Effects of positive end-expiratory pressure increments can be predicted by computer simulation based on a physiological profile in acute respiratory failure

Abstract

Objective: We examined whether computer simulation predicts airway pressures after increments of positive end-expiratory pressure (PEEP) in acute respiratory failure. Design and setting: Prospective, nonrandomized comparative trial in an intensive care unit of a university hospital. Patients: Twelve consecutive acute respiratory failure patients. Interventions: PEEP increments from 0 to 2.5, 5, 7.5, 10, and 15 cmH2O. Measurements and results: A physiological profile comprising values for compliance, respiratory resistance and CO2 elimination as a function of tidal volume was established from a recording of ordinary breaths prior to increments of PEEP. Airway pressures and CO2 elimination were measured 30 s after resetting, pressures also after 10 min. Values from simulation of the resetting, based on the profile, were compared to measured values. The profiles indicated vast differences in physiology between the 12 subjects. Errors of simulation of airway pressures were nonsignificant or trivial up to PEEP levels of 10 cmH2O (95% of errors <3 cmH2O). After 10 min plateau pressure averaged 1.5 cmH2O lower than 30 s after resetting. At increments to PEEP 7.5, 10, and 15, CO2 elimination fell by on average 4%, 8%, and 11%, respectively. As tidal volume and respiratory rate was unchanged this was not predicted. Conclusions: On the basis of a simple lung model, simulation predicted effects of moderate increments of PEEP on airway pressures in patients with complex physiology.