OP030 Landmark accuracy for spinal anaesthesia in obese obstetric patients: should we use lumbar ultrasound routinely?

<h3></h3> <b>Please confirm that an ethics committee approval has been applied for or granted</b>: Yes: I’m uploading the Ethics Committee Approval as a PDF file with this abstract submission <h3>Background and Aims</h3> Obesity complicates landmark-based spinal anaesthesia, increasing misidentification of intervertebral levels and needle insertions. While various meta-analyses have compared ultrasound to landmark techniques, obstetric studies remain scarce. In this study, we aimed to determine if obesity impacts injection site accuracy in landmark-based spinal anaesthesia among Obstetric patients. <h3>Methods</h3> Ethical approval was obtained for this observational prospective cohort study(HRA,England 16/NE/0410). Two cohorts were defined as lower BMI &gt;/=35 kgm-2 or higher BMI &lt;35 Kgm-2, based on our local population’s median booking BMI(35 kgm-2). Intervertebral space was determined by the anaesthetist using landmark-based approach which assumes the line intersecting top of iliac crests at the level of L4 vertebra and distal end of spinal cord at L1 vertebra. Using ultrasound(U/S), the research team determined whether there was a difference between the landmark and the U/S-derived spinal level and then quantified the difference in levels. We also recorded difficulty in identifying the landmarks. <h3>Results</h3> 111 women were included. Palpating landmarks was significantly easier in the lower BMI group (n=55) than higher BMI group(n=56), (p &lt; 0.0001). Spinal level was correctly determined only approximately 50% of the time in both the lower and the higher BMI group (50.9% v 44.6%, p=0.7); however, with the higher BMI group, 100% inaccuracies resulted from aiming too high, compared to 69.8% in lower BMI group(p=0.001). <h3>Conclusions</h3> Obesity increases the risk of aiming higher than intended intervertebral space for spinal anaesthesia in obstetric patients using traditional landmark-based approach, which highlights the need for routinely incorporating pre-procedural ultrasound, especially in this group of patients.