Patients with an underactive bladder are unable to produce an effective voiding (emptying) contraction. This is sometimes referred to as voiding difficulty. The International Continence Society refers to the condition of detrusor under activity, defined as a contraction of reduced strength and/or duration, resulting in prolonged bladder emptying and/or failure to achieve complete bladder emptying within a usual time span. It is characterized by the loss of usual sensation of the bladder filling and failure of the detrusor muscle to contract as forcefully as it should, resulting in incomplete bladder emptying. This condition has also been referred to as a hypotonic or flaccid bladder or detrusor hypoactivity. The prevalence of underactive bladder
- Incomplete bladder emptying
- Recurrent Urinary Tract Infections
Common causes of underactive bladder
The most common causes of detrusor underactivity can be classified as:
Damage to the peripheral nerves of the bladder or the lower spinal cord may cause the sensation of bladder filling to be absent or reduced, and the bladder is emptied by frequent voiding of small amounts of urine. Large residual volumes may accumulate (500-2,000ml), which are associated with difficulty in emptying the bladder and overflow urinary incontinence.
Patients with spinal cord lesions frequently present with lack of detrusor-sphincter synergy and it is a particular feature of voiding difficulties in older people following CVA. Normal voiding also relies on a synergy between the bladder contracting and the bladder neck opening. When this is interrupted, the patient will experience constant urinary urge due to detrusor contraction and inability to relax the internal sphincter. The result is incomplete bladder emptying with significant residual volumes and urge incontinence.
Suprapontine lesions usually result in detrusor areflexia (a non-contractile bladder). The bladder fails to empty because it has little muscular activity and assisted voiding may take place by
straining. The patient may present with symptoms of incomplete bladder emptying, frequency and urgency, but on further examination there is a poor flow rate and often a significant post-void residual urine volume.
With parasympathetic nerve stimulation the muscarinic receptors in the bladder should contract. Following an epidural this muscle activity may be absent or reduced, leading to acute retention of urine and insidious voiding difficulty. Ischaemia of the detrusor can also be the result of unrelieved urine retention.
It is reported that 80 per cent of patients with voiding disturbance after pelvic procedures will resume usual voiding within six months. Injury to the hypogastric, pelvic and sometimes the pudendal nerve supply results in damage to the sympathetic, parasympathetic and somatic
nerve fibres. Decreased parasympathetic nerve supply results in decreased bladder contractility and potentially areflexia.
In addition to metabolic changes, the volume and elasticity of the bladder can change as we get older. The amount of nerves per mm2 of muscle decreases with age and occurs to the same extent in men and women.
Prostatic enlargement which causes obstruction is due to hyperplasia or, less frequently, prostate cancer and urethral strictures. Severe vaginal prolapse can lead to obstructed voiding. Faecal impaction is a well recognised cause of obstruction.
Cystitis, urethritis or vulval abscess cause acute retention because of the reduced contractility of the detrusor muscle.
Drugs with antimuscarinic properties block the chemical transmission of acetylcholine so that the muscles relax - examples are tricyclics, antihistamines, ganglion blockers, alphaadrenergic stimulants, phenothiazines and monoamine oxidase inhibitors.
Spinal cord injury
The degree of dysfunction is related to the severity and level of impairment. For example, if the injury is above T12, the patient may have a reflex bladder action, which will require minimal intervention. The bladder still has some or all of its reflexes. Patient with injuries at L1 and
below, for example, in spina bifida, may have a flaccid bladder which does not
contract. Bladder emptying may need to be assisted.