Nursing care
Acute Kidney Injury nursing care: what to assess and what to do first
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated September 2026
Short answer
Acute kidney injury nursing care starts with identifying the cause, because prerenal, intrarenal, and postrenal AKI require different, sometimes opposite, treatment. Fluids correct prerenal AKI but can worsen intrarenal injury through overload. Assessment focuses on urine output trends, fluid status, and the events preceding the drop in renal function.
Recognising it at the bedside
Acute kidney injury is defined by a rapid decline in renal function, usually tracked through rising serum creatinine and falling urine output over hours to days rather than a single abnormal value. Oliguria, urine output below 0.5 mL/kg/hour, is the classic finding nurses are taught to watch for, though a meaningful proportion of AKI presents with normal or even increased urine output.
Look beyond the urine output chart to the clinical context: recent hypotension, sepsis, nephrotoxic medication exposure, contrast administration, or a new obstruction such as an enlarged prostate or blocked catheter. The trigger event usually precedes the biochemical change by hours, so a careful history often identifies AKI before the labs confirm it.
Why the classic presentation misleads
AKI is not one condition with one fix. Prerenal AKI results from reduced renal perfusion, from causes such as hypovolaemia, heart failure, or sepsis, and the kidneys themselves are structurally intact. Intrarenal AKI involves direct damage to the nephron, commonly from acute tubular necrosis, nephrotoxic drugs, or prolonged untreated prerenal injury. Postrenal AKI results from obstruction anywhere from the renal pelvis to the urethra.
The reason this distinction matters clinically is that treatment for one cause can harm a patient with a different cause. Fluid resuscitation restores perfusion and often reverses prerenal AKI, but the same fluid load in a patient with established intrarenal damage, where the kidneys cannot yet excrete it, risks pulmonary oedema and fluid overload. Nurses should never assume fluids are the default answer to falling urine output without understanding which category is in play.
Priority nursing actions
Confirm and document urine output hourly, and correlate it with fluid intake, weight, and haemodynamic status rather than treating output in isolation. Review the medication list for nephrotoxic agents, including NSAIDs, aminoglycosides, and iodinated contrast, and hold or flag these for the prescriber.
If obstruction is suspected, check for bladder distension and confirm catheter patency before assuming intrinsic renal failure, since a blocked catheter is a fast, reversible cause of apparent AKI. Report any hypotensive episode promptly, since timely correction of perfusion can prevent prerenal AKI progressing to intrarenal injury. Monitor for signs of fluid overload, including new crackles, oedema, and rising blood pressure, particularly before administering further fluid boluses.
Labs and diagnostics to expect
Serum creatinine and blood urea nitrogen (BUN) rise as filtration falls, and the BUN:creatinine ratio helps distinguish cause: a ratio above 20:1 suggests prerenal injury, while a ratio closer to 10:1 to 15:1 points toward intrarenal damage. Urinalysis showing muddy brown granular casts is characteristic of acute tubular necrosis, an intrarenal cause.
Fractional excretion of sodium (FENa) below 1% suggests prerenal AKI, since the kidneys are still concentrating sodium normally, whereas a FENa above 2% suggests intrarenal damage. Renal ultrasound is typically ordered to rule out obstruction. Expect potassium, calcium, and phosphate to be monitored closely, since impaired excretion disturbs all three.
Complications and their early signs
Hyperkalaemia is the most immediately dangerous complication, since impaired renal excretion allows potassium to accumulate quickly. Watch for peaked T waves on ECG, muscle weakness, and cardiac arrhythmia, and report any potassium above the normal range without delay.
Fluid overload presents as new or worsening dyspnoea, crackles, jugular venous distension, and weight gain, and can progress to pulmonary oedema if unrecognised. Metabolic acidosis develops as the kidneys lose the ability to excrete hydrogen ions, presenting as Kussmaul respirations and confusion in advanced cases. Uraemia affects multiple systems, and nurses should watch for pericardial friction rub, altered mental status, and platelet dysfunction as renal function continues to decline.
Teaching that changes outcomes
Patients recovering from AKI need clear instruction on avoiding nephrotoxic over-the-counter medications, particularly NSAIDs, and on maintaining adequate hydration unless fluid restriction has been prescribed. Explain why any new medication, including herbal supplements, should be checked with a pharmacist or prescriber during recovery.
Teach patients to recognise and report decreasing urine output, swelling, or unusual fatigue promptly, since these can signal recurrence or incomplete recovery. Where AKI followed a hypotensive event or sepsis, review the specific circumstances with the patient so they understand their individual risk factors rather than receiving generic renal advice.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our renal and genitourinary practice questions are the closest set to what this page covers.
Common questions
What is the difference between prerenal, intrarenal, and postrenal AKI?
Prerenal AKI results from reduced blood flow to otherwise healthy kidneys, intrarenal AKI involves direct damage to kidney tissue such as acute tubular necrosis, and postrenal AKI results from obstruction of urine outflow. Each requires a different treatment approach, which is why identifying the cause comes before choosing an intervention.
Why can IV fluids make AKI worse?
Fluids help prerenal AKI by restoring renal perfusion, but in intrarenal AKI the damaged kidneys cannot yet excrete the extra volume, so the same fluids risk overload and pulmonary oedema. Assessing which category of AKI is present is essential before administering fluid boluses.
What is the priority nursing action for a patient with AKI?
Establish the likely cause by reviewing recent events, medications, and haemodynamic status, and monitor hourly urine output alongside fluid balance. Hold nephrotoxic medications and check catheter patency before assuming the cause is intrinsic renal damage.
What lab value distinguishes prerenal from intrarenal AKI?
A BUN:creatinine ratio above 20:1 and a FENa below 1% suggest prerenal AKI, while a ratio nearer 10:1 to 15:1 with a FENa above 2% points to intrarenal injury. Muddy brown granular casts on urinalysis are specific to acute tubular necrosis.
What is the most dangerous early complication of AKI?
Hyperkalaemia is the most immediately life-threatening complication, since impaired renal excretion allows potassium to rise quickly. Peaked T waves on ECG and muscle weakness are early warning signs that require urgent reporting.