Pulmonary surfactant composition early in development of acute lung injury after cardiopulmonary bypass: prophylactic use of surfactant therapy.

Cardiopulmonary bypass surgery (CPB) causes lung injury and at least 2% of adult patients and more children develop the most severe form acute respiratory distress syndrome (ARDS). Pulmonary surfactant deficiency contributes to the pathogenesis of ARDS. It has been proposed that surfactant therapy immediately after CPB might arrest progression to ARDS. However, many patients develop only mild lung injury after CPB. Thus early markers are needed to identify those patients at highest risk to guide selection for treatment. The aim of this study was to determine whether changes in surfactant phospholipids occur, and reflect severity of lung injury within the first few hours after bypass. Because of the relatively low incidence of ARDS in adult patients, this study was conducted using young pigs highly susceptible to bypass-induced lung injury. Eight pigs were given 2 hours bypass. Six controls underwent 'sham' bypass. At 3 h after bypass pulmonary vascular endothelial permeability was assessed by transcapillary leakage of radiolabelled transferrin. A 4 hour broncho-alveolar lavage (BAL) was used to assess intra-alveolar levels of surfactant, inflammatory cells and oedema protein. Bypass caused falls in arterial oxygenation and lung compliance (P<0.01), but at this early stage in progression of lung injury BAL surfactant phospholipid and albumin levels were within the control range indicating that the alveolar epithelium had not yet suffered major damage. The main abnormalities were increases in vascular endothelial permeability (P<0.01), BAL neutrophils (P<0.01), total protein and sphingomyelin (SM) (P<0.05). Lung histology showed that the main damage was interstitial oedema located around the bronchioles and their associated vessels. A single instilled dose of surfactant phospholipids in 5 animals caused excess in vivo supplementation and did not reduce the early pathophysiologic changes. Our findings suggest that surfactant phospholipid deficiency does not make a major contribution in the initial stages of lung injury after CPB, and that excessive phospholipid supplementation at this stage can be deleterious.