Identification of the lumbar interspinous spaces by palpation and verified by X-rays

Palpation has been shown to be rather inaccurate at identifying lumbar interspinous spaces in neuraxial anesthesia. The aim of this study is to assess the accuracy of the determination of the lumbar interspinous spaces by anesthesiologist's palpation using postoperative X-rays in obstetric patients.

We reviewed the anesthetic record and the post-operative abdominal X-rays of the cesarean sections. We indwelled the epidural catheter for post-operative one-shot analgesia. We included combined spinal and epidural anesthesia cases and compared the interspinous level which the anesthesiologist recorded and the epidural catheter insertion level confirmed by abdominal X-ray for each case. We also evaluated the factors (age, body weight, height, Body Mass Index, gestational age, and the type of surgery [planned / emergency]) leading to misidentification of interspinous level.

Nine hundred and sixty seven cesarean sections were performed and a total of 835 cases were evaluated. The levels of the puncture documented by the anesthesiologists were in agreement with the actual catheter insertion levels in 563 (67%) cases. When the anesthesiologists aimed at L2-3 level, we found the catheter insertion at L1-2 in 5 cases (4.9%), none of which had any post-operative neurological deficits. No variables evaluated were significantly associated with misidentification of interspinous level by the anesthesiologists.

There was a discrepancy between the anesthesiologists' estimation by palpation and the actual catheter insertion level shown in X-rays. It seems to be safer to choose the interspinous level L3-4 or lower in spinal anesthesia.