A client with subdural hematoma was given mannitol to decrease intracranial pressure (ICP). Which of the following results would best show the mannitol was effective?
A. Urine output increases.
B. Pupils are 8 mm and nonreactive.
C. Systolic blood pressure remains at 150 mm Hg.
D. BUN and creatinine levels return to normal.
Correct Answer: A. Urine output increases.
Mannitol promotes osmotic diuresis by increasing the pressure gradient in the renal tubes. The mannitol causes the cells in the brain to dehydrate mildly. The water inside the brain cells (intracellular water) leaves the cells and enters the bloodstream as the mannitol draws it out of the cells and into the bloodstream. Once in the bloodstream, the extra water is whisked out of the skull. When the mannitol gets to the kidneys, the kidneys filter the mannitol into the urine. The mannitol again draws the water with it, and diuresis (increased urination) ensues.
Option B: Fixed and dilated pupils are symptoms of increased ICP or cranial nerve damage. Clinical suspicion for intracranial hypertension should be raised if a patient presents with the following signs and symptoms: headaches, vomiting, and altered mental status varying from drowsiness to coma. Visual changes can range from blurred vision, double vision from cranial nerve defects, photophobia to optic disc edema, and eventually optic atrophy.
Option C: There is no indication that mannitol is being given for renal dysfunction or blood pressure maintenance. Intradialytic hypotension and dialysis disequilibrium symptoms are common in hemodialysis patients. This is due to a drop in intradialytic osmolality. Mannitol can be used to prevent intradialytic hypotension by raising serum osmolality.
Option D: No information is given about abnormal BUN and creatinine levels. Much like mannitol given for oliguria of acute renal failure, mannitol can be given to increase the excretion of toxic materials, substances, and drugs. The kidneys excrete mannitol. The mannitol is poorly reabsorbed once excreted and thus draws extra water with it into the renal collecting ducts. The extra water in the renal collecting ducts can help increase the excretion of water-soluble toxic materials, substances, and drugs.
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