A Small Constant External Negative Pressure Improves Lung Aeration at Birth in Rabbit Kittens with a Diaphragmatic Hernia.

Abstract

Rationale: Infants with a congenital diaphragmatic hernia often require high peak inflation pressures to aerate and ventilate their stiff, hypoplastic lungs at birth. However, while 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. Objectives: To investigate whether a small constant external negative pressure can improve lung aeration at birth in rabbit kittens with a diaphragmatic hernia. Methods: A diaphragmatic hernia was surgically induced in 2-3 rabbit fetuses per doe (n=20) at 24d gestation. At 30d, 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: 8mL/kg for control, 4mL/kg for diaphragmatic hernia kittens) with either an external negative pressure (-6cmH₂O) without a positive end-expiratory pressure (PEEP; Negative/0PEEP) or at atmospheric pressure (0cmH₂O) with or without PEEP (Atmos/5PEEP and Atmos/0PEEP). Meaurements: Lung aeration was measured using phase contrast X-ray imaging and plethysmography. Data (means±SD) were analysed using a repeated measures linear mixed model (p<0.05). Main Results: 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 cmH₂O; p=0.004) and Atmos/0PEEP kittens (14.2±2.6 cmH₂O; p=0.052). They also had greater functional residual capacities compared to 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). Conclusions: A small constant external negative pressure increased lung aeration with lower peak inflation pressures in mechanically ventilated diaphragmatic hernia rabbit kittens.