Effects of xenon anaesthesia on the circulatory response to hypoventilation

Abstract

Background. Circulatory response to hypoventilation is aimed at eliminating carbon dioxide and maintaining oxygen delivery (DO2) by increasing cardiac output (CO). The hypothesis that this increase is more pronounced with xenon than with isoflurane anaesthesia was tested in pigs. Methods. Twenty pigs received anaesthesia with xenon 0.55 MAC/ remifentanil 0.5 μg kg-1 min-1 (group X, n=10) or isoflurane 0.55 MAC/remifentanil 0.5 μg kg-1 min-1 (group I, n=10). CO, heart rate (HR), mean arterial pressure (MAP) and left ventricular fractional area change (FAC) were measured at baseline, after 5 and 15 min of hypoventilation and after 5, 15 and 30 min of restored ventilation. Results. CO increased by 10-20% with both anaesthetics, with an equivalent rise in HR, maintaining DO2 in spite of a 20% reduction in arterial oxygen content. Decreased left ventricular (LV) afterload during hypoventilation increased FAC, and this was more marked with xenon (0.60-0.66, P<0.05 compared with baseline and isoflurane). This difference is attributed to negative inotropic effects of isoflurane. Increased pulmonary vascular resistance during hypoventilation was found with both anaesthetics. Conclusion. The cardiovascular effects observed in this model of moderate hypoventilation were sufficient to maintain DO2. Although the haemodynamic response appeared more pronounced with xenon, differences were not clinically relevant. An increase in FAC with xenon is attributed to its lack of negative inotropic effects. © The Board of Management and Trustees of the British Journal of Anaesthesia 2005. All rights reserved.