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Oral Rehydration

by Michael F. Cellucci, MD

Oral fluid therapy is effective, safe, convenient, and inexpensive compared with IV therapy. Oral fluid therapy is recommended by the American Academy of Pediatrics and the WHO and should be used for children with mild to moderate dehydration who are accepting fluids orally unless prohibited by copious vomiting or underlying disorders (eg, surgical abdomen, intestinal obstruction).

Solutions

Oral rehydration solution (ORS) should contain complex carbohydrate or 2% glucose and 50 to 90 mEq/L of Na. Sports drinks, sodas, juices, and similar drinks do not meet these criteria and should not be used. They generally have too little Na and too much carbohydrate to take advantage of Na/glucose cotransport, and the osmotic effect of the excess carbohydrate may result in additional fluid loss. The Na/glucose cotransport in the gut is optimized with an Na:glucose ratio of 1:1.

ORS is recommended by the WHO and is widely available in the US without prescription. Most solutions come as powders that are mixed with tap water. An ORS packet is dissolved in 1 L of water to produce a solution containing (in mmol/L) Na 90, K 20, Cl 80, citrate 10, and glucose 111 (standard WHO ORS) or Na 75, K 20, Cl 65, citrate 10, and glucose 75 (WHO reduced-osmolarity ORS). It can also be made manually by adding 1 L of water to 3.5 g NaCl, 2.9 g trisodium citrate (or 2.5 g NaHCO 3 ), 1.5 g KCL, and 20 g glucose. ORS is effective in patients with dehydration regardless of age, cause, or type of electrolyte imbalance (hyponatremia, hypernatremia, or isonatremia) as long as their kidneys are functioning adequately.

Premixed commercial rehydration solutions are readily available in most pharmacies and supermarkets. These solutions are effective despite having an Na:glucose ratio of about 1:3 (45 mEq/L Na to 140 mmol/L glucose). After rehydration, this solution must be replaced by a lower-Na fluid to avoid hypernatremia.

Administration

Generally, 50 mL/kg is given over 4 h for mild dehydration and 100 mL/kg for moderate. For each diarrheal stool, an additional 10 mL/kg (up to 240 mL) is given. After 4 h, the patient is reassessed. If signs of dehydration persist, the same volume is repeated. Patients with cholera may require many liters of fluid/day.

Vomiting usually should not deter oral rehydration (unless there is bowel obstruction orĀ other contraindication) because vomiting typically abates over time. Small, frequent amounts are used, starting with 5 mL every 5 min and increasing gradually as tolerated. The calculated volume required over a 4-h period can be divided into 4 separate aliquots. These 4 aliquots can then be divided into 12 smaller aliquots and given every 5 min over the course of an hour with a syringe if needed.

In children with diarrhea, oral intake often precipitates a diarrheal stool, so the same volume should be given in fewer aliquots.

Once the deficit has been replaced, an oral maintenance solution containing less Na should be used. Children should eat an age-appropriate diet as soon as they have been rehydrated and are not vomiting. Infants may resume breastfeeding or formula.

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