Mannitol dose quiz (see notes on diuretics)

Acute renal failure fluid needs quiz (see ARF notes)

• Multiple choice review questions : Review 1
• Multiple choice review questions : Review 2
• Multiple choice review questions : Review 3
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Mannitol dose quiz

Tessa is having seizures suspected to be induced by cerebral edema. She weighs 50 kg. You plan to deliver a dose of 1g/kg IV of mannitol to Tessa. How much fluid might this mobilize from her intracellular space to the vascular space? By what percent will this increase her blood volume?

Mannitol is usually dosed at 1 to 2 grams per kilogram given IV.

The dose for Tessa is 50g to 100g.

To give 50 grams how much of a 25% solution is required?

25 % = 25 g per 100 ml

so 200 ml will contain the 50 grams required for this dog

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Each 50 ml of 25% mannitol shifts 225 ml of water from the intracellular to extracellular compartment. (I found these numbers in a book.... I do not know how they were derived.)

This dog is receiving 200 ml which will result in a fluid shift of 900 ml (4 x 225 ml).

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Tessa's blood volume is 50kg x 90ml/kg = 4,500ml

the mannitol can expand her blood volume by 1,100 ml

200 ml (volume infused)+ 900 ml (volume shifted from cells) = 1,100 ml

1,100 ml / 4,500 ml = 24.4% expansion of volume

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The entire 1,100 ml of fluid will NOT ALL be excreted as urine. Some will move back into the cells (remember that fluid shifts are dynamic) some will be filtered by the kidney and reabsorbed, some will be filtered and NOT reabsorbed and thus will be excreted in urine.

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The purpose of this example is to demonstrate the magnitude of fluid shifts that can occur in response to osmotic diuretics. Other classes of diuretics do not cause this temporary expansion of blood volume as they move fluid from the extracellular fluid compartment.

Animals that cannot tolerate a rapid expansion of blood volume, such as patients with cardiac disease may develop worsening of cardiac dysfunction (for example may develop pulmonary edema.) Patients that have acute renal failure and do not filter and excrete the mannitol and the water that it drew from the cells will become hypertensive.

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ARF fluid quiz

A 25 kg dog is 10% dehydrated based on physical parameters. What volume of fluid is required to rehydrate this patient?

25 kg x 0.1 (10%) = 2.5 kg deficit of fluid

1,000 ml is required to replace one kg of fluid deficit

2.5 kg x 1,000 ml/kg = 2,500 ml of fluid is required to rehydrate this patient.

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