Ultrasound-Guided Neuraxial Blocks: Recent Developments

Abstract

Peripheral nerve blocks and neuraxial blocks are one of the most common procedures performed by anaesthetists. There has been enormous development in the use of ultrasound (US) for regional anaesthesia during last decade. In our previous article, 1 we reviewed such use of US in regional anaesthesia. Many studies have been published on this subject but most of the studies are on the use of ultrasound for peripheral nerve blocks and only few look into its use for neuraxial blocks. This article is a review of recently published papers on the subject of ultrasound for neuraxial blocks. IDENTIFICATION OF INTERVERTEBRAL LEVEL Spinal anaesthesia is commonly performed at L3-4 level. Performing a subarachnoid injection above this level has potential for spinal damage in a proportion of normal adult population. 2 Position of conus medullaris varies from middle third of T 12 to upper third of L 3 in adult population and mean position of conus is lower third of L 1 . 3 The importance of correctly identifying the intervertebral level during regional anaesthesia has been highlighted in the past. 4 Tuffier’s line is commonly used to identify the lumbar interspaces but this does not bear constant relationship to these spaces. Reliance on this landmark might lead to more cranial placement of epidural or spinal needles than intended and this subsequently will increase the risk of spinal cord damage. 5-8 Broadbent C R and colleagues 5 in their study of 100 patients undergoing spinal MRI scans demonstrated that identification of lumbar space by anaesthetists by palpatory method is not reliable. The study included total 200 observations from 100 patients by different observers. All observers had more than five years anaesthetic experience and had performed several hundred spinal anaesthetics. Correct space was identified in 58 (29%) observations. In six (3%) observations, anaesthetist identified a lower space than intended. In remaining 136 (68%) observations, anaesthetist marked higher spaces than intended. This was one, two and three spaces higher in 102 (51%), 31 (15.5%) and two (1%) occasions respectively. The marker was four spaces higher in one (0.5%) observation. Study by Furness G and colleagues 6 showed that US can identify correct intervertebral level in upto 71% of case as compared to 30% by palpatory method. The same study showed that ultrasound was inaccurate by one level only in all inaccurate cases, while palpatory method was inaccurate by more than one level in 27% of inaccurate cases. This study considered identification of intervertebral space by lateral lumbar spine X-ray as a benchmark. Watson and colleagues 9 in their study-correctly identified the L3-4 space with ultrasound in nearly 76% (13/17) of cases when confirmed with MRI scan. In four cases, the anaesthetist identified one space lower than intended. It is small but otherwise simple and relevant study, where investigator used the gold standard (MRI) to confirm the level of intervertebral space. Study by Whitty R and colleagues 10 demonstrated that there was poor agreement between palpation and ultrasound estimation of the specific lumbar interspace. When there was disagreement between the two methods, the ultrasound estimate was more often higher than the palpatation estimate. This study compares the two methods but does not use any gold standard to conclude superiority of one method over the other. Based on the fact from previous studies that by palapatory method clinicians select interspaces that are one or two spaces higher than intended, this study indirectly supports that US is more accurate in identifying the lumbar inetrspaces. In their study, Schlotterbeck H and colleagues 11 reviewed