Step I Mannitol vs pulmonary edema

[acciddropping]

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Can someone please explain why mannitol causes Pulm. edema? I have seen some explanations here but still not understanding 100%.

I saw one post indicating that the oncotic pressure was increased - but I didn't understand why so.

Thanks in an advance!

 

[bucks900]

My understanding is mannitol increases ECF fluid volume -> increases hydrostatic pressure -> pulmonary edema.

 

[shigella123]

I would like to know too. I would take bucks900 answer if its correct.

 

[001100010010011]

http://forums.studentdoctor.net/threads/why-does-mannitol-produce-pulmonary-edema.937227/

 

[acciddropping]

Let's see if I understand this correctly.. feel free to correct me if I am wrong -

1) Mannitol is given parenterally and since Mannitol is an osmotic diuretic, it immediately increases blood osmolarity (ie. because of the higher solutes in the blood, it draws in "non-vascular fluid" into the blood vessels, resulting in the increased "blood volume".

2) So, this is going to give you several bad outcomes -
a) Increase blood volume ==> increased workload on the Heart ==> increased BP (hence, increased hydrostatic pressure in the capillaries)
- Increased GFR => Increased volume depletion
- Capillary hydrostatic pressure is determined by BP and BV, and increased capillary hydrostatic pressure pushes more fluid out to the extracellular space - creating edema (I don't know why it's Lung specific though)

Question 1 - with Mannitol, what are the serum Na and K status? Do you get Hyponatremia or Hypernatremia? Same question for Potassium...
Quesstion 2 - why does Mannitol give you metabolic acidosis?