Respiratory mechanics during xenon anesthesia in pigs: comparison with nitrous oxide.

BACKGROUND: Because of its high density and viscosity, xenon (Xe) may influence respiratory mechanics when used as an inhaled anesthetic. Therefore the authors studied respiratory mechanics during xenon and nitrous oxide (N2O) anesthesia before and during methacholine-induced bronchoconstriction. METHODS: Sixteen pentobarbital-anesthetized pigs initially were ventilated with 70% nitrogen-oxygen. Then they were randomly assigned to a test period of ventilation with either 70% xenon-oxygen or 70% N2O-oxygen (n = 8 for each group). Nitrogen-oxygen ventilation was then resumed. Tidal volume and inspiratory flow rate were set equally throughout the study. During each condition the authors measured peak and mean airway pressure (Pmax and Pmean) and airway resistance (R(aw)) by the end-inspiratory occlusion technique. This sequence was then repeated during a methacholine infusion. RESULTS: Both before and during methacholine airway resistance was significantly higher with xenon-oxygen (4.0 +/- 1.7 and 10.9 +/- 3.8 cm H2O x s(-1) x 1(-1), mean +/- SD) when compared to nitrogen-oxygen (2.6 +/- 1.1 and 5.8 +/- 1.4 cm H2O x s(-1) x l(-1), P < 0.01) and N2O-oxygen (2.9 +/- 0.8 and 7.0 +/- 1.9, P < 0.01). Pmax and Pmean did not differ before bronchoconstriction, regardless of the inspired gas mixture. During bronchoconstriction Pmax and Pmean both were significantly higher with xenon-oxygen (Pmax, 33.1 +/- 5.5 and Pmean, 11.9 +/- 1.6 cm H2O) when compared to N2O-oxygen (28.4 +/- 5.7 and 9.5 +/- 1.6 cm H2O, P < 0.01) and nitrogen-oxygen (28.0 +/- 4.4 and 10.6 +/- 1.3 cm H2O, P < 0.01). CONCLUSIONS: Airway pressure and resistance are increased during xenon anesthesia. This response is moderate and not likely to assume major importance for the general use of xenon in anesthesia.