Neurological Disorders Q 10 - Gyan Darpan : Learning Portal
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Tuesday, 19 April 2022

Neurological Disorders Q 10

A client with a subdural hematoma becomes restless and confused, with dilation of the ipsilateral pupil. The physician orders mannitol for which of the following reasons?
     A. To reduce intraocular pressure.
     B. To prevent acute tubular necrosis.
     C. To promote osmotic diuresis to decrease ICP.
     D. To draw water into the vascular system to increase blood pressure.

Correct Answer: C. To promote osmotic diuresis to decrease ICP.

Mannitol promotes osmotic diuresis by increasing the pressure gradient, drawing fluid from intracellular to intravascular spaces. Although mannitol is used for all the reasons described, the reduction of ICP in this client is a concern. 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.

Option A: Mannitol may be used to reduce intraocular pressure when given intravenously. The mannitol is a new solute in the intravascular space, which increases the tonicity of the blood plasma. The increased tonicity of the blood plasma draws water out of the vitreous humor of the eye and into the intravascular space. Once in the intravascular space, the mannitol and associate water are excreted by the kidney. The decreased water of the vitreous humor lowers the intraocular pressure.
Option B: 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.
Option D: 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.

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