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Old 09-06-2012
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Default Help needed: Renal pharmacology

Is anyone here can explain the mechanism by mannitol causing pulmonary edema?

I'm stucked here: in my mind, mannitol increases plasma osmotic pressure, in which way keep water in capillaries around the alveolar walls, so there won't be water drained from blood vessels into alveolar space. How can pulmonary edema happen?

Thanks!
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Old 09-06-2012
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This is what I understand.

Mannitol is used ONLY for Intracerebral edema. It removes water from the brain which moves into the plasma increasing the hydrostatic pressure of plasma. Now, this increased hydrostatic pressure causes a fluid overload in the plasma which pushes water back into the lungs and pericardium (esp. in CHF pts)..Causing Pulm edema and worsening CHF.

Hope this makes sense.
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Old 09-06-2012
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im not sure about mannitol removing water just directly form brain and this contributing to pulmonary edema... it does increase oncotic pressure as it is infused IV ans starts "sucking" or draining water throughout all its path (including brain) until it reaches the kidneys. in this way it greatly increases preload and can worsen congestive heart failure.

hope this helps
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Old 09-06-2012
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Quote:
Originally Posted by megz2107 View Post
This is what I understand.

Mannitol is used ONLY for Intracerebral edema. It removes water from the brain which moves into the plasma increasing the hydrostatic pressure of plasma. Now, this increased hydrostatic pressure causes a fluid overload in the plasma which pushes water back into the lungs and pericardium (esp. in CHF pts)..Causing Pulm edema and worsening CHF.

Hope this makes sense.
Thanks for your reply! It makes sense. It's also a good way to remember the fact.

By the way, can mannitol not only be used in intracranial high pressure, it also can be applied in high intraocular pressure to prevent glaucoma from happening, and it is useful in shock and drug overdose as well.
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Old 09-06-2012
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Quote:
Originally Posted by Ramon Santos View Post
im not sure about mannitol removing water just directly form brain and this contributing to pulmonary edema... it does increase oncotic pressure as it is infused IV ans starts "sucking" or draining water throughout all its path (including brain) until it reaches the kidneys. in this way it greatly increases preload and can worsen congestive heart failure.

hope this helps
Hey! Thanks.
This makes more sense. I always wondered how it could work on one organ and not the other.
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Old 12-08-2013
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Mannitol exerts its ICP-lowering effects via two mechanisms—an immediate effect because of plasma expansion and a slightly delayed effect related to its osmotic action. The early plasma expansion reduces blood viscosity and this in turn improves regional cerebral microvascular flow and oxygenation. It also increases intravascular volume and therefore cardiac output. Together, these effects result in an increase in regional cerebral blood flow and compensatory cerebral vasoconstriction in brain regions where autoregulation is intact, resulting in a reduction in ICP. Cardiac output may subsequently decrease to lower than baseline levels because of the peripheral vasodilatation induced by mannitol and care must be taken to ensure that cerebral perfusion pressure is maintained at this time. Mannitol also establishes an osmotic gradient between plasma and brain cells, drawing water from the cerebral extracellular space into the vasculature, thereby reducing cerebral oedema. An intact blood–brain barrier (BBB) is a prerequisite for mannitol's osmotic action and cerebral oedema may be worsened by mannitol administration if the BBB is disrupted.

[Source : Contin Educ Anaesth Crit Care Pain (2012) doi: 10.1093/bjaceaccp/mkr063 ]
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