EFFECTS OF 1 MAC DESFLURANE ON CEREBRAL METABOLISM, BLOOD-FLOW AND CARBON-DIOXIDE REACTIVITY IN HUMANS

We investigated the cerebral haemodynamic effects of 1 MAC desflurane anaesthesia in nine male patients scheduled for elective coronary bypa ss grafting. For the measurement of cerebral blood flow (CBF) a modifi ed Kety-Schmidt saturation technique with argon as inert tracer gas wa s used. Measurements of CBF were made before induction of anaesthesia and 30 min after induction under normocapnic, hypocapnic and hypercapn ic conditions in sequence. Changes in mean arterial pressure after ind uction of anaesthesia and during the course of the study were minimize d using norepinephrine infusion. In comparison with the awake state un der normocapnic conditions, desflurane reduced mean cerebral metabolic rate of oxygen (CMRO2) by 51% and mean cerebral metabolic rate of glu cose (CMRglc) by 35%. Concomitantly, CBF was significantly reduced by 22%; jugular venous oxygen saturation (Sjv(O2)) increased from 58 to 7 4%. Hypo- and hypercapnia caused a 22% decrease and a 178% increase in CBF, respectively. These findings may be interpreted as the result of two opposing mechanisms: cerebral vasoconstriction induced by a reduc tion of cerebral metabolism and a direct vasodilator effect of desflur ane. CBF alterations under variation of Pa-CO2 indicate that cerebrova scular carbon dioxide reactivity is not impaired by application of 1 M AC desflurane.