Ultrasound Guided Epidural Depth Estimates : A Comparison Between Transverse Median Plane And Parasagittal Oblique Plane For Lower Thoracic Epidural

Epidural analgesia is a form of regional analgesia which involving the drugs through   injection or a catheter placed in the epidural space.It is still considered as a gold standard for perioperative pain management in major abdominal and thoracic surgeries as it improves the postoperative outcome. Advantage includes a lower risk of postoperative myocardial infarction, better pulmonary mechanics and decreased hyper-coagulable reaction to stress which all lead to better recovery after surgery (1 ,2).Epidural analgesia through an indwelling catheter decreases intra and postoperative opioid usage (3). It has been observed that in Thoracic and Intra-abdominal surgeries the incidence of postoperative gastrointestinal dysfunction, sedation and respiratory depression were reduced with continuous Thoracic Epidural Analgesia (TEA).  TEA was linked to early ambulation, improved recovery throughout the peri-operative phase with decreased need of analgesia. TEA also promotes better control of neuroendocrine stress response in intraoperative phase due to protein catabolism and reduced insulin resistance hence aiding in better pain control management (4). It is difficult to access the Thoracic epidural space using the standard anatomic landmark-based Loss Of Resistance (LOR) technique because of spinous processes have a sharp caudal angle and the laminae are densely packed on top of one another , resulting in very limited inter laminar space. Therefore adopting the anatomic landmark based technique for thoracic epidural makes it technically more challenging.And it may leads to” multiple attempts and a relatively higher failure rate (12-40%) which  increases  patient discomfort and morbidity (5).Nowadays, ultrasound based localisation of the epidural space has become a popular teaching tool. Ultrasonography is useful in planning the insertion angle for the needle trajectory, seeing the anatomy and measuring the depth from the skin to the epidural space therefore it reduces the failure rate, improves learning curve and decrease puncture attempts (6).Ultrasound guided lumbar epidural has gained popularity as it is easily performed, provides opportunity to confirm the landmarks and deposit the local anaesthetic at correct place besides being associated with improved safety and decreased rate of complications. To visualise the lumbar epidural space Ultrasound imaging of the spine is performed in transverse axial plane at the level of desired intervertebral space (7).Use of thoracic epidurals for intra and postoperative analgesia for open abdominal surgeries has exponentially increased over the last decade mainly using conventional methods based on loss of resistance technique (8).Ultrasound guided epidural depth assessment has been primarily used for lumbar region (9). So far, the data on use of ultrasound guided assistance in Thoracic region for depth assessment in both transverse median plane and parasagittal oblique plane is very limited. Therefore, with this background we are planning to evaluate skin epidural depth assessment with conventional loss of resistance technique with ultrasound to assess the accuracy of ultrasound in both the planes.