Correlation of actual epidural depth with ultrasound estimates in paramedian sagittal oblique and transverse median plane in parturients: a prospective cross-sectional study

Abstract

Purpose: In this prospective, cross-sectional, observational study, the accuracy and precision of actual epidural depth (ND) with ultrasound estimates of epidural depth (ED) in the paramedian sagittal oblique plane (PSO) and transverse median plane (TM) in parturients was assessed. Methods: Ninety parturients scheduled for cesarean section asking for combined spinal epidural anesthesia were recruited. ED was assessed in PSO and TM planes with a 5-2 MHz curved array probe. The least possible pressure was applied on the probe during ultrasound examination. All epidurals were located by a midline approach at L3-4 level by an anesthesiologist blinded to ED but informed about the insertion point. ND was marked on the needle with a sterile marker. Precision between the measurements were assessed by Pearson correlation coefficient and Lin's concordance correlation coefficient (CCC). Bland-Altman test was used to assess the 95% limits of agreement (LOA) between measurements. Results: The mean (SD) ultrasound estimated ED in the PSO and TM plane and ND were 56.07 (9.31) mm, 55.99 (9.15) mm, and 56.17 (9.28) mm respectively. CCC between ND and US estimated ED in PSO plane was 0.9929, and 0.9928 in TM plane. Bland-Altman analysis showed -1.13-1.03 mm 95% limits of agreement between ND and ultrasound estimated ED in PSO plane and -1.15-0.98 mm in TM plane. There was a strong correlation between the ND and ultrasound estimates of epidural depth in PSO and TM planes. Conclusion: Both planes can be used interchangeably for preprocedural estimation of ED in parturients asking for labor epidurals.