Acute Kidney Injury
Acute Kidney Injury is a sudden loss of kidney function, often due to decreased blood flow, toxins, or blockages, leading to a dangerous buildup of waste and fluids.
Emergency Management: Indications for urgent Hemodialysis (AEIOU): Acidosis (severe, refractory), Electrolytes (refractory hyperkalemia), Intoxications (lithium, toxic alcohols), Overload (refractory pulmonary edema), Uremia (pericarditis, encephalopathy).
An abrupt (within 48 hours to 7 days) decline in renal function, resulting in the retention of nitrogenous waste products and dysregulation of extracellular volume and electrolytes. The core pathology involves an abrupt fall in the glomerular filtration rate (GFR), primarily affecting the renal tubules (most commonly) or glomeruli.
Detailed Overview
AKI is clinically classified into pre-renal (hypoperfusion), intrinsic (tubular, glomerular, or interstitial damage), and post-renal (obstruction) etiologies. Acute Tubular Necrosis (ATN) is the most common intrinsic cause, often secondary to prolonged ischemia or nephrotoxins. Rapid recognition is essential because severe AKI can lead to life-threatening hyperkalemia, metabolic acidosis, and fluid overload. The condition is often reversible, but severe or repeated episodes increase the risk of developing Chronic Kidney Disease (CKD).
Epidemiology & Demographics
Incidence: Complicates 5-7% of acute hospital admissions and up to 30-50% of ICU admissions. Mortality in ICU patients with severe AKI approaches 50%. Increased incidence with advancing age and pre-existing CKD.
Etiological Mechanism
Pre-renal: Hypovolemia (hemorrhage, severe dehydration) or decreased effective circulating volume (heart failure). Intrinsic: ATN (ischemia, aminoglycosides, contrast dye), Acute Interstitial Nephritis (AIN, often drug-induced), Glomerulonephritis. Post-renal: BPH, kidney stones, pelvic malignancies.
Primary Causes
Sepsis (causing vasodilatory shock)
Nephrotoxic drugs (NSAIDs, aminoglycosides, contrast media)
Profound dehydration
Urinary tract obstruction (e.g., severe BPH)
In pre-renal AKI, reduced renal perfusion triggers the RAAS and sympathetic nervous systems, causing afferent vasodilation and efferent vasoconstriction to maintain GFR. If prolonged, this autoregulation fails, leading to ischemic Acute Tubular Necrosis (intrinsic AKI). In ATN, tubular epithelial cells, particularly in the highly metabolically active proximal tubule and thick ascending limb, undergo necrosis and slough off into the lumen, forming obstructing casts. This obstruction increases intratubular pressure, opposing the hydrostatic filtration pressure in the glomerulus, causing a sharp drop in GFR. Concurrently, damaged tubules leak filtrate back into the interstitium.
Diagnostic Criteria & Guidelines
KDIGO criteria: Increase in serum creatinine by >= 0.3 mg/dL within 48 hours, or increase in serum creatinine to >= 1.5 times baseline within the prior 7 days, or urine volume < 0.5 mL/kg/h for 6 hours.
Treat the underlying cause: For pre-renal, volume expansion with IV crystalloids (0.9% Normal Saline or Lactated Ringer's). For post-renal, immediate decompression (Foley catheter or percutaneous nephrostomy). Discontinue all nephrotoxins (NSAIDs, ACEi/ARBs temporarily).
Second-Line & Adjunctive Therapy
If fluid overloaded: Loop diuretics (e.g., Furosemide 40-80 mg IV). Management of hyperkalemia: Calcium gluconate IV (cardioprotection), Insulin + D50 IV, Albuterol nebs, and Sodium Zirconium Cyclosilicate PO.
Surgical & Procedural Management
Surgical relief of obstruction if not amenable to catheterization (e.g., ureteral stenting for stones, TURP for BPH).
Patient Counseling & Advice
Inform the patient that AKI requires careful monitoring of fluids and diet until kidney function recovers, which may take weeks. Warn that they are now at higher risk for chronic kidney disease and must avoid nephrotoxic medications indefinitely.
Follow-Up & Monitoring Schedule
Daily BMP to monitor Creatinine, Potassium, and Bicarbonate until stabilizing. Post-discharge follow-up in 1-2 weeks with a repeat BMP. Long-term follow-up annually to screen for CKD.
Preventive Strategies
Adequate hydration during illness or before contrast dye exposure. Judicious use of nephrotoxic medications, especially in the elderly and those with CKD.
Pre-renal and post-renal AKI often reverse completely if treated quickly. ATN can take 1-3 weeks to recover as tubular cells regenerate. Mortality correlates with the severity of the underlying illness (e.g., severe sepsis).