Ultrasound using the transverse approach to the lumbar spine provides reliable landmarks for labor epidurals

Ultrasound imaging of the spine has recently been proposed to facilitate identification of the epidural space. In this study, we assessed the accuracy and precision of the transverse approach, using a "single-screen" method, to facilitate labor epidurals.

We enrolled 61 patients requesting labor epidurals. Ultrasound imaging (transverse approach, 2-5 MHz curved array probe) identified the midline, the intervertebral space, and the distance from the skin to the epidural space (ultrasound depth/UD). During the epidural puncture, we recorded the success of the insertion point, and measured the distance to the epidural space to the nearest half-centimeter of the marked Tuohy needle (needle depth/ND). We calculated the agreement between UD and ND by the concordance correlation coefficient and Bland-Altman analysis with 95% limits of agreement.

The average maternal age was 33 +/- 4.6 yr, body mass index 29.7 +/- 4.8, UD 4.66 +/- 0.68 cm, and ND 4.65 +/- 0.72 cm. The success of the insertion point was 91.8%, with no need to redirect the needle in 73.8% of the patients. The concordance correlation coefficient between UD and ND was 0.881 (95% CI 0.820-0.942). The 95% limits of agreement were -0.666 to 0.687 cm.

We found a good level of success in the ultrasound-determined insertion point, and very good agreement between UD and ND. This suggests that our proposed ultrasound single-screen method, using the transverse approach, can be a reliable guide to facilitate labor epidural insertion.