How ORS volume is calculated
WHO defines two weight-based fluid plans depending on hydration status, plus routine zinc supplementation for children under 5.
Normal / reference values
| WHO Plan | Setting | Volume |
|---|---|---|
| Plan A | No visible dehydration | 10 mL/kg per loose stool, given at home |
| Plan B | Some dehydration | 75 mL/kg over 4 hours, reassess |
| Plan C | Severe dehydration / shock | IV fluids urgently — ORS is not sufficient |
| Zinc, <6 months | — | 10 mg/day for 14 days |
| Zinc, ≥6 months | — | 20 mg/day for 14 days |
Clinical use
Oral rehydration therapy is first-line for acute diarrhoeal dehydration in children and adults where the patient can tolerate oral/NG fluids. Reassess hydration status frequently during Plan B; signs of severe dehydration (lethargy, sunken eyes, very slow skin pinch return, inability to drink) mean escalation to IV fluids (Plan C) without delay. Zinc supplementation, given alongside ORS, shortens the duration and severity of the current episode and reduces incidence over the following months.
Frequently asked questions
What is ORS?
Oral Rehydration Solution — a precise mix of glucose and electrolytes in water, designed to replace fluid and salts lost during diarrhoea more effectively than water alone, by using glucose to drive intestinal salt and water absorption.
How much ORS should a child drink?
For no visible dehydration (Plan A), about 10 mL/kg after each loose stool. For some dehydration (Plan B), about 75 mL/kg over the first 4 hours, then reassess.
What is the WHO ORS formula?
A standardised low-osmolarity formulation of glucose and electrolytes (sodium, potassium, chloride, citrate) in water, proven to be safe and effective across all ages for rehydration during diarrhoeal illness.
When does diarrhoea need IV fluids instead of ORS?
When there are signs of severe dehydration or shock (lethargy, sunken eyes, very slow skin pinch return, inability to drink) — WHO Plan C — ORS alone is not sufficient and IV fluids are needed urgently.
References
- WHO/UNICEF Joint Statement. Clinical Management of Acute Diarrhoea, 2004.
- World Health Organization. Pocket Book of Hospital Care for Children, 2nd ed., 2013 — Diarrhoea chapter.