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A comparison of the lumbar ultrasound acoustic window in parturients in the standard sitting and crossed leg positions
Abstract Number: F-04
Abstract Type: Original Research
Inroduction: Lumbar Spine Ultrasonography (LSUS) facilitates performance of neuraxial anesthesia in parturients.1. In ultrasonography (US), improved visualization of the Paravertebral Longitudinal Ligament (PLL) suggests an ‘open acoustic window’, or unobstructed path to the dura between the laminae of the lumbar spine 4. In addition, the effect of patient position on the visualized length of the PLL has been previously demonstrated 2,3. We hypothesized that the crossed legged position would increase the measured lengths of the PLL, Interlaminar Distance (ILD) and Ligamentum Flavum (LF) in the paramedian view during LSUS when compared to the standard sitting position.
Methods: Local REB approval was obtained. Thirty term pregnant, non-labouring women provided written informed consent . Two anesthesiologists independently scanned the L3-4 right paramedian space using a curvilinear ultrasound transducer (SonoSite M-Turbo, Bothell, WA, USA). Two positions were investigated for each patient: traditional sitting position (SP) with lumbar flexion; and cross legged position (CLP), where the patients sat on the bed with their legs crossed, neck and lower back flexed. The PLL, ILD and LF lengths were measured using the ultrasound calliper software and recorded, with the anesthesiologists blinded to the results and to each others’ scans. Patients were asked to rate their comfort level in both positions using a Likert scale.
Results: We were able to obtain scans in both positions in all patients. There was a small but statistically significant increase in the measured lengths of the PLL, ILD and LF in the CLP position (Table 1). Comfort levels were not different between groups (Odds Ratio CLP/SP = 0.88 (95% CI 0.3 to 2.8; P > 0.999).
Discussion: This study demonstrates the feasibility of using LSUS to visualize PLL, LF, and ILD at L3-4 intervertebral space using paramedian view in term pregnant women in both CLP and SP. Measurements were found to be longer in CLP which suggests the possibility of easier lumbar neuraxial access in the CLP. . Future studies are needed to correlate these findings with ease of needle insertion in parturients.
1. Grau T et al. J Clin Anaesth (2002): 14:169-175.
2. Ramsay N et al Br J Anaesth. 2014 Mar; 112(3):556-62.
3. Jones AR et al Anesthesia, 2013 Jan; 68(1):27-30.
4. Weed J et al. Anaesthesia, 2011, 66: 925–930