Lung function after cardiac surgery : With special reference to atelectasis and ventilation-perfusion relationships

Abstract: Patients undergoing cardiac surgery were investigated before and after the operation.Ventilation-perfusion (VA/Q) relationships were examined by the multiple inert gas elimination method, and atelectasis and aeration of the lungs were examined by computedtomography (CT). Oxygenation was assessed by arterial and mixed venous blood gases, andvenous admixture was calculated according to standard formulas. Ventilation was examinedby respiratory inductive plethysmography. Tidal and minute volumes, respiratory frequencyand the co-ordination of breathing were measured. Forced vital capacity (FVC), forcedexpiratory volume in one second (FEV1), peak expiratory and inspiratory airway pressures(PEmax, PImax) were measured by spirometry.Atelectasis corresponding to 20 % of the lung tissue, was found in dependent parts of both lungs on the first postoperative day in 50 of 55 patients. There were more changes in the left compared to the right lung, and the changes increased from the apex of the lungs towards the base. Atelectasis correlated well to intrapulmonary shunt in the mitral valve patients, but the correlation in the coronary artery bypass graft patients was poor. With thoracic epidural analgesia (TEA) the postoperative time in respirator was shortened, and less intravenous morphine analgesics were given. TEA did not influence VA/Q, atelectasis formation or oxygenation. TEA improved PEmax after surgery while FVC, FBV1, PImax and ventilation at rest were uninfluenced.A vital capacity manoeuvre (VCM), i.e. an inflation of the lungs to an airway pressure of 30 cm H20, performed before the end of extracorporeal circulation (ECC) improved intrapulmonary shunt and oxygenation after surgery, and reduced atelectasis. Some of the effects lasted until the first postoperative day. No further improvement was achieved by repeating the manoeuvre four hours after ECC, and no increased signs of barotrauma were found. A VCM performed at the end of the surgical procedure is thus a simple and efficient method to improve lung function in the immediate postoperative period.

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