Effect of positive end-expiratory pressure on respiratory compliance in children with acute respiratory failure.

We studied the effect of positive end-expiratory pressure (PEEP) on the compliance of the respiratory system (Crs) in 25 children (age, 3 weeks to 10 years) requiring mechanical ventilation. Functional residual capacity (FRC) measurements were performed at 2 cm H2O increments, from 0 to 18 cm H2O of PEEP, and the FRC values were regressed versus PEEP. Static Crs, Crs/kg, and specific compliance (Crs/FRC) were calculated for each PEEP level. When FRC normality was reached Crs/kg improved in 15/25 (60%) patients but decreased in 2/25 (8%). Overall, Crs/kg increased from a mean +/- SE of 0.94 +/- 0.09 to 1.35 +/- 0.13 mL/cm H2O/kg (P = 0.003) and Crs/FRC from a mean +/- SE of 0.067 +/- 0.006 to 0.077 +/- 0.007 mL/cm H2O/mL (P = 0.057). The maximum compliance (mean Max Crs/kg, 1.56 +/- 0.12 mL/cm H2O/kg, and mean Max Crs/FRC, 0.089 +/- 0.005 mL/cm H2O/mL) was significantly higher than the compliance at the clinically chosen PEEP level and the compliance at the PEEP that normalized FRC. Maximum compliance was achieved within 4 cm H2O of the PEEP that normalized FRC. In 14/25 (60%) of cases the PEEP at maximum compliance coincided with the PEEP that resulted in FRC normalization. We concluded that static respiratory compliance improves in most (but not all) children with acute respiratory failure when FRC is normalized. Static respiratory compliance reaches maximum levels at PEEP values that are close (but not equal) to those that result in FRC normalization. Thus, assessment of the effect of PEEP on compliance is required in individual patients.