Ventilation and metabolism during propofol anesthesia in rats

Many anesthetics are known to decrease ventilation (V(E)) and metabolic rate (MR). Because MR is known to contribute to the V(E) level, one would expect some parallelism between the changes in V(E) and MR during anesthesia. We tested this hypothesis in normoxia and hypoxia (12% O2) on male Wistar rats (n = 10; 221-288 g) by using a short-acting intravenous anesthetic, propofol. Propofol anesthesia was induced with a 7-7.5 mg kg(-1) (60-70 s) dose and maintained with a 20-22 mg kg(-1) h(-1) (<40 min) dose. In normoxia, propofol significantly decreased V(E) and MR and maintained the V(E)/MR ratio. In hypoxia, propofol decreased MR without a significant decrease in V(E), and the V(E)/MR ratio tended to increase. As a result, both in normoxia and hypoxia, propofol did not significantly increase the partial pressure of CO2 in arterial blood (PaCO2). Propofol was also associated with decreased body temperature and mean arterial pressure. The results suggest that during anesthesia, a large part of the drop in V(E) can be accounted for by the drop in MR, and that in both normoxia and hypoxia the V(E)/MR ratios and PaCO2values are maintained close to the levels of the conscious state.