Abstract: The clinical study of median effective dose of ropivacaine for lumbar plexus blockade in elderly patients MA Lin,YangYong, YU Yong-hao Department of Anesthesiology, General Hospital, Tianjin Medical University, Tianjin 300052, China Abstract Objective： To determine the median effective dose（ED50） of ropivacaine for lumbar plexus blockade in elderly patients. Methods：Forty patients ,aged 65～85(n=20) or 18～35(n=20) underwent lumbar plexus and sciatic nerve blockade for operations of unilateral lower extremities. The volume of local anesthetic used in each patient was based on the up-and-down method for lumbar plexus blockade. The ratio of two consecutive dose was 1.12. Successful nerve block was defined as complete loss of pinprick sensation in the femoral nerve distribution , with concomitant inability to extend the affected leg within 30 min after local anesthetic injection. Results：The ED50 of 0.375% ropivacaine was 28.84 ml in the older group and 34.28 ml in the younger group （P<0.05）.The 95% confidence interval was 27.42～30.45 ml in the older group and 32.24～35.61 ml in the younger group. Conclusion：The ED50 of ropivacaine for lumbar plexus blockade is significant decrease in elderly patients.

Key words: Ropivacaine, Lumbar plexus, Anesthesia, Median effective dose