Improving lung aeration in ventilated newborn preterm rabbits with a partially aerated lung.

Preterm newborns commonly receive intermittent positive pressure ventilation (iPPV) at birth, but the optimal approach that facilitates uniform lung aeration is unknown, particularly in a partially aerated lung. As both inflation time and exogenous surfactant facilitate uniform lung aeration, we investigated whether they can improve lung aeration and lung mechanics in a partially aerated lung immediately after birth. Preterm rabbit kittens (29 days gestation, term ~32 days) were delivered by caesarean section and partial lung aeration was created by intubating and mechanically ventilating the right lung. The tube was then withdrawn to ventilate both lungs using inflation times of 0.2 s or 1.0 s, with or without exogenous surfactant (Curosurf 200 mg/kg), and a tidal volume (Vt) of 8 mL/kg. Simultaneous phase contrast X-ray imaging and plethysmography were used to measure lung aeration and mechanics. Kittens ventilated with longer inflation times (1.0 s) reached their target Vt with fewer inflations, required lower inflation pressures (28.5 ± 1.1 vs. 33.5 ± 1.3 cmH2 O, p=0.01) and had higher dynamic lung compliances (0.54 ± 0.3 vs. 0.40 ± 0.3 cmH2 O/mL/kg, p=0.003). Surfactant increased functional residual capacity (FRC; 31.9 ± 3.2 vs. 18.0 ± 3.9 mL/kg, p=0.02) and the proportion of the Vt entering the previously unaerated lung but had no effect on dynamic lung compliance. Combining early surfactant treatment with longer inflation times increases FRC levels, improves dynamic lung compliance, reduces inflation pressures and markedly increases the proportion of the lungs being ventilated during iPPV in preterm kittens with a partially aerated lung.