Reducing the Dose of Local Anesthetic Reduces the Duration of Analgesia—Myth or Reality: A Double-Blind Randomized Study

Abstract

Background: The aim of the study is to determine the effect of a reduction in dose of local anesthetic blockade on the development of the sciatic nerve. Methods: Forty blocks of sciatic nerve were used in a double-blind randomized research, under ultrasonic guidance, using an electric stimulator with the peripheral nerves. Forty patients were divided into 2 equal groups. In the first group, a sciatic nerve block was performed with 5 ml of 0.75% ropivacaine solution (37.5 mg); in the second group, 10 ml of 0.75% ropivacaine solution (75 mg) was used. The assessment of the time required for developing sensory and motor blocks was carried out from the beginning of local anesthetic solution injection in the fascial sheath of the sciatic nerve. Results: Demographic data of patients were identical in the two sample groups. The time required for achieving a complete sensory block in groups treated with 5 and 10 ml ropivacaine was 45 (40; 48) and 30 (28; 30) min, respectively, (р < 0.01). There was no difference in analgesic duration in the postoperative period among groups at p > 0.05. Conclusions: Complete blockade of the sciatic nerve is developed using 5 ml of 0.75% ropivacaine. Reducing the dose of ropivacaine prolongs the latent period of the LA during the blockade of the sciatic nerve. Time of postoperative analgesia was not significantly changed.