Effect of positive end-expiratory pressure on lung injury and haemodynamics during experimental acute respiratory distress syndrome treated with extracorporeal membrane oxygenation and near-apnoeic ventilation

BACKGROUND: Lung rest has been recommended during extracorporeal membrane oxygenation (ECMO) for severe acute respiratory distress syndrome (ARDS). Whether positive end-expiratory pressure (PEEP) confers lung protection during ECMO for severe ARDS is unclear. We compared the effects of three different PEEP levels whilst applying near-apnoeic ventilation in a model of severe ARDS treated with ECMO. METHODS: Acute respiratory distress syndrome was induced in anaesthetised adult male pigs by repeated saline lavage and injurious ventilation for 1.5 h. After ECMO was commenced, the pigs received standardised near-apnoeic ventilation for 24 h to maintain similar driving pressures and were randomly assigned to PEEP of 0, 10, or 20 cm H(2)O (n=7 per group). Respiratory and haemodynamic data were collected throughout the study. Histological injury was assessed by a pathologist masked to PEEP allocation. Lung oedema was estimated by wet-to-dry-weight ratio. RESULTS: All pigs developed severe ARDS. Oxygenation on ECMO improved with PEEP of 10 or 20 cm H(2)O, but did not in pigs allocated to PEEP of 0 cm H(2)O. Haemodynamic collapse refractory to norepinephrine (n=4) and early death (n=3) occurred after PEEP 20 cm H(2)O. The severity of lung injury was lowest after PEEP of 10 cm H(2)O in both dependent and non-dependent lung regions, compared with PEEP of 0 or 20 cm H(2)O. A higher wet-to-dry-weight ratio, indicating worse lung injury, was observed with PEEP of 0 cm H(2)O. Histological assessment suggested that lung injury was minimised with PEEP of 10 cm H(2)O. CONCLUSIONS: During near-apnoeic ventilation and ECMO in experimental severe ARDS, 10 cm H(2)O PEEP minimised lung injury and improved gas exchange without compromising haemodynamic stability.