A 62-year-old man is brought to the emergency department with a 1-hour history of sudden-onset severe headache and progressive lethargy. Medical history is significant for hypertension. Temperature is 37 C (98.6 F) , blood pressure is 180/95 mm Hg, pulse is 60/min, and respirations are 10/min. On physical examination, the patient responds to painful stimuli only but does not move his left extremities to pain. The right pupil is larger than the left and is sluggish to react. CT scan of the head shows right basal ganglia hemorrhage causing compression of the right lateral ventricle and shift of the midline structures. Blood cell counts, serum chemistry studies, and coagulation profile are within normal limits. Endotracheal intubation is performed for airway protection, and an intravenous bolus of mannitol is administered. Which of the following is the most likely acute effect of the medication given to this patient?

Question

Quizplus · Accepted Answer

This patient with an acute intraparenchymal hemorrhage resulting in a midline shift was treated with mannitol. Mannitol, a sugar alcohol, is an osmotic diuretic that increases plasma osmolality, resulting in the flow of water down its concentration gradient from the intracellular space to the plasma. It does not cross the blood-brain barrier, therefore it is frequently used to treat elevated intracranial pressure because it draws water from the brain parenchyma into the vasculature, reducing intracranial volume and pressure. As a result of the plasma volume expansion, the serum sodium concentration decreases (dilutional hyponatremia) and renal blood flow increases, resulting in increased glomerular filtration and renal tubular flow. Mannitol is freely filtered at the glomerulus but is not resorbed by the renal tubules; the resultant hyperosmolar glomerular filtrate reduces tubular reabsorption of free water, causing increased diuresis (Choices D and E). Dehydration (decreased total body free water) can eventually result if free water is not replaced after mannitol therapy, resulting in hypernatremia, elevated glomerular filtrate osmolality, and reduced renal tubular blood flow. However, this is a delayed effect that does not occur acutely following administration (Choices B and C). Educational objective: Mannitol increases plasma osmolality, leading to the flow of water down its concentration gradient from the intracellular space to the plasma, helping to reduce intracranial pressure. The resulting plasma expansion also reduces serum sodium levels and increases glomerular filtration/tubular flow. Mannitol is freely filtered and not reabsorbed by the renal tubules, resulting in a hyperosmolar glomerular filtrate.

A 62-Year-Old Man Is Brought to the Emergency Department with a 1-Hour