Acute Kidney Injury

Key considerations: Post-renal obstruction (bilateral ureteral, bladder outlet), Renal artery thrombosis/dissection, Thrombotic microangiopathy (TTP/HUS)

Cannot miss

Post-renal obstruction (bilateral ureteral, bladder outlet)
Renal artery thrombosis/dissection
Thrombotic microangiopathy (TTP/HUS)
Rapidly progressive glomerulonephritis
Rhabdomyolysis with renal failure

Likely diagnoses

Pre-renal (hypovolemia, cardiorenal)
ATN from sepsis or nephrotoxins
Drug-induced (NSAIDs, ACEi, contrast)
Urinary obstruction

Red flags

Anuria (<50mL/24hr)
Hyperkalemia with ECG changes
Severe metabolic acidosis
Uremic encephalopathy
Pulmonary edema unresponsive to diuretics

Workup

history: Baseline creatinine, recent trends; Nephrotoxic medications (NSAIDs, ACEi, contrast, aminoglycosides); Volume status — intake, output, weights; Urinary symptoms (hesitancy, hematuria); exam: Volume assessment — JVP, skin turgor, mucous membranes, edema; Bladder distension; Flank tenderness; Signs of uremia — asterixis, pericardial rub; labs: BMP (Cr trend, K, bicarb); UA with microscopy (casts, eosinophils); FENa or FEUrea; CK if rhabdomyolysis suspected; CBC, LDH, haptoglobin if TMA suspected; imaging: Renal US (hydronephrosis, kidney size); Bladder scan for post-void residual; bedside: Point-of-care ultrasound for hydronephrosis and IVC assessment

Management

immediate: Correct hypovolemia with isotonic crystalloid; Relieve obstruction (Foley if urinary retention); Treat hyperkalemia if present (calcium, insulin/dextrose, kayexalate); Hold nephrotoxic medications; general: Determine pre-renal vs intrinsic vs post-renal; Optimize hemodynamics; Avoid further nephrotoxic insults; Dose-adjust all renally cleared medications; specific: diagnosis: Pre-renal AKI; steps: Volume resuscitation; Hold diuretics, ACEi/ARB, NSAIDs; Treat underlying cause (sepsis, CHF, hemorrhage); diagnosis: ATN; steps: Supportive care; Maintain euvolemia; Avoid further insults; Consider RRT if refractory; diagnosis: Post-renal; steps: Foley catheter for bladder outlet obstruction; Urology consult for ureteral obstruction; Monitor for post-obstructive diuresis

Disposition

admit: AKI requiring IV fluids or monitoring; Hyperkalemia or severe metabolic acidosis; Need for dialysis; Oliguric or anuric AKI; discharge: Mild pre-renal AKI resolving with oral hydration; Stable Cr with clear reversible cause; consults: Nephrology for intrinsic AKI, dialysis needs, GN workup; Urology for obstructive causes

Clinical pearls

FENa <1% suggests pre-renal; >2% suggests ATN (unreliable on diuretics — use FEUrea instead)
Muddy brown granular casts = ATN; RBC casts = glomerulonephritis; WBC casts = pyelonephritis/AIN
Post-obstructive diuresis can cause massive fluid and electrolyte losses — monitor closely after relief

Source and review

KDIGO AKI Guidelines 2012. Last reviewed: 2024-11-01