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Acute kidney injury: urine output, fluid balance, potassium and kidney-harming medicines

  • Assessment

In acute kidney injury the nurse watches urine output, weight, fluid status and potassium, and flags medicines that can harm the kidneys.

Updated

What it is

Acute kidney injury is a rapid loss of the kidneys' ability to clear waste and balance fluid and electrolytes. It is detected through two measures the nurse helps track: serum creatinine and urine output. Patients with sepsis, shock, major surgery or older age are at the highest risk, so they need close urine output and creatinine monitoring. The nurse keeps a strict intake–output record and daily weights, looks for fluid overload or fluid deficit, follows potassium results, and raises kidney-harming medicines with the prescriber and pharmacist. Fluid intake is often matched to urine output, and dialysis may be needed if potassium, fluid or waste cannot be controlled.

Reference values

  • Two markers define AKI: serum creatinine and urine output; follow both against the patient's baseline.
  • Urine output is reported when it falls below the hourly threshold in the institutional protocol, or stops.
  • Potassium reference range in MedlinePlus: 3.5 to 5.1 mEq/L; use your laboratory's range.
  • Daily weight on the same scale, at the same time and in similar clothing shows whether fluid is building up.

What you need

  • Intake–output chart, urine measuring container or catheter bag with hourly measure if ordered.
  • Scale, vital-sign monitor and the patient's medicine list.
  • Latest creatinine, urea and potassium results.

How to measure it (and why)

  1. Identify the patients at risk (sepsis, shock, major surgery, older age) — they need the closest watch.
  2. Measure urine output at the interval ordered and compare it with the previous hours — a falling output is often the first sign.
  3. Keep strict intake–output and weigh daily under the same conditions — together they show fluid retention or loss.
  4. Look for fluid overload: oedema, crackles, shortness of breath, rising blood pressure — the kidneys may not be removing fluid.
  5. Look for fluid deficit: low blood pressure, fast pulse, dry mouth — low blood flow can cause or worsen kidney injury.
  6. Review the medicine list with the prescriber and pharmacist for kidney-harming drugs — avoiding them protects the kidney.
  7. Follow creatinine, urea and potassium results and report each rise — high potassium can cause dangerous arrhythmias.
  8. Watch for confusion, nausea, persistent hiccups and easy bleeding — signs of waste building up in the blood.
  9. Apply the ordered fluid limit and diet (often low in salt and potassium) — it keeps fluid and toxins from building up.
  10. At discharge, explain follow-up tests and checking medicines with the doctor — AKI can leave lasting kidney damage.

How to read it

  • Low urine output with weight gain, oedema and crackles suggests fluid retention.
  • Low urine output with low blood pressure, fast pulse and dry mouth suggests low volume.
  • A rising creatinine with steady urine output still counts as kidney injury.
  • Rising potassium with ECG changes is an emergency; dialysis can save life when potassium is dangerously high.

Next step: when to call for help

  • Call if urine output falls below the protocol threshold or stops, or the catheter drains nothing.
  • Call for a high potassium result, palpitations, a slow or irregular pulse, weakness or a new ECG change.
  • Call for shortness of breath, new crackles, quick weight gain or spreading oedema.
  • Call for confusion, a seizure, chest pain or bleeding.
  • Before giving a kidney-harming medicine to a patient with AKI, check with the prescriber.

Test yourself

Think of the answer, then tap the question to see it.

Which two measures are used to detect acute kidney injury?

Serum creatinine and urine output; the nurse measures output exactly and reports a fall early.

Why does the nurse weigh a patient with AKI every day under the same conditions?

Because a change in weight shows fluid building up or being lost, which is often hard to see at the bedside.

Which medicines does the nurse raise with the prescriber in a patient with AKI?

Kidney-harming ones such as NSAIDs, some antibiotics and blood pressure medicines and IV contrast; the prescriber decides.

Which electrolyte is most dangerous in AKI, and why?

Potassium: when it builds up it can cause arrhythmias and cardiac arrest, so a high result or ECG change needs a call.

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Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.

Sources: Acute kidney failure, MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Booke H, von Groote T, Zarbock A. Ten tips on how to reduce iatrogenic acute kidney injury. Clin Kidney J (Clinical Kidney Journal (Europe PMC, open access), 2025); Nursing Fundamentals (Open RN), 15.6 Applying the Nursing Process (Fluids and Electrolytes) (Open RN, Wisconsin Technical College System (CC BY 4.0), LibreTexts, 2021); Low blood potassium, MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).

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