Epidural catheter tip position and distribution of injectate evaluated by computed tomography

Background: The distribution of solutions injected into the epidural space has not been determined. The author therefore examined the site of catheter tips and the spread of contrast material in the epidural space using compu ted tomographic (CT) imaging in patients receiving successful epidural anal gesia. Methods: Lumbar epidural catheters were placed in 20 female patients by a m idline technique, Anesthetic effect was determined by motor and sensory exa minations during analgesic infusion, CT images were obtained for Identifica tion of the catheter tip and after radiographic contrast injection of 4 mi and then an additional 10 mi, Results: Catheter tips were most often found lateral to the dura in the int ervertebral foramen, In these subjects with normally functioning epidural a nalgesia, there was remarkable interindividual variability in patterns of s pread, including various amounts of anterior passage, layering along the du ra, and compression of the dura creating a posterior fold. Accumulation bec omes more symmetric with increasing injectate volume. Spread through the in tervertebral foramina was seen in all subjects. Air and fat in the region o f the catheter interfered with solution spread in three subjects, but only over a limited area. Asymmetry in anesthetic effect was attributable to cat heter position. No substantial barriers to solution spread were observed. Conclusions: A variety of catheter tip positions and patterns of solution s pread underlie normal epidural anesthesia Nonuniform distribution of inject ate is common and is compatible with uniform anesthesia. Posterior midline structures play a minimal role in impeding distribution of injectate, A far lateral catheter position is a more common cause of asymmetric block than anatomic barriers to solution spread.