A novel method for assessing analgesic effects during nerve block using ultrasonography: An experimental study in a canine model

Abstract

Introduction Ultrasound (US)-guided nerve block is a type of regional anesthesia and is used as periprocedural analgesia during orthopedic surgery and endovascular treatment. Since this technique requires ample time to elicit the required analgesic effect, it is important to determine whether the appropriate analgesic effect has been attained before initiating a painful procedure. A skin sensation test is commonly used to evaluate analgesic effects. However, this method is subjective and sometimes fail to accurately evaluate the analgesic effect. Alternatively, although electrical nerve stimulation is used as an objective method, it is invasive. To determine the efficacy of the nerve block, the development of a novel evaluation method that is both objective and non-invasive is required. Purpose To evaluate the feasibility of ultrasonographic evaluation for analgesic effect during US-guided nerve block. Method US-guided sciatic nerve block was performed in five dogs under general anesthesia. In the same dog, 2% mepivacaine was injected into one leg and normal saline was injected into the other leg. Each leg was assigned to the block group and the control group. In each group, cross sectional area (CSA), shear wave elastography (SWE), and superb micro-vascular imaging (SMI) of the sciatic nerve were serially measured at 0, 30, 60, and 90 minutes after nerve block. For SWE, the value of the muscle innervated by the sciatic nerve was also measured, and the nerve/muscle ratio of SWE was calculated. Each value was compared between the block group and the control group. Electrical nerve stimulation was used as the reference standard for assessing the analgesic effect. Results Nerve block was successful in all dogs, and the effect of nerve block was observed from 30 to 90 minutes. In the block group, the nerve/muscle ratio of SWE significantly increased at 60 and 90 minutes and was 1.13 and 1.21, respectively (p Conclusion Ultrasonographical evaluation using the nerve/muscle ratio of SWE could be a novel and feasible method to assess the analgesic effect during nerve block.