Decreased Urine Output (Post-Operative Complications)

Jun 12, 2024

Decreased Urine Output (Post-Operative Complications)

Why Decreased Urine Output Matters

  • Indicator of kidney function and total body volume status.
  • Difficult to maintain due to fluid shifts post-op.
  • Early sign of complications such as sepsis or bleeding.

Normal Urine Output

  • Rule of thumb: 0.5 cc/kg/hr
    • For a 70 kg person: ~35 cc/hour
    • Usually reported as urine output per 8-hour shift: ~250 cc/shift

Initial Steps

  1. Fluid Bolus:
    • Often the first step: 500 cc to 1 liter of isotonic fluid (e.g., lactated ringers or normal saline).
    • Avoid hypotonic fluids (e.g., D5 half normal saline) and hypertonic fluids (like 3% saline).
    • Fluid status often results in hypovolemia post-op due to multiple factors (NPO status, losses in surgery).

Maintenance Fluids

  • Calculated using the 4-2-1 Rule:
    • First 10 kg: 4 cc/kg/hr
    • Second 10 kg: 2 cc/kg/hr
    • Remaining weight: 1 cc/kg/hr
    • Simplified: Add 40 cc/hr to body weight in kg
    • Example: 70 kg person = 110 cc/hr

Hypovolemia Signs

  • Symptoms: Thirst, dry mouth.
  • Vital Signs: Uptrending heart rate.
  • Labs: Elevated creatinine, contraction alkalosis (hypokalemia, hypochloremia, metabolic alkalosis), hemoconcentration (e.g., increased hemoglobin).

Clinical Trends Post-Op

  • Day 0-2: High chance of fluid loss due to inflammatory state.
  • Beyond Day 2: Urine output typically increases as inflammation subsides.

If Fluid Bolus Fails

  • Consider causes: Pre-renal, intra-renal, post-renal.
  • Bladder Ultrasound:
    • Check for post-renal issues (e.g., urinary retention).

Types of Acute Kidney Injury (AKI)

Pre-Renal AKI

  • Cause: Insufficient blood flow to kidneys (e.g., hypovolemia, heart failure).
  • Treatment: Address fluid balance, underlying cause.

Intra-Renal AKI

  • Cause: Kidney injury affecting glomeruli (e.g., Acute Tubular Necrosis).
  • Treatment: Supportive care, monitor kidney recovery.

Post-Renal AKI

  • Cause: Obstruction in urinary tract (e.g., BPH, stones).
  • Treatment: Relieve obstruction (e.g., straight cath, Foley catheter).

Diagnostic Tools

  • Bladder Scan: Assess for urinary retention.
  • FENa (Fractional Excretion of Sodium)
    • Formula: Urine Na * Plasma Cr / Plasma Na * Urine Cr
    • < 1%: Pre-renal
    • 1-4%: Intra-renal

    • 4%: Post-renal

  • FEUrea (Fractional Excretion of Urea) if on diuretics.
    • < 20%: Pre-renal

    • 40%: Intra-renal/Post-renal

Treatment Summary

  1. Post-Renal: Relieve obstruction (e.g., Foley catheter).
  2. Intra-Renal: Monitor and wait for kidney recovery.
  3. Pre-Renal: Ensure adequate fluid resuscitation, identify underlying issues like heart failure or sepsis.

Review

  • Systematic approach: Pre-renal, Intra-renal, Post-renal causes.
  • Initial fluid bolus for hypovolemia.
  • Use diagnostics and clinical signs to identify the type of AKI.
  • Treat according to the identified type of AKI.

These videos are for educational purposes only. Consult a healthcare provider for diagnosis and treatment.