Bladder management after SCI

Urinary system function after spinal cord injury

The kidneys and ureters work normally after a spinal cord injury (SCI). The involuntary functions of the kidney, such as general metabolism, osmotic regulation, and the filtration and production urine are also unaffected by SCI.

Bladder filling and micturition prior to SCI

Bladder filling

1. Bladder filling requires detrusor relaxation and pelvic floor contraction. The capacity of a normal bladder is approximately 500mL.

2. First sensation to void occurs at around 250ml. The frontal cortex can initiate or suppress void volition and maintain continence by limiting voiding to desired times.

3. Normal desire to void: progressive distention of the bladder leads to increasing afferent input to the sacral and pontine micturition centres until detrusor contraction and sphincter relaxation are initiated

Normal micturition

To allow micturition, the pelvic floor and sphincters relax and then the detrusor contracts. The timing and coordination of detrusor contraction and sphincter relaxation is mediated by the pontine micturition centre.

Micturition requires:

• Intact nerve pathway
• Normal muscle tone (detrusor, sphincter and pelvic floor)
• Absence of obstruction
• Normal capacity

A SCI disrupts communication between the sacral micturition centre in the spinal cord and the pons and cerebrum in the brain. This results in the loss of coordinated bladder filling and emptying. A SCI can affect bladder function in different ways depending on the level of the injury. Most people with SCI have some degree of bladder dysfunction.