Prediction of the distance from skin to epidural space for low-thoracic epidural catheter insertion by computed tomography

Background. It may be clinically useful to predict the depthof the epidural space. Methods. To investigate the accuracy of preoperative abdominalcomputed tomography (CT) in prediction of the distance for low-thoracicepidural insertion, a single group observational study was conductedin 30 male patients undergoing elective major abdominal surgeryrequiring epidural analgesia for postoperative pain relief.Using the paramedian approach, low-thoracic epidural insertionat T10–11 interspace was performed with a standardizedprocedure to obtain an actual insertion length (AIL). Accordingto the principles of trigonometry, an estimated insertion length(EIL) was calculated as 1.26 times the distance from skin toepidural space measured from the preoperative abdominal CT. Results. The mean (SD) EIL and AIL were 5.5 (0.7) and 5.1 (0.6)cm, respectively, with a significant correlation (r=0.899, P<0.01).The EIL tended to have a higher value than the AIL (0.4 (0.3)cm). There were significant correlations of both EIL and AILwith weight (P<0.01), BMI (P<0.01), and body fat percentage(P<0.01), but not with height (P>0.05). Conclusions. We conclude that the preoperative abdominal CTis helpful in prediction of the distance for low-thoracic epiduralinsertion using the paramedian approach. Br J Anaesth 2004; 92: 271–3