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Acute kidney injury
AKI is common, often silent, and frequently preventable. Spot the dangerous complications first (potassium, fluid, acid), then work out why the kidneys have stopped: not enough blood in, something wrong inside, or something blocking the way out. Built for revision, not live patient decisions.
Settle them, and check the basics
potassium, fluid, acidRed flags — what each should make you think
The creatinine tells you there is a problem; it doesn't tell you how dangerous it is. The things that kill in AKI are high potassium, fluid on the lungs and severe acidosis, so check a gas and an ECG before you worry about the cause.
The first things to do
- ECG12-lead ECG + VBG potassium
- A–EAssess volume status
- IVFluids if hypovolaemic
- ✕Hold nephrotoxic drugs
- UOMeasure urine output
- ☎Escalate early
Understand the patient & find the cause
pre · renal · postStage it (KDIGO)
- Stage 1 — creatinine 1.5–1.9× baseline, or a rise of ≥26 µmol/L in 48 h, or urine output under 0.5 mL/kg/h for 6 h
- Stage 2 — creatinine 2–2.9× baseline, or urine output under 0.5 mL/kg/h for 12 h
- Stage 3 — creatinine ≥3× baseline or ≥354 µmol/L, or starting dialysis, or under 0.3 mL/kg/h for 24 h, or anuria for 12 h
Always look for a baseline creatinine. Without one, you can't tell AKI from chronic kidney disease. Small, scarred kidneys on ultrasound and anaemia point to chronic disease.
Pre, renal or post?
- Pre-renal (most common) — dehydration, vomiting and diarrhoea, bleeding, sepsis, heart failure, ACEi/ARB, NSAIDs
- Renal — acute tubular necrosis after prolonged hypoperfusion, nephrotoxins (gentamicin, contrast), rhabdomyolysis, interstitial nephritis (PPIs, antibiotics), glomerulonephritis
- Post-renal — prostatic retention, blocked catheter, bilateral stones, pelvic or bladder tumours
Work A–E — assess and act as you go
The diagnoses you must not miss
tap to open eachWhat points toward it, what would rule it in, and how to manage it.
K⁺ ≥6.5 mmol/L, or any level with ECG changes. Often silent until the heart stops.
Lab potassium (a gas is fine to act on); ECG.
Calcium gluconate to protect the heart, insulin–glucose and salbutamol to shift potassium, then remove it. See the electrolyte emergencies page.
Breathlessness, crackles, raised JVP, falling SpO₂ in an oliguric patient, often after generous IV fluids.
Clinical, CXR.
Stop IV fluids, sit up, oxygen, IV furosemide (higher doses in AKI), CPAP if needed. No response → urgent renal/ITU for dialysis.
Anuria or fluctuating output, palpable bladder, prostatic symptoms, known stones or pelvic cancer. Fever and loin pain mean pyonephrosis.
Bladder scan; urgent renal tract ultrasound (hydronephrosis).
Catheterise retention (watch for post-obstructive diuresis). An infected obstructed kidney needs IV antibiotics and emergency decompression (nephrostomy or stent) — urology now.
Haematuria and proteinuria without a catheter or infection, rash, haemoptysis, joint pain, sinus symptoms, rising creatinine without an obvious cause.
Urine dip and protein:creatinine ratio, ANCA, anti-GBM, complement, ANA, immunoglobulins.
Refer to nephrology the same day. Delays cost kidneys.
Long lie after a fall, crush injury, seizures, extreme exercise, drugs, statins. Muscle pain, dark urine (dipstick blood positive with no red cells).
CK (often over 5× normal, may be very high), potassium, phosphate, calcium.
Aggressive IV fluids aiming for good urine output, treat hyperkalaemia, check for compartment syndrome.
Remember the "sick day" drugs
Pause diuretics, ACE inhibitors and ARBs, metformin, NSAIDs and SGLT2 inhibitors while the patient is unwell, and review all doses (antibiotics, opioids, anticoagulants) against the current kidney function. Restart them deliberately when the AKI recovers.
Investigate — what to order, when, and what it tells you
test with a question in mindBloods
Urine — before any catheter
Imaging
Track
Specialist screen
How the plan comes together
disposition · handoverward / home
Stage 1–2, clear pre-renal cause, improving with fluids and drug review. Recheck U&E within 24–48 h.
Document the AKI and the drugs held, and tell the GP when to restart them.
renal / ITU
Refractory hyperkalaemia, acidosis or fluid overload, uraemic complications, stage 3, or suspected GN → renal team. Dialysis indications: Acidosis, Electrolytes (K⁺), Intoxication, Overload, Uraemia.
Hand over: baseline, trend, K⁺, fluid status, urine output, drugs held.
Most AKI is pre-renal and drug-related, and gets better with fluid, time and stopping the wrong tablets. Your job is to catch the minority who need a catheter, a nephrostomy or a nephrologist today. Nicely done getting here.
Clerking template
copy or downloadAcute kidney injury — documentation structure
A structure and prompt list to help you document and think systematically. It is not a completeness check and cannot guarantee nothing is missed — use your trust's own proforma, your seniors, and your clinical judgement.
Test yourself
active recallCover the answer, say it out loud, then reveal. Retrieval beats re-reading.
0 / 12 knownFrequently asked questions
quick answersWhat are the red flags for acute kidney injury (AKI)?
- K⁺ ≥6.5 or ECG changes — think hyperkalaemia — treat now
- Breathless, crackles, hypoxic — think pulmonary oedema
- pH below 7.15 / bicarb very low — think severe metabolic acidosis
- Anuria or palpable bladder — think obstruction
- Fever + loin pain + AKI — think infected obstructed kidney
- Blood and protein on dipstick — think glomerulonephritis / vasculitis
- Muscle pain, very high CK — think rhabdomyolysis
- Pericardial rub, confusion — think uraemic complications
What is the initial management of acute kidney injury (AKI)?
- 12-lead ECG + VBG potassium — peaked T, wide QRS → treat hyperkalaemia immediately
- Assess volume status — dry and hypotensive vs wet and overloaded — they need opposite things
- Fluids if hypovolaemic — 500 mL crystalloid bolus over 15 min, then reassess
- Hold nephrotoxic drugs — NSAIDs, ACEi/ARB, diuretics, metformin, gentamicin; avoid contrast if possible
- Measure urine output — fluid balance chart, bladder scan; catheter if retention or strict monitoring needed
- Escalate early — renal team for stage 3, failing medical management, or suspected GN
Always alongside senior support and your local guideline.
What diagnoses must you not miss in acute kidney injury (AKI)?
- Hyperkalaemia — peaked T · wide QRS
- Pulmonary oedema — wet · hypoxic · oliguric
- Obstruction / infected obstructed kidney — retention · loin pain · fever
- Rapidly progressive GN / vasculitis — blood + protein on dip
- Rhabdomyolysis — long lie · CK in the thousands
Open each one in the must-not-miss section for what points toward it, how to rule it in, and how to manage it.
What investigations should a junior doctor order for acute kidney injury (AKI)?
- Bloods — Creatinine, urea, potassium, compared with baseline.
- Urine — before any catheter — Blood + protein without infection → think GN, refer.
- Imaging — Retention at the bedside.
- Track — Input/output chart, daily weights.
- Specialist screen — ANCA, anti-GBM, ANA, complement, immunoglobulins, myeloma screen.
Admit or discharge: how is the plan decided for acute kidney injury (AKI)?
- Ward / home — Stage 1–2, clear pre-renal cause, improving with fluids and drug review. Recheck U&E within 24–48 h.
- Renal / itu — Refractory hyperkalaemia, acidosis or fluid overload, uraemic complications, stage 3, or suspected GN → renal team. Dialysis indications: A cidosis, E lectrolytes (K⁺), I ntoxication, O verload, U raemia.
Is there a clerking template for acute kidney injury (AKI)?
Yes — there is a free clerking template for acute kidney injury (AKI) on this page, structured as presenting complaint, red flags asked, history, examination (A–E), investigations, differentials, plan and escalation. You can copy it or download it as a Word document. Jump to the template.
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