RESUMO
Objective:To investigate the effects of deep hypothermia on MAC,cardiac anesthetic index and myocardial stability of valotile anesthetics. Method: Forty New Zealand white rabbits were randomly divided into 4 groups:halothane, enflurane,isoflurane and sevoflurane. MAC of valotile agents were determined with the test of clamping tail at normal(38 C?0.5 C )and deep hypothermic(23 C?0.5 C )temperatures. The end-tidal valotile agent concentration at which ventricular arrhythmia appeared by increasing valotile agent concentration and stimulating the heart with extrathoracic electric shock(25V 50Hz)were recorded. Result:MAC of halothane, enflurane,isoflurane and sevoflurane were decreased by average percentage of 5.1,3.6,4.4 and 4.3 per degree from 38 C to 23 C respectively. Cardiac anesthetic indexes during deep hypothermia were 4.4,3.18.6.25 and 4.6. There was significantly higher incidence of ventricular fibrilation in halothane and enflurane groups (100％) than that in isoflurane and sevoflurane groups(40％)under 8 MAC anesthetics. Conclusion:Isoflurane is the most suitable valotile agent for deep hypothermic anesthesia, while enflurane is the least.