Prediction of midline depth from skin to cervical epidural space by lateral cervical spine X-ray

ABSTRACT

BACKGROUND: Previous studies have shown that measuring the distance from the skin to the ligamentum flavum by ultrasound preceding cervical epidural block can be beneficial in excluding false loss of resistance. However, the measurement value using ultrasound may vary depending on the degree of operator experience. Therefore, we aimed to determine the depth from skin to cervical epidural space by using lateral cervical spine X-ray, which is a more intuitive method. METHODS: We enrolled 102 adult patients who were scheduled to undergo cervical epidural anesthesia for vascular bypass surgery of upper arm. After attaching a steel rod on the needle insertion site, lateral cervical spine X-ray was taken before the epidural procedure. We measured the distance from the steel rod to the midpoint of interlaminar space on the spinolaminar line. The X-ray depth was compared with needle depth. RESULTS: Of the 102 enrolled patients, 18 patients including 13 in whom we were unable to measure X-ray depth were excluded from the analysis. In total, 84 patients were included in the analysis. Concordance correlation coefficient between the X-ray-measured depth and needle depth was 0.925. Bland-Altman analysis indicated a mean difference of ± 1.96 SD with 0.06 ± 0.56 cm. CONCLUSIONS: Lateral cervical spine X-ray can be useful for prediction of the midline depth from skin to epidural space, particularly for operators who are not skilled at spine ultrasound or the use the C-arm fluoroscopy.