Effect of positive end expiratory pressure on functional residual capacity and compliance in surfactant-treated preterm infants

Positive end expiratory pressure is routinely used when ventilating preterm infants. Elevation of PEEP increases lung. volume, as does surfactant treatment. The purpose of this study was to investigate the effect of various levels of PEEP within the range of 0.2 to 0.4 kPa on lung volume, compliance and gas exchange. We measured functional residual capacity, compliance of the respiratory system and arterial blood gases in 20 infants (median birth weight 1240 g, range 660-1690 g; median gestational age 28 weeks, range 24-32 weeks; postnatal age 3-4 days). The infants were studied at 72 hours after their last dose of natural surfactant. At this time the patients were routinely nursed at 0.3 kPa of PEEP, the PEEP level was lowered to 0.2 kPa or raised to 0.4 kPa in random order. The PEEP level was then changed to the third level 0.4 kPa or 0.2 kPa. Each new setting was maintained for 20 min before FRC, compliance and blood gases were measured. FRC was assessed using SF6 washout technique. Increasing PEEP from 0.2 to 0.3 to 0.4 kPa resulted in increases in FRC (p < 0.01) and oxygenation (ns) in all infants. In 16 infants compliance decreased and paCO(2) increased with elevation of PEEP. Only in 4 infants compliance increased and CO2 fell. Conclusion: In the majority of our infants reduction of PEEP from 0.4 to 0.2 kPa resulted in increases in compliance and CO2 reduction. Our results might suggest that relatively low levels of PEEP < 0.3 kPa may be appropriate at 72 hours after surfactant replacement. Furthermore, these results underline the importance of PEEP test in clinical practice.