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

 Acute urinary retention is one of the most common complications after surgery and anesthesia.
 It can occur in patients of both sexes and all age groups and after all types of surgical
 procedures. It is linked to several factors including increased intravenous fluids,
 postoperative pain and type of anaesthesia 1.

 Micturition depends on coordinated actions between the detrusor muscle and the external
 urethral sphincter. Motorneurons of both muscles are located in the sacral spinal cord and
 coordination between them occurs in the pontine tegmentum of the caudal brain stem.
 Motorneurons innervating the external urethral sphincter are located in the nucleus of Onuf,
 extending from segment S1 to S3. The detrusor smooth muscle is innervated by parasympathetic
 fibers, which reside in the sacral intermediolateral cell group and are located in S2-4.
 Sympathetic fibers innervating the bladder and urethra play an important role in promoting
 continence and are located in the intermediolateral cell group of the lumbar cord (L1-L4).
 Most afferent fibers from the bladder enter the sacral cord through the pelvic nerve at
 segments L4-S2 and the majority are thin myelinated or unmyelinated.

 There are few studies on the urodynamic effects of various anaesthetic agents 2-8, which
 mainly focused on lumbar epidural anaesthesia. Under the influence of epidural analgesia,
 patients may not feel the sensation of bladder filling, which can result in urinary retention
 and bladder overdistension. Overfilling of the bladder can stretch and in some cases
 permanently damage the detrusor muscle.

 Because epidural anesthesia 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 knowledge
 of the bladder innervations, it can be assumed that epidural analgesia within segments T4-6
 to T10-12 has no or minimal influences on lower urinary tract function.

 In a previous study, we found, against our expectations that thoracic epidural analgesia
 significantly inhibits the detrusor muscle during voiding, resulting in clinically relevant
 post void residuals which required monitoring or transurethral catheterisation 9. Because the
 study adopted a before-after design, we could not definitively identify the mechanisms
 responsible for bladder dysfunction. In particular, we could not say whether thoracic
 epidural analgesia per se or surgery was the cause of bladder dysfunction. Furthermore, it
 remains which ingredients, whether the local anesthetic, the opioid or both are behind
 changes in voiding function.

 Objective

 In our previous studies, we found that TEA significantly inhibits the detrusor muscle during
 voiding, resulting in clinically relevant post-void residuals which required monitoring or
 catheterization with similar findings 5,30.

 Because these studies adopted a before-after design, we could not definitively identify the
 mechanisms responsible for lower urinary tract dysfunction. In particular, we could not say
 whether TEA per se or surgery was the cause of lower urinary tract dysfunction. Furthermore,
 it remains unclear which compounds in the epidural solution, the local anesthetic, the opioid
 or both are behind the observed changes in lower urinary tract function.

 The objectives of this study are to determine if TEA per se or surgery are the cause of
 bladder dysfunction and which drugs in the epidural solution are responsible for this effect.

 Methods

 Randomised controlled double-blind study. Patients will be randomly allocated to one of the
 two groups by a computer-generated randomization list. Randomization will be stratified by
 gender, in order to reach an equal number of male and females in the two groups. Patients and
 investigators will be blinded to the epidural solution administrated.
Inclusion Criteria:

 -  Written informed consent

 -  Open kidney surgery with lumbotomy

 -  Thoracic epidural analgesia

 -  International Prostate Symptom Score (IPSS) < 7

 -  Preoperative residual urine volume < 100ml

 Exclusion Criteria

 -  Contraindications to epidural analgesia or refusal

 -  Preoperative residual urine volume > 100ml

 -  International Prostate Symptom Score (IPSS) > 7

 -  Pregnancy