distribution of bupivacaine in epidural space

Background: there is no consensus regarding the spread of local anesthesia in thoracic epidural space to obtain regional analgesia or anesthesia. we aimed to determine the distribution of bupivacaine injected into the thoracic epidural space to evaluate its cranial or caudal spread in patients undergoing epidural anesthesia. materials and methods: in a prospective clinical trial, thirty adults patients (12 males and 18 females) with asa class i and ii, scheduled for elective cholecystectomy under thoracic epidural anesthesia with 0.5% isobaric bupivacaine were studied. clinical and radiological outcomes were evaluated to assess the correlation between the volume of the local anesthetic injected to the thoracic epidural space and the extension of its spread within the epidural space. immediately after insertion and fixation of epidural catheter, patients were transferred to mri unit to receive 8 ml of 5% bupivacaine plus 1 ml magnevist through the epidural catheter. then, the patterns of spread were evaluated. data were obtained prospectively during the procedure. results: mean distribution of bupivacaine in thoracic epidural space was 0.64 level/ml of local anesthetics and the average of spread was 5.21 levels. the mean spread of bupivacaine was more in females (5.5 ± 1.1) than males (4.8 ± 1.1); but the difference was not significant. unlike patients’ age and weight, the height and body mass index had a significant negative correlation with the distribution of bupivacaine. conclusion: distribution of bupivacaine in epidural space in female patients is more than male ones and the tendency of spread is more toward the cephalad direction than caudal.