Background: 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.
Methods: 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.
Results: 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.
Conclusions: 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.