Can mannitol be used in subarachnoid hemorrhage patients with elevated intracranial pressure?

Mannitol Use in Subarachnoid Hemorrhage

Yes, mannitol is allowed and recommended in subarachnoid hemorrhage patients with elevated intracranial pressure, specifically when there are clinical signs of intracranial hypertension or impending brain herniation. 1

Clinical Indications for Mannitol in SAH

Mannitol should be administered when specific clinical criteria are met, not routinely based on diagnosis alone:

• Declining level of consciousness suggesting elevated ICP 1
• Pupillary abnormalities (anisocoria, bilateral mydriasis, or non-reactive pupils) 1
• Acute neurological deterioration not explained by systemic factors 1
• Documented ICP >20 mmHg if monitoring is in place 1
• Signs of impending herniation (Cushing's triad: hypertension with wide pulse pressure, bradycardia, irregular respirations) 1

Standard Dosing Protocol

Administer 0.25 to 0.5 g/kg IV over 20 minutes, repeated every 6 hours as needed. 1 The maximum daily dose is 2 g/kg to avoid adverse effects. 1

For acute intracranial hypertensive crisis with imminent herniation, higher doses of 0.5–1 g/kg IV over 15 minutes may be appropriate. 1

The onset of action occurs within 10–15 minutes, with peak effect shortly after administration and duration of 2–4 hours. 1

Evidence Supporting Mannitol in SAH

Multiple studies demonstrate mannitol's efficacy in SAH patients:

• Mannitol effectively reduces ICP in SAH patients, with studies showing significant ICP reduction when compared to baseline or placebo. 2
• Several randomized controlled trials included SAH patients and confirmed mannitol's ICP-lowering effects. 2
• Mannitol is the only ICP-lowering therapy associated with improved cerebral oxygenation, making it particularly valuable in brain injury. 1, 3
• One study showed mannitol increased cerebral blood flow in SAH patients, with effects lasting up to 24 hours when given as a bolus. 4

Comparison with Hypertonic Saline

At equiosmolar doses (approximately 250 mOsm), mannitol and hypertonic saline have comparable efficacy for ICP reduction in SAH patients. 1, 3, 5

Choose mannitol when:

• Hypernatremia is already present 1, 3
• Improved cerebral blood flow rheology is desired 1
• Improved cerebral oxygenation is the priority 3

Choose hypertonic saline when:

• Hypovolemia or hypotension is present or a concern 1, 3
• The patient requires longer duration of ICP control 3

Critical Monitoring Requirements

Serum osmolality must be checked every 6 hours and mannitol discontinued if it exceeds 320 mOsm/L to prevent renal failure. 1, 6

Electrolytes (sodium, potassium, chloride) should be monitored every 6 hours during active therapy. 1

Maintain cerebral perfusion pressure at 60–70 mmHg throughout treatment. 1

Essential Pre-Administration Steps

• Insert a Foley catheter before administration to manage the profound osmotic diuresis that follows. 1, 7
• Administer through an in-line filter and avoid solutions containing crystals. 1
• Ensure adequate volume status, as mannitol causes significant osmotic diuresis requiring volume compensation with crystalloid solutions. 1, 3, 7

Intraoperative and Perioperative Use

Mannitol is routinely used during aneurysm surgery (both clipping and endovascular coiling) for brain relaxation and acute ICP reduction. 1 The American Heart Association/American Stroke Association gives this a Class IIa, Level B-R recommendation. 1

Mannitol can be combined with brief hyperventilation, barbiturate therapy, and/or ventricular drainage to control ICP elevations during endovascular vasospasm treatment. 1

Important Clinical Caveats

Hypovolemia is particularly problematic in SAH patients because euvolemia is critical for preventing vasospasm. 1 Mannitol's potent diuretic effect can cause hypovolemia and hypotension, which may be detrimental in the SAH population where maintaining adequate cerebral perfusion is essential. 1

Rebound intracranial hypertension can occur with prolonged use or rapid discontinuation, particularly when mannitol accumulates in CSF and reverses the osmotic gradient. 1 Gradual tapering by extending dosing intervals is recommended when discontinuing therapy. 1

Avoid hypoosmolar IV fluids (such as 5% dextrose in water) during mannitol therapy, as these can exacerbate cerebral edema. 1 Use isotonic or hypertonic maintenance fluids instead. 1

Absolute Contraindications

Do not administer mannitol to SAH patients who are hypotensive due to active bleeding until hemorrhage is controlled. 1 Other contraindications include well-established anuria due to severe renal disease, severe pulmonary edema, active intracranial bleeding (except during craniotomy), and severe dehydration. 8

Evidence Limitations

The European Stroke Organisation notes that there is insufficient evidence from randomized controlled trials to make strong recommendations on ICP-lowering measures for adults with acute intracerebral hemorrhage, though this applies more to parenchymal hemorrhage than SAH. 9 Despite this limitation, in life-threatening emergencies with signs of herniation, the benefits of osmotic therapy clearly outweigh the risks. 9

Neither mannitol nor hypertonic saline has proven benefit for improving long-term neurological outcomes or survival in SAH, despite effectiveness in reducing ICP. 2, 3 These agents serve as temporizing measures before definitive treatment. 1, 3