Comparison of exogenous surfactant and positive end-expiratory pressure therapies in a model of human breast milk-induced acute lung injury in rabbits

Abstract

To evaluate surfactant and positive end-expiratory pressure (PEEP) as potential therapies for the acute lung injury after tracheal instillation of 0.8 ml kg-1 human breast milk (HBM) acidified to pH 1.8, adult white rabbits were anaesthetized, tracheostomized, ventilated and randomized to (six rabbits per treatment): (i) no treatment after HBM (control); (ii) exogenous Bovine surfactant (100 mg kg-1) 1 h after HBM; (iii) PEEP-pre (0.5 kPa PEEP) before and after HBM; or (iv) PEEP-post (0.5 kPa PEEP) after HBM. A fifth group of six rabbits received no tracheal instillate (no aspirate). The alveolar to arterial oxygen tension gradient (A-aDO2) and dynamic compliance were measured pre-injury and hourly for 4 h. At post-mortem, the lungs were examined histologically. A-aDO2 in all four HBM-injured groups increased to a maximum at 1 h post-injury; A-aDO2 then returned towards the baseline in the surfactant and PEEP-post groups, but remained increased in the PEEP-pre and control groups. Dynamic compliance decreased in all four HBM-injured groups. A-aDO2 and compliance were unchanged in the no aspirate group. Bronchoalveolar architecture after surfactant therapy was normal. We conclude that surfactant is a more effective therapy for HBM-induced lung injury than either 0.5 kPa PEEP-post or PEEP-pre injury.