Static pressure-volume curve characteristics are moderate estimators of optimal airway pressures in a mathematical model of (primary/pulmonary) acute respiratory distress syndrome

Abstract

Objective: To study the value of objective pressure-volume characteristics for predicting optimal airway pressures and the development of atelectasis and overstretching during a structured lung volume recruitment procedure with subsequent reduction in airway pressures. Methods: We used a mathematical model of a lung with adjustable characteristics of acute respiratory distress syndrome (ARDS) characteristics. Simulations were performed in five grades of ARDS in the presence of pure alveolar or combined alveolar-small airway closure as well complete or incomplete lung volume recruitability. For each simulation optimal end-expiratory pressure was determined. A static pressure-volume curve was constructed and objective characteristics of this curve calculated. The predictive value of these characteristics for end-expiratory atelectasis, overstretching, and optimal end-expiratory pressure was assessed. Results: Simultaneous alveolar recruitment and overstretching during inflation were more pronounced than alveolar derecruitment and overstretching during deflation. End-expiratory pressure needed to prevent significant alveolar collapse in severe ARDS resulted in maximal safe tidal volumes that may be insufficient for adequate ventilation using conventional mechanical ventilatory modes. Plateau pressures well below the "upper corner point" (airway pressure where compliance decreases) resulted in significant alveolar overstretching. Conclusions: A recruitment maneuver followed by subsequent reduction in airway pressure limits end-expiratory atelectasis, overstretching, and pressure. None of the objective characteristics of the pressure-volume curve was predictive for end-expiratory atelectasis, overstretching, or optimal airway pressure. © Springer-Verlag 2004.