From the Guidelines
Mannitol is effective in reducing intracranial pressure (ICP) through its osmotic effect, and its use is recommended in the management of patients with spontaneous intracerebral hemorrhage, with a recommended dosage of 0.5-1 g/kg of 20% mannitol solution administered intravenously over 20-30 minutes 1. The effect of mannitol on brain osmoregulation is dose-dependent, and the optimal dose required for individual patients with intracerebral hemorrhage (ICH) can be calculated by determining hemorrhage location, hematoma volume, and pretreated ICP measurement 1. Key considerations when using mannitol include:
- Ensuring adequate hydration to prevent renal toxicity
- Monitoring serum osmolality to keep it below 320 mOsm/L
- Using a urinary catheter due to mannitol's diuretic effect
- Being cautious with repeated doses to avoid rebound ICP elevation
- Avoiding use in patients with congestive heart failure or renal failure when possible Mannitol works by establishing an osmotic gradient that draws water from brain tissue into the intravascular space, thereby reducing cerebral edema and ICP, and it also improves cerebral blood flow through reduced blood viscosity and may have free radical scavenging properties 1. However, it is essential to note that the duration of transient effects from hyperosmolar therapy in the setting of ICH is unclear, and further studies are needed to determine the effective treatment durations and whether hyperosmolar agents are effective in preventing poor outcomes 1. In terms of comparative effectiveness, a 2011 meta-analysis suggested that hypertonic saline may be more effective than mannitol in treating acutely elevated ICPs, but mannitol is still a commonly used and recommended treatment option 1. Overall, mannitol is a valuable treatment option for reducing ICP in patients with ICH, but its use should be carefully managed and monitored to minimize potential adverse effects and optimize patient outcomes.
From the FDA Drug Label
By increasing the osmotic pressure of plasma and the extracellular space, intravenously administered mannitol will induce the movement of intracellular water to the extracellular and vascular spaces. This action underlies the role of mannitol in reducing intracranial pressure, intracranial edema, and intraocular pressure.
The effect of Mannitol on brain osmoregulation is to reduce intracranial pressure and intracranial edema by increasing the osmotic pressure of plasma and the extracellular space, which induces the movement of intracellular water to the extracellular and vascular spaces 2.
- Key points:
- Mannitol increases osmotic pressure of plasma and extracellular space
- Induces movement of intracellular water to extracellular and vascular spaces
- Reduces intracranial pressure and intracranial edema
- Reduces intraocular pressure
From the Research
Effect of Mannitol on Brain Osmoregulation
- Mannitol is widely used to treat patients with high intracranial pressure and/or cerebral edema by increasing serum osmolarity, creating an osmotic gradient that draws excess water from the brain 3.
- The administration of mannitol can increase the osmolarity gap between the brain and the blood, leading to the removal of excess water from the brain 3.
- Long-term administration of mannitol can induce significant increases in cerebrospinal fluid osmolarity, which may be an undesirable and potentially dangerous effect 3.
- The ability of mannitol to reduce cerebral edema is related to the total amount of intravenous fluid replacement, implying that careful monitoring of fluid administration is necessary 4.
Mechanisms of Mannitol in Brain Osmoregulation
- Mannitol works by creating an osmotic gradient that draws cerebral edema fluid from brain tissue into the circulation 5.
- Hyperosmolar solutions, including mannitol, are effective in reducing elevated intracranial pressure through two distinct mechanisms: plasma expansion and the creation of an osmotic gradient 5.
- Mannitol can exert additional effects on brain circulation through a possible improvement in blood rheology 6.
Comparison with Other Osmotic Agents
- Equimolar doses of mannitol and hypertonic saline are equally effective in reducing intracranial pressure in patients with brain injury 6.
- Mannitol and hypertonic saline have different effects on serum sodium, osmolality, and urine output, which should be considered when choosing between the two treatments 6, 7.
- Both mannitol and hypertonic saline are effective and have an acceptable risk profile for use in the treatment of elevated intracranial pressure secondary to brain edema 7.