Effect of Sustained Inflation Length on Establishing Functional Residual Capacity at Birth in Ventilated Premature Rabbits

The effect of inflation length on lung aeration pattern, tidal volumes, and functional residual capacity (FRC) immediately after birth was investigated. Preterm rabbits (28 d), randomized into four groups, received a 1-, 5-, 10-, or 20-s inflation (SI) followed by ventilation with 5 cm H2O end-expiratory pressure. Gas volumes were measured by plethysmography and uniformity of lung aeration by phase contrast x-ray imaging for 7 min. The first inspiratory volume significantly (p < 0.001) increased with inflation duration from a median (IQR) of 0.2 (0.1-3.1) mL/kg for 1-s inflation to 23.4 (19.3-30.4) mL/kg for 20-s SI. The lung was uniformly aerated, and the FRC and tidal volume fully recruited after 20-s SI. A 10-s SI caused a higher FRC (p < 0.05) at 7 min, and a 20-s SI caused a higher FRC (p < 0.05) at 20 s and 7 min than a 1- or 5-s SI. The mean (SD) time for 90% of the lung to aerate was 14.0 (4.1) s using 35 cm H2O peak inflation pressure. In these rabbits, 10- and 20-s SI increased the inspiratory volume and produced a greater FRC, and a 20-s SI uniformly aerated the lung before ventilation started. (Pediatr Res 66: 295-300,2009)