AKI: Workup & Management

• Stage with KDIGO (creatinine/urine output); causes split into pre-renal, post-renal (bladder scan + ultrasound), and intrinsic (ATN, AIN, GN, vascular).
• Stop nephrotoxins (NSAIDs, ACEi/ARB in AKI, contrast, aminoglycosides); aim for euvolemia, neither wet nor dry.
• Dialysis triggers (AEIOU): Acidosis, Electrolytes (K⁺), Ingestions, Overload, Uremic complications.
• AIN: stop the culprit drug (PPIs, antibiotics, NSAIDs) ± corticosteroids. Diagnosis is clinical, supported by urine microscopy; kidney biopsy is the gold standard when uncertain.
• A deferred RRT strategy is safe (STARRT-AKI); when CRRT runs, dose 20–25 mL/kg/h with regional citrate anticoagulation preferred unless contraindicated.

Distinguishing the Three Categories of Acute Kidney Injury

• ACUTE KIDNEY INJURY
• PRE-RENAL: bland urine sediment · FENa <1% · FEUrea <35% → check volume status
• Dry mucosal membranes, low JVP, low CVP, no edema, low PCWP, negative fluid balance — dynamic assessment (IVC/PLR) → VOLUME DEPLETION · edema plus hypotension, elevated JVP, respiratory compromise → DECREASED CARDIAC OUTPUT · cold extremities, low SVR, high cardiac output, low PCWP → SEPSIS
• INTRINSIC: FENa >1% · FEUrea >50% · cells or casts seen on urine microscopy
• TUBULAR (acute tubular necrosis): granular casts · recent ↓BP · recent exposure to toxin/drug
• GLOMERULAR (vasculitic, microvascular, immune complex disorders): dysmorphic RBCs · RBC casts · systemic illness · pulmonary hemorrhage
• INTERSTITIAL (acute interstitial nephritis): urine eosinophils · WBC casts · new drug · peripheral eosinophilia · skin rash
• POST-RENAL: post-void residual volume >100 mL · hydronephrosis seen on renal ultrasound

Managing Prerenal Causes of Acute Kidney Injury

• PRERENAL acute kidney injury
• INTRAVASCULAR VOLUME DEPLETION: stop ACE inhibitors, ARBs, COX II inhibitors, NSAIDs, and potential nephrotoxins · give intravenous volume expansion — balanced crystalloids favored over normal saline; avoid colloids (starches harmful) · treat the underlying cause of volume depletion — blood loss, gastrointestinal losses, extensive burns, extravasation into extravascular compartments (e.g., peritonitis, intestinal obstruction)
• EFFECTIVE VOLUME DEPLETION: treat the underlying cause (sepsis, cardiogenic shock, abdominal compartment syndrome) · judicious diuretics in CHF exacerbation · avoid nephrotoxins (NSAIDs, iodinated contrast when possible, aminoglycosides) to prevent progression to tubular injury