Acute Kidney Injury (AKI), previously known as Acute Renal Failure, is a sudden decline in kidney function that leads to the accumulation of waste products, fluids, and electrolytes in the body. Unlike chronic kidney disease, AKI develops rapidly—within hours to days—but can be reversible with timely intervention.
The kidneys’ role in filtering toxins, balancing electrolytes, and maintaining fluid equilibrium makes them highly vulnerable to sudden disruptions. Understanding causes, phases, and treatment strategies is crucial for both medical students and healthcare providers.
What is Acute Kidney Injury?
AKI is defined as a sudden reduction in glomerular filtration rate (GFR), leading to the retention of nitrogenous waste products (urea, creatinine), electrolyte imbalance, and fluid overload.
Key features include:
- Rapid onset (hours to days).
- Can be prerenal, intrarenal, or postrenal in origin.
- Potentially reversible with early detection and intervention.
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Types of Acute Kidney Injury
The causes of AKI are classified based on the location of damage relative to the kidneys:
1. Prerenal Failure (Damage before the kidneys)
Occurs due to reduced blood flow (perfusion) to the kidneys.
Causes:
- Cardiac damage (myocardial infarction, impaired output).
- Hypovolemia (hemorrhage, dehydration, burns).
- Vasodilation and shock states.
- GI losses (severe vomiting or diarrhea).
2. Intrarenal Failure (Damage within the kidneys)
Results from direct injury to renal tissue, often prolonged ischemia.
Causes:
- Myoglobinuria (muscle breakdown, rhabdomyolysis).
- Hemoglobinuria (hemolysis).
- Nephrotoxic drugs (NSAIDs, aminoglycosides, chemotherapy, contrast dyes).
- Infections (glomerulonephritis, sepsis).
3. Postrenal Failure (Damage after the kidneys)
Occurs due to urinary tract obstruction.
Causes:- Renal calculi (kidney stones).
- Blood clots.
- Benign Prostatic Hyperplasia (BPH).
- Tumors compressing the urinary tract.
- Neurological damage (e.g., stroke affecting bladder emptying).
Phases of Acute Kidney Injury
A helpful mnemonic to remember the AKI phases is “OH OH DARN RENAL”:
1. Onset / Initiation Phase
- Triggering event (prerenal, intrarenal, or postrenal cause).
- Early recognition is vital to prevent irreversible damage.
2. Oliguric Phase
- Urine output <400 mL/24 hours.
- Decreased GFR impairs filtration.
- Retention of waste products: ↑ BUN & creatinine.
- Electrolyte imbalances (especially hyperkalemia).
3. Diuretic Phase
- Underlying cause corrected.
- Gradual increase in urine output.
- Risk of dehydration and hypokalemia due to excessive fluid loss.
- Improvement in kidney function.
- May take 6–12 months for complete recovery.
- Some patients may progress to chronic kidney disease (CKD) if damage is severe.
Interventions in AKI
Correcting the Cause
Identify and treat the underlying factor (infection, obstruction, hypovolemia, or toxins).Fluid & Dietary Management
- Low protein diet – Reduces nitrogenous waste buildup.
- Limit fluid intake – Prevents fluid overload.
- Strict intake-output monitoring – Helps assess kidney recovery.
- Daily weights – Detects hidden fluid retention.
Monitoring & Supportive Care
- Monitor EKG & labs – Hyperkalemia (>5.0 mEq/L) can cause dangerous arrhythmias.
- Dialysis – May be required temporarily if kidneys fail to recover.
- Antihypertensives & diuretics – To control fluid balance and blood pressure.
Diuretic & Recovery Phases Care
- Large amounts of dilute urine require electrolyte monitoring.
- Patients are prone to hypokalemia and dehydration.
- Supportive therapy until full recovery.
Prognosis
- Good prognosis if diagnosed and treated early.
- Reversible in many cases, especially prerenal causes.
- Poor outcomes associated with sepsis, multi-organ failure, or untreated obstruction.
- Some patients progress to chronic kidney disease (CKD).
Frequently Asked Questions (FAQ)
Q1: Is acute kidney injury reversible?
Yes, AKI is often reversible, especially if the cause is corrected quickly (e.g., dehydration, obstruction).
Q2: What is the most common cause of AKI in hospitals?
Sepsis, nephrotoxic drugs (like aminoglycosides), and contrast-induced nephropathy are common hospital-related causes.
Q3: How is AKI different from CKD?
- AKI is sudden, rapid, and often reversible.
- CKD is progressive, long-term, and usually irreversible.
Q4: How do doctors diagnose AKI?
Through lab tests (BUN, creatinine, electrolytes), urine output monitoring, and imaging to rule out obstruction.
Q5: Can AKI lead to permanent kidney damage?
Yes, in some cases, especially if untreated or severe, AKI can progress to chronic kidney disease (CKD) or end-stage renal failure.
