Acute kidney injury (AKI) is a sudden decline in kidney function over hours to days. It is common in hospital, especially among older adults and people with sepsis, dehydration, heart failure or after surgery, and it is linked to longer stays, chronic kidney disease and death. Many cases are preventable or reversible if spotted early. Nurses, who measure urine output and fluid balance, are often the first to notice.
Definition and stages (KDIGO)
| Stage | Serum creatinine | Urine output |
|---|---|---|
| 1 | Rise of 26.5 µmol/L (0.3 mg/dL) or more in 48 hours, or 1.5–1.9 times baseline | Below 0.5 mL/kg/hr for 6–12 hours |
| 2 | 2.0–2.9 times baseline | Below 0.5 mL/kg/hr for 12 hours or more |
| 3 | 3 times baseline, or 354 µmol/L (4.0 mg/dL) or more, or starting dialysis | Below 0.3 mL/kg/hr for 24 hours or more, or no urine for 12 hours or more |
Note that urine output can fall before creatinine rises, which is why accurate fluid charts matter.
Causes
- Pre-renal (reduced blood flow to the kidneys, the most common): dehydration, bleeding, sepsis, heart failure, low blood pressure.
- Renal (damage to the kidney itself): nephrotoxic drugs, severe infections including malaria, rhabdomyolysis, snakebite, glomerulonephritis.
- Post-renal (obstruction): enlarged prostate, blocked catheter, stones, tumours.
Who is at risk?
Older adults, people with chronic kidney disease, diabetes, heart failure or liver disease, people with sepsis or dehydration, those having surgery or contrast scans, and anyone on nephrotoxic medicines.
Nursing actions
Monitor
- Accurate fluid balance: every input and output, totalled.
- Hourly urine output in unwell patients (catheter if needed and clinically justified).
- Vital signs and early warning scores: low BP and sepsis are common causes.
- Daily weight.
- Blood results: creatinine, urea, potassium, sodium, bicarbonate.
- Check catheters for blockage, and bladder scan for retention.
Review medicines
Many drugs can harm the kidneys or build up when kidneys fail. Flag to the prescriber:
- NSAIDs (ibuprofen, diclofenac).
- ACE inhibitors and ARBs (e.g. lisinopril, losartan).
- Diuretics.
- Metformin (risk of lactic acidosis).
- Aminoglycosides (e.g. gentamicin), vancomycin: monitor drug levels.
- Contrast media for scans.
- Herbal remedies, which can be nephrotoxic.
In the UK, these are sometimes called “sick day” medicines that patients may need to pause temporarily when unwell and dehydrated. Doses of renally cleared drugs, including some antibiotics and opioids such as morphine, may need adjusting.
Fluids
Hypovolaemic patients need fluids, as prescribed, with reassessment after each bolus. But fluid overload is dangerous once kidneys stop making urine. Watch for breathlessness, crackles, rising oxygen needs and oedema.
Emergencies in AKI
- Hyperkalaemia (high potassium): can cause fatal arrhythmias. A potassium of 6.5 mmol/L or more, or ECG changes, is an emergency. Treatment may include IV calcium gluconate to protect the heart and insulin with glucose to shift potassium into cells, as prescribed.
- Pulmonary oedema from fluid overload.
- Severe acidosis.
- Uraemic complications: confusion, pericarditis.
These may require dialysis. Access to dialysis is limited and expensive in many countries, which makes prevention and early action even more important.
Prevention
- Keep patients hydrated; help with drinks.
- Treat sepsis and low blood pressure promptly.
- Review medicines on admission and when patients become unwell.
- Identify at-risk patients before surgery and contrast scans.
- Educate patients with chronic conditions about sick-day rules.
Related: IV fluids and fluid balance · Sepsis Six · ECG basics
Based on KDIGO Clinical Practice Guideline for Acute Kidney Injury, NICE NG148 (Acute kidney injury) and UK Kidney Association hyperkalaemia guidance. Educational content: follow local protocols.