Synopsis
Detect lower- and upper-tract obstruction early, drain the urinary system at the correct level, treat infected obstruction as an emergency and manage post-decompression physiology safely.
- Post-renal AKI occurs when urine-flow resistance affects both kidneys, a solitary functioning kidney, or the lower tract below both ureteric outlets; unilateral obstruction with two functioning kidneys may not raise creatinine.
- Lower-tract causes include benign prostatic enlargement, prostate or bladder malignancy, urethral stricture, clot, constipation and neurogenic bladder; upper-tract causes include stones, tumour, retroperitoneal fibrosis and iatrogenic ureteric injury.
- Pain may be absent in chronic retention, neuropathy and retroperitoneal disease. Ask about hesitancy, weak stream, incomplete emptying, overflow, loin pain, haematuria, pelvic cancer and recent urinary or gynaecological surgery.
- A palpable bladder or high bladder scan supports retention, but ascites, pelvic cysts and scanner limitations can mislead. Urethral catheterisation is both diagnostic and therapeutic when it is safe.
- NICE advises urgent urinary-tract ultrasonography when AKI has no identified cause or obstruction risk, and immediate imaging when pyonephrosis is suspected; local radiology pathways determine exact delivery.
- Hydronephrosis can be absent very early, in dehydration or with retroperitoneal encasement, while chronic non-obstructive dilatation can persist after relief. Imaging must be interpreted with the clinical probability.
- Fever, rigors, hypotension or raised inflammatory markers with an obstructed collecting system define a urological source-control emergency requiring prompt antimicrobials and nephrostomy or ureteric stenting.
- After relief, monitor for post-obstructive diuresis, haematuria, hypotension and electrolyte loss. Rapid free drainage is usual; routine intermittent clamping is not supported and can re-obstruct the system.
Key red flags
Painful inability to void, suprapubic distension and a large residual volume suggest acute retention. Older or neuropathic patients may instead have painless overflow, confusion or renal failure from high-pressure chronic retention.
Loin-to-groin pain, hydronephrosis, pelvic malignancy, retroperitoneal disease or recent pelvic surgery raises ureteric blockage. Creatinine may remain normal with unilateral disease, so renal function cannot assess the threatened kidney alone.
Fever, rigors, pyuria, hypotension or systemic toxicity plus hydronephrosis or an obstructing calculus indicates pyonephrosis or infected obstruction. This can progress rapidly to urosepsis and shock and requires immediate source-control planning.
Visible haematuria, suprapubic pain, failure to drain and clot in tubing suggest bladder outlet obstruction by blood. Ongoing bleeding, anticoagulation and malignancy require concurrent assessment and often large-bore irrigation under urological guidance.
Investigation priorities
Identify lower-tract retention and rule out a simple mechanical explanation for apparent anuria.
Management branches
A large residual, palpable bladder, painful retention or blocked urethral catheter is suspected.
- 1. Assess haemodynamics, lower urinary history, urethral trauma risk, previous difficult catheterisation and visible bleeding, and obtain a bladder volume where it will not delay relief.
- 2. Perform urethral catheterisation with appropriate asepsis and anaesthetic gel by a competent clinician; stop and seek urology if resistance, false passage or urethral injury is possible.
- 3. If urethral access is unsafe or unsuccessful, arrange urgent urological assessment for cystoscopic or suprapubic drainage rather than repeated traumatic attempts.
- 4. Record initial volume and colour, allow free drainage, investigate the cause and start post-obstructive urine, pressure and electrolyte monitoring.