Higher CPAP levels improve functional residual capacity at birth in preterm rabbits.

Abstract

Preterm infants are commonly supported with 4-8 cm H₂O continuous positive airway pressures (CPAP), although higher CPAP levels may improve functional residual capacity (FRC). Preterm rabbits delivered at 29/32 days (~26-28 weeks human) gestation received 0, 5, 8, 12, 15 cm H₂O of CPAP or variable CPAP of 15 to 5 or 15 to 8 cm H₂O (decreasing ~2 cm H₂O/min) for up to 10 min after birth. FRC was lower in the 0 (6.8 (1.0-11.2) mL/kg) and 5 (10.1 (1.1-16.8) mL/kg) compared to the 15 (18.8 (10.9-22.4) mL/kg) cm H₂O groups (p = 0.003). Fewer kittens achieved FRC > 15 mL/kg in the 0 (20%), compared to 8 (36%), 12 (60%) and 15 (73%) cm H₂O groups (p = 0.008). While breathing rates were not different (p = 0.096), apnoea tended to occur more often with CPAP < 8 cm H₂O (p = 0.185). CPAP belly and lung bulging rates were similar whereas pneumothoraces were rare. Lowering CPAP from 15 to 5, but not 15 to 8 cm H₂O, decreased FRC and breathing rates. In all, 15 cm H₂O of CPAP improved lung aeration and reduced apnoea, but did not increase the risk of lung over-expansion, pneumothorax or CPAP belly immediately after birth. FRC and breathing rates were maintained when CPAP was decreased to 8 cm H₂O. Although preterm infants are commonly supported with 4-8 cm H₂O CPAP at birth, preclinical studies have shown that higher PEEP levels improve lung aeration. In this study, CPAP levels of 15 cm H₂O improved lung aeration and reduced apnoea in preterm rabbit kittens immediately after birth. In all, 15 cm H₂O CPAP did not increase the risk of lung over-expansion (indicated by bulging between the ribs), pneumothorax, or CPAP belly. These results can be used when designing future studies on CPAP strategies for preterm infants in the delivery room.