Comments on: 15 days at the VA – day 6

By: rcentor

rcentor — Tue, 22 Dec 2009 14:29:52 +0000

Please read the article that I linked to yesterday. These patients actually have decreased arterial volume. They do also have increased aldosterone, but that has no impact on serum sodium. Aldo does not adjust free water excretion. Hyponatremia results from decreased free water excretion.

By: pcb

pcb — Tue, 22 Dec 2009 13:40:54 +0000

shouldn't decreased arterial volume also stimulate aldosterone secretion which should cause retention of sodium to match the ADH related retention of water? (if the patient is not drinking too much free water)

By: cory

cory — Tue, 22 Dec 2009 13:14:22 +0000

Sorry. when I used the term intravascular I was referring to arterial blood volume, but my question still remains.
What constitutes decreased effective arterial blood volume? How do you measure it in a complex system of pipes that are quite elastic and subject to all sorts of forces?
Low blood pressure? But many of these people don't have low blood pressure – unless you are saying it is relatively low, which sort of begs the question.
You may tell me increased BUN/Cr or decreased Fe Na but those are quite indirect measurements and are neither sensitive nor specific.
Yes , we often have increased ADH in "low EABV states" but what does that specifically correlate with? What measurement?
Low PCWP? Working in intensive care for many years I found that quite unreliable
In the absence of acute bleeding, it's still unclear to me what constitutes decreased effective arterial blood volume in a chronic situation.