Does Thoracic Epidural Analgesia Influence Urinary Micturition by Patients Undergoing Thoracic Surgery? An Observational, Prospective Study

Background

1. 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 the S1 to the S3 segment. 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.

Unlike spinal anesthesia, which is an all or none block, epidural anesthesia has applications ranging from analgesia with minimal motor block to dense anesthesia (differential blockade). 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). Therefore it can be assumed that epidural analgesia within segments Th 4-6 to Th 10-12 has no or minimal influence on the micturition reflex.

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