A Comparative Study Between Different Local Anesthetic Volumes Injected During Erector Spinae Block to Reduce Postoperative Opioid Consumption in Patients Undergoing Open Simple Nephrectomy Operations; a Randomized Controlled Trial

INTRODUCTION In recent years a number of important fascial plane blocks have been described blocking the dorsal, lateral and anterior cutaneous nerves of the thorax and abdome].The advantage common to all of these blocks is that they are technically easier to perform with lower risk for serious complications.Since its first description by Forero et al. there have been many articles and case reports including an increasingly number of indications for the ESP block: chronic and acute pain treatment , rib fractures management in the emergency setting , treatment of abdominal surgical pain , hip arthroplasty , analgesic management in breast surgery ,or in spinal surgery.The ESP block targets the erector spinae plane, which lies in the chest wall between the anterior surface of the cephalo caudal oriented erector spinae muscles and the posterior surface of the spinal transverse processes. LA is deposited in the fascial plane deep to the erector spinae muscle and superficial to the tips of the transverse processes, from where it diffuses to the dorsal and ventral rami of spinal nerves, achieving an extensive multi-dermatomal sensory block of the posterior, lateral, and anterior thoracic wall .Chin et al reported that an injection of 20 ml into the ESP produces clinical and radiographic evidence of spread that extends at least three vertebral levels cranially and four levels caudally from the site of injection.A study with magnetic resonance imaging demonstrated and confirmed that its mechanism of action is likely linked to the transforaminal and epidural spread, which may be a potential advantage because the ESP block provides abdominal visceral analgesia unlike the others .beside its ability to spread to paravertebral and intervertebral spaces and ability to block the sympathetic nerve fibers. the ESP block is considered as a peri-paravertebral regional anesthesia technique.LAs, is injectted with volumes ranging from 20 mL to 40 mL, and concentrations ranging from 0.25%-0.5%.even though a higher LA concentration might allow for better diffusion into the paravertebral space .

Open surgery remains common for patients requiring radical or partial nephrectomy and is associated with a high incidence of intense immediate postoperative pain and chronic pain in the months following surgery. ESP block was for open partial nephrectomy with excellent results both in the intraoperative and postoperative period, with a large reduction in the use of opioids.

Although ESP block successfully reduced postoperative opioid consumption in clinical reports, no studies thus have investigated the optimum volume of bupivacaine for ESP block as regard a review of the medical literature on December 27th, 2017 that searched terms in 14 articles clearly stated the volume of the bolus and the spread of the anesthetic after an injection of LA, the volume needed to cover one dermatome widely varies from 2.5 mL to 6.6 mL, with a median value of 3.4 mL. Furthermore, the maximum number of dermatomes reached by a single bolus in ESP was of 9 dermatomes after a 30 mL bolus.

Thus, in this study, the investigators evaluate the effect of ESP block which will be performed by using three different volumes (2.5, 3.4 ,6.6 ml/segment) of bupivacaine with the same concentration ,technique ,site of injection and operation.

Methodology: