MAC OF XENON AND HALOTHANE IN RHESUS-MONKEYS

Local cerebral blood flow (LCBF) maps produced by 33% xenon-enhanced c omputed tomographic scanning (Xe/CT LCBF) are useful in the clinical d iagnosis and management of patients with cerebrovascular disorders. Ho wever, observations in humans that 25-35% xenon (Xe) inhalation increa ses cerebral blood flow (CBF) have raised concerns that Xe/CT LCBF mea surements may be inaccurate and that Xe inhalation may be hazardous in patients with decreased intracranial compliance. In contrast, 33% Xe does not increase CBF in rhesus monkeys. To determine whether this int erspecies difference in the effect of Xe on CBF correlates with an int erspecies difference in the anesthetic potency of Xe, we measured the minimum alveolar concentration (MAC) of Xe preventing movement to a ta il-clamp stimulus in rhesus monkeys. Using a standard protocol for the determination of MAC in animals, we first measured the MAC of halotha ne (n = 5), and then used a combination of halothane and Xe to measure the MAC of Xe (n = 7). The halothane MAC was 0.99 +/- 0.12% (M +/- SD ), and the Xe MAC was 98 +/- 15%. These results suggest that the MAC o f Xe in rhesus monkeys is higher than the reported human Xe MAC value of 71%. Thus the absence of an effect of 33% Xe on CBF in the rhesus m onkey may be related to its lower anesthetic potency.