Quantifying ventilator unloading in CPAP ventilation

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Abstract

The intrinsic (muscular) patient effort driving inspiration in non-invasive ventilation modes, such as continuous positive airway pressure (CPAP) therapy, has not been identified from non-invasive data. Current CPAP settings are based on clinical judgment and assessment of symptoms of respiratory distress. Non-optimal settings, including too much positive end expiratory pressure (PEEP) can cause unintended lung injury and ventilator unloading, where patient effort drops and the CPAP device enables too much work being imposed on the injured lung. Currently, there is no non-invasive means of quantifying or identifying these effects.

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Most cited references 39

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A. Raue, C. Kreutz, T Maiwald … (2009)

Mathematical description of biological reaction networks by differential equations leads to large models whose parameters are calibrated in order to optimally explain experimental data. Often only parts of the model can be observed directly. Given a model that sufficiently describes the measured data, it is important to infer how well model parameters are determined by the amount and quality of experimental data. This knowledge is essential for further investigation of model predictions. For this reason a major topic in modeling is identifiability analysis. We suggest an approach that exploits the profile likelihood. It enables to detect structural non-identifiabilities, which manifest in functionally related model parameters. Furthermore, practical non-identifiabilities are detected, that might arise due to limited amount and quality of experimental data. Last but not least confidence intervals can be derived. The results are easy to interpret and can be used for experimental planning and for model reduction. An implementation is freely available for MATLAB and the PottersWheel modeling toolbox at http://web.me.com/andreas.raue/profile/software.html. Supplementary data are available at Bioinformatics online.

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Alain Mercat, Jean-Christophe Richard, Bruno Vielle … (2008)

The need for lung protection is universally accepted, but the optimal level of positive end-expiratory pressure (PEEP) in patients with acute lung injury (ALI) or acute respiratory distress syndrome remains debated. To compare the effect on outcome of a strategy for setting PEEP aimed at increasing alveolar recruitment while limiting hyperinflation to one aimed at minimizing alveolar distension in patients with ALI. A multicenter randomized controlled trial of 767 adults (mean [SD] age, 59.9 [15.4] years) with ALI conducted in 37 intensive care units in France from September 2002 to December 2005. Tidal volume was set at 6 mL/kg of predicted body weight in both strategies. Patients were randomly assigned to a moderate PEEP strategy (5-9 cm H(2)O) (minimal distension strategy; n = 382) or to a level of PEEP set to reach a plateau pressure of 28 to 30 cm H(2)O (increased recruitment strategy; n = 385). The primary end point was mortality at 28 days. Secondary end points were hospital mortality at 60 days, ventilator-free days, and organ failure-free days at 28 days. The 28-day mortality rate in the minimal distension group was 31.2% (n = 119) vs 27.8% (n = 107) in the increased recruitment group (relative risk, 1.12 [95% confidence interval, 0.90-1.40]; P = .31). The hospital mortality rate in the minimal distension group was 39.0% (n = 149) vs 35.4% (n = 136) in the increased recruitment group (relative risk, 1.10 [95% confidence interval, 0.92-1.32]; P = .30). The increased recruitment group compared with the minimal distension group had a higher median number of ventilator-free days (7 [interquartile range {IQR}, 0-19] vs 3 [IQR, 0-17]; P = .04) and organ failure-free days (6 [IQR, 0-18] vs 2 [IQR, 0-16]; P = .04). This strategy also was associated with higher compliance values, better oxygenation, less use of adjunctive therapies, and larger fluid requirements. A strategy for setting PEEP aimed at increasing alveolar recruitment while limiting hyperinflation did not significantly reduce mortality. However, it did improve lung function and reduced the duration of mechanical ventilation and the duration of organ failure. clinicaltrials.gov Identifier: NCT00188058.