Diarrhea can cause metabolic acidosis while hyperemesis can cause metabolic alkalosis. Does this, along with other electrolyte differences between diarrhea and vomiting, necessitate different oral rehydration solutions?
Interesting question. My first thought was whether the rehydration for vomiting may need to be intravenous?
I tried to find the relevant answer including in the 2008 WHO Model Formulary, but couldn't. It will be interesting to read the responses of others.
The fluid loss in vomiting is rich in acid while the fluid loss in diarrhea is rich in alkali, however the oral rehydration solution used in both condition in most countries is the same.
For vomiting, the efficacy of an oral solution is dependent on whether it is absorbed. Generally, intravenous isotonic solutions are needed such as saline. However, a common mistake is not adding KCl to the solution since vomiting causes a large deficit of K+ due to renal losses. Simply giving saline without KCl only partially corrects the associated metabolic alkalosis. Once KCl is added, intracellular protons (H+) move out of cells in exchange for K+. The H+ then binds the bicarbonate, which is converted into water and CO2, correcting the alkalosis. Since NaCl and KCl are salts, it is not palatable and may worsen vomiting.
For the normal anion gap metabolic acidosis (NAGMA) due to diarrhoea, ORS contain K+, Na+ and a citrate buffer. Clearly, one cannot use this type of solution in a vomiting patient due to the citrate buffer which may worsen the metabolic alkalosis.
Yazied Chothia I sincerely thank you very much for your very well thought-out and well-explained answer. It is a huge help and it really means to me. Thank you!
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