Oral rehydration solution (ORS) remains the first-line therapy to replenish lost body water and salts due to gastroenteritis. Global deaths due to diarrhoeal disease have substantially reduced – thanks to improved sanitation, rotavirus vaccine enrolment, and oral hydration therapy. Since its inception, ORS has remained an invaluable treatment option for children with dehydration of varying degrees. However, in today’s discussion, we take an insightful assessment to rethink what you know about ORS. Let’s get started.
2019 WHO Global Health estimates showed that diarrhoeal diseases were among the top ten causes of death in low- and lower-middle-income countries. However, these deaths have substantially reduced when compared to the global estimates in 2000. ORS, the gold standard oral rehydration therapy, remains an invaluable treatment until we’ve eliminated all diarrhoeal diseases.
By WHO standard, any ORS regimen should contain equal amounts of both sodium and glucose. It should contain citrate, potassium and chloride at specified concentrations. At a standard osmolarity of 245 millimoles per litre, ORS comprises glucose 13.5g, trisodium citrate dihydrate 2.9g, sodium chloride 2.6g, and potassium chloride 1.5g. The concentration equivalents are 75, 75, 10, 20, and 65 millimoles per litre.
It isn’t a coincidence that the glucose concentration is equal to that of sodium. It has implications that dwell down on how water moves across the intestinal lumen to replenish the contracted blood volume during dehydration (hypovolaemia).
Water moves across the intestinal lumen by passive absorption through channels that: (1) exchange hydrogen for sodium (sodium/hydrogen exchange ports), (2) transport sodium together with organic solutes like glucose. More still, water may diffuse across the lumen by an electrochemical gradient. Any disease that blocks or reverses any of the above transport channels will lead to diarrhoea. It is, however, fascinating to understand that gastroenteritis – the most common cause of diarrhoea in children blocks or reverses all the channels above except the one that couples sodium with glucose to facilitate water absorption. Equimolar amounts of sodium and glucose utilise the preserved transport channel that gastroenteritis hasn’t distorted.
Any other fluid that either contains more or less glucose compared to sodium may worsen the diarrhoeal episode. It is due to an imbalance in the solute concentrations within the intestinal lumen. The glucose-sodium co-transporter channels cannot use one without the other. These fluids include fruit juice and soft drinks.
Vomiting and diarrhoea cause potassium depletion in the body. It’s why all ORS formulations contain potassium to counteract the losses. Citrate helps the luminal border cells regenerate – Zinc fastens this process. When there’s a loss of potassium and sodium, chloride, one of the main body electrolytes, follows suit. It explains the inclusion of the chloride salts of potassium and sodium to replenish the stores.
Oral rehydration solution is cheap, affordable, and safe with proven efficacy to treat dehydration compared to intravenous fluid therapy among patients with mild-to-moderate dehydration. Read more about oral rehydration therapy from here.