Original Article Comparison of subarachnoid anesthetic effect of emulsified volatile anesthetics in rats

* Equal contributors. Received October 29, 2014; Accepted November 13, 2014; Epub December 1, 2014; Published December 15, 2014 Abstract: Spinal cord is an important target of volatile anesthetics in particular for the effect of immobility. Intrathe- cal injection of volatile anesthetics has been found to produce subarachnoid anesthesia. The present study was designed to compare spinal anesthetic effects of emulsified volatile anesthetics, and to investigate the correlation between their spinal effects and general effect of immobility. In this study, halothane, isoflurane, enflurane and sevoflurane were emulsified by 30% Intralipid. These emulsified volatile anesthetics were intravenously and intra - thecally injected, respectively. ED 50 of general anesthesia and EC 50 of spinal anesthesia were determined. The dura- tions of general and spinal anesthesia were recorded. Correlation analysis was applied to evaluate the anesthetic potency of volatile anesthetics between their spinal and general effects. ED 50 of general anesthesia induced by emulsified halothane, isoflurane, enflurane and sevoflurane were 0.41 ± 0.07, 0.54 ± 0.07, 0.74 ± 0.11 and 0.78 ± 0.08 mmol/kg, respectively, with significant correlation to their inhaled MAC (R 2 = 0.8620, P = 0.047). For intrathe- cal injection, EC 50 of spinal anesthesia induced by emulsified halothane, isoflurane, enflurane and sevoflurane were 0.35, 0.27, 0.33 and 0.26 mol/L, respectively, which could be predicted by the product of inhaled MAC and olive oil/ gas partition coefficients (R 2 = 0.9627, P = 0.013). In conclusion, potency and efficacy of the four emulsified volatile anesthetics in spinal anesthesia were similar and could be predicted by the product of inhaled MAC and olive oil/ gas partition coefficients (MAC × olive oil/gas partition coefficients).