Acute Renal Failure - In Depth Notes

Objectives
  • Define acute renal failure
  • Understand initial evaluation and diagnostics of acute renal failure
  • Identify common causes of acute renal failure
  • Identify evidence-based management on treatment options and common complications
  • Learn about uncommon causes of acute renal failure
Definition of Acute Renal Failure
  • Abrupt loss of kidney function
    • Results in retention of metabolic wastes like blood urea nitrogen (BUN) and creatinine, which are normally excreted by the kidneys
  • Possible manifestations:
    • Decreased urine output
    • Fluid overload
    • Electrolyte abnormalities
Classification of Acute Renal Failure
  • Urine Output (UOP) classification:
    • Anuric: < 50 ml urine/24 hours
    • Oliguric: < 500 ml/24 hours
    • Nonoliguric: > 500 ml/24 hours
Clinical Presentation
  • Varies based on severity of illness
  • Asymptomatic: mild to moderate disease; incidental finding during lab tests
History & Review of Systems

  • Pertinent Questions by System:

    • Constitutional: Fatigue, infectious symptoms

    • ENT: Oral/nasal ulcers, vision changes

    • Cardiovascular: Weight gain/loss, heart failure

    • Respiratory: Shortness of breath, cough

    • Gastrointestinal: Nausea, appetite changes

    • Genitourinary: Urine characteristics, history of stones

    • Musculoskeletal: Cramping, trauma

    • Neurological: Confusion, mental status changes

    • Medications: - Any new prescribed or OTC medications?

    • Any contrast administration?

    • Any chronic comorbid conditions? DM, HTN, etc.

Physical Examination
  • Findings by System:
    • Constitutional: Hyper or hypotension
    • Cardiovascular: Signs of heart failure, peripheral edema
    • Respiratory: Crackles, signs of effusions
    • Gastrointestinal: Ascites
    • Genitourinary: Prostate issues, bladder distension
    • Integumentary: Rash, poor skin turgor
    • Musculoskeletal: Weakness, cramping
    • Hematologic/Lymphatic: Signs of bleeding
Causes of Acute Renal Failure
  1. Prerenal
    • Reduction in blood flow to kidneys.
    • Causes: sepsis, heart failure, dehydration
  2. Intrarenal
    • Damage to kidney tissue.
    • Most common: Acute Tubular Necrosis (ATN)
  3. Postrenal
    • Urinary tract obstructions leading to back pressure on kidneys
Initial Evaluation & Diagnostics
  • Key Tests to Review:
    • Electrolytes (magnesium, phosphorus, calcium)
    • Blood gas analysis (ABG)
    • Chest X-Ray for volume overload
    • Baseline creatinine, BUN
    • Kidney imaging (ultrasound) if necessary
Measurement of Kidney Function
  • Understand a patient's baseline creatinine levels
    • Influenced by age, gender, race, muscle mass, and protein intake
  • Creatinine Production: Byproduct from muscle metabolism, less accurate for certain populations
Staging of Acute Renal Failure
  • Stage 1: Increase in serum creatinine (SCr) by ≥ 0.3 mg/dL or 1.5-2.0 x baseline; UOP < 0.5 mL/kg/hr for > 6 hrs
  • Stage 2: Increase in SCr by 2.0-3.0 x baseline; UOP < 0.5 mL/kg/hr for > 12 hrs
  • Stage 3: Increase in SCr by > 3.0 x baseline; UOP < 0.3 mL/kg/hr for 24 hrs
Diagnostic Testing
  • Urinalysis parameters: Evaluate appearance, osmolality, specific gravity, etc.
  • FeUrea and FeNa: Differentiate prerenal from ATN conditions
    • BUN/Cr urine ratio, with normal findings indicating prerenal issues and elevated findings suggesting ATN
Management Strategies
  • Monitor kidney function, adjust fluid balance, and dietary needs
  • Avoid Nephrotoxic Medications: NSAIDs, ACE inhibitors, etc.
  • Treatment based on cause (i.e., fluid therapy for prerenal, correcting electrolyte imbalances)
Common Complications
  • Fluid overload, electrolyte imbalances, infection
  • Consider Nephrology Consultation: For unclear causes or severe cases
Uncommon Causes of Acute Renal Failure
  • Idiopathic: Rhabdomyolysis, cardiorenal syndrome, hepatorenal syndrome, and specific medications
  • Zebra Testing: Evaluate for autoimmune conditions and vasculitides if indicated.
  • Contrast-Induced Nephropathy: Risk in patients with existing renal impairment.
Documentation Terminology
  • Use AKI/ARF interchangeably; specify causes and associated abnormalities clearly in documentation.
Conclusion
  • Acute renal failure is a critical condition requiring timely identification and management to improve patient outcomes and prevent complications.