Xenon increases total body oxygen consumption during isoflurane anaesthesia in dogs

Background This study was designed to examine whether the coupling between oxygen consumption ( V ˙o 2 ) and cardiac output (CO) is maintained during xenon anaesthesia. Methods We studied the relationship between V˙ o 2 (indirect calorimetry) and CO (ultrasound flowmetry) by adding xenon to isoflurane anaesthesia in five chronically instrumented dogs. Different mixtures of xenon (70% and 50%) and isoflurane (0–1.4%) were compared with isoflurane alone (1.4% and 2.8%). In addition, the autonomic nervous system was blocked (using hexamethonium) to study its influence on V˙ O 2 and CO during xenon anaesthesia. Results Mean (sem) V˙ o 2 increased from 3.4 (0.1) ml kg −1  min −1 during 1.4% isoflurane to 3.7 (0.2) and 4.0 (0.1) ml kg −1  min −1 after addition of 70% and 50% xenon, respectively ( P V˙ o 2 [from 3.4 (0.1) to 3.1 (0.1) ml kg −1  min −1 ] and CO [from 96 (5) to 70 (3) ml kg −1  min −1 ] ( P V˙ o 2 and CO correlated closely during isoflurane anaesthesia alone and also in the presence of xenon ( r 2 =0.94 and 0.97, respectively), but the regression lines relating CO to V˙ O 2 differed significantly between conditions, with the line in the presence of xenon showing a 0.3–0.6 ml kg −1  min −1 greater V˙ o 2 for any given CO. Following ganglionic blockade, 50% and 70% xenon elicited a similar increase in V˙ o 2 , while CO and blood pressure were unchanged. Conclusions Metabolic regulation of blood flow is maintained during xenon anaesthesia, but cardiovascular stability is accompanied by increased V˙ o 2 . The increase in V˙ O 2 is independent of the autonomic nervous system and is probably caused by direct stimulation of the cellular metabolic rate.