Hypothermia in the Surgical Treatment of Ruptured Intracranial Aneurysms

Abstract

H YPOTHERMIC anaesthesia for cerebrovascular surgery was begun in the Toronto General Hospital in the summer of 1954. This followed upon the general physiological studies of hypothermia by Bigelow and his co-workers, 1,2 the experimental studies of Lougheed and Kahn 7 regarding the effects of hypothermia in the prevention of cerebral anoxia, and the clinical experience of Lougheed et al. s using hypothermic anaesthesia for one case of arteriovenous malformation and one hemispherectomy for glioblastoma multiforme. Cerebrovascular surgery presents all the difficulties encountered in the surgery of large vessels throughout the body and there are problems inherent in the relatively small size of cerebral vessels; even the internal carotid artery is small in proportion to the aorta, pulmonary artery or subclavian artery. The accurate repair of a ruptured aneurysm is facilitated by partial or complete interruption of the circulation, as described by Hamby, 5 so that surgery may be done in a dry field. The resultant cerebral ischemia may cause infarction of the brain. Hypothermlc anaesthesia provides protection against anoxia and infarction, allowing occlusion of the blood flow for longer, though still short periods. Additionally, dissection of an aneurysm and manipulation of the cerebral artery bearing it may cause arterial spasm and traction damage to the perforating vessels with resulting anoxia. The deleterious effects of spasm may be avoided when hypothermia outlasts the spasm. The reduction in brain volume accompanying hypothermia provides a slack brain, facilitating exposure of an aneurysm of the circle of Willis. The results of the treatment of ruptured aneurysms by intracranial repair two or more weeks following bleeding as reported by Norl6n and Barnum, 1~ Norl6n and Olivecrona H and Falconer 4 show a low mortality and morbidity rate. The results of the direct surgical treatment of a large group of patients with ruptured aneurysms, approximating a consecutive series, within days following bleeding have not yet been reported. The value of early surgical treatment is difficult to assess for the natural history of a consecutive series of angiographically verified aneurysms is not yet available as a control.