What is the role of mannitol (mannitol) in managing increased intracranial pressure (ICP) in aseptic meningitis?

Mannitol is Not Recommended for Aseptic Meningitis

Routine use of mannitol for managing increased intracranial pressure in aseptic meningitis is not recommended based on current clinical guidelines. 1

Pathophysiology and Management of ICP in Meningitis

• Patients with meningitis may develop increased intracranial pressure (ICP) due to cerebral edema, which requires appropriate management to prevent mortality 1
• Basic measures to control raised ICP and maintain cerebral perfusion pressure should be implemented, including:
  • Maintaining euvolemia 1
  • Head elevation 1
  • Avoiding hyperthermia and hyponatremia 1
  • Maintaining normocarbia and normoglycemia 1
  • Targeting appropriate mean arterial pressure (MAP) (≥65 mmHg) 1

Evidence Against Mannitol in Aseptic Meningitis

• The European Society of Clinical Microbiology and Infectious Diseases (ESCMID) explicitly states: "Routine adjuvant therapy with mannitol, acetaminophen, antiepileptic drugs or hypertonic saline is not recommended" for bacterial meningitis 1
• While mannitol is FDA-approved for reduction of intracranial pressure and brain mass 2, this indication is not specifically supported for aseptic meningitis
• Fluid restriction to reduce cerebral edema is not recommended in meningitis 1

Alternative Management Approaches

• Patients should be kept euvolemic to maintain normal hemodynamic parameters 1
• When intravenous fluid therapy is required, crystalloids are the initial fluid of choice 1
• For patients with persistent hypotensive shock, albumin should be considered 1
• Early treatment of seizures is recommended as they occur in approximately 15% of patients with acute bacterial meningitis and are associated with worse outcomes 1

Specific Management of Raised ICP in Meningitis

• Control of raised ICP is essential to prevent mortality, though the optimal method remains unclear 1
• Routine use of ICP monitoring is not recommended in meningitis 1
• For patients with suspected or proven raised ICP, basic measures to control this and maintain cerebral perfusion pressure should be implemented 1
• In cryptococcal meningitis (a form of aseptic meningitis), the principal intervention for reducing elevated ICP is percutaneous lumbar drainage, not mannitol 1

Research on Osmotic Agents in Meningitis

• Comparative studies between mannitol and hypertonic saline in bacterial meningitis models have shown that 3% hypertonic saline was superior to 20% mannitol in:
  • Lowering ICP for longer duration 3
  • Reducing leukocyte number and protein content in cerebrospinal fluid 3
  • Reducing water content in the brain 3
  • Inhibiting aquaporin 4 expression 3
  • Attenuating pathologic brain damage 3

Potential Pitfalls and Caveats

• Mannitol can cause significant side effects including:
  • Rebound phenomenon (reported in 12% of cases) 4
  • Volume overload in patients with renal impairment 5
  • Electrolyte disturbances 2
• If mannitol is used despite these recommendations, serum osmolality should be monitored to ensure it remains below 320 mOsm/L 5, 6
• Mannitol's efficacy is partly dependent on hemodynamic mechanisms that allow vasoconstriction to occur, which may be limited in certain clinical scenarios 7

In conclusion, while mannitol is indicated for reduction of intracranial pressure in certain conditions, current clinical guidelines do not support its routine use in aseptic meningitis. Basic measures to control ICP and maintain cerebral perfusion pressure, along with appropriate fluid management, should be the primary approach.