Ability of anaesthetists to identify a marked lumbar interspace. (Nuffield Department of Anaesthetics, John Radcliffe Hospital, Oxford, United Kingdom) Anaesthesia 2000;55:1122–1126.

Abstract

This article assessed anesthetists' ability to identify correctly a marked lumbar interspace in 100 patients undergoing spinal magnetic resonance imaging scans. Using ink, the first anesthetist marked an interspace on the lower spine and attempted to identify its level with the patient in the sitting position. The second anesthetist attempted to identify the level with the patient in the flexed lateral position. A marker capsule was taped over the ink mark and a routine scan performed. The actual level of markers ranged from 1 space below to 4 spaces above the level at which the anesthetist believed it to be. The marker was 1 space higher than assumed in 51% of cases and was identified correctly in only 29%. Accuracy was unaffected by patient position (sitting or lateral), although it was impaired by obesity and positioning of the markers high on the lower back. The spinal cord terminated below L1 in 19% of the patients. This, together with the risk of accidentally selecting a higher interspace than intended for intrathecal injection, implies that spinal cord trauma is more likely when higher interspaces are selected. Comment by Alan Kaye, M.D. Previous studies have demonstrated inaccuracies regarding identification of lumbar interspaces. This study by Broadbent et al involved 104 patients scheduled for lumbar magnetic resonance imaging and essentially anesthesiologists were asked to mark with washable ink the skin overlying any interspace on the lower spine after palpation of the lumbar region. Different positions were evaluated including sitting and lateral. Only 29% were demonstrated to be correct through magnetic resonance imaging. Within the lumbar region, there were tremendous errors by the anesthesiologist at all levels. Further, a common mistake included the assumption of location based on the landmark provided from the iliac crest. Therefore, with the potential of neurological damage from misidentification of the vertebral column, the authors recommend lower rather than higher sites when more than 1 site is identified. The authors provide a clever investigation; however, this is a relative small study population and there is little mention of the variation existing within the population studied. However, this study suggests that if an option exists as to which lumbar space to enter, the lower would seem safer and more prudent to minimize the potential of neurologic injury.