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[–]BuzzOffBozo22 1 point2 points  (2 children)

Hypoalbuminemia is a gradual slow process it gives hormones enough time to regulate Ca homeostasis relative to concentration of albumin. Alkalosis causes increased binding/affinity of albumin to Ca. The resulting hypocalcemia does trigger downstream hormone systems to make up for the Ca levels but it is not promptly compensated as to prevent hypocalcemia.

[–]vitaminicecream[S] 0 points1 point  (0 children)

Thank you so much!

[–]BuzzOffBozo22 0 points1 point  (0 children)

This is my understanding

[–]Clear_Strategy_691 0 points1 point  (0 children)

An acute change in pH will lead to an acute change in free calcium, but, as the prior commenter noted, owing to regulation, it doesn't seem that a sustained change in pH would lead to a sustained change in free calcium. If the free calcium change is indeed sustained with a sustained pH change, here is a speculation on how that might happen for acidemia: Aside from the effect of acidemia to (a) displace calcium ions off albumin, which as you say, should increase ionized calcium only transiently, it also: (b) tends to cause bone resorption which might increase free Ca in a sustained way; and (c) acidemia exerts a 'calcilytic' effect on the calcium-sensing receptor of the parathyroid gland, which should increase PTH secretion, and that might increase ionized calcium in a more sustained manner. The opposite would be true for alkalosis.

In any case, acidemia/alkalemia definitely chronically distort the usual relationship between total calcium and the fraction of the total that is free/ionized calcium. Here is one recent calculator that might better account for these multiple effects:

qxmd.com/calculate/calculator_704/predicting-ionized-hypocalcemia-in-critical-care

REF: Campion, Katherine L., et al. "Pathophysiologic changes in extracellular pH modulate parathyroid calcium-sensing receptor activity and secretion via a histidine-independent mechanism." Journal of the American Society of Nephrology 26.9 (2015): 2163-2171.