Maintenance Fluid Calculation
The Holliday-Segar formula remains the recommended method for calculating maintenance fluid requirements: 100 ml/kg/day for the first 10 kg of body weight, plus 50 ml/kg/day for the next 10 kg, plus 25 ml/kg/day for each kg above 20 kg. 1
The Holliday-Segar Formula
The calculation is structured as follows:
- First 10 kg: 100 ml/kg/day (or 4 ml/kg/hour) 1
- Next 10 kg (11-20 kg): Add 50 ml/kg/day (or 2 ml/kg/hour) 1
- Each kg above 20 kg: Add 25 ml/kg/day (or 1 ml/kg/hour) 1
This formula is based on the principle that water requirements parallel energy needs at approximately 1 kcal per 1 ml of water. 1
Fluid Type Selection
Use isotonic fluids (0.9% saline or balanced crystalloids) for maintenance hydration in acutely ill children, especially during the first 24 hours. 1 This strong recommendation stems from Level 1+ evidence showing that hypotonic fluids significantly increase the risk of hospital-acquired hyponatremia and potentially fatal hyponatremic encephalopathy. 1
For initial resuscitation in critically ill children, balanced/buffered crystalloids are preferred over 0.9% saline, though this is a weaker recommendation based on lower quality evidence. 1
Volume Adjustments for Critically Ill Patients
In acutely and critically ill children at risk of increased antidiuretic hormone (ADH) secretion, restrict maintenance fluid volume to 65-80% of the Holliday-Segar calculated volume to prevent hyponatremia and fluid overload. 1 This restriction addresses the common pitfall of administering full maintenance rates to patients with impaired free water excretion.
For patients with specific organ dysfunction:
- Heart failure, renal failure, or hepatic failure: Restrict to 50-60% of calculated volume 1
- Critical illness with mechanical ventilation: Water requirements decrease in temperature-controlled environments 1
Clinical Situations Requiring Modification
Water requirements increase with: 1
- Fever
- Hyperventilation
- Hypermetabolism
- Gastrointestinal losses
Water requirements decrease with: 1
- Renal failure
- Congestive heart failure
- Critical illness with mechanical ventilation
Total Fluid Accounting
Calculate total daily maintenance fluid by including ALL sources: IV fluids, blood products, IV medications (infusions and boluses), arterial/venous line flushes, and enteral intake. 1 This comprehensive accounting prevents "fluid creep"—the insidious accumulation of unintended fluid administration that leads to fluid overload. 2
Fluid overload (defined as >10% increase in cumulative fluid balance from baseline) is an independent predictor of morbidity, mortality, prolonged mechanical ventilation, and increased length of stay. 1, 2
Monitoring Requirements
Reassess fluid balance and clinical status at least daily, with regular monitoring of serum electrolytes, especially sodium. 1 The induced change in serum osmolality should not exceed 3 mOsm/kg/hour during fluid replacement. 1
Electrolyte Supplementation
Add 20-40 mEq/L of potassium (2/3 KCl and 1/3 KPO4) once renal function is assured and serum potassium is known. 1 Sodium requirements are 1-3 mmol per 100 kcal, and potassium requirements are 1-3 mmol per 100 kcal. 1
Critical Pitfalls to Avoid
- Never prescribe maintenance fluids as routine continuous infusions without clear indication—fluids are drugs and should be prescribed only when needed. 2
- Avoid hypotonic fluids in sick children—they carry unacceptable risk of hyponatremia. 1
- Do not use full maintenance rates in patients with elevated ADH states (postoperative, critically ill, CNS pathology)—this leads to dangerous hyponatremia. 1
- Account for all fluid sources—failure to include medication diluents, flushes, and blood products leads to unrecognized fluid overload. 1