Urinary retention in dogs – symptoms, causes and treatment

Overview

Bladder filling and emptying are different functions

During urine storage, the bladder wall relaxes and the urethral sphincter stays closed. During urination, the bladder's detrusor muscle contracts and the urethra relaxes. Connections between the spinal cord, brain and peripheral nerves control this activity.

A dog initiates normal voluntary urination when the place and time are suitable.

With an emptying disorder, more urine than normal remains in the bladder after urination. This residual urine distinguishes the problem from many common continence disorders. Urinary retention therefore does not always mean passing no urine at all. In overflow incontinence, pressure in an overfull bladder exceeds urethral closing pressure and urine leaks out.

Causes

A blockage or functional emptying disorder

A mechanical obstruction can be caused by a urinary stone, tumour or urethral narrowing, for example. Pressure from outside the urethra can also impede urine flow. In a functional outflow disorder, the urethra does not relax enough, the bladder does not contract effectively or both functions are impaired.

In an idiopathic functional disorder, no clear central nervous system disease has been identified. It was previously called reflex dyssynergia or detrusor–urethral dyssynergia. The current term is functional outflow obstruction, as the earlier name would require more detailed pressure and function testing.

Widespread autonomic nervous system dysfunction, or dysautonomia, can cause severe overflow incontinence and impaired bladder emptying. A blood clot or foreign object in the urethra can also obstruct urine flow. A bladder displaced backwards in a perineal hernia can cause mechanical urinary obstruction.

Nerve damage and bladder stretching

Damage to the sacral spinal cord or pelvic nerve can leave the bladder large and difficult to empty voluntarily. A lesion higher in the spinal cord can prevent the urethral sphincter relaxing. Bladder overstretching, in turn, can weaken detrusor contraction. Prolonged stretching disrupts connections between muscle cells and impairs the spread of contraction. Atony means this marked loss of bladder contraction strength.

Risk factors

Idiopathic functional outflow obstruction occurs particularly in middle-aged male dogs of large and giant breeds. Both neutered and entire males are affected. Spinal cord disease or injury can predispose to disturbed nerve control of the bladder and sphincter. Orthopaedic or neurological disease can also prevent your dog adopting a proper urination posture.

Previous urethral injury or surgery can leave narrowing that impedes urine flow. Prolonged mechanical or functional obstruction predisposes to bladder muscle damage. Breed alone cannot establish the cause; its relevance depends on what is causing retention.

Typical symptoms

Difficult urination and urine remaining in the bladder are characteristic of an emptying disorder. You may notice these changes at home:

• Your dog adopts a urination posture more often than usual.
• The urine stream starts normally but quickly weakens.
• Urine comes in interrupted spurts or only drops.
• Urination looks painful or your dog vocalises while trying.
• Urine leaks at rest or after an attempt to urinate.
• Bladder filling causes abdominal pain or tension.

With a spinal cord-related disorder, hindlimb strength or movement may also decline. A neurological patient may be unable to urinate voluntarily even if the bladder does not feel firm.

With urinary stones, blood may be visible in urine. Your dog may also lick the penis or vulva more than usual.

Complications and consequences

Overstretching and effects on the body

Prolonged urinary obstruction can damage the bladder lining and muscle function. In severe cases, the bladder or urethra can rupture. Chronic obstruction can also impair bladder nerve function. A normal urine stream therefore does not always return immediately after the obstruction is relieved.

In prolonged urinary obstruction, the number of contractile filaments in bladder smooth muscle cells can decrease.

Acute urinary obstruction can involve azotaemia, an accumulation of nitrogenous waste products in blood. Blood potassium may rise. Acid–base balance can also be disturbed, making the body more acidic. Severe hyperkalaemia, or high blood potassium, can cause life-threatening heart rhythm disturbances.

Catheter-associated urinary tract infections have been reported in 8–32% of catheterised dogs. This figure concerns dogs catheterised in studies, rather than every urinary retention patient's individual risk.

Continuous urine leakage can wet the hair around the genitals and irritate surrounding skin.

Diagnosis at the vet

Observing urination and measuring residual urine

Your vet establishes whether there is involuntary leakage or a conscious but ineffective attempt to urinate. Observing the urine stream or a video of it helps investigation. Bladder size is assessed before and after urination. A large bladder after urination suggests impaired emptying.

Residual urine of 0.2–1.0 millilitres per kilogram of body weight can be normal in dogs. More than 3 millilitres per kilogram of body weight is abnormal and indicates urine retention. The range of 1–3 millilitres per kilogram of body weight is interpreted alongside other findings. Measurement is performed within 10 minutes of urination. Your dog is given enough time to urinate, as a male in particular may not empty the bladder in one attempt.

Ultrasound can assess residual urine without catheterisation. It can also examine the bladder wall, stones or mass-like changes.

Investigating obstruction and the nervous system

The examination includes bladder palpation, a rectal examination and a targeted neurological examination. Hindlimb function, tail tone, reflexes and spinal pain help assess possible nerve damage. Routine urinalysis and bacterial culture investigate infection's contribution to signs. In acute obstruction, kidney values, electrolytes and acid–base balance are also tested.

Bladder palpation also assesses its abdominal position and sensitivity to pain.

Reduced anal tone and perineal reflex can relate to sacral spinal cord or pelvic nerve damage. Spinal pain, faecal incontinence or abnormal coordination between the forelimbs and hindlimbs may require a more detailed neurological examination and spinal MRI.

In a functional disorder, a catheter may pass easily through the urethra. Mechanical obstruction is excluded using tests such as contrast imaging, CT or endoscopy. Endoscopy shows the lower urinary tract surface. A biopsy can be taken from an abnormal area. Pressure and function testing may be used in difficult cases unresponsive to treatment.

In one study from northern Europe involving endoscopy in 47 dogs, 79% received a diagnosis. In the remaining 21%, the cause of signs remained unclear, but the examination helped exclude inflammatory and tumour diseases. These were selected urinary patients, rather than investigation results for all dogs with urinary retention.

Treatment

Emptying the bladder and stabilising your dog

Your vet ensures urine can drain, using a catheter if needed. Other treatment targets the identified cause. An unwell dog with obstruction first needs stabilisation. Intravenous fluids correct dehydration and inadequate circulation. Dangerous potassium elevation is treated without delay. The heart's electrical activity may be monitored by ECG.

A mechanical obstruction is relieved by catheterisation or a procedure if needed. For example, an obstructing stone can be flushed back into the bladder at the practice for later removal. In functional or neurological disorders, intermittent catheterisation helps keep the bladder sufficiently small. In severe cases unresponsive to medication, a bladder drainage tube through the abdominal wall may be considered.

For neurological emptying disorders, intermittent catheterisation is generally preferred to an indwelling catheter. In an entire male, castration may be considered to reduce prostate size and prevent androgen-dependent problems.

Medication depends on the functional disorder

Functional outflow obstruction is treated with an alpha-antagonist that relaxes urethral smooth muscle. A skeletal muscle relaxant may also be used if needed. Adverse effects of these medicines can include low blood pressure. A muscle relaxant can also cause drowsiness. A medicine to strengthen bladder contraction is considered in certain cases of atony. However, any mechanical obstruction must be relieved before using a medicine that increases bladder contraction.

A positive bacterial finding does not always explain functional difficulty urinating. An antibiotic may be used if bacteria are suspected of contributing to signs. The effect on emptying is checked afterwards too.

Bladder recovery and monitoring

A bladder damaged by overstretching may need to be kept empty for the first week to allow muscle recovery. This is achieved through a veterinary catheter care plan. Response is assessed by improvement in the urine stream and reduced residual urine. Blood tests are repeated if needed to monitor correction of electrolyte and acid–base disturbances. If residual urine remains high after obstruction is relieved, a functional emptying disorder is also investigated.

Prevention

Adequate drinking and several daily opportunities to go outside form part of preventing stone problems in susceptible dogs. A dog with urinary stones may need a special diet to prevent recurrence for the rest of their life. In neurological emptying disorders, reducing bladder size through planned catheter care prevents further overstretching.

Investigating difficulty urinating promptly helps avoid prolonged bladder distension. Recurrence of a functional disorder is also monitored using the urine stream and residual urine. An occasional puddle on the floor alone does not show whether the bladder empties properly.

Unnecessary catheterisation can be avoided by measuring residual urine with ultrasound, reducing exposure to catheter-associated infection.

Important for dog owners

Observations help, but emergency care must not wait for a video

Record when your dog last passed a normal amount of urine and when signs began. Observe stream strength, interruptions, the number of attempts and any pain. A short video of a typical urination attempt helps at the consultation if you can obtain it without delaying care. Direct observation or a video of urination forms part of assessing a functional disorder.

Report previous spinal or pelvic injuries, surgery, nervous system diseases and medicines. Follow the bladder-emptying and catheter care instructions provided. At discharge, ask how to recognise adequate emptying and when residual urine will be checked. Dribbling may continue as overflow despite too much urine remaining in the bladder. Renewed inability to urinate requires immediate return for care, even if a previous obstruction has already been relieved.

Frequently asked questions

Can a dog have urinary retention despite dribbling urine?

Yes. In overflow incontinence, the bladder is too full and urine leaks out. This can resemble ordinary loss of bladder control. Investigation therefore also assesses how much remains after urination; urine on the floor alone does not show the bladder has emptied.

Is urinary retention always caused by a stone?

No. Mechanical causes include tumours and narrowing as well as stones. Emptying can also fail because of weakened bladder contraction or a functional failure of urethral relaxation. Treatment depends on investigating the cause, but a dog unable to urinate needs urgent assessment before this distinction is established.

How much urine can remain in the bladder?

Residual urine of 0.2–1.0 millilitres per kilogram of body weight can be considered normal. More than 3 millilitres per kilogram of body weight is abnormal. The range of 1–3 millilitres per kilogram of body weight is interpreted alongside other findings. This measurement is performed at the practice; it cannot be estimated from puddle size.

Why does a catheter pass through when my dog cannot urinate?

In functional outflow obstruction, a catheter may pass easily through the urethra. Your dog still cannot empty the bladder normally because muscle activity or bladder contraction is impaired. Tests investigate mechanical causes, and further treatment is selected according to the functional problem identified.

Does urination return immediately after an obstruction is relieved?

Not always. Prolonged overstretching can damage the bladder's detrusor muscle. The bladder may therefore need controlled emptying for the first week to allow muscle recovery. The response is monitored using the urine stream and residual urine so further treatment also reflects actual bladder emptying.