Mannitol 20%

How it works

As an osmotically active solute that does not cross the intact blood-brain barrier, it draws water from brain tissue into the intravascular space and promotes an osmotic diuresis.

Prescribing in practice

• The concentrated solution can crystallise, so it must be inspected and administered through an in-line filter, and extravasation causes tissue damage.
• It is contraindicated in established anuria, severe heart failure and significant pulmonary oedema, and can cause an initial circulatory overload followed by dehydration.
• Repeated dosing risks electrolyte disturbance, hyperosmolality and acute kidney injury.

Monitoring

Monitor fluid balance, serum osmolality and electrolytes, renal function and cardiorespiratory and neurological status closely during use.

Counselling the patient

• The team should use an in-line filter and inspect the solution for crystals before infusion.
• Track urine output and serum osmolality to guide repeat dosing.
• Watch for signs of fluid overload or worsening renal function.

Evidence & guidelines

Osmotic therapy with mannitol is a long-established intervention for acutely raised intracranial pressure in neurocritical care.