Hyperosmolar therapy

Hyperosmolar therapy is widely used in neuro-anesthesia and neurological intensive care. In neurosurgical patients, hyperosmolar therapy is known to lower intracranial pressure (ICP) after traumatic brain injury and is associated with decreased mortality rate and is thus the gold standard for treatment of patients with elevated ICP. Mannitol and hypertonic saline (HTS) are the most commonly used hyperosmotic/hyperosmolar agents in neurosurgical patients. These two agents have many similar mechanisms of action on the brain: predominantly, an increase in plasma osmotic pressure drawing water from the intracellular spaces with a subsequent decrease in volume of both edematous and normal brain tissue, and an improvement in blood rheology, both leading to a decrease in ICP and improvement of cerebral perfusion and oxygen delivery to the brain. Although the reduction in ICP has been consistently demonstrated with both mannitol and HTS, there is a suggestion that HTS provides a more robust and durable effect in lowering ICP than mannitol, provides more hemodynamic stability, and does not cause a rebound increase in ICP. The choice of hyperosmolar agent should be guided by the nature of the disease, patient’s comorbidities, familiarity with the pharmacokinetic and pharmacodynamics of both agents, and awareness of their side effects. In neurocritical care, both mannitol and HTS are indicated for patients with neurologic deterioration and an increase of ICP higher than normal. Future research examining the effect of hyperosmolar therapy on the delayed neurological outcome is warranted.