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Acute and Chronic Urinary Retention

In chronic retention, there's incomplete bladder emptying over a long period of time. With this, the bladder tends to grow larger and larger and may eventually fail to contract at all. Compared to those in acute retention, they tend to hold a lot more urine. Chronic retainers also don't have any pain or urgency.


Chronic retention is classified into low or high pressure by the presence of detrusor activity. High pressure (detrusor activity increases the pressure) is worse as it comes with a higher risk of upper renal tract damage.


Complications - UTI, Kidney stones, Hydronephrosis, AKI


Causes

  • Obstructive

    • BPH (most common)

    • Constipation

    • Urethral strictures

    • Prostate cancer

  • Neurological

    • Cauda Equina Syndrome

    • Spinal cord injury

    • MS

  • Infectious

    • UTIs - Can cause weakness of the bladder or swelling of the urethra esp. in those with already narrowed outflow tracts

    • Prostatitis

  • Iatrogenic

    • Anticholinergics e.g. Oxybutynin – Block parasympathetic activity on detrusor and their inhibitory effects on the sphincters

    • A1 agonists e.g. Phenylephrine


N.B. Post-operative retention is common in older patients who were under GA.


Presentation

Acute:

  • Suprapubic pain and tenderness

  • Inability to micturate


Chronic - Most only have LUTS and a palpable bladder if it becomes large


O/E - Palpable distended bladder, Enlarged prostate if it’s the cause

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“Large, elderly, thin patient with bulging bladder” © Frivadossi (Licensed under CC-BY 3.0) https://creativecommons.org/licenses/by/3.0/


Investigations

  • Bloods – FBC, CRP, U&Es

  • Urinalysis

  • Bladder US

  • Post-void bladder scan – Shows volume of retained urine

  • DRE – check for BPH

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Ultrasound of the urinary bladder of an 85 year old man. It shows a trabeculated wall, which is a sign of urinary retention - Mikael Häggström

Management

The most important thing to do is immediate catheterisation (measure the volume drained post-catheterisation). Once this is done, it's important to treat the underlying cause.


Those with a large retention volume need to be monitored post-catherisation for Post-obstructive Diuresis (> 200ml/hr for 2 consecutive hrs). With this, the kidneys can over-diurese due to the loss of their medullary concentration gradient, which can take time to re-equilibrate. The management of this differs depending on the osmolarity of the urine:

  • Iso-osmolarity – Indicates the kidneys don’t need to concentrate the urine and is consistent with physiological diuresis and is generally self-limiting

  • Hyper-osmolarity – Indicates the kidneys are concentrating the urine so post-obstructive diuresis has/is resolving

  • Hypo-osmolarity – Indicates salt-wasting and the inability for the kidneys to concentrate urine. This is pathological and the patient needs replacement IVF.



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