Fluid and electrolyte management: Maintenance fluids (Holliday-Segar), dehydration assessment and WHO plans A/B/C, hyponatremia and hypernatremia correction rates.

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This topic has four linked areas:

Maintenance IV fluids
Holliday-Segar calculation, daily requirements, and choice of isotonic fluid.
Dehydration in children
Clinical assessment of no, some, and severe dehydration, followed by WHO Plans A, B, and C.
Hyponatremia
Classifying by symptoms and volume status, emergency hypertonic saline use, and safe limits for sodium rise to prevent osmotic demyelination.
Hypernatremia
Water-deficit replacement, monitoring, and slow correction to reduce risk of cerebral edema.

High-level rule: maintenance fluid is not resuscitation fluid. In shock or severe dehydration, restore circulation first with isotonic fluid, then calculate ongoing deficit, maintenance, and electrolyte needs. Sodium disorders require closely monitored, controlled correction rather than simply “normalizing the number” quickly.

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Fluid and electrolyte management

Safety note: Fluid and sodium prescriptions must be individualized using age, weight, clinical state, renal/cardiac function, glucose, electrolytes, urine output, and ongoing losses. Sodium emergencies need frequent laboratory and neurologic monitoring.

1. Maintenance fluids: Holliday-Segar method

Maintenance fluid replaces normal daily water losses, not existing dehydration, shock, or abnormal ongoing losses.

A. Daily requirement: 100-50-20 rule

Body weight	Fluid requirement
First 10 kg	100 mL/kg/day
Next 10 kg	50 mL/kg/day
Each kg above 20 kg	20 mL/kg/day

B. Hourly requirement: 4-2-1 rule

Body weight	Hourly fluid rate
First 10 kg	4 mL/kg/hour
Next 10 kg	2 mL/kg/hour
Each kg above 20 kg	1 mL/kg/hour

The Holliday-Segar calculation is based on estimated caloric expenditure. It should not generally be used unchanged for neonates younger than 14 days, or in patients who need fluid restriction or replacement therapy. The Harriet Lane Handbook, p. 389.

Examples

Child weighs 8 kg

Daily: 8 × 100 = 800 mL/day
Hourly: 8 × 4 = 32 mL/hour

Child weighs 15 kg

Daily: (10 × 100) + (5 × 50) = 1250 mL/day
Hourly: (10 × 4) + (5 × 2) = 50 mL/hour

Child weighs 25 kg

Daily: (10 × 100) + (10 × 50) + (5 × 20) = 1600 mL/day
Hourly: 40 + 20 + 5 = 65 mL/hour

C. What maintenance fluid to prescribe

For most hospitalized children, use an isotonic crystalloid containing glucose, for example:

0.9% sodium chloride with 5% glucose, with
potassium added only after adequate urine output is established and after considering serum potassium and renal function.

Modern pediatric practice favors isotonic maintenance fluids because hospitalized children often have non-osmotic ADH secretion and are susceptible to hospital-acquired hyponatremia with hypotonic fluids. The recent meta-analysis of pediatric trials found isotonic maintenance fluids reduce hyponatremia risk compared with hypotonic fluids (PMID 37365423). NICE also recommends isotonic crystalloids for routine maintenance in children and young people (NICE NG29).

D. Adjust maintenance downward or upward

Reduce maintenance in:

Renal failure or oliguria
Heart failure
Liver failure/cirrhosis
SIADH
Major surgery, CNS disease, pulmonary disease
Existing edema or fluid overload

Add replacement separately for measured abnormal ongoing losses:

Vomiting, diarrhea, NG aspirate, stoma, drains, polyuria
Replace loss volume with an appropriate fluid based on the composition of the loss and serum electrolytes.
Do not add losses into “maintenance” without documenting them.

E. Maintenance is not resuscitation

A shocked child needs rapid intravascular expansion first, usually 10-20 mL/kg isotonic crystalloid, reassessed after each bolus. Maintenance begins only after resuscitation and after estimating deficit plus ongoing losses.

2. Dehydration assessment

This section refers to the WHO/IMCI classification for children with acute diarrhea.

A. Clinical severity

No dehydration

The child does not meet criteria for some or severe dehydration.

Typical findings:

Alert, active
Normal drinking
No abnormal skin pinch
No clinically important sunken eyes
Normal perfusion and urine output

Some dehydration

Classify as some dehydration if there are 2 or more of:

Restless or irritable
Sunken eyes
Drinks eagerly, thirsty
Skin pinch returns slowly

A useful approximate estimate is about 5-10% dehydration, though treatment is guided clinically rather than by percentage alone.

Severe dehydration

Classify as severe dehydration if there are 2 or more of:

Lethargic or unconscious
Sunken eyes
Unable to drink or drinks poorly
Skin pinch returns very slowly, generally 2 seconds or longer

Also look for shock:

Cold extremities
Weak, rapid pulse
Delayed capillary refill
Hypotension, which is late in children
Oliguria/anuria
Altered sensorium

WHO emphasizes that severe dehydration requires rapid IV rehydration with isotonic fluid, while hypotonic solutions such as 5% dextrose alone or 0.18% saline with glucose should not be used for rehydration because of hyponatremia risk (WHO Hospital Care for Children).

3. WHO diarrhea treatment plans A, B, and C

Plan A: Treat diarrhea at home

Indication: No dehydration.

Give extra fluids

Continue breastfeeding frequently. Give ORS after each loose stool:

Age	ORS after each loose stool
Child under 2 years	50-100 mL
Child 2 years or older	100-200 mL
Older child/adolescent	As much as wanted

Alternative practical method: give small, frequent sips by spoon or cup. If vomiting occurs, wait 5-10 minutes, then restart more slowly.

Continue feeding

Continue breastfeeding.
Continue normal age-appropriate food.
Avoid unnecessary fasting.
Avoid high-sugar soft drinks, undiluted juice, and very sweet drinks.

Zinc

WHO diarrhea programs commonly recommend zinc for children:

Under 6 months: 10 mg once daily for 10-14 days
6 months and older: 20 mg once daily for 10-14 days

Follow local policy, especially in young infants and children with malnutrition.

Advise return immediately if

Unable to drink or breastfeed
Drinking poorly
Repeated vomiting
Fever or worsening illness
Blood in stool
Increasing thirst
Becoming lethargic, unusually sleepy, or sicker
Diarrhea persisting or caregiver concern

Plan B: Treat some dehydration with ORS at a facility

Indication: Some dehydration, with no severe dehydration/shock.

ORS dose

Give 75 mL/kg of low-osmolarity ORS over 4 hours.

Example: a 12-kg child receives:

12 × 75 = 900 mL over 4 hours

Breastfeeding should continue.

Administration

Give frequent small amounts by cup, spoon, syringe, or nasogastric tube if necessary.
If the child vomits, pause briefly and restart slowly.
Give more ORS if the child wants more.
Reassess regularly for worsening signs.

Reassess at 4 hours

Then reclassify:

No dehydration: move to Plan A.
Still some dehydration: repeat Plan B or reconsider diagnosis/ongoing losses.
Severe dehydration: move to Plan C.

WHO provides age/weight approximations when weight is unavailable, but 75 mL/kg over 4 hours is the preferred calculation (WHO Plan B).

Plan C: Treat severe dehydration urgently

Indication: Severe dehydration or shock.

Preferred IV fluid

Use an isotonic crystalloid:

Ringer lactate/Hartmann solution preferred by WHO, or
0.9% sodium chloride if Ringer lactate is unavailable.

Do not use dextrose-only solutions or hypotonic saline for initial resuscitation.

Total volume

Give 100 mL/kg IV, divided by age:

Age	First 30 mL/kg	Then 70 mL/kg	Total time
Infant under 12 months	Over 1 hour	Over 5 hours	6 hours
Child 12 months or older	Over 30 minutes	Over 2.5 hours	3 hours

During Plan C

Reassess circulation, mental status, respiratory status, and hydration frequently.
If pulse remains very weak or not detectable, repeat the initial 30 mL/kg as appropriate.
Begin ORS at about 5 mL/kg/hour as soon as the child can drink:
- Usually after 3-4 hours in infants
- Usually after 1-2 hours in older children
Reassess an infant after 6 hours and a child after 3 hours. Then classify again and continue with Plan A, B, or C.

If IV access cannot be obtained

If the child can drink and trained staff are available, give ORS by nasogastric tube or mouth:

20 mL/kg/hour for 6 hours, total 120 mL/kg
Reassess every 1-2 hours.
Transfer for IV treatment if the child worsens or does not improve.

Important exception: severe acute malnutrition

Children with severe acute malnutrition need a separate cautious rehydration protocol. Do not automatically apply standard rapid Plan C volumes because of their higher risk of heart failure and fluid overload.

4. Hyponatremia

A. Definition and danger

Hyponatremia is serum sodium below 135 mmol/L. The important issue is tonicity, acuity, symptoms, and volume status, not sodium alone.

Symptoms of acute/severe hyponatremia

Headache, nausea, vomiting
Confusion, agitation, altered consciousness
Seizures
Coma
Respiratory arrest from cerebral edema

Severe neurologic symptoms are an emergency.

B. First classify the patient

Is it hypotonic hyponatremia?
Check serum osmolality and glucose. Hyperglycemia can lower measured sodium without true hypotonicity.
Assess volume status
- Hypovolemic: GI loss, diuretics, adrenal insufficiency, renal salt loss
- Euvolemic: SIADH, glucocorticoid deficiency, hypothyroidism, drugs, excess water intake
- Hypervolemic: heart failure, cirrhosis, nephrotic syndrome, kidney failure
Assess severity and duration
- Severe symptoms need immediate treatment.
- Chronic or duration unknown hyponatremia has a high risk of osmotic demyelination if corrected too rapidly.

C. Emergency treatment: seizure, coma, marked confusion

Use 3% hypertonic saline.

A common pediatric regimen is:

3% saline 2-3 mL/kg IV over 10-20 minutes
Repeat if severe neurologic symptoms persist, with sodium remeasurement and senior/critical-care input.

The immediate goal is not normal sodium. It is to raise serum sodium by about 4-6 mmol/L or until seizures/major cerebral edema symptoms resolve.

Adult protocols commonly use fixed 100-150 mL 3% saline boluses. In children, weight-based boluses are safer.

D. Safe correction limits

For chronic hyponatremia or when duration is unknown:

Aim for no more than 8 mmol/L in 24 hours.
A conventional absolute upper limit is 10 mmol/L in the first 24 hours, then 8 mmol/L per 24 hours thereafter, but the safer target is 6-8 mmol/L/day.
In patients at high risk of osmotic demyelination, keep the limit at 6-8 mmol/L/24 hours.

High-risk patients include:

Very low sodium, especially ≤105 mmol/L
Alcohol use disorder
Malnutrition
Advanced liver disease
Hypokalemia

Complication of overcorrection: osmotic demyelination syndrome, classically central pontine myelinolysis. It may cause dysarthria, dysphagia, quadriparesis, locked-in state, or death.

E. Cause-directed treatment

Setting	Usual principle
Hypovolemic hypotonic hyponatremia	Restore volume with isotonic saline, then monitor closely
SIADH/euvolemic hyponatremia	Fluid restriction and treat cause; selected cases may need other therapy
Hypervolemic hyponatremia	Restrict salt/water, diuretics and management of heart/liver/renal disease
Drug-related	Stop or modify causative drug where appropriate
Adrenal insufficiency	Give glucocorticoids plus appropriate volume/sodium management

Avoid assuming all hyponatremia needs normal saline. In SIADH, for example, isotonic saline may fail to correct or can worsen hyponatremia.

F. Monitoring

Serum sodium every 2-4 hours during active correction
Strict input/output chart
Urine output and urine electrolytes/osmolality when indicated
Frequent neurologic observations
If sodium is rising too fast, stop corrective therapy and seek specialist input. Desmopressin and electrolyte-free water may be used in controlled settings to prevent/reverse overcorrection.

5. Hypernatremia

A. Definition and danger

Hypernatremia is serum sodium above 145 mmol/L, usually reflecting water deficit relative to sodium.

Common causes:

Diarrhea/vomiting with inadequate water intake
Fever, burns, diabetes insipidus
Osmotic diuresis, including hyperglycemia
Impaired thirst or limited access to water
Sodium loading, which is less common but potentially severe

Symptoms

Thirst, irritability, weakness
Lethargy, hyperreflexia, increased tone
Seizures, coma
Signs of dehydration may be subtle because extracellular volume is relatively preserved

B. Initial priorities

Secure airway, breathing, circulation.
If hypovolemic or shocked, restore perfusion first with isotonic crystalloid. Do not delay resuscitation for fear of sodium correction.
Measure glucose, urea/creatinine, potassium, bicarbonate, serum osmolality, urine output, and serial sodium.
Identify acute sodium loading versus water-loss hypernatremia and estimate duration.

C. Calculate free-water deficit

A commonly used estimate:

[ \text{Water deficit (L)} = \text{TBW} \times \left(\frac{\text{serum Na}}{140} - 1\right) ]

Approximate total body water:

Group	TBW fraction of body weight
Infant	0.6-0.7
Child	0.6
Adult male	0.6
Adult female or older adult	0.5

This is an estimate only. Recalculate and revise fluid therapy based on serial sodium values, clinical state, and ongoing losses.

D. Correction rate

For chronic hypernatremia or hypernatremia of unknown duration:

Lower sodium no faster than 0.5 mmol/L/hour
Do not lower by more than 10-12 mmol/L in 24 hours
Replace the deficit gradually, often over about 48 hours, while also providing maintenance and replacing ongoing losses.

Why slow? Brain cells adapt to hypernatremia by accumulating osmoles. Rapid lowering can shift water into the brain and cause cerebral edema, seizures, herniation, and death.

The textbook-based conventional ceiling is 0.5 mmol/L/hour. Current Surgical Therapy, Hypernatremia section. In pediatric hypernatremic dehydration, NICE describes deficit replacement over 48 hours when IV treatment is required (NICE diarrhea guideline).

E. Fluid choice

After initial stabilization:

Replace water deficit with a carefully calculated regimen using an appropriate sodium-containing glucose solution per local protocol.
The exact fluid depends on volume status, sodium concentration, glucose, urine output, and whether the cause is renal or extrarenal water loss.
Avoid giving large volumes of electrolyte-free water intravenously without close monitoring.
Add potassium only once renal function and urine output are adequate.

F. Monitoring

During active correction:

Serum sodium every 2-4 hours initially
Hourly urine output, fluid input/output, weight where feasible
Frequent neurologic observations
Review the actual sodium trajectory against the intended rate and adjust fluids promptly

If sodium is falling too quickly, reduce free-water delivery and obtain urgent senior/nephrology/critical-care help.

6. Quick comparison: correction rates

Disorder	Main acute risk	Initial emergency therapy	Usual safe rate after stabilization
Acute symptomatic hyponatremia	Cerebral edema, seizures	3% saline boluses	Raise 4-6 mmol/L initially for symptom control; generally limit total rise to 6-8 mmol/L/day, maximum usually 8-10 mmol/L in first 24 h
Chronic/unknown-duration hyponatremia	Osmotic demyelination if corrected too fast	Hypertonic saline only if severe symptoms	Usually ≤8 mmol/L/24 h, particularly in high-risk patients
Hypernatremia, chronic/unknown duration	Cerebral edema if corrected too fast	Isotonic resuscitation first if shocked	Fall ≤0.5 mmol/L/h and ≤10-12 mmol/L/24 h, often over 48 h

7. Exam-oriented practical approach

A. Child with diarrhea

Assess ABCs and shock.
Classify as no, some, or severe dehydration.
Use:
- No dehydration: Plan A
- Some dehydration: Plan B, ORS 75 mL/kg over 4 h
- Severe dehydration: Plan C, IV isotonic fluid 100 mL/kg divided by age
Continue breastfeeding and restart feeding early.
Monitor urine output, mental state, stool/vomit losses, glucose, and electrolytes when severe.
Reassess and reclassify after therapy.

B. Any patient receiving IV fluid

Prescribe four components separately:

Resuscitation: bolus for shock/hypoperfusion.
Maintenance: Holliday-Segar calculated daily requirement.
Deficit replacement: existing dehydration or water deficit.
Ongoing replacement: measured abnormal losses.

Then specify:

Fluid type
Rate and duration
Potassium plan
Monitoring frequency
Stop/review criteria

The recent evidence base supports isotonic rather than hypotonic maintenance IV fluids in most hospitalized children, with lower hyponatremia risk (2024 systematic review).

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