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Impact of spinal ultrasound training on landmark identification of L3/L4 interspace
Abstract Number: T2C-348
Abstract Type: Original Research
Background: Tuffier's line, commonly used to identify the L3/4 interspace, can be unreliable with several studies identifying that operators tend to be more cephalad 1,2. This can potentially damage the conus following spinal anaesthesia. We explored whether training in lumbar spine ultrasound (LSU) improved accuracy of the landmark identification of the L3/4 interspace.
Method: We assessed the accuracy of landmark identification of the L3/4 interspace by anaesthetists pre and post intervention, the intervention being two LSU teaching sessions, 2 weeks apart with practice interim. Participants were asked to identify the L3/4 interspace on models. The accuracy of their marking was assessed against hidden markings of the intervertebral spaces, identified earlier using ultrasound by a clinician trained in LSU. Participants were unblinded to the purpose of the study, but remained blinded to their results. Post-intervention, participants were again asked to identify the L3/4 interspace on models and the accuracy was assessed as before, by a trained clinician.
Results: We studied 6 participants with 10 models at preintervention, and 8 models at post-intervention giving us 60 and 48 data points respectively. Pre-intervention there was significantly higher identification of the L3/4 interspace by candidates using the landmark technique (avg 0.6 interspinous space above L3/4) compared to post-intervention (avg 0.75 interspinous space below L3/4). Assuming non-parametric distribution, the Wilcoxon rank test gives a p=0.031, rejecting the hypothesis that these results are due to chance, with 95% CI.
Discussion: Forty five per cent of candidates identified the L3/4 at a higher interspace using the landmark technique. After a short period of training in LSU, candidates did not identify the L3/4 interspace at extreme cephalad levels. Once unblinded candidates may have been overcautious in their landmark identification of L3/4, but arguably that is the value of training in LSU. Our data suggests that training in LSU could reduce the incidence of identification of high interspinous spaces for neuraxial block. We recommend LSU be used alongside the current landmark technique when teaching neuraxial procedures. Our study was limited by a small sample size, self selection of candidates and lack of control group and random sampling.
1. Anaesthesiology clinics. Elsevier journals 2008, 26:1, 145 -58
2. Anaesthesia 2001; 56:235 -47