What caution is associated with mannitol use in TBI?

• A. It has no risk in renal impairment
• B. It always increases blood pressure
• C. It rapidly causes hyponatremia in all patients
• D. It can cause hypovolemia/hypotension; monitor osmolality; renal risk

Answer: (D)

Mannitol acts as an osmotic diuretic to lower intracranial pressure by drawing water from brain tissue into the blood. That same diuretic effect can rapidly reduce circulating volume, leading to hypovolemia and possibly hypotension. In a brain-injury patient, maintaining adequate circulating volume and cerebral perfusion pressure is crucial, so this potential drop in blood pressure is a major safety concern.

Because the body is exposed to a large osmotic load, monitoring serum osmolality is essential to avoid creating an overly hyperosmolar state, which can cause further complications. Mannitol can also put stress on the kidneys, so watching renal function and urine output is important to catch any signs of renal risk early.

Electrolyte disturbances can occur with mannitol, but hyponatremia is not an inevitable or universal outcome. The most consistent cautions are volume status, osmolality management, and renal risk, which is why this option best reflects the key safety considerations in using mannitol for TBI.