Pathophysiology
Clinical meaning
The clinician diagnoses acute kidney injury using the KDIGO criteria: Stage 1 (serum creatinine increase of 26.5 micromol/L or greater within 48 hours, OR 1.5-1.9 times baseline within 7 days, OR urine output less than 0.5 mL/kg/hr for 6-12 hours), Stage 2 (creatinine 2.0-2.9 times baseline, OR urine output less than 0.5 mL/kg/hr for 12 or more hours), Stage 3 (creatinine 3.0 or more times baseline, OR increase to 353.6 micromol/L or greater, OR initiation of renal replacement therapy, OR urine output less than 0.3 mL/kg/hr for 24 or more hours, OR anuria for 12 or more hours). The clinician categorizes AKI etiology as prerenal (60-70% of cases -- decreased renal perfusion from hypovolemia, heart failure, hepatorenal syndrome, sepsis; BUN/Cr ratio greater than 20:1, FENa less than 1%, urine specific gravity greater than 1.020), intrinsic (25-30% -- acute tubular necrosis from ischemia or nephrotoxins, acute interstitial nephritis, glomerulonephritis; FENa greater than 2% in ATN, muddy brown granular casts), or postrenal (5-10% -- urinary tract obstruction; hydronephrosis on renal ultrasound). The clinician performs comprehensive evaluation: medication review (NSAIDs, aminoglycosides, contrast, ACEIs/ARBs,...