Identification of the lumbar interspinous spaces: palpation versus ultrasound.

BACKGROUND Palpation has been shown to be inaccurate at identifying lumbar interspinous spaces. Our goal in this study was to compare ultrasound imaging of the region to palpation. METHODS Using ultrasound in the postpartum period, we estimated the interspinous level used for obstetric neuraxial anesthesia in 121 women and compared this estimation with the level estimated by palpation and documented in the chart by the anesthesiologist. RESULTS In 67 of 121 (55%) patients, the vertebral level of the puncture mark documented by the treating anesthesiologist was in agreement with vertebral level as assessed using ultrasound, and in 39 (32%) women, the skin puncture level was estimated by ultrasound to be at least one interspace higher. The unweighted kappa was 0.08 (95% confidence interval: 0.02, 0.14). CONCLUSIONS There was poor agreement between palpation and ultrasound estimation of the specific lumbar interspace, and when there was disagreement, the ultrasound estimate was more often higher than the palpitation estimate.