Clinical meaning
Ischemia or toxins cause sloughing of tubular epithelial cells, obstructing tubules (muddy brown casts). Afferent arteriolar constriction (Pre-renal) reduces GFR. Post-renal obstruction increases Bowman's capsule pressure, halting filtration.
Diagnosis & workup
Diagnostics & workup: - Order BMP with creatinine trending every 6-12 hours - Order urinalysis with microscopy (muddy brown casts = ATN) - Calculate FeNa (< 1% = pre-renal, > 2% = intrinsic/ATN) - Order renal ultrasound to rule out post-renal obstruction - Order urine electrolytes (Na, Cr) for FeNa calculation - Order CK and myoglobin if rhabdomyolysis suspected - Apply RIFLE/AKIN/KDIGO criteria for staging - Order nephrology consultation for AKIN Stage 2 or higher
Risk factors: - Sepsis (most common cause of AKI in ICU) - Major surgery (especially cardiac) - Contrast dye administration - Nephrotoxic drugs (vancomycin, aminoglycosides, amphotericin B) - Rhabdomyolysis - Cardiorenal syndrome - Hepatorenal syndrome - Tumor lysis syndrome - Abdominal compartment syndrome