EFFECT OF 33-PERCENT XENON INHALATION ON WHOLE-BRAIN BLOOD-FLOW AND METABOLISM IN AWAKE AND FENTANYL-ANESTHETIZED MONKEYS

Background and Purpose: Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood How and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys. Methods: Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect. Results: In awake monkeys, 33% Xe compared with 33% N2 reduced (p < 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml . 100 g-1 . min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml . 100 g-1 . min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood How, 84 +/- 26 versus 79 +/- 23 ml . 100 g-1 . min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml . 100 g-1 . min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg . 100 g-1 . min-1. Conclusions: In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.