A patient receiving repeated mannitol boluses for intracranial hypertension has a measured serum osmolality of 322 mOsm/kg. What is the MOST appropriate action regarding further mannitol therapy?
- A Stop mannitol because efficacy is lost and the risk of acute kidney injury rises sharply above approximately 320 mOsm/kg ✓
- B Continue mannitol, since benefit persists up to 350 mOsm/kg
- C Double the mannitol dose to overcome tachyphylaxis
- D Switch immediately to furosemide monotherapy
Correct answer: A. Stop mannitol because efficacy is lost and the risk of acute kidney injury rises sharply above approximately 320 mOsm/kg
Explanation
Mannitol loses osmotic effectiveness once serum osmolality exceeds roughly 315 to 320 mOsm/kg, and beyond this level the risk of acute tubular necrosis and acute kidney injury rises substantially. Standard practice is to withhold further doses once osmolality crosses about 320 mOsm/kg. Furosemide alone does not provide the osmotic gradient across an intact blood-brain barrier and is not an equivalent substitute for mannitol in acute intracranial hypertension.
Reference: Miller's Anesthesia, 9th ed.
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