RESUMO
The noble gas xenon seems to have minimal cardiovascular side-effects and so may be an ideal anaesthetic agent when investigating cardiovascular physiology. In comparison with standard modern anaesthetics, we investigated the haemodynamic and hormonal effects of xenon in Beagle dogs. After a 30 min baseline period, anaesthesia was induced with propofol and maintained with either (1) 1.2% isoflurane/70% nitrous oxide (N(2)O), (2) 0.8% isoflurane/0.5 microg/kg/min remifentanil or (3) 63% xenon/0.5 microg/kg/min remifentanil (n = 6 per group). Haemodynamics were recorded and blood samples taken before and 60 min after induction. Mean arterial blood pressure (MAP) was higher in conscious dogs than during isoflurane/N(2)O (86 +/- 2 vs. 65 +/- 2 mmHg, mean +/- SEM) and isoflurane/remifentanil anaesthesia (95 +/- 2 vs. 67 +/- 3 mmHg), whereas MAP did not decrease significantly in response to xenon/remifentanil anaesthesia (96 +/- 4 vs. 85 +/- 6 mmHg). Bradycardia was present during isoflurane/remifentanil (54 +/- 2/min) and xenon/remifentanil (40 +/- 3/min), but not during isoflurane/N(2)O anaesthesia (98 +/- 3/min, P < 0.05). Xenon/remifentanil anaesthesia induced the highest reduction in cardiac output (CO) (-61%), and the highest increase in systemic vascular resistance (+120%) among all treatment groups (P < 0.05). A simultaneous increase in endogenous adrenaline and noradrenaline concentrations could only be observed in the xenon/remifentanil group, whereas angiotensin II and vasopressin concentrations increased in all groups. In conclusion, xenon/remifentanil anaesthesia maintains MAP but reduces heart rate and CO and is associated with a considerable stimulation of vasopressor hormones in Beagle dogs. Therefore, xenon/remifentanil exerts a new quality of adverse haemodynamic effects different from volatile anaesthetics and may not perform better during studies of cardiovascular physiology.
