Tuesday, February 28, 2012

Topic Discussion: Old and New view of "Contraction Alkalosis"

Older View ( traditional taught to us)
Name: Contration Alkalosis
Prevalence: Most common cause of metabolic alkalosis
Primary Insult: Change in Extracellular volume
View Then: increase in sodium absorption in the proximal tubule led to obligatory bicarbonate absorption rather than chloride.
View Then: Correct the volume with expansion of ECF.
Culprit: Volume

Venue to play a major role: Proximal tubule
Dogma: Volume expansion is the key and correct with any volume expander to correct the alkalosis.

Newer View( the new data)
Name: Chloride Depletion Alkalosis
Prevalence: Most common cause of metabolic alkalosis
Primary insult: Chloride depletion
View Now: chloride depletion is the problem and not volume and Na depletion. repeating with Chloride will correct the insult.
View Now: Correct the volume and expand ECF but also make sure it has a Chloride containing fluid as just albumin or Na Bicarbonate will not correct this problem.
Culprit: Chloride depletion

Venue to play a major role: Cortical Collecting Duct
Dogma: Chloride administration without volume expansion is necessary and sufficient to correct this alkalosis.

What happens: There is chloride depletion which leads to reduced Cl delivery to cortical collecting duct(CCD)__>  pendrin activity increases secretion of Hc03 is limited as there isn't much Cl that can be absorbed in exchange.  You deliver more Cl to the CCD, pendrin activity shuts down and Hco3 is released and alkalosis starts resolving. In the principal cell, the K is exchanged for Na and there is kaliuresis.
The urinary Cl is low, Hco3 is low, Ph is low and K is high
The serum Cl is low, Hco3 is high and ph is alkaline

Pendrin is a newly discovered Cl/ HCo3 exchanger on the luminal side of the CCD's intercalated cells.  It is very dependent on the Cl delivery to CCD. So low chloride diet, Chloride depletion alkalosis increase its activity and high chloride diet, met acidosis, resp acidosis and K depletion alkalosis decreases pendrin activity.

Take a look at the recent editorial from JASN and original article:

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