A small constant external negative pressure improves lung aeration at birth in rabbit kittens with a diaphragmatic hernia

Abstract

Infants with a congenital diaphragmatic hernia often require high peak inflation pressures to aerate and ventilate their stiff, hypoplastic lungs at birth. However, although high peak inflation pressures are associated with ventilator-induced lung injury, lower peak inflation pressures (considered to be gentle) may not sufficiently aerate the lungs. The objective of the study was to investigate whether a small constant external negative pressure can improve lung aeration at birth in rabbit kittens with a diaphragmatic hernia. A diaphragmatic hernia was surgically induced in 2-3 rabbit fetuses per doe (n = 20) at 24 d gestation. At 30 d, diaphragmatic hernia kittens (n = 21) and control littermates (n = 19) were delivered by caesarean section, intubated, and placed in a water-filled plethysmograph. Kittens were ventilated (volume targeted: 8 mL/kg for control, 4 mL/kg for diaphragmatic hernia kittens) with either an external negative pressure (-6 cmH(2)O) without a positive end-expiratory pressure (PEEP; Negative/0PEEP) or at atmospheric pressure (0 cmH2O) with or without PEEP (Atmos/5PEEP and Atmos/0PEEP). Lung aeration was measured using phase-contrast X-ray imaging and plethysmography. Data (means +/- SD) were analyzed using a repeated-measures linear mixed model (P < 0.05). Diaphragmatic hernia kittens ventilated in Negative/0PEEP required lower peak inflation pressures to achieve the target tidal volume than Atmos/5PEEP (10.9 +/- 2.6 vs. 15.4 +/- 2.6 cmH(2)O; P = 0.004) and Atmos/0PEEP kittens (14.2 +/- 2.6 cmH(2)O; P = 0.052). Negative/0PEEP diaphragmatic hernia kittens also had greater functional residual capacities compared with Atmos/5PEEP (19.9 +/- 3.9 vs. 13.8 +/- 3.9 mL/kg; P = 0.015) and Atmos/0PEEP kittens (6.4 +/- 3.9 mL/kg; P < 0.001). A small constant external negative pressure increased lung aeration with lower peak inflation pressures in mechanically ventilated diaphragmatic hernia rabbit kittens.