What is the recommended dose of mannitol (osmotic diuretic) for a patient with increased intracranial pressure?

Mannitol Dosing for Increased Intracranial Pressure

For adults with increased intracranial pressure, administer mannitol 0.25 to 0.5 g/kg IV over 20 minutes, repeated every 6 hours as needed, with a maximum daily dose of 2 g/kg. 1, 2, 3

Standard Dosing Protocol

The recommended dose is 0.25-0.5 g/kg (approximately 250 mOsm) infused over 15-20 minutes for acute intracranial hypertension or signs of brain herniation. 1, 2 This translates to roughly 17.5-35 grams for a 70 kg patient. 1

• Smaller doses (0.25 g/kg) are as effective as larger doses (0.5-1 g/kg) for acute ICP reduction, with ICP decreasing from approximately 41 mm Hg to 16 mm Hg regardless of dose. 1, 4
• The maximum effect occurs 10-15 minutes after administration, with duration of action lasting 2-4 hours. 1, 2
• Repeat dosing every 6 hours as needed, with a maximum total daily dose of 2 g/kg. 1, 3

Pediatric Dosing

For pediatric patients, administer 1-2 g/kg body weight or 30-60 g/m² body surface area over 30-60 minutes. 3 For acute intracranial hypertensive crisis in children, larger doses of 0.5-1 g/kg given over 15 minutes may be appropriate. 1

Critical Indications for Administration

Mannitol should only be given when there are clear clinical signs of elevated ICP or impending herniation, not routinely based on imaging findings alone. 1, 2 Specific indications include:

• Declining level of consciousness 1, 2
• Pupillary abnormalities (anisocoria or bilateral mydriasis) 1, 2
• Glasgow Coma Scale motor response ≤5 1
• Acute neurological deterioration suggesting herniation 1, 2
• ICP monitoring showing sustained ICP >20 mm Hg (if monitoring is in place) 1

Essential Monitoring Parameters

Serum osmolality must be monitored and mannitol discontinued when it exceeds 320 mOsm/L to prevent renal failure. 1, 2, 3

• Check electrolytes (sodium, potassium, chloride) and serum osmolality every 6 hours during active therapy. 1, 2
• Serum osmolality increases of ≥10 mOsm are associated with effective ICP reduction. 1
• Monitor cerebral perfusion pressure (CPP), maintaining it between 60-70 mm Hg during mannitol administration. 1, 2

Hemodynamic Considerations and Contraindications

In patients with hypotension (systolic BP <90 mm Hg or MAP <70 mm Hg), hypertonic saline is superior to mannitol because mannitol causes osmotic diuresis requiring volume compensation and can worsen hypotension. 2, 5

• Initiate aggressive fluid resuscitation with crystalloids before or concurrent with mannitol if hypotension is present. 2
• At equiosmotic doses (250 mOsm), mannitol and hypertonic saline have comparable efficacy for ICP reduction. 1, 2, 5
• Mannitol is contraindicated in well-established anuria, severe pulmonary edema, active intracranial bleeding (except during craniotomy), and severe dehydration. 3

Important Clinical Caveats

Avoid excessive cumulative dosing, as this allows mannitol to cross into the brain parenchyma and increases the risk of rebound intracranial hypertension. 1, 6 The initial administration of more mannitol than absolutely needed may lead to larger doses being required to control ICP later. 6

• For cryptococcal meningitis with elevated CSF pressure, mannitol has no proven benefit and is not routinely recommended; CSF drainage by lumbar puncture is the preferred intervention. 7
• Place a urinary catheter before administration due to osmotic diuresis. 1
• Administer through a filter; do not use solutions containing crystals. 1
• Do not add mannitol to whole blood for transfusion. 3

Tapering and Discontinuation

When discontinuing mannitol after prolonged use, employ a gradual dose reduction strategy by extending dosing intervals progressively (e.g., from every 6 hours to every 8 hours, then every 12 hours) to prevent rebound intracranial hypertension. 1 Acute renal failure is an absolute contraindication requiring immediate discontinuation rather than taper. 1