This issue of Nephsap has an interesting editorial about the nomenclature of this entity and the pathophysiology behind it. Most of the time, severe volume contraction, leads to lactic acidosis, and not metabolic alkalosis unless you have a selective chloride depletion. Hence, the authors feel that this entity should be really called Chloride Depletion Metabolic Alkalsois (CDMA).
Studies summarized showed that such alkalosis corrected more when Na or any other cation was supplemental Cl rather than any other anion. CDMA was produced by gastric aspiration, chloruretic diuretics , NaNo3 infusions, and post hypercapnia and all got better with Cl- repletion and not Na or K replacements.
So CDMA is corrected by selective Cl repletion despite maintained or increasingly negative Na or K balance, continued Hc03 loading and high levels of Ang II.
It was not corrected by Na or K repletion without Cl-. It was hard to correct with Cl- alone in abnormal renal function. What happens is the distal nephron in the collecting duct ensures a bicarbonate diuresis in response to Cl repletion.
Take a look in more detail at Nephsap March 2011
Also other good ref:
http://www.ncbi.nlm.nih.gov/pubmed/4875677
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