Dehydration can occur due to many reasons. The most common reasons to become dehydrated are vomiting, diarrhea and lack of oral intake. Doctors prefer to use the term “intravascular volume depletion”, however, it sounds too long and complicated. For the sake of simplicity I will consider “dehydration” and “intravascular volume depletion” equivalent terms.
Many people believe that drinking water or beverages like juices or tea are good to rehydrate a dehydrated person. The problem is that when someone becomes dehydrated he or she loses salts together with water. The content of salts in the above mentioned solutions is minimal. As a consequence of that, the body loses salts and water and gets back water. The sodium (the main electrolyte in the extracellular fluid) becomes diluted. Too much sodium dilution can cause problems like headaches and lack of balance. Severe sodium dilution can cause seizures and death.
In addition to what I have just mentioned, when the body is dehydrated, there is a hormone called anti-diuretic hormone (ADH) which is secreted. This hormone does not allow water to leave the body. This can have the effect of diluting further the sodium in the body. This is why, we need the right amount of salts when rehydrating.
There are over the counter solutions available can can help with the rehydration process. A good salty broth can also do the trick. However, if the dehydration is severe and vomiting does not allow proper oral rehydration, you might need to go to the closest emergency department before there is kidney failure or before you collapse
Marco A. Ramos MD