Acute urinary retention

From greek.doctor

Acute urinary retention refers to when there is an acute inability to pass urine. It's a urological emergency which can cause permanent injury to the bladder and kidneys, severe suprapubic pain, and bladder rupture in severe cases. Initial management involves bladder catheterisation to drain the bladder.

Urinary retention is more common in males, mostly because of benign prostatic hyperplasia.

Urinary retention can also be chronic, which is a painless condition characterised by increased residual urine volume.

Bladder tamponade is a special and severe form of acute urinary retention where blood and blood clots fill the entire bladder.

Etiology

Most common causes according to age:

Bladder tamponade typically occurs following urological surgery or bleeding from urinary tract malignancy.

Clinical features

Acute onset suprapubic or lower abdominal pain, an urge to urinate, as well as not passing urine, are the typical symptoms. For elderly, urinary retention may present with only delirium. Patients are often restless and appear in distress.

The bladder is usually tender on palpation and felt to be distended.

Complications

If treated early, complications rarely occur. Otherwise, acute urinary retention can have severe complications. Pressure may spread upward in the urinary tract, causing hydronephrosis and acute kidney injury.

Large urine volumes in the bladder causes overdistension of the bladder. The stretching of the bladder detrusor muscle fibres injure them and makes the bladder atonic, possibly permanently. Injury is more severe the higher the volume and the longer time the retention has lasted. Bladder volume of more than 2000 mL is associated with permanent atonic bladder. Volume < 1000 mL usually has very good detrusor recovery.

In the most severe cases, the bladder can rupture, causing urinary extravasation into the pelvic cavity.

Diagnosis

The diagnosis is confirmed if bladder ultrasound shows a bladder volume of > 300 mL, or if after bladder catheterisation > 200 mL of urine is drained. To measure the bladder volume on ultrasound we measure the width, depth, and height of the bladder and multiply by 0.7 (to account for the bladder not being cube-shaped). The ultrasound should be performed post-void, i.e., after the patient has (tried to) pass urine.

After the bladder has been drained, the underlying cause should be sought, and the patient should be evaluated for complications. Urinary dipstick analysis can show signs of haematuria in case of stone disease or signs of infection. Kidney ultrasound may show hydronephrosis. Kidney function tests can show acute kidney injury. CT can show stone.

Management

If the clinical suspicion is high enough and ultrasound cannot be performed, or if the ultrasound showed signs of retention, urgent bladder catheterisation is indicated to decompress the bladder. Previously, it was recommended to drain the bladder intermittently, 750 mL at a time to reduce complications, but nowadays we know that this is not necessary.

Bladder catheterisation is usually performed transurethrally, however this is contraindicated in case of recent urethral or bladder surgery, or acute prostatitis. In these cases, suprapubic catheterisation should be performed instead.

Following catheterisation, one must decide whether to leave the catheter in place (permanently or temporarily) or to remove it after full bladder drainage. This decision depends on the amount of urine drained and if any complications have occured, and whether the presumed cause is reversible. If urinary retention has caused complications, or if the drained volume is > 400 mL the catheter should be left in place. In other cases, it may be safe to remove it.

Voiding trial

A voiding trial refers to removal of a bladder catheter, followed by the patient trying to pass urine normally (after giving it some time for urine to be produced), followed by a bladder ultrasound to determine whether a lot of urine remains in the bladder, which indicates whether the patient can pass the normal amount of urine. A post-voiding residual (PVR) volume of < 100 mL is physiological, but even volumes < 200 mL is considered a success for voiding trial purposes.

The optimal time to wait until attempting a voiding trial has not been determined by studies and mostly varies accoring to local practices and experience. Generally, if the retention is determined to be due to a reversible cause it's appropriate to attempt a voiding trial after the cause is reversed. For irreversible causes, it may be appropriate to attempt a voiding trial after 7-10 days if the maximum bladder volume was < 800 mL. In other cases, the voiding trial should wait until 2-3 weeks.

If the patient can empty their bladder satisfactorily, the catheter does not need to be re-inserted. If not, the patient must either receive a new indwelling bladder catheter and attempt a new voiding trial a few weeks later, or the patient must be taught clean intermittent catheterisation, where they catheterise themselves multiple times a day. If the patient is unable to self-catheterise, or if the second voiding trial fails, the patient should use an indwelling catheter permanently.