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Oliguria

Table of Contents

Overview #

  • Oliguria is often the first sign of a developing kidney injury
  • Oliguria is not always pathological, but urine output <0.5mls/kg/hr for ≥ 2 consecutive hours warrants review
  • New hypotension plus oliguria may be the first sign of shock ([link to shock guideline?])
  • Causes can be divided into pre-renal, renal and post renal: Pre-renal accounts for ~90% of inpatient AKI, but always consider obstruction (post-renal) and renal causes before prescribing a fluid bolus
  • There are 4 urgent complications for AKI : refractory fluid overload, acidosis, hyperkalaemia, and uraemic complications (encephalopathy, serositis, etc.)

Triage #

Attend within one hour

Causes #

Pre-renal – ie: hypoperfused kidney(s)

  • Hypovolaemia – intravascular fluid depletion (eg: GI losses, prolonged fasting, haemorrhage)
  • Low output states – Heart failure
  • Focal reduction in renal perfusion – Decompensated liver failure, renal artery stenosis, abdominal compartment syndrome

Renal 

  • The vessels
    • Loss of autoregulation of afferent/efferent arterioles from NSAIDs or ACEi
  • The glomerulus
    • Glomerulnephridities – a group of conditions which can be categorised, based on presentation, into nephrotic and nephritic syndromes
  • The tubules
    • Acute tubular necrosis (longstanding pre-renal failure)
    • Rhadbomyolysis
    • Tumour lysis syndrome
  • The interstitium
    • Acute interstitial nephritis
      • Diagnostic triad = fever, skin rash, eosinophilia
      • Usually drug related and takes several weeks of exposure to develop – suspect PPI, NSAIDs, sulphonamides, b-lactams, cephalosporins, fluroquinolones, isoniazid, rifampicin. 
      • Less commonly due to tumour lysis syndrome, Sjogrens, SLE or RA
    • Thrombotic thrombocytopenic purpura
      • Diagnostic pentad = AKI, anaemia, thrombocytopaenia, fever and neurological dysfunction

Post renal

  • Blocked IDC
  • Kidney stones
  • Prostatic hyperplasia 
  • Urinary retention, which can be caused by:
    • Drugs (especially anticholinergics)
    • Constipation
    • Haematuria with clot
  • Retroperitoneal pathology

Diagnosis #

Oliguria is often the first sign of developing kidney injury.

Take seriously a urine output of

  • <0.5mls/kg/hr for more than two consecutive hours
  • <400mls/day

Approach #

Review the chart, check:

  • Fluid balance over the last few days (daily weights even better)
  • Renal function – establish baseline and current trend
  • Any nephrotoxins or on the drug chart (Appendix A)
  • Any nephrotoxic insults in recent days (Appendix A)
  • Current vital signs
History #

Check for:

  • Abdominal pain
  • Macroscopic haematuria or abnormal urinalysis
  • Obstructive symptoms – “lower urinary tract symptoms” (LUTS)
    • Difficulty starting or maintaining stream
    • Nocturnal voiding
  • Previous kidney stones
  • Infective symptoms
    • Dysuria
    • Frequency
    • Urgency
Exam #
  • Check if there is a catheter in situ – if so, could it be blocked?
  • Is the bladder palpable? If so, it’s grossly enlarged
  • Note what the urine looks like, specifically:
    • Any haematuria, and if present if there are clots
    • If it froths when you shake the IDC box (sign of proteinuria)
    • Dark and concentrated or clear/straw coloured
  • Fluid state (are they grossly dehydrated or fluid overloaded?)
  • Any signs of complications of renal failure
    • Confusion, asterixis
    • Kussmaul breathing (metabolic acidosis)
    • Pericardial rub (uraemic pericarditis)

Investigations #

All patients

InvestigationSignificance
Bladder scanExclude urinary retention/blocked catheter
UECs

Unless the cause is clearly pre-renal and responds quickly to a bolus of IV fluid also arrange:

Urine dipstick Bedside test for infection and proteinuria
Urine MCS and protein:creatinine ratioFormal assessment for infection and proteinuria
Renal tract ultrasoundExclude a post renal cause (ie: obstruction)If renal artery stenosis is suspected then specifically request a doppler study

To workup an intrarenal cause, particularly if abnormal proteinuria or haematuria detected on dipstick, consider the below (in consultation with the renal team)

#HIV/HCV/HBVBlood borne virus screen
#ANA/ENA/dsDNA/ANCA/anti GBM/Anti-strep Ab/PLA2R/C3/C4Vasculitis screen
CKExclude rhabdomyolysis

For patients in frank renal failure

ECGExclude features of hyperkalaemia
VBGCheck pH and potassium
CXRCheck for pulmonary oedema

Management #

All patients

  • Strict fluid balance chart (consider IDC if not already in situ)
  • Daily weights (often more accurate than fluid balance chart)
  • Daily UECs
  • Withhold nephrotoxic drugs (if possible)
  • Check drug chart for anything that needs to be dose reduced based on current renal function
    • Especially antibiotics, clexane, NOACs, insulin and blood sugar lowering medications, digoxin
    • If significant AKI strongly consider ceasing any potassium supplements
  • Consider if there is an indication for dialysis (and if so urgently refer renal +/- ICU)
    • Acidaemia (pH <7.2)
    • Hyperkalaemia (K>6 despite medical management, see here)
    • Intoxication with dialysable drug
    • Pulmonary oedema (see here)
    • Uraemic encephalopathy or uraemic pericarditis (or, if urea >40 dialysis should at least be considered)

Treatment dependent on cause

  • Pre-renal
    • Treat cause if identified
    • If clinically hypovolemic bolus IV crystalloid and review. Be mindful of cardiac function, avoid pulmonary oedema
    • If clinically overloaded the problem is more challenging. Discuss with senior.
  • Renal
    • investigations as above
    • refer renal team
  • Post renal
    • Relieve obstruction
      • Most often this involves inserting an IDC, or replacing one that’s blocked
      • If obstruction higher in urinary tract (eg: vesicoureteric junction) will need urology consult
    • Monitor for post-obstruction diuresis (suspect after obstruction is relieved if urine output >200ml/hour for >2 hours or >3litres in 24 hours)
    • If post obstructive diuresis does occur
      • Start strict fluid balance chart
      • Commence normal saline at 50-80% of the urine output/hour
      • Check electrolytes BD – TDS and replace electrolytes 

Appendix A: Common nephrotoxins and nephrotoxic events #

  • Surgery which involved clamping arterial supply
  • Things that cause dehydration
    • Vomiting/diarrhoea/polyuria
  • Things that cause rhabdomyolysis
    • trauma/crush injury/immobilization
  • Drugs
    • ACEi/ARBs
    •  NSAIDs
    • Diuretics
    • PPIs (AIN)
    • Gentamicin/vanocymin (tubular toxins)
    • Penicillins/cephalosporins/rifampicin (AIN)
    • IV Contrast scans
  • Angiogram – cholesterol emboli
  • Hypercalcaemia –tubular toxin

  • Contributors

  • Reviewing Consultant/Senior Registrar

Dr Scott Santinon

Dr Euzebiusz Jamrozik

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