Dehydration assessment in children is a clinical process of estimating the degree of total body water deficit based on the presence and severity of physical signs and symptoms. Unlike adults, children have proportionally higher body surface area relative to volume, higher metabolic rates, and greater renal immaturity, making them more vulnerable to dehydration and its consequences. Dehydration is classified by percentage body weight lost: mild dehydration (3-5% in infants, 3-4% in older children) presents with thirst and mildly dry mucous membranes with minimal clinical signs; moderate dehydration (6-9%) is characterised by sunken eyes, decreased skin turgor (skin returns slowly after pinch), tachycardia, reduced urine output, and irritability; severe dehydration (≥10%) involves poor peripheral perfusion, mottled or cold extremities, markedly prolonged capillary refill, altered consciousness, and hypotension as a late sign. The most common cause of childhood dehydration globally is acute gastroenteritis, and the WHO estimates that appropriate oral rehydration therapy (ORT) could prevent hundreds of thousands of child deaths annually. Fluid management combines deficit replacement (estimated volume lost), maintenance requirements (calculated by the Holliday-Segar method), and ongoing losses (from continued diarrhoea, vomiting, or fever). Accurate dehydration assessment guides whether a child can be safely managed with oral rehydration at home or requires intravenous fluids in hospital, making it one of the most clinically impactful assessments in paediatric emergency medicine.
Fluid Deficit (mL) = % Dehydration × Weight (kg) × 10; Mild 3-5% deficit; Moderate 6-9%; Severe ≥10%; Maintenance by Holliday-Segar: 100 mL/kg/day (first 10kg) + 50 mL/kg/day (next 10kg) + 20 mL/kg/day (remaining); Total fluid = Deficit + Maintenance + Ongoing losses
- 1Assess clinical signs systematically: examine mucous membranes (dry/cracked = dehydration), skin turgor (pinch mid-chest or abdomen — slow return >2 seconds indicates ≥5% dehydration), eyes (sunken = moderate-severe), fontanelle in infants (sunken = significant dehydration), and mental status.
- 2Classify dehydration severity: mild (3-5%) if thirst and dry mouth only, no other signs; moderate (6-9%) if two or more of sunken eyes, reduced skin turgor, tachycardia, reduced urine output, or irritability; severe (≥10%) if any of poor perfusion, cold extremities, mottling, CRT >3 seconds, altered consciousness, or hypotension.
- 3Estimate fluid deficit: multiply percentage dehydration by weight in kg by 10. For example, a 15 kg child with 8% dehydration has a deficit of 0.08 × 15 × 1000 = 1200 mL.
- 4Calculate maintenance fluid requirements using Holliday-Segar: 100 mL/kg/day for first 10 kg, plus 50 mL/kg/day for next 10 kg, plus 20 mL/kg/day for each kg above 20 kg.
- 5Add ongoing losses: estimate stool and vomit output; typically add 5-10 mL/kg per diarrhoeal stool or vomiting episode to ongoing replacement.
- 6Decide route of administration: mild-moderate dehydration without vomiting = WHO oral rehydration solution (ORS) 50-100 mL/kg over 4 hours; moderate with persistent vomiting or severe = intravenous fluid (20 mL/kg NS bolus if shocked, then 0.9% NaCl with glucose for replacement and maintenance).
- 7Reassess after initial fluid administration: recheck clinical signs, urine output (target >1 mL/kg/hour), heart rate, and mental status to gauge response and titrate further therapy.
Can be managed at home with oral rehydration; reassess if vomiting increases
Mild dehydration with intact oral intake. ORS given by small frequent sips (5-10 mL every 2-3 minutes) is highly effective and avoids hospitalisation. Maintenance feeds can resume as tolerated.
IV 0.9% NaCl + 5% dextrose; reassess after 4-hour deficit replacement phase
Moderate dehydration requires supervised rehydration. If nasogastric ORS is refused or vomiting prevents oral intake, IV fluids are given over 24 hours split as deficit replacement in first 8 hours and maintenance over 24 hours.
Treat shock first; reassess after bolus; consider HDU/PICU admission
Signs of hypovolaemic shock demand immediate IV access and fluid resuscitation. Isotonic saline 20 mL/kg over 5-10 minutes, reassessing after each bolus. Deficit replacement follows stabilisation.
Rapid correction risks cerebral oedema from osmotic shift; specialist paediatric guidance required
Hypernatraemic dehydration (Na >145) occurs when free water loss exceeds sodium loss (e.g., inadequate breastfeeding). Paradoxically, skin turgor may appear relatively normal (doughy). Slow correction is mandatory to prevent cerebral oedema.
Emergency department triage and management of children presenting with acute gastroenteritis and dehydration — the most common paediatric emergency worldwide.. This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
Guiding decision-making for home discharge versus hospitalisation based on dehydration severity and ability to tolerate oral fluids.. Industry practitioners rely on this calculation to benchmark performance, compare alternatives, and ensure compliance with established standards and regulatory requirements
Calculating IV fluid regimens in hospitalised children who cannot tolerate enteral rehydration.. Academic researchers and students use this computation to validate theoretical models, complete coursework assignments, and develop deeper understanding of the underlying mathematical principles
Monitoring response to rehydration therapy: tracking weight gain, urine output, and clinical sign improvement.. Financial analysts and planners incorporate this calculation into their workflow to produce accurate forecasts, evaluate risk scenarios, and present data-driven recommendations to stakeholders
Community health worker training in low-resource settings for recognition of severe dehydration requiring urgent referral and ORS administration for mild-moderate cases.. This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
Hypernatraemic Dehydration
When serum sodium exceeds 145 mmol/L, skin turgor may appear deceptively normal (doughy texture) because hypertonicity draws water from the intracellular space. Do not underestimate severity. Use hypotonic solutions carefully and correct no faster than 10-12 mmol/L of sodium per 24 hours to prevent cerebral oedema.
Malnourished Child
In severely malnourished children, standard dehydration signs (skin turgor, sunken eyes) are unreliable because chronic malnutrition independently causes these findings. Use recent history of fluid losses, reduced urine output, and weight trend. Management should follow WHO severe acute malnutrition rehydration protocols, not standard IV fluid guidelines.
Neonate Exclusive Breastfeeding
Neonates may develop significant hypernatraemic dehydration due to insufficient breastmilk transfer in the first week of life. Weight loss >10% from birth weight warrants urgent evaluation of feeding and hydration status. Early supplementation with expressed breastmilk or formula prevents this serious and often underrecognised complication.
Diabetic Ketoacidosis (DKA)
Children presenting with DKA are invariably dehydrated, but fluid management must be cautious. Aggressive fluid resuscitation in DKA is associated with cerebral oedema — a potentially fatal complication. Use DKA-specific fluid protocols with careful calculation of deficit over 36-48 hours; do not apply standard dehydration fluid calculations.
| Feature | Mild (3-5%) | Moderate (6-9%) | Severe (≥10%) |
|---|---|---|---|
| Mucous membranes | Slightly dry | Dry | Very dry/parched |
| Eyes | Normal | Sunken | Markedly sunken |
| Skin turgor | Normal | Reduced (2-3s return) | Very poor (>3s) |
| Fontanelle (infant) | Normal/flat | Sunken | Markedly sunken |
| Heart rate | Normal | Tachycardia | Marked tachycardia |
| Capillary refill | ≤2 seconds | 3-4 seconds | ≥5 seconds |
| Mental status | Alert, thirsty | Irritable | Lethargic/obtunded |
| Blood pressure | Normal | Normal | Hypotension (late sign) |
| Management | ORS at home | ORS or NG/IV in hospital | IV bolus + HDU admission |
What is the most reliable clinical sign of dehydration in children?
Prolonged skin turgor (>2 seconds return after skin pinch) and dry mucous membranes are most consistently associated with ≥5% dehydration in validated studies. Sunken eyes and abnormal capillary refill are also highly predictive of moderate-to-severe dehydration. In practice, this concept is central to dehydration assessment because it determines the core relationship between the input variables. Understanding this helps users interpret results more accurately and apply them to real-world scenarios in their specific context.
What is WHO oral rehydration solution (ORS) and why is it used?
WHO ORS is a standardised electrolyte solution containing glucose 75 mmol/L, sodium 75 mmol/L, chloride 65 mmol/L, potassium 20 mmol/L, and citrate 10 mmol/L (osmolarity 245 mOsm/L). The glucose-sodium co-transport mechanism drives sodium — and therefore water — absorption even in the presence of diarrhoea, making it more effective than plain water.
When should IV fluids be used instead of ORS?
IV fluids are indicated when: the child is in shock or has severe dehydration (≥10%); there is persistent vomiting preventing oral/NG intake; there is ileus or bowel obstruction; the child is obtunded or unable to protect the airway; or dehydration is hypernatraemic with Na >155 mmol/L requiring controlled slow correction.
What is the Holliday-Segar formula?
The Holliday-Segar formula calculates daily maintenance fluid requirements based on weight: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kg above 20 kg. The 4-2-1 rule (mL/kg/hour) is the equivalent hourly rate and is commonly used in clinical practice.
Does weight loss accurately reflect dehydration percentage?
Acute weight loss in the context of illness is the most accurate measure of dehydration percentage (1 gram loss = 1 mL of water). However, pre-illness weight is often unknown. Clinical signs are used when this is unavailable, and serial weights during rehydration confirm progress. This is an important consideration when working with dehydration assessment calculations in practical applications. The answer depends on the specific input values and the context in which the calculation is being applied.
What is hypernatraemic dehydration and why is it dangerous?
Hypernatraemic dehydration occurs when water loss exceeds sodium loss, resulting in serum sodium >145 mmol/L. The brain adapts by producing intracellular osmoles. Rapid IV rehydration causes free water to rush into brain cells, causing cerebral oedema. Correction must not exceed 10-12 mmol/L of sodium reduction per 24 hours. In practice, this concept is central to dehydration assessment because it determines the core relationship between the input variables.
Can children with diarrhoea continue to eat?
Yes — early re-feeding is recommended as soon as rehydration begins. Age-appropriate foods should be offered throughout oral rehydration. The old practice of bowel rest is no longer recommended. Continued feeding reduces stool output, speeds recovery, and prevents nutritional deficiency. This is an important consideration when working with dehydration assessment calculations in practical applications. The answer depends on the specific input values and the context in which the calculation is being applied.
What urine output target confirms adequate rehydration?
A urine output of ≥1 mL/kg/hour in children (or ≥0.5 mL/kg/hour in older children and adolescents) indicates adequate renal perfusion and hydration. In infants, wet nappies every 4-6 hours and the return of tears are practical clinical markers of adequate hydration. This is an important consideration when working with dehydration assessment calculations in practical applications. The answer depends on the specific input values and the context in which the calculation is being applied.
Pro Tip
For moderate dehydration with initial vomiting, try ORS via syringe in small aliquots (5 mL every 2-3 minutes) before resorting to IV cannulation. Most children tolerate this, avoiding the pain and risk of IV access. If the child accepts ORS after 15-20 minutes, the volume can be gradually increased.
Did you know?
Oral rehydration therapy (ORT) for diarrhoeal illness was called 'potentially the most important medical advance of the 20th century' by The Lancet in 1978. Its discovery emerged from cholera research during the 1960s-70s when scientists found that glucose and sodium share an intestinal co-transporter — meaning even a cholera-damaged gut could absorb fluid if glucose was present alongside salt. This simple, cheap discovery has since saved an estimated 50 million lives.
References
- ›WHO. The Treatment of Diarrhoea: A Manual for Physicians and Other Senior Health Workers, 4th revised ed. 2005.
- ›Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics 1957.
- ›NICE Guideline CG84 — Diarrhoea and vomiting caused by gastroenteritis in under 5s. 2009 (updated 2020).
- ›Steiner MJ et al. Is this child dehydrated? JAMA 2004.