Currently, combined spinal-epidural anesthesia (CSE) is frequently administered, especially in obstetrics and orthopedic surgery. The aim of this study is to determine the appropriate concentration of bupivacaine to use with epidural volume extension that is suitable for total knee replacement during CSE.

Eighty patients (ASA physical status I and II) scheduled for totalknee replacement were randomly allocated to four groups of 20 patients each: All patients intrathecally received 2 ml of 0.5% hyperbaric bupivacaine. After fixation of spinal anesthesia, the groups received the following treatments. Group S patients received a 10 ml administration of normal saline for 15 min followed by a continuous 10 ml/hr epidural infusion. Group B1 patients received a 10 ml administration of 0.125% bupivacaine for 15 min followed by a continuous 10 ml/hr epidural infusion. Group B2 patients received a 10 ml administration of 0.25% bupivacaine for 15 min followed by a continuous 10 ml/hr epidural infusion. Group B3 patients received a 10 ml administration of 0.5% bupivacaine for 15 min followed by a continuous 10 ml/hr epidural infusion.

The incidence of intraoperative movement in group S and group B1 patients were significantly greater than the incidence for group B2 and B3 patients. The incidence of intraoperative pain in group S patients was significantly greater than for patients in any of the other groups.

We conclude that it is necessary to administer more than a 0.25% concentration of epidural bupivacaine load and provide continuous administration after a spinal block during total knee replacement.