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
- Acute interstitial nephritis
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
Investigation | Significance |
Bladder scan | Exclude 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 ratio | Formal assessment for infection and proteinuria |
Renal tract ultrasound | Exclude 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/HBV | Blood borne virus screen |
#ANA/ENA/dsDNA/ANCA/anti GBM/Anti-strep Ab/PLA2R/C3/C4 | Vasculitis screen |
CK | Exclude rhabdomyolysis |
For patients in frank renal failure
ECG | Exclude features of hyperkalaemia |
VBG | Check pH and potassium |
CXR | Check 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
- Relieve obstruction
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