Anticonvulsant action of midazolam on the convulsion induced by ropivacaine overdose / 中华麻醉学杂志

ABSTRACT

Objective To determine the dose of ropivacaine leading to convulsion and the convulsant action of midazolam. Methods Twenty healthy adult rabbits weighing 2.5-3.5kg were randomly divided into two groups with ten animals in each group ropivacaine group(R) and midazolam-ropivacaine group(MR). Middle artery of ear was cannulated for MAP, HR monitoring and blood sampling for blood gas analysis and determination of plasma lactate and ropivacaine concentrations. Edge vein of ear was cannulated for administration of drugs. In both groups animals received intravenous infusion of 0.75% ropivacaine at a rate of 0.5m1/min until convulsion occurred. In MR group midazolam 0.8 mg/kg was given intravenously before ropivacaine.Results The dose of ropivacaine leading to convulsion was 4.86mg/kg for R group and 12.26mg/kg for MR group. Plasma ropivacaine concentration was 11 .52pg/ml in group Rand 16.77pg/ml in MR group. Convulsion lasted for 7.25 mm(R group) and 8.59mm(MR group) . Plasma lactate concentration increased significantly during convulsion in R group but remained unchanged in MR group. Blood pH decreased significantly during convulsion in R group but there was little change in PaCO2 and PaO2. Blood pH, PaO2 and PaCO2 did not change significantly during convulsion in MR group. There was no significant change in MAP and HR during convulsion in R group. In MR group MAP and HR decreased by 31 % and 35% respectively during convulsion and returned to baseline value gradually after ropivacaine infusion was stopped. All animals survived the experiment in both groups. Conclusions Ropivacaine is less cardiovascular toxic. Pretreatment with 0 . 8mg/kg midazolam greatly increases the dose of ropivacaine leading to convulsion. Midazolam can effectively prevent and treat CNS toxicity of ropivacaine.