Mannitol infusion is being considered for cerebral edema in a patient with severe left ventricular dysfunction and pulmonary congestion. The main concern with mannitol in this setting is:
- A It rapidly crosses the blood brain barrier and worsens cerebral edema
- B It causes profound hypokalemia that precipitates arrhythmias
- C It first expands extracellular fluid volume, acutely increasing preload before diuresis begins ✓
- D It lowers serum osmolality, shifting water into neurons
Correct answer: C. It first expands extracellular fluid volume, acutely increasing preload before diuresis begins
Explanation
Before its diuretic phase, mannitol is retained in the extracellular compartment and draws water out of cells, transiently expanding intravascular volume and raising preload. In heart failure this can precipitate pulmonary edema, which is why mannitol is relatively contraindicated in established pulmonary congestion or anuria. Mannitol does not cross an intact blood brain barrier, which is precisely how it lowers intracranial pressure, and it raises rather than lowers serum osmolality.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.