Thirty-one patients who were undergoing cardiopulmonary bypass for elective aortic valve replacement were studied. The effects on some aspects of lung function of intravenous methyl prednisolone, administered immediately before bypass, were assessed by measuring alveolar-arterial oxygen differences and shunt fractions. No significant differences in pulmonary function were found between the treated and control groups. The use of methyl prednisolone in this context is not justified.Although the frequency and severity of pulmonary dysfunction after open intracardiac surgery using cardiopulmonary bypass has decreased, it may cause significant morbidity and is occasionally the primary factor in mortality. The aetiology of pulmonary dysfunction has been disputed since the early days of open heart surgery, and no consensus exists at present. Denaturation of plasma proteins (Lee et al, 1961;Pruitt et al, 1971) at the gas air interface in the oxygenator has been the most widely supported cause. It is postulated that damage to the pulmonary capillary membrane is an essential feature of the classic pathological findings, which in all degrees are associated with an increase in interstitial alveolar fluid (Baerand Osborn, 1960). Wilson (1972) proposed that polymorphonuclear leucocytes and platelets may be incriminated in the presumed membrane damage and suggested that methyl prednisolone hemisuccinate could reduce it. He reported a significant reduction in membrane damage in patients undergoing cardiopulmonary bypass who received methyl prednisolone, as assessed by lung biopsy at the end of operation. However, there was no physiological evidence to support the histological evidence. Extravascular lung water, measured by a double indicator dilution technique, increases after cardiac surgery using extracorporeal circulation. There was no change in the colloid and hydrostatic forces that act on the capillary membrane (Parker et al, 1972). These changes are associated with a deterioration in the gas exchange of the lungs, which is maximal about 48 hours after operation and has not returned to normal after seven days.To determine whether methyl prednisolone hemisuccinate can produce changes in gas exchange to parallel the changes in histology, a double-blind trial of the effect of the drug given immediately before the onset of bypass has been undertaken. MethodsThirty-one patients who were undergoing elective operations for aortic valve disease were studied. A standard random selection technique was used, excluding any patients with obvious lung disease or frank left ventricular failure. Informed consent for the investigations was obtained and if at any time the subject found the tests intolerable the study on that patient was terminated, and the results excluded. These exclusions account for the odd numbered total. Investigations were performed at the following time intervals: (1) before operation, (2) 48 hours after operation, and (3) one week after operation.The investigation consisted of arterial blood sampling while...

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