Alterations of the pulmonary microcirculation after open heart surgery. Correlation between the pulmonary vascular dynamics and ultrastructural changes after the operation.

The study of pulmonary hemodynamics after mitral valve repiacement in 30 patients, during the first 18 post-operative hours, did show elevated pulmonary vascular resistance from rhe pre-operative leveis in the majority of them. This rise varied directly,wirh the bypass time and was associated with increased right ventricular work, intrapulmonary shunt and more severe ultrastr4ctural lesions of the alveolar-capillary membrane. The pulmonary vas cular resiscance had tendency to lower tu the pre-operative values at the end of 18 hours. The microscopic changes, very similar with the observed on shock lung, fat emboli and in ali non-hemodynamic pulmonary edemas, may well be due to excessive and prolonged stimu lation of catechoiamines, microemboli and hypoxia. The control of perfusion pressure, better synthetic surfaces and oxygenators, and the use of assisted ventiiation with positive end-expiratory pressure must be investigate to precise their exact role on the alterations of the puimonary microcirculation after open hearr surgery.