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

In ten young normal adults the cerebral blood flow and oxygenuptake 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 significantincrease of 27 per cent in cerebral blood flow was found duringanaesthesia while the oxygen uptake was reduced by 26 per cent.After discussing previous conflicting reports, it is concludedthat halothane per se acts as a cerebral vasodilator. Ten patientsfrom the neurological service with and without cerebrovasculardisease were studied when awake and during hypotensive hypercapnichalothane anaesthesia (1 per cent). In five cases a third studywas made during either hypotension (three cases) or hypercapnia(two cases) alone. Cerebral blood flow was measured by the ¹³³Xeinjection method. The results suggested a potentiation of thecerebral vasodilatation of halothane by hypotension and/or hypercapniaeven in patients with cerebrovascular disease. The very highblood flows found during normotensive, moderately hypercapnichalothane anaesthesia indicated a sort of controlled cerebralhyperoxygenation, the application of which is discussed.