In this episode, I’ll discuss the administration of mannitol for elevated intracranial pressure.
The definitive treatment for elevated intracranial pressure is to fix the underlying cause. Common causes are traumatic brain injury, intracranial hemorrhage, CNS infection, or intracranial neoplasm.
Until definitive treatment can be arranged, temporary treatments to lower intracranial pressure such as mannitol may be employed.
When given as a bolus, mannitol is an osmotic diuretic that does not cross the blood-brain barrier. Mannitol lowers intracranial pressure by osmotically drawing free water out of the brain and into circulation where it can be eliminated. If given as a continuous prolonged infusion, mannitol will eventually cross the blood-brain barrier and have no effect on intracranial pressure. This means that the rate of administration must be fast enough in order to get the desired effect.
The typical bolus dose for mannitol to lower ICP is 1 g/kg administered over 30 minutes. Mannitol should have an onset time of 15-30 minutes and a duration of up to 6 hours when given this way.
Mannitol is needed STAT
Often, the decision to administer mannitol is made due to an acute, severe change in the patient’s neurological status that leads the physician/provider to believe the intracranial pressure is too high. The request is usually for mannitol to be given “STAT.” Variability in dose and administration technique can cause significant delays between the time mannitol is needed and the time it actually gets administered.
Administration
Mannitol is available in 25% 50mL vials (12.5g per vial) and 20% 500mL bags (100g per bag). Both preparations may crystallize at room temperature. Mannitol should be carefully inspected for crystals before it is administered, and it should be administered with an in-line filter, typically 5 micron or smaller in size.
Ideally, the 1g/kg dose of mannitol is administered as a bolus over 30 minutes. Comparing the available forms of mannitol against this dosing regimen, it becomes clear that the 12.5g vials are not practical. For a 75kg patient, the nurse would have to draw up six 12.5g vials and stand at the bedside pushing them for 30 minutes.
That leaves the 20% 500mL infusion as the most reasonable option for delivering a 1g/kg bolus of mannitol over 30 minutes.
While the 20% infusion option is the best, it too has some drawbacks. Many patients will receive less than 100g, and it is somewhat unusual to dispense an infusion that contains more than the intended dose of an IV medication. It is also not practical to transfer the exact amount of mannitol needed to a second container due to the time this takes and the urgency of the need for mannitol.
Fortunately, features available on “smart pumps” can facilitate administering the exact amount of mannitol needed. Smart pumps are able to specify a limit on the total volume of any medication that is to be infused, regardless of the rate of infusion. Nurses at my institution routinely use this feature on all IV infusions to ensure that the infusion rate is assessed frequently. In the context of a mannitol infusion, the nurse can set the pump to stop administration after the exact amount of mannitol has been delivered.
Check your smart pump library to make sure that the mannitol entry and limits allow for administration of a weight-based bolus over 30 minutes as needed to manually figure out how to run the infusion outside of the pump library can delay administration and increase the chance of an error.
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Is an in-line filter enough if crystals are visible or should the crystals be dissolved before administration? If they need to be dissolved, what is the quickest and safest way to warm the solution?