A simple method for measuring the effect of PEEP on functional residual capacity during mechanical ventilation.

An indirect method for measuring the increment of functional residual capacity (FRC) produced by positive end-expiratory pressure (PEEP) during controlled mechanical ventilation was evaluated in 13 patients with acute respiratory failure. The actual FRC with and without PEEP was measured with a computerized nitrogen washout method. The results obtained did not show significant differences between the measured and the calculated increment of FRC. This indirect method accurately measures how much alveolar recruitment (estimated as increment of FRC) is produced by PEEP.