CEREBRAL VASODILATATION BY HALOTHANE ANAESTHESIA IN MAN AND ITS POTENTIATION BY HYPOTENSION AND HYPERCAPNIA

Abstract

In ten young normal adults the cerebral blood flow and oxygen uptake during normotensive and normocapnic halothane anaesthesia (1 per cent) were studied by means of the ⁸⁵Kr inhalation method. Compared with a similar group studied when awake, a significant increase of 27 per cent in cerebral blood flow was found during anaesthesia while the oxygen uptake was reduced by 26 per cent. After discussing previous conflicting reports, it is concluded that halothane per se acts as a cerebral vasodilator. Ten patients from the neurological service with and without cerebrovascular disease were studied when awake and during hypotensive hypercapnic halothane anaesthesia (1 per cent). In five cases a third study was made during either hypotension (three cases) or hypercapnia (two cases) alone. Cerebral blood flow was measured by the ¹³³Xe injection method. The results suggested a potentiation of the cerebral vasodilatation of halothane by hypotension and/or hypercapnia even in patients with cerebrovascular disease. The very high blood flows found during normotensive, moderately hypercapnic halothane anaesthesia indicated a sort of controlled cerebral hyperoxygenation, the application of which is discussed.