Effects of Thoracic Epidural Analgesia and Surgery on Lower Urinary Tract Function: A Randomized, Controlled Study

Postoperative urinary retention (POUR) is one of the most common complications after surgery and neuraxial anesthesia of which the treatment of choice is bladder catheterization 1. It has been a common practice to place an indwelling catheter in the bladder in patients receiving epidural analgesia and to leave the catheter as long as the epidural analgesia is maintained despite a lack of evidence supporting this approach.

Transurethral catheterization is associated with significant morbidity such as patient discomfort, urethral trauma and urinary tract infections (UTI). Prolonged catheterization is the primary risk factor for catheter associated UTI (CAUTI), which is one of the most common nosocomial infections and can prolong hospitalisation 2. For this reason there is a growing focus on limiting the duration of catheterization and finding methods to avoid unnecessary catheterization in perioperative medicine 3,4.

Lower urinary tract function depends on coordinated actions between the detrusor muscle and the external urethral sphincter. Motorneurons of both muscles are located in the sacral spinal cord between L1 and S4. Most afferent fibers from the bladder enter the sacral cord through the pelvic nerve at segments L4-S2.

Because epidural analgesia can be performed at various levels of the spinal cord, it is possible to block only a portion of the spinal cord (segmental blockade). Based on the innervation of the bladder and sphincter between L1 and S4 it can be assumed that epidural analgesia within segments T4-6 to T10-12 has no or minimal influence on lower urinary tract function.

In a previous study, we found, against our expectations that thoracic epidural analgesia (TEA) significantly inhibits the detrusor muscle during voiding, resulting in clinically relevant post-void residuals which required monitoring or catheterisation 5. Because the study adopted a before-after design, we could not definitively identify the mechanisms responsible for this change in bladder function. In particular, we could not determine whether TEA per se or surgery was the main cause. Concerning TEA, it remains unclear which compounds of the solution, the local anesthetic, the opioid or both are responsible for the observed changes in lower urinary tract function.

The aim of this study is to compare lower urinary tract function before and during TEA with two different epidural solutions (group 1: bupivacaine 1.25 mg/ml vs group 2: bupivacaine 1.25 mg/ml combined with fentanyl 2 µg/ml) within segments T4-6 to T10-12 for postoperative pain treatment in patients undergoing lumbotomy for open renal surgery.

We expect that a better understanding of lower urinary tract function during TEA could lead to a more restrictive use of indwelling transurethral catheters perioperatively.