An Extension to the First Order Model of Pulmonary Mechanics to Capture a Pressure dependent Elastance in the Human Lung

Mechanical ventilation (MV) is a lifesaving therapy for patients with the acute respiratory distress syndrome. However, selecting the optimal MV settings is a difficult process as setting a high positive end-expiratory pressure (PEEP) value will improve oxygenation, but can produce ventilator induced lung injuries (VILI). To find a suitable value is patient specific and depends on different things like the underlying illness and the current state. In this study, a respiratory model that defined constant bronchial resistance and pressure-dependent variable elastance was fitted to pressure volume (PV) responses for 12 datasets of 10 acute respiratory distress syndrome (ARDS) patients which underwent a recruitment maneuver (RM) to open previous collapsed alveoli. We believe that the range of minimal elastance represents that range in which oxygenation can be improved by recruitment with reducing the risk of VILI. The first order model with a variable elastance (E(drs)) described by Chiew et al. (2011) was modified with a factor α to express added end-expiratory volume due to an increased PEEP. Model parameters were identified using a nonlinear least square method that optimized E(drs) agreement across PEEP-levels. The model yielded an increase in overlapping quality of pressure dependent E(drs)-curves. A best pressure range for PEEP could be identified in 9 of 12 datasets. The model could potentially provide a simple method of decision support at the bedside for clinicians and could prospectively an automated extend in mechanical ventilation devices.