Indications for Intraoperative Diuretic Use

🔹 1. To Promote Urine Output (Intraoperative Oliguria)

  • Especially in:
    • Renal transplantation (after graft reperfusion)
    • Prolonged aortic cross-clamping
    • Aortic aneurysm repair (to prevent ischemic renal injury)
    • Liver transplantation (hepatorenal protection)

🔹 2. Forced Diuresis in Toxic Ingestions

  • Example: Crush injury, myoglobinuria (rhabdomyolysis), hemoglobinuria

🔹 3. Prevention of Acute Kidney Injury (AKI) – select situations

  • High-risk patients (e.g., hypotension + nephrotoxins)
  • Goal: maintain tubular flow, reduce ischemia

🔹 4. Control of Intracranial Pressure (ICP) (mannitol)

  • In neurosurgery
  • Dehydrates brain parenchyma, reduces volume

🔹 5. Management of Volume Overload

  • ESRD or heart failure patients if hypervolemic
  • Must balance against hypovolemia risk


🔷 IV. Specific Uses

🔹 A. Renal Transplantation

Phase

Use

Pre-reperfusion

Mannitol (0.25–0.5 g/kg) – improves renal perfusion, free radical scavenger

Post-reperfusion

Furosemide (0.5–1 mg/kg) – stimulates urine from new graft


🔹 B. Neurosurgery

  • Mannitol (0.25–1 g/kg IV over 15 min) for:
    • Brain relaxation
    • Reduce ICP
    • Temporize herniation

🔹 C. Crush Injury / Rhabdomyolysis

  • Mannitol + fluid → prevent tubular cast formation
  • Aim for UO > 200–300 mL/hr


🔷 V. Risks and Complications of Intraoperative Diuretics

🔺 1. Volume Depletion / Hypovolemia

  • Rapid diuresis → ↓ preload → hypotension
  • Especially dangerous under anesthesia where compensatory mechanisms are blunted

🔺 2. Electrolyte Disturbances

Diuretic

Risk

Furosemide

Hypokalemia, hyponatremia, hypomagnesemia, metabolic alkalosis

Mannitol

Hyperkalemia, dilutional hyponatremia, ↑ plasma osmolality


🔺 3. Ototoxicity (with furosemide)

  • Especially with rapid high-dose IV
  • Potentiated with aminoglycosides

🔺 4. Mannitol-specific Risks

  • Acute pulmonary edema (in cardiac/renal failure)
  • Hyperosmolar state (if poor renal excretion)
  • Paradoxical ↑ ICP if BBB is disrupted (mannitol leaks into brain)

🔺 5. No Mortality Benefit in AKI Prevention

  • Trials show no consistent benefit of diuretics in preventing AKI
  • Diuretics should not be used solely to convert oliguric to non-oliguric AKI


🔷 VI. Viva & MCQ Pearls

  • ❓Which diuretic protects kidneys from free radical injury?
    ➤ Mannitol
  • ❓Which diuretic is safest in renal transplant?
    ➤ Furosemide or mannitol (timed appropriately)
  • ❓Electrolyte effect of loop diuretics?
    ➤ ↓ Na⁺, ↓ K⁺, ↓ Ca²⁺, ↓ Mg²⁺, metabolic alkalosis
  • ❓What is a paradoxical effect of mannitol?
    ➤ ↑ ICP if BBB is disrupted
  • ❓Why avoid diuretics in early intraoperative oliguria?
    ➤ May mask true hypovolemia and worsen perfusion