Oral rehydration therapy (also called oral rehydration salts or oral electrolyte solutions) is a simple, cheap, and effective treatment for diarrhoea-related dehydration. It consists of a solution of salts and other substances such as glucose, sucrose, citrates or molasses, which is administered orally.
Oral rehydration therapy is widely considered to be the best method for combating the dehydration caused by diarrhea and/or vomiting.
Various diseases cause damage to the intestine, allowing water to flow from the blood into the intestine, depleting the body of both fluid and electrolytes. This may be
* a direct destruction of the cells lining the intestine (the enterocytes), * a toxic effect causing them to lose their microvilli (the brush border), * a toxic effect (by an enterotoxin) causing them to secrete water.
In the human body, water is absorbed and secreted passively; it follows the movement of salts, based on a principle called osmosis. So, in many cases, diarrhea is caused by intestine cells secreting salts (primarily sodium) and water following passively along.
Simply drinking water is ineffective for 2 reasons: (1) the large intestine is usually secreting instead of absorbing water, and (2) electrolyte losses also need compensating. As such, the standard treatment is to restore fluids intravenously with water and salts. This requires trained personnel and materials which are not sufficiently available in the Third World.
However, it was discovered that the body can absorb a simple solution containing both sugar and salt. The dry ingredients can be mixed and packaged, and then the solution can be prepared and delivered by people with minimal training. One diarrhea mechanism (like in cholera, which is a very dangerous form of profuse diarrhea), is an enterotoxin interfering with enterocyte cAMP and G-proteins. However, water can still be absorbed by cAMP-independent mechanisms, like the SGLT-transporter (sodium and glucose transporter, of which two types exist). This is achieved by combining salts and glucose.
Oral rehydration can be accomplished by drinking frequent small amounts of an oral rehydration salt solution.
It is important to rehydrate with solutions that contain electrolytes, especially sodium and potassium, so that electrolyte disturbances may be avoided. Sugar is important to improve absorption of electrolytes and water, but if too much is present in ORS solutions, diarrhea can worsen. Oral rehydration does not stop diarrhea, but keeps the body hydrated and healthy until the diarrhea passes.
Often sodium bicarbonate or sodium citrate is also added to formulas in an attempt to revert metabolic acidosis.
Adults and children with dehydration who are not vomiting can be allowed to drink these solutions in addition to their normal diet. People who are vomiting should be fed small frequent amounts of ORS solution until dehydration is resolved. Once they are rehydrated, they may resume eating normal foods when nausea passes.
Vomiting itself does not mean that oral rehydration cannot be given. As long as more fluid enters than exits, rehydration will be accomplished. It is only when the volume of fluid and electrolyte loss in vomit and stool exceeds what is taken in that dehydration will continue.