Doctor Ly Kieu Diem, Head of General Internal Medicine Department at City Children's Hospital, states that in medicine, dehydration is classified based on the balance between water and electrolytes, as each type damages the body in a different way. For example, dehydration due to diarrhea (isotonic) involves fluid loss from the bloodstream, where the body loses both water and salt (sodium ions) in equivalent proportions. This condition depletes the blood vessels, leading to a drop in blood pressure and severe fatigue. The goal in this situation is to use properly mixed oresol to retain fluid in the bloodstream.

In contrast, dehydration due to fever or exercise (hypertonic) involves fluid loss through sweat and breath, with more water lost than salt. This results in concentrated blood with high salt levels, and according to the law of osmosis, water is directly drawn from inside cells to dilute the bloodstream. Consequently, brain and muscle cells shrink and dehydrate. In this case, drinking only plain water will fill the blood vessels but lacks electrolytes (sodium, potassium, chloride ions...) to draw water back into the cells via osmosis. "Plain water at this point lacks the 'force' to push into cells, so whatever is consumed is largely excreted, while cells remain 'thirsty' and shrunken. Severe cases can lead to lethargy and prolonged muscle cramps," Doctor Diem adds.

Doctor Ly Kieu Diem – Head of General Internal Medicine Department, City Children's Hospital. Photo: Provided.

In practice, people with high fever or intense exercise often experience tremors, limb weakness, and rapid fatigue. Cells at this point are not only "thirsty" but also "hungry." In medicine, there is a principle called the Q10 law: when body temperature increases by one degree, the basal metabolic rate doubles or triples.

To sustain life and combat fever, cells must burn stored energy many times faster than usual, leading to tremors and fatigue. To address these two urgent needs simultaneously, a "multi-layered fluid replenishment" approach is necessary, including hydration, energy regeneration, and water retention.

First, rapid hydration is essential, utilizing the "SGLT1 co-transporter channel" (a transport protein on the cell membrane, which helps bring glucose into cells by "hitching a ride" with sodium ions) in the small intestine to deliver a solution containing sodium and sugar. With the correct ratio of sodium and glucose, this channel acts like a high-pressure pump, pushing water across the intestinal lining into the bloodstream many times faster than plain water. Afterward, patients need timely energy supplementation to ensure the body's energy supply. Finally, patients can use micronutrients like zinc to stabilize cell membranes, helping cells "retain" water more effectively and boosting the immune system.

High fever makes cells both "thirsty" and "energy-hungry" many times faster. Illustration: Vecteezy.

Doctor Diem also notes that when the body is dehydrated due to intense exercise or fever, electrolyte solutions with sugar can be used. At this point, the body enters a state of "dynamic isotonicity," and sugar needs to be introduced into the body to perform two tasks: first, it combines with the sodium co-transporter channel to draw water into cells; second, it is activated by vitamin B3 (an important coenzyme) to immediately convert into energy, fueling depleted cells. As sugar enters, it is "burned" into energy, preventing hypertonicity or reverse thirst. Products with an appropriate sugar concentration of 4-8% (equivalent to 4g-8g/100ml of fluid) are recommended by the American College of Sports Medicine (ACSM) and help avoid putting pressure on the stomach. Electrolyte solutions with sugar concentrations exceeding 10% can cause reverse osmosis.

To effectively rehydrate during fever or exercise-induced dehydration, people can flexibly choose solutions appropriate for their body's condition, such as:

Using natural fluids: Coconut water or low-sugar fruit juices are excellent natural sources of hydration, containing inherent minerals and electrolytes, helping quench thirst and cool the body quickly in cases of mild dehydration.

Using electrolyte replenishment formulas: For cases of fever or intense exercise, electrolyte solutions with appropriate sodium and sugar concentrations, containing vitamins and zinc, can help rehydrate quickly, provide timely energy, and support the immune system's self-recovery. Hydration is needed immediately upon the onset of fever or exercise.

For severe dehydration, dehydration due to illness, acute diarrhea, or other conditions, people must strictly follow the instructions of healthcare professionals.

Yen Chi