1The 4-2-1 Rule Explained
The Holliday-Segar method was published in 1957 by Malcolm Holliday and William Segar. The authors linked resting caloric expenditure in hospitalized children with physiological fluid turnover, demonstrating that water requirements approximate 100 mL per 100 kcal metabolized.
The method models resting metabolic rate across weight tiers:
- First 10 kg: 100 kcal/kg/day = 100 mL/kg/day = 4 mL/kg/hour
- Next 10 kg (11–20 kg): 50 kcal/kg/day = 50 mL/kg/day = 2 mL/kg/hour
- Each kg > 20 kg: 20 kcal/kg/day = 20 mL/kg/day = 1 mL/kg/hour
2NICE 2015 (NG29) Fluid Type Recommendations
National and international guidelines (NICE NG29, AAP, and Indian Academy of Pediatrics) have established clear safety standards to prevent fatal hospital-acquired hyponatraemic encephalopathy:
- Isotonic Fluid Mandate: Use 0.9% sodium chloride with 5% glucose (or balanced crystalloids like Hartmann's/Plasmalyte) as the default maintenance fluid.
- Potassium Requirement: Add 20 mmol/L KCl once renal perfusion is established, unless acute kidney injury, oliguria, or pre-existing hyperkalaemia is documented.
- Avoid Hypotonic Fluids: Historically utilized 0.18% saline ("Fifth Normal") and 0.45% saline without clinical indication are strictly discouraged for routine maintenance due to non-osmotic ADH secretion triggering profound hyponatraemia.
3When to Adjust Maintenance Rates
| Clinical Condition | Recommended Adjustment | Pathophysiological Mechanism |
|---|---|---|
| Fever (>37.5 °C) | Increase by 10%–12% per 1 °C rise | Accelerated insensible cutaneous and respiratory evaporative losses. |
| Mechanical Ventilation | Decrease by 15%–20% | Humidified inspiratory circuit eliminates respiratory evaporative losses. |
| SIADH / Meningitis / CNS Injury | Restrict to 50%–70% of maintenance | Non-osmotic ADH hypersecretion impairs free water clearance. |
| Oliguric Acute Kidney Injury | Insensible allowance (~400 mL/m²/day) + urine output | Compromised renal ultrafiltration risks acute volume overload. |
| Severe Diarrhoea / Vomiting | Replace output mL-for-mL separately | Ongoing pathological fluid losses must not be merged into baseline rate. |
4Maintenance vs. Resuscitation Fluids
Maintenance therapy replaces obligate daily physiological losses (urinary, skin, pulmonary, and fecal) in stable, euvolemic individuals unable to maintain enteral hydration. It must never be confused with resuscitation boluses (10–20 mL/kg balanced isotonic crystalloid over 15–30 minutes) given to correct hypovolemic shock, sepsis, or acute dehydration. Resuscitate first; calculate maintenance second.