Measurements of Epidural Space Depth Using Pre-Existing CT-Scan Correlate with Loss of Resistance Depth during Lumber Epidural Catheter Placement

Abstract

Background: The use of epidural catheters provides the best quality intra- and post-operative pain relief for various major thoraco-abdominal and lower limb surgeries. The process of placing an epidural catheter into the epidural space between the vertebrae can be challenging due to variations in spinal anatomy of different level, narrow intervertebral spaces and can cause catastrophic neurological complications. Though various studies have been shown to overcome the placement of epidural catheter using standard ultrasound method, using the pre-existing computer tomography depth correlate with loss of resistance in placing the epidural catheter would be a well adjunct tool for the procedure. Objectives: To correlate measurements taken from pre-existing computed tomography (CT) imaging to the loss of resistance depth as recorded during epidural placement. Methods: This Single procedural observational study was performed in Combined Military Hospital (CMH), Dhaka from 1st December 2018 to 30th November 2019. Fifty adult patients scheduled for lower abdominal and lower limb surgery under epidural anaesthesia (EA). The patient’s advised/routine abdominal CT film was inspected by a radiologist, who was blinded to the results of the actual needle length, to determine the distance from the skin to the ligamentum flava the corresponding level of L2 to L5 interspinous spaces. The distance on the CT film in the midline was measured using a ruler against the measurement scale, conventionally represented as a 5 cm-10 cm scale with 1-cm divisions. The CT-derived depth was calculated using the principle of Pythagorean triangle trigonometry. Result: In this study, Sixty eight percentages of patients (68%) Epidural- skin distance (ESD) had 4.7-6.8cm. Mean Epidural-skin distance 5.8±1.7cm. On evaluation of Loss of Resistance Depth, 46% of patients had 5.2-7.3cm depth of LOR, followed by 30% patients had 3.0-5.1cm and 12% patients had 7.4-9.5cm. Mean loss of resistance depth was 6.3±1.4 cm. It was evident from this study that positive significant correlation (r=0.941; p=0.001) between the CT-derived distance and Loss of Resistance Depth. Conclusion: It is conclude that using pre-existing CT-scan derived distance is helpful in prediction of the epidural space depth and it is correlates with actual loss of resistance epidural needle insertion depth placing the catheter in lumber region.