What causes dehydration in a child with diarrhoea?
WHO defines diarrhoea as the passage of unusually loose or watery stools, usually at least three times in 24 hours — but it is the consistency, not the number, that matters most. Frequent formed stools are not diarrhoea, and the loose 'pasty' stools of exclusively breastfed babies are normal.
During diarrhoea the child loses water and electrolytes (sodium, chloride, potassium and bicarbonate) in liquid stool, and also through vomit, sweat, urine and breathing. Dehydration develops when these losses are not replaced. Stool losses range from about 5 ml/kg/day (near normal) to 200 ml/kg/day or more. WHO lists rotavirus and enterotoxigenic *E. coli* among the most common causes of dehydrating diarrhoea.
How does WHO classify dehydration — no, some or severe?
The WHO assessment chart (Table 1 of the WHO diarrhoea manual) uses four bedside signs. Column A describes a child with no signs of dehydration, column B some dehydration and column C severe dehydration.
| Sign | A — No signs of dehydration | B — Some dehydration | C — Severe dehydration |
|---|---|---|---|
| Condition | Well, alert | Restless, irritable | Lethargic or unconscious |
| Eyes | Normal | Sunken | Sunken |
| Thirst | Drinks normally, not thirsty | Thirsty, drinks eagerly | Drinks poorly or not able to drink |
| Skin pinch | Goes back quickly | Goes back slowly | Goes back very slowly (more than 2 seconds) |
| Treatment plan | Plan A | Plan B | Plan C |
- Severe dehydration: two or more signs from column C.
- Some dehydration: not severe, but two or more signs from column B (and C).
- No signs of dehydration: neither of the above.
| Assessment | Deficit as % of body weight | Deficit in ml/kg |
|---|---|---|
| No signs of dehydration | Less than 5% | Less than 50 ml/kg |
| Some dehydration | 5–10% | 50–100 ml/kg |
| Severe dehydration | More than 10% | More than 100 ml/kg |
WHO's three categories replace the older 'mild, moderate, severe' textbook terms. Exam stems still use both, so map mild ≈ no signs, moderate ≈ some and severe ≈ severe — the deficit bands above (under 5%, 5–10%, over 10%) make the translation easy.
What is WHO Plan A for a child with no signs of dehydration?
Plan A is home therapy to prevent dehydration and malnutrition. WHO frames it as four rules for the mother:
- Give more fluids than usual (ORS, home fluids, breast milk) to prevent dehydration.
- Give zinc daily for 14 days (India): 10 mg if under 6 months, 20 mg if 6 months or older (WHO allows 10–14 days).
- Continue to feed the child — breastfeeding should always continue; food should never be withheld or diluted.
- Return to a health worker if there are signs of dehydration or other problems.
| Age | Amount after each loose stool |
|---|---|
| Under 2 years | 50–100 ml (a quarter to half a large cup) |
| 2 up to 10 years | 100–200 ml (half to one large cup) |
| Older children and adults | As much as they want |
How is some dehydration treated under Plan B?
Plan B is supervised oral rehydration therapy at the health facility. The approximate ORS requirement for the first 4 hours is the child's weight in kg × 75 ml. If the weight is unknown, age-based estimates are used; if the child wants more and there are no signs of over-hydration, give more.
ORS in the first 4 hours (ml) ≈ 75 × body weight (kg)
Example: a 10 kg child with some dehydration needs about 750 ml of ORS over 4 hours.
- Puffy eyelids are a sign of over-hydration — stop ORS, give breast milk or plain water, and do not give a diuretic.
- Reassess after 4 hours with the same chart: severe signs → Plan C; still some dehydration → repeat Plan B and start food; no signs → Plan A at home.
- Start zinc as soon as the child can eat after the initial 4-hour rehydration.
- Send the mother home with enough ORS packets for two days.
How are IV fluids given in severe dehydration (Plan C)?
Severe dehydration needs rapid intravenous rehydration — start IV fluids immediately. If the child can drink, give ORS by mouth until the drip is running. WHO's preferred fluid is Ringer's lactate; normal saline may be used if RL is unavailable.
| Age | First give 30 ml/kg in | Then give 70 ml/kg in | Total time |
|---|---|---|---|
| Infants (under 12 months) | 1 hour | 5 hours | 6 hours |
| Older children | 30 minutes | 2½ hours | 3 hours |
- Repeat the first 30 ml/kg once if the radial pulse is still very weak or not detectable.
- Reassess every 15–30 minutes until a strong radial pulse returns, then at least hourly.
- Start ORS (about 5 ml/kg/hour) as soon as the child can drink — usually after 3–4 hours in infants or 1–2 hours in older children — to supply base and potassium.
- After 6 hours (infants) or 3 hours (older), reassess fully and choose Plan A, B or C.
What is the composition of low-osmolarity ORS?
For more than 25 years WHO and UNICEF recommended a single glucose-based ORS with an osmolarity of 311 mOsm/L. Trials then showed that reducing sodium to 75 mEq/L, glucose to 75 mmol/L and total osmolarity to 245 mOsm/L improved efficacy in children with acute non-cholera diarrhoea. WHO and UNICEF now recommend this reduced (low) osmolarity ORS in place of the old formula.
| Ingredient | Grams per litre | Component | mmol/L |
|---|---|---|---|
| Sodium chloride | 2.6 | Sodium | 75 |
| Glucose, anhydrous | 13.5 | Chloride | 65 |
| Potassium chloride | 1.5 | Glucose, anhydrous | 75 |
| Trisodium citrate, dihydrate | 2.9 | Potassium | 20 |
| — | — | Citrate | 10 |
| Total | — | Total osmolarity | 245 |
With the 245 mOsm/L solution, the need for unscheduled IV therapy fell by 33% compared with standard ORS. In a combined analysis of reduced-osmolarity trials, stool output fell by about 20% and vomiting by about 30%. It also appeared as safe and at least as effective as standard ORS in children with cholera.
What is the dose of zinc in childhood diarrhoea?
The WHO/UNICEF Joint Statement (2004) recommends 20 mg of zinc per day for 10–14 days, and 10 mg per day for infants under six months. Zinc can be given as a syrup or dispersible tablet, started as soon as diarrhoea begins (in Plan B, once the child can eat after the first 4 hours).
| Age | Daily dose | Duration |
|---|---|---|
| Under 6 months | 10 mg | 14 days in India (WHO: 10–14) |
| 6 months and older | 20 mg | 14 days in India (WHO: 10–14) |
- Zinc reduces the duration of a diarrhoeal episode by about 25% and is associated with a 30% reduction in stool volume (WHO fact sheet).
- A 10–14 day course replaces zinc lost during diarrhoea and reduces new episodes in the following 2–3 months.
Which drugs are avoided, and what are the common exam traps?
- Antimicrobials are not used routinely. They are indicated for bloody diarrhoea (presumed shigellosis), suspected cholera with severe dehydration, and specific infections. For dysentery, WHO advises ciprofloxacin for 3 days (or another locally effective antibiotic for 5 days).
- Antimotility drugs (loperamide, diphenoxylate, opiates) do not reduce stool volume in young children and can cause paralytic ileus — not used in children.
- The 2005 WHO manual advised against sedating antiemetics such as prochlorperazine and chlorpromazine because they interfere with ORT; StatPearls notes that ondansetron is now commonly used to help ORS succeed in children with severe vomiting.
- Cardiac stimulants, vasopressors and blood products have no role in dehydration shock — the treatment is rapid IV balanced electrolyte solution.
Link the topic to its neighbours: hypokalaemia and metabolic acidosis from stool bicarbonate loss (see anion gap and ABG interpretation), the bacterial causes in diarrhoeagenic bacteria, and the malnutrition overlap in kwashiorkor vs marasmus.