Abstract: AIM: To investigate the effect of isovolemic hemodilution on pharmacokinetics of ropivacaine for sciatic nerve block in dogs.METHODS: Twelve healthy adult mongrel dogs (6 male, 6 female) weighing 13.5-15.8 kg were divided into 2 groups (n=6 each): isovolemic hemodilution group and control group.The animals were anesthetized with intramuscular 3% pentobarbital 30 mg/kg.A polyethylene catheter was surgically inserted into the sheath of sciatic nerve for nerve block with ropivacaine. Femoral artery and vein was cannulated respectively. Isovolemic hemodilution group was conducted by removing blood from femoral artery and replacing it with 6% hydroxyethyl starch(HES) until hematocrit(Hct) was reduced to 25%. Ropivacaine 10 mg/kg was injected into the sheath of sciatic nerve through the catheter at 48 hours after cannulation.Arterial blood samples (5 mL)were taken for determination of plasma ropivacaine concentration (using HPLC) before and at 10, 20, 30, 60, 90, 120, 150, 180, 240, 360 and 720 min after ropivacaine injection.The pharmacokinetic parameters were determined from concentration-time data using DAS 1.0 software package.Electrocardiogram(ECG),blood pressure(BP), heart rate(HR)and heart rate(HR)were continuously monitored before and after ropivacaine injection.RESULTS: No signs of cardiovascular or central nervous system(CNS) toxicity were observed after sciatic nerve block with ropivacaine in the two groups.The pharmacokinetic parameters of t_1/2α,C_max,AUC,AUMC were decreased in the isovolemic hemodilution group, but t_1/2β,t_max were increased.CONCLUSION: Normovolemic hemodilution leads to lower plasma ropivacaine concentrations after epidural anesthesia, probably due to an increased volume of distribution.

Key words: Ropivacaine, Pharmacokinetics, Hemodilution