Isoflurane actions on central nervous system and cardiovascular toxicity of bupivacaine in rats

Regional anesthesia is frequently used to supplement light general anesthesia (GA). Central nervous system (CNS) and cardiovascular (CV) toxicity of local anesthetics (LA) such as bupivacaine (BUP) are well described including CV collapse. Effects of GA on LA toxicity are not well defined. To examine the possible interactions between GA-LA, we studied the responses to intravenous (iv) BUP in conscious (CON) rats (n=9) and in rats anesthetized with isoflurane (ISO, via endotracheal tube, n=5). In CON rats, BUP, 2mg/kg, caused hypertension, bradycardia, dysmythmias and tonic-clonic seizures (75%); all following early (within a few sec), transient, complex EKG wave form changes. Compared to CON, ISO (1%) eliminated BUPinduced seizures and dysrhythmias and reduced but did not eliminate CV response to BUP or EKG changes. ISO attenuated baroreflex (BRX) gain, but ISO + BUP eliminated BRX. Our results suggest that ISO prevents early signs of CMS (seizures) and CV (MAP, dysrhythmias) toxicity of BUP. > This may exacerbate impending CV collapse and BRX depression may ' facilitate the crisis induced by BUP.