Acute Renal Failure, now more commonly termed Acute Kidney Injury (AKI), is the sudden loss of the kidneys’ ability to filter waste products, excess fluids, and electrolytes from the blood — developing over hours to days.
When the kidneys fail acutely, toxic byproducts like creatinine and urea nitrogen accumulate in the bloodstream (a state called azotemia), and the body loses its ability to regulate fluid and electrolyte balance.
Classification by Cause (the “Pre/Intra/Post” framework)
- Pre-renal — reduced blood flow to the kidneys
- Dehydration, hemorrhage, heart failure, sepsis, severe burns
- Most common cause; kidneys are structurally intact but underperfused
- Intrinsic (Intrarenal) — direct damage to kidney tissue
- Acute tubular necrosis (ATN) — most common intrinsic cause
- Rhabdomyolysis, nephrotoxic drugs (NSAIDs, aminoglycosides, contrast dye), glomerulonephritis, ischemia
- Post-renal — obstruction downstream from the kidneys
- Kidney stones, enlarged prostate, bladder obstruction, tumors
Signs & Symptoms
- Decreased or absent urine output (oliguria/anuria)
- Fluid retention — swelling in legs, ankles, face
- Shortness of breath (pulmonary edema)
- Fatigue, confusion, nausea
- Chest pain or pressure
- Arrhythmias (from high potassium/hyperkalemia)
Diagnosis
- Rising serum creatinine — hallmark lab finding
- BUN (blood urea nitrogen) elevation
- Decreased GFR (glomerular filtration rate)
- Urinalysis — may show casts, protein, or blood
- Renal ultrasound to assess for obstruction
AKI is formally defined by any of:
- Creatinine rise ≥ 0.3 mg/dL within 48 hours
- Creatinine rise ≥ 1.5× baseline within 7 days
- Urine output < 0.5 mL/kg/hr for ≥ 6 hours
Complications
- Hyperkalemia — potentially fatal cardiac arrhythmias
- Metabolic acidosis
- Pulmonary edema / fluid overload
- Uremia — toxic buildup causing encephalopathy, pericarditis
- Progression to Chronic Kidney Disease (CKD)
Treatment
- Treat the underlying cause first (fluids for pre-renal, relieve obstruction for post-renal)
- Aggressive fluid management
- Correct electrolyte imbalances (especially potassium)
- Avoid nephrotoxic agents
- Dialysis — for severe cases unresponsive to conservative management (fluid overload, refractory hyperkalemia, severe acidosis, uremic symptoms)
ARF/AKI is a medical emergency with significant mortality in hospitalized patients. However, if caught early and the underlying cause is reversible, kidney function can fully recover — particularly in pre-renal cases. The condition seen in rhabdomyolysis (as above) is a classic example of intrinsic ARF driven by myoglobin-mediated tubular injury.