[Unexpected air embolism during an aneurysmal operation in supine position--a case report and a speculation about its pathogenesis].

The occurrence of air embolism in supine position operation is extremely rare. We reported a case of air embolism during the operation of a ruptured middle cerebral artery aneurysm in supine position. A 58-year-old woman was admitted to our hospital in semicomatous state. A CT scan revealed diffuse subarachnoid hemorrhage. Cerebral angiogram showed a middle cerebral artery aneurysm. Massive pinkish foamy sputum and butterfly shadow on chest x-ray strongly suggested an association of neurogenic pulmonary edema (NPE). Barbiturate therapy and controlled ventilation with positive end-expiratory pressure (5cmH2O) were started. Her airway pressure was about 35cmH2O. Decrease of pinkish foamy sputum and an improvement of chest x-ray findings on the next day encouraged us to perform a clipping operation. Just before a clip application, air bubbles were observed to pass through the middle cerebral artery under the microscope. Subsequently cardiac standstill was brought out. Fortunately, she was resuscitated, and a clip application was finished. A postoperative CT scan revealed an infarction in the middle cerebral artery area. A postoperative cerebral angiogram showed occlusion of a temporal branch of the right middle cerebral artery, P1 portion of the left posterior cerebral artery, and the right superior cerebellar artery. We speculated that high endotracheal pressure brought out pulmonary alveolar rupture, and in spite of supine position operation massive air, which flowed into systemic circulation from ruptured alveoli, caused cerebral infarction and cardiac arrest. We consider that unrecognized air embolism might be the one of the factors influencing the prognosis of severe subarachnoid hemorrhage, especially in the cases associated with neurogenic pulmonary edema.