between the total dead space calculated in the simulation model and VT for each virtual patient
Summary
A recent prospective trial using porcine models of severe acute respiratory distress syndrome (ARDS) indicated that positive-pressure ventilation delivered by a conventional intensive care ventilator at a moderately high frequency allows safe reduction of tidal volume below 6 ml/kg, leading to more protective ventilation. Hickling et al [5] reported a 60 % decrease in the expected mortality rate among patients with ARDS by lowering VT In another trial, Amato et al [6] investigated changing conventional VT (12 ml/kg of predicted body weight, PBW) to low VT and reported a 46 % reduction in mortality. Amato et al [6] investigated changing conventional VT (12 ml/kg of predicted body weight, PBW) to low VT and reported a 46 % reduction in mortality This benefit was confirmed in the ARDS Network study with mortality decreased by 22 % in the low tidal volume intervention group [7]. Reducing VT by itself leads to worsened partial pressures of arterial oxygen (PaO2) and carbon dioxide (PaCO2) and arterial pH [8]
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