24. Dr. Jonas, the anesthesiologist, is assisting the orthopod with Mr. J\'s sur

Question

24. Dr. Jonas, the anesthesiologist, is assisting the orthopod with Mr. J's surgery. He decides to use Mannitol along with his usual choices of anesthesia medications. Why has the physician chosen to include Mannitol as an IV medication? It 1. is an osmotic diuretic 2. prevents postoperative nausea and vomiting . reduces intracranial pressure 4. may help with laryngospasms since Mr. J. arrived to the OR in an unconscious state 5. reduces brain mass and cerebral edema 6. is always used when a patient has a skull fracture A. 1,4,5 B. 2, 3, 6 C. 1,3,5 D. 2,4,6

Explanation / Answer

C. 1, 3, 5

1. Mannitol is an osmotic diuretic

         It inhibits the Para cellular reabsorption of water and sodium chloride in the proximal tubules by reducing the osmotic driving force

3. Mannitol reduces intracranial pressure

         Mannitol has rheological and osmotic effects. After infusion of mannitol there is an expansion of plasma volume and a reduction in haematocrit and in blood viscosity, this increases Cerebral Blood Flow and increases oxygen delivery to the brain.

These rheological effects of mannitol depend on the status of pressure autoregulation. In patients with absent pressure autoregulation, infusion of mannitol increases CBF, and the decrease in ICP is less pronounced

5. Mannitol reduces cerebral oedema

         Mannitol is thought to decrease brain volume by decreasing overall water content, reduce blood volume by vasoconstriction and reduce CSF volume by decreasing water content.

Mannitol may also improve cerebral perfusion by decreasing viscosity or altering red blood cell rheology as mentioned above.

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