How should I manage a 58‑year‑old woman with a presumed intracranial tumor who is intubated (Glasgow Coma Scale E1 V? M2), receiving mannitol and dexamethasone, now developing polyuria (>150 mL/h for 12 hours) and hypernatremia (serum sodium 152 mmol/L)?

Management of Mannitol-Induced Polyuria and Hypernatremia in Intubated Brain Tumor Patient

Stop mannitol immediately and switch to hypertonic saline (3% continuous infusion or 7.5% bolus) for ongoing intracranial pressure control, while aggressively replacing urinary losses with isotonic crystalloids to correct the hypernatremia and prevent further volume depletion. 1, 2, 3

Immediate Actions Required

Discontinue Mannitol

• Mannitol must be stopped now because the patient has developed osmotic diuresis (>150 mL/h for 12 hours) with resulting hypernatremia (152 mmol/L), indicating excessive fluid loss that threatens cerebral perfusion and can worsen outcomes. 1, 4
• The FDA label explicitly warns that "excessive loss of water and electrolytes may lead to serious imbalances" and that "loss of water in excess of electrolytes can cause hypernatremia." 4
• Continuing mannitol risks progression to severe hypernatremia (>155 mmol/L), which increases risk of seizures, hemorrhagic encephalopathy, and osmotic demyelination syndrome. 2

Fluid Resuscitation Protocol

• Insert or verify Foley catheter placement to accurately monitor ongoing urinary losses. 1
• Administer isotonic crystalloid (0.9% normal saline) at a rate matching urine output to restore euvolemia while avoiding rapid sodium correction. 2, 4
• Target sodium correction rate: maximum 10 mmol/L per 24 hours to prevent osmotic demyelination syndrome. 2
• Check serum sodium, potassium, chloride, and osmolality immediately, then repeat every 6 hours during active management. 1, 2

Transition to Alternative Osmotic Therapy

Hypertonic Saline as Primary Agent

• Hypertonic saline is superior to mannitol in this clinical scenario because it provides ICP control without the profound diuretic effect that caused this patient's current crisis. 1, 2, 3
• For acute ICP control: administer 7.5% hypertonic saline 250 mL IV over 15-20 minutes if there are signs of elevated ICP or neurological deterioration. 2, 3
• For sustained ICP management: initiate 3% hypertonic saline continuous infusion at 1 mL/kg/h, titrated to maintain serum sodium 145-155 mmol/L. 2, 3
• Do not administer additional hypertonic saline boluses until serum sodium falls below 155 mmol/L. 2, 3

Advantages of Hypertonic Saline Over Mannitol

• Hypertonic saline has minimal diuretic effect and actually increases blood pressure, directly addressing the volume depletion caused by mannitol. 1, 2
• Hypertonic saline does not cause rebound cerebral edema because it does not accumulate in CSF like mannitol does with prolonged use. 3
• At equiosmolar doses, hypertonic saline and mannitol have comparable ICP-lowering efficacy, but hypertonic saline provides more sustained control. 1, 3

Ongoing Monitoring Requirements

Electrolyte Surveillance

• Measure serum sodium, potassium, chloride, and osmolality every 6 hours throughout osmotic therapy. 1, 2
• Target serum sodium range: 145-155 mmol/L for optimal ICP control while avoiding complications. 2
• Hold hypertonic saline if serum osmolality exceeds 320 mOsm/L or if osmolality gap reaches ≥40. 2

Neurological Assessment

• Monitor Glasgow Coma Scale, pupillary responses, and motor examination every 1-2 hours to detect signs of elevated ICP or herniation. 1
• Signs requiring immediate intervention: pupillary changes, declining GCS, new focal deficits, or Cushing's triad (hypertension, bradycardia, irregular respirations). 1

Hemodynamic Monitoring

• Maintain cerebral perfusion pressure 60-70 mmHg by monitoring blood pressure and estimated ICP. 1, 2
• Avoid hypotension as it critically compromises cerebral perfusion in the setting of presumed elevated ICP. 1

Adjunctive ICP Management Measures

Concurrent Interventions to Continue

• Continue dexamethasone 4 mg QID for vasogenic edema control around the tumor. 5
• Elevate head of bed to 20-30 degrees with head in neutral position to promote venous drainage. 1
• Maintain adequate sedation and analgesia to reduce metabolic demand and prevent ICP spikes from agitation. 1
• Ensure normothermia, normoglycemia, and adequate oxygenation as these factors significantly impact ICP. 1

Critical Pitfalls to Avoid

Do Not Resume Mannitol

• Restarting mannitol after this complication would be inappropriate because the patient has already demonstrated intolerance with severe osmotic diuresis and hypernatremia. 1, 4
• If mannitol had been continued, the risk of rebound intracranial hypertension increases with prolonged use, particularly when serum osmolality rises excessively. 1

Avoid Hypotonic Fluids

• Never administer hypotonic fluids (e.g., 5% dextrose in water, 0.45% saline) as these will worsen cerebral edema by creating an osmotic gradient that draws water into brain tissue. 1, 2
• Use only isotonic (0.9% saline) or hypertonic fluids during this acute management phase. 1, 2

Do Not Restrict Fluids

• Fluid restriction is absolutely contraindicated in this patient because it would worsen hypernatremia and hypovolemia, increasing risk of cerebral infarction. 2

Definitive Management Considerations

Neurosurgical Consultation

• Urgent neurosurgical evaluation is mandatory for a patient with presumed brain tumor, altered sensorium requiring intubation, and complications from medical management. 5
• Consider ICP monitoring placement if not already present, as it would guide osmotic therapy more precisely than clinical examination alone in an intubated patient. 1
• Evaluate for surgical intervention (tumor resection, decompressive craniectomy, or CSF diversion) as osmotic therapy is only a temporizing measure. 1, 3

Realistic Outcome Expectations

• Neither mannitol nor hypertonic saline has been shown to improve long-term neurological outcomes or survival in patients with elevated ICP, despite their effectiveness in reducing ICP acutely. 1, 3
• The primary goal is prevention of secondary brain injury from herniation while definitive treatment is arranged. 1, 2