Merck Manual

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Oral Rehydration


Michael F. Cellucci

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Reviewed/Revised Apr 2023

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 World Health Organization (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 Intestinal Obstruction Intestinal obstruction is significant mechanical impairment or complete arrest of the passage of contents through the intestine due to pathology that causes blockage of the bowel. Symptoms include... read more Intestinal Obstruction ).

Solutions for Oral Rehydration

Oral rehydration solution (ORS) should contain

  • Complex carbohydrate or 2% glucose

  • 50 to 90 mEq/L (50 to 90 mmol/L) of sodium

Sports drinks, sodas, juices, and similar drinks do not meet these criteria and should not be used. They generally have too little sodium and too much carbohydrate to take advantage of sodium/glucose cotransport, and the osmotic effect of the excess carbohydrate may result in additional fluid loss. The sodium/glucose cotransport in the gut is optimized with a sodium:glucose ratio of 1:1.

Oral rehydration solution is recommended by the WHO and is widely available without a 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 the following (in mmol/L):

  • Standard WHO ORS: Sodium 90, potassium 20, chloride 80, citrate 10, and glucose 111

  • WHO reduced-osmolarity ORS: Sodium 75, potassium 20, chloride 65, citrate 10, and glucose 75

Premixed commercial rehydration solutions are readily available in many pharmacies and supermarkets. These solutions are effective despite having a sodium:glucose ratio of about 1:3 (45 mEq/L [45 mmol/L] sodium to 140 mmol/L glucose).

Administration of Oral Rehydration

Generally, 50 mL/kg is given over 4 hours for mild dehydration and 100 mL/kg for moderate dehydration. For each diarrheal stool, an additional 10 mL/kg (up to 240 mL) is given. After 4 hours, the patient is reassessed. If signs of dehydration persist, the same volume is repeated. Patients with cholera Fluid replacement Cholera is an acute infection of the small bowel by the gram-negative bacterium Vibrio cholerae, which secretes a toxin that causes copious watery diarrhea, leading to dehydration, oliguria... read more may require many liters of fluid per day.

Vomiting usually should not deter oral rehydration (unless there is bowel obstruction or other contraindication to taking fluid by mouth) because vomiting typically abates over time. Small, frequent amounts are used, starting with 5 mL every 5 minutes and increasing gradually as tolerated. The calculated volume required over a 4-hour period can be divided into 4 separate aliquots. These 4 aliquots can then be divided into 12 smaller aliquots and given every 5 minutes 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 sodium 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.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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