Research Article Measurements of Epidural Space Depth Using Preexisting CT Scans Correlate with Loss of Resistance Depth during Thoracic Epidural Catheter Placement Nathaniel H. Greene, 1 Benjamin G. Cobb, 1 Ken F. Linnau, 2 and Christopher D. Kent 1 1 Department of Anesthesiology and Pain Medicine, University of Washington School of Medicine, Seattle, WA 98195, USA 2 Department of Radiology, University of Washington School of Medicine, Seattle, WA 98195, USA Correspondence should be addressed to Nathaniel H. Greene; nathanielgreene@me.com Received 8 August 2014; Accepted 21 December 2014 Academic Editor: Enrico Camporesi Copyright © 2015 Nathaniel H. Greene et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Toracic epidural catheters provide the best quality postoperative pain relief for major abdominal and thoracic surgical procedures, but placement is one of the most challenging procedures in the repertoire of an anesthesiologist. Most patients presenting for a procedure that would beneft from a thoracic epidural catheter have already had high resolution imaging that may be useful to assist placement of a catheter. Methods. Tis retrospective study used data from 168 patients to examine the association and predictive power of epidural-skin distance (ESD) on computed tomography (CT) to determine loss of resistance depth acquired during epidural placement. Additionally, the ability of anesthesiologists to measure this distance was compared to a radiologist, who specializes in spine imaging. Results. Tere was a strong association between CT measurement and loss of resistance depth ( < 0.0001); the presence of morbid obesity (BMI > 35) changed this relationship ( = 0.007). Te ability of anesthesiologists to make CT measurements was similar to a gold standard radiologist (all individual ICCs > 0.9). Conclusions. Overall, this study supports the examination of a recent CT scan to aid in the placement of a thoracic epidural catheter. Making use of these scans may lead to faster epidural placements, fewer accidental dural punctures, and better epidural blockade. 1. Introduction Local anesthetics and opioid medications administered by thoracic epidural catheters provide the best quality post- operative pain relief for major abdominal and thoracic surgical procedures [1]. Te process of placing a catheter into the epidural space between the thoracic vertebrae can be challenging due to variations in thoracic spinal anatomy and narrow intervertebral spaces. One of the consequent risks is excessively deep placement of the needle with the potential complication of dural puncture headache and, rarely, needle induced injury to the spinal cord, making thoracic epidural placement a riskier procedure than a lumbar epidural. Anesthesiologists increasingly use ultrasound imaging to guide the placement of needles into the body for the purpose of doing medical procedures. Te bony vertebral column largely precludes the use of bedside sonography for steep angle neuraxial procedures owing to the lack of ultrasound transmission in bone. Tese challenges are magnifed in the patients in whom neuraxial procedures are most difcult (those with morbid obesity or spinal abnormalities). While most anesthesiologists have a general idea at what depth they should expect to encounter the epidural space, there can be a wide range of variability between individuals [2]. Te depth from the skin to the epidural space is infuenced by both patient factors including body mass index [3] and procedural factors such as the needle angle required to enter the epidural space between the posterior elements of the vertebrae [4]. For any individual patient it would be helpful to know the specifc depth to the epidural space prior to epidural needle placement. With increased utilization of computed tomography (CT) for not only diagnostic purposes but also preoperative plan- ning, most patients undergoing epidural catheter placement Hindawi Publishing Corporation Anesthesiology Research and Practice Volume 2015, Article ID 545902, 6 pages http://dx.doi.org/10.1155/2015/545902