Internal MedicineNephrologyAcute Kidney Injury (AKI)

Acute Kidney Injury (AKI)

Must-Not-Miss / Red Flags

  • Hyperkalemia >6.5 mEq/L – life‑threatening arrhythmia risk
  • Pulmonary edema from fluid overload
  • Uremic pericarditis – indication for urgent dialysis
Patient Explanation
“Your kidneys have suddenly slowed down and aren’t filtering your blood properly. We’ll find the cause and give you fluids or medications to help them recover.”
Board Fact
“The most common cause of AKI in hospitalized patients is pre‑renal azotemia due to volume depletion.”
ICD-10
N17.9

Definition & Core Concept

Acute Kidney Injury (AKI) is a sudden decline in renal function, defined by a rise in serum creatinine ≥0.3 mg/dL within 48 hours or a ≥1.5‑fold increase from baseline, accompanied by oliguria or anuria.

Epidemiology & Risk Factors

  • Occurs in 5‑7% of hospitalized patients and 20‑50% of ICU patients
  • Mortality rates range from 10‑80% depending on severity and setting
  • Common risk factors: advanced age, CKD, diabetes, sepsis, nephrotoxins

Pathophysiology (Rule of 3)

  1. Pre‑renal: reduced renal perfusion → tubuloglomerular feedback → Na⁺/H₂O retention
  2. Intrinsic: acute tubular necrosis (ATN) from ischemia or nephrotoxins → tubular cell damage
  3. Post‑renal: urinary outflow obstruction → hydronephrosis → tubular pressure increase

Clinical Presentation

  • Oliguria (<400 mL/day) or anuria (<100 mL/day)
  • Fatigue, confusion, nausea, fluid overload (edema, dyspnea)
  • Flank pain if obstructive; palpable bladder if post‑renal

Diagnostic Workup

BUN/Creatinine: ratio >20:1 suggests pre‑renal. Urinalysis: muddy brown casts = ATN. Renal ultrasound: rule out obstruction (hydronephrosis). Fractional excretion of Na (FeNa): 2% ATN.

Management Protocol

  1. Optimize hemodynamics: IV fluids for pre‑renal; vasopressors if distributive shock
  2. Avoid nephrotoxins: stop NSAIDs, ACEi/ARB, aminoglycosides
  3. Manage electrolytes: treat hyperkalemia with calcium gluconate, insulin+glucose, beta‑agonists
  4. Renal replacement therapy (RRT): indicated for refractory hyperkalemia, acidosis, uremia, fluid overload

Complications & Prognosis

  • Hyperkalemia → cardiac arrest
  • Volume overload → pulmonary edema
  • Uremic complications (pericarditis, encephalopathy, bleeding)
  • Progression to chronic kidney disease

ICU Criteria

ICU admission if: oliguric AKI requiring RRT, hemodynamic instability, or multi‑organ failure.

Clinical Vignette

A 72‑year‑old man with HTN and CKD stage 3 develops oliguria 48 hours after receiving IV contrast for a CT angiogram. Creatinine rises from 1.5 to 3.8 mg/dL. Urine sediment shows muddy brown casts.

Pearls & Pitfalls

  • Contrast‑induced nephropathy is a diagnosis of exclusion – always rule out other causes first.
  • FeNa may be unreliable in patients on diuretics; use FeUrea (<35% suggests pre‑renal).

Discharge & Follow-Up

Monitor renal function weekly until recovery. Avoid repeat contrast exposure. Adjust medication doses based on GFR.

Literature & Guidelines

KDIGO 2024 Clinical Practice Guideline for AKI. PMID: 35122189.

Personal Clinical Notes