USMLE Prep - Medical Reference Library

Acute Kidney Injury — KDIGO Staging, Volume Optimization, and RRT Indications

System: Nephrology • Reviewed: Sep 1, 2025 • Step 1Step 2Step 3

Synopsis:

AKI is defined by creatinine rise or oliguria. Apply KDIGO staging, optimize hemodynamics and volume, avoid nephrotoxins, and initiate renal replacement therapy for standard emergent indications or persistent severe AKI after optimization.

Key Points

  • Use the highest‑yield diagnostic test early; do not let testing delay time‑critical therapy.
  • Set objective targets (hemodynamic, neurologic, respiratory) and reassess frequently.
  • Plan definitive source control or immunomodulation when indicated; document follow‑up and patient education.

Algorithm

  1. Identify AKI by KDIGO criteria; stage severity.
  2. Assess volume status and hemodynamics; give fluids if hypovolemic, vasopressors if in shock.
  3. Stop nephrotoxins; dose‑adjust meds; correct obstructive uropathy.
  4. Consider RRT for refractory hyperkalemia, acidosis, volume overload, or uremic complications; consult nephrology.

Clinical Synopsis & Reasoning

AKI is defined by creatinine rise or oliguria. Apply KDIGO staging, optimize hemodynamics and volume, avoid nephrotoxins, and initiate renal replacement therapy for standard emergent indications or persistent severe AKI after optimization.


Treatment Strategy & Disposition

Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced or procedural interventions based on explicit failure criteria. Define ICU, step‑down, and ward disposition triggers; involve specialty teams early.


Epidemiology / Risk Factors

  • Risk varies by comorbidity and precipitants; see citations for condition‑specific data.

Investigations

TestRole / RationaleTypical FindingsNotes
Serum creatinine/urine outputDiagnosis/stagingKDIGO 1–3Trend kinetics
Urinalysis/urine microscopyEtiologyCasts, crystalsGuide diagnosis
Ultrasound kidneys/bladderObstruction assessmentHydronephrosis/retentionPrompt relief if obstructed

Pharmacology

Medication/InterventionMechanismOnsetRole in TherapyLimitations
Isotonic crystalloids (balanced)Volume optimizationHoursRestore perfusionAvoid fluid overload
Vasopressors (if shock)Perfusion supportMinutesMaintain MAP targetsTitrate carefully
Avoid/adjust nephrotoxinsPreventionImmediateDose by GFRStewardship

Prognosis / Complications

  • Outcome depends on timeliness of diagnosis and definitive therapy; monitor for complications.

Patient Education / Counseling

  • Provide red‑flag education, adherence guidance, and explicit return precautions; arrange timely specialty follow‑up.

References

  1. KDIGO Clinical Practice Guideline for AKI (2012) — Link