Contraction alkalosis

[medman88]

How come contraction alkalosis can be corrected with chloride?

Same thing goes for metabolic alkalosis due to nasogastric suction or vomiting, how come these can be corrected with chloride?

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[Phloston]

How come contraction alkalosis can be corrected with chloride?

Same thing goes for metabolic alkalosis due to nasogastric suction or vomiting, how come these can be corrected with chloride?

I had encountered a practice question some time ago that asked for which medication's effects most closely related to those naturally caused by cystic fibrosis. The answer was loop diuretic.

Apparently CF-induced chloride-loss through excessive sweating is similar to being on a loop. Both loops and CF induce contraction alkalosis. CF's effects apparently aren't as similar to thiazide-use because the extent of hypokalaemia in CF and loops is more comparable.

Anyway, to answer your question, I'm not 1000% sure, but my guess would be that if someone is alkalotic and hypovolaemic, it's because his or her aldosterone had been increased as a compensatory response to volume loss. PCT HCO3- reabsorption and intercalated cell proton secretion both increase concomitantly. When giving chloride, that would mean increased filtration of it through the glomerulus. Remember that there's a Cl-/base- antiporter on the apical membrane of the PCT; chloride moves into the tubular cell and base moves out into the lumen. Therefore, with increased Cl- diuresis secondary to administration, this pump would be more active based on the presence of a more favorable gradient, thereby increasing PCT base secretion. The result would be mitigation of the alkalosis.

Hope that helps. Yet again, that's just my guess.

 

[OveractiveBrain]

How come contraction alkalosis can be corrected with chloride?

Same thing goes for metabolic alkalosis due to nasogastric suction or vomiting, how come these can be corrected with chloride?

it isnt corrected with chloride, its corrected with sodium chloride, usually of the 0.9% variety, i.e. Normal Saline, i.e. fluid resuscitation. if you gave some one a chloride tablet they wouldnt get better.

Complicated process, but sit tight.

Watch this video, it explains the function of the aldosterone system pretty well. Ill paraphrase:

1. Large circulating volume, macula densa shut off, no renin, no ang ii, no aldo. Effect? not alot of sodium pulled back, so not a lot of water follows, AND... also in the Collecting Duct, not a lot of acid is lost, so not a lot of base it absorbed.

2. Small circulating volume (i.e. dehydration) causes low flow through macula densa. Macula densa turned on. Renin high. ANG II high, Aldo high. The effect? Sodium is reabsorbed in the collecting tubule, drawing water with it AND... also in the collecting duct, lots of acid is lost (under direction of aldo), and a lot of base gets absorbed.

The idea is dehydration = high aldo = acid secretion and bicarb retention. The "contraction" part of contraction alkalosis is "contraction" of the vascular volume. The "alkalosis" part of contraction alkalosis is the loss of acid under direction of increased aldo.

So if the person is dehydrated, what do you think they are going to need? HYDRATION! So... you give them volume back. Hopefully you can feel that if you had a contraction alkalosis, in order to get them back to normal, there will be an "expansion acidosis".

Now youre confusion comes from the fact that you learned in acid base studying, metabolic alkalosis is either Chloride responsive or unresponsive and that you could check a urine chloride to tell the difference. Hopefully now you can see that it means "normal saline responsive." Its called chloride responsive because thats the lab you check, not what you give.

But lets see how that works. If the kidney is working, and aldo gets reved up because of dehyrdation, what gets pulled into the body? Sodium. What goes with sodium. Water, i said that already. But... oh yeah.. chloride! So increased aldo pulls out NaCl. So what should be the urine chloride, the chloride that is lost, if aldo saves a lot of chloride? Answer: not that much. So a low urine chloride is indicative of the kidney working.

If the kidney is broken and the body is dehydrated. No matter how much aldo you put into that system, if the collecting tubule cant reabsorb NaCl, it can't reabsorb NaCl. Thus, an elevated urine chloride is indicative of a cause other than simple volume depletion.

Keep in mind I erroneously used volume depletion and dehydration interchangably. Technically, they aren't the same thing, but the idea they convey for this purpose is.

Bottom line: contraction alkalosis is from aldo, is responsive to volume expansion, and is tested by a low urine chloride, showing the kidney is working...ANY WAY you get volume down you will get a contraction alkalosis

 

[bballev]

im probably over simplifying it, and missing some crucial steps, but i remember it like this:
CF - increases cl, and so Na and h2o loss from skin.
it also increases CL concentration in cells which drags in Na.

So there is less Na delivery to macula densa +/- hypovolemia from h2o loss.

the end result is an increase in renin from JG apparatus - which would increase aldosterone. so you save Na(which is still low in serum) and dump K. Cl is also low in serum

so effectively in serum, you have low cl, low K and low Na --> which is like what a loop could do(Na/K/2Cl)

again, im sure im way over simplifying it.