What is the recommended calculation for maintenance fluid requirements in a patient who is Nil Per Os (NPO)?

Maintenance Fluid Calculation for NPO Patients

Use the Holliday-Segar formula to calculate maintenance fluid requirements: 100 mL/kg/day for the first 10 kg, plus 50 mL/kg/day for the next 10 kg, plus 25 mL/kg/day for each kg above 20 kg (or equivalently: 4 mL/kg/h for first 10 kg, 2 mL/kg/h for next 10 kg, 1 mL/kg/h for remaining weight). 1, 2, 3

Calculation Method by Patient Age

For Adults

• Standard calculation: 25-30 mL/kg/day for baseline maintenance, which translates to approximately 2,000-2,500 mL/day for an average adult 1, 3
• The Holliday-Segar formula remains appropriate and can be applied: 100 mL/kg/day for first 10 kg + 50 mL/kg/day for next 10 kg + 25 mL/kg/day for remaining weight 1, 2

For Children

• Use the Holliday-Segar formula: This provides 100 mL/kg/day (4 mL/kg/h) for every kg <10 kg, plus 50 mL/kg/day (2 mL/kg/h) for weight between 10-20 kg, plus 25 mL/kg/day (1 mL/kg/h) for each kg above 20 kg 1, 2, 4
• Example: A 30 kg child requires 40 mL/h (first 10 kg) + 20 mL/h (next 10 kg) + 10 mL/h (remaining 10 kg) = 70 mL/h total 4

For Neonates

• Term neonates: 140-170 mL/kg/day during intermediate phase 1
• Preterm neonates >1500g: 140-160 mL/kg/day 1
• Preterm neonates <1500g: 140-160 mL/kg/day with careful adjustment for high urinary sodium losses 1

Fluid Type Selection

Administer isotonic crystalloid solutions (0.9% saline or balanced crystalloids) as the standard maintenance fluid, especially during the first 24 hours. 1, 2, 3

• Isotonic fluids significantly reduce the risk of hospital-acquired hyponatremia compared to hypotonic solutions 1, 2
• Balanced crystalloids may be preferred over 0.9% saline to avoid hyperchloremic acidosis, though evidence is not definitive in adults 3
• Critical exception: In nephrogenic diabetes insipidus or similar conditions with severe polyuria, use 5% dextrose instead of saline-containing solutions, as the tonicity of 0.9% saline (~300 mOsm/kg) exceeds typical urine osmolality and can worsen hypernatremia 1

Volume Adjustments for Clinical Conditions

Reduce Maintenance Volume (50-80% of calculated)

• Heart failure, renal failure, or hepatic failure: Restrict to 50-60% of calculated volume 2, 3
• Critically ill children at risk of increased ADH secretion: Restrict to 65-80% of Holliday-Segar volume 2
• Critical illness with mechanical ventilation: Decrease requirements 1, 2

Increase Maintenance Volume

• Fever: Add 2-2.5 mL/kg/day for each 1°C rise above 37°C 3
• Hyperventilation, hypermetabolism: Increase baseline requirements 1, 2
• Gastrointestinal losses: Add replacement volume on top of maintenance 1, 2
• Phototherapy in neonates: Add 10-20% to baseline volume 1

Electrolyte Supplementation

Once renal function is confirmed and serum potassium is known, add 20-40 mEq/L of potassium (2/3 KCl and 1/3 KPO4) to maintenance fluids. 1, 2

Standard Daily Electrolyte Requirements

• Sodium: 1-3 mmol/kg/day 2, 3
• Potassium: 1-3 mmol/kg/day 2, 3
• Chloride: 2-4 mmol/kg/day 3

Pediatric-Specific Requirements

• Term neonates: Na 2-3 mmol/kg/day, K 1-3 mmol/kg/day 1
• Preterm neonates: Na 2-5 mmol/kg/day (up to 7 mmol/kg/day in <1500g infants with high urinary losses), K 1-3 mmol/kg/day 1

Critical Monitoring Requirements

Reassess fluid balance and serum electrolytes (especially sodium) at least daily, ensuring the induced change in serum osmolality does not exceed 3 mOsm/kg/hour. 1, 2, 3

• Monitor hemodynamic status, urine output, and clinical examination for signs of adequate perfusion or fluid overload 1
• In neonates <1500g, careful adjustment is needed at onset of diuresis and in polyuric states 1
• Venous pH monitoring is adequate for most patients; repeat arterial blood gases are usually unnecessary 1

Account for All Fluid Sources

Calculate total daily fluid by including ALL sources: IV maintenance fluids, blood products, IV medications, arterial/venous line flushes, and enteral intake. 2

• "Fluid creep" (unintentional volume as medication vehicle) can represent up to 32.6% of total daily fluid volume 5
• Maintenance and replacement fluids typically account for 24.7% of daily volume, far exceeding resuscitation fluids at 6.5% 5
• Failure to account for all sources leads to inadvertent volume, sodium, and chloride overload 5

Critical Pitfalls to Avoid

• Never use salt-containing solutions in patients with severe polyuria (e.g., nephrogenic diabetes insipidus), as this creates excessive renal osmotic load and worsens hypernatremia 1
• Avoid hypotonic maintenance fluids in acutely ill patients, as they significantly increase hyponatremia risk and potentially fatal hyponatremic encephalopathy 2, 3
• Prevent fluid overload (>10% cumulative fluid balance increase), which independently predicts prolonged mechanical ventilation, increased ICU length of stay, and higher mortality 2, 3
• Do not use the standard 30 mL/kg/day formula in underweight patients, as it produces unrealistically low recommendations; the Holliday-Segar formula adjusts better for extremes in body weight 6
• Avoid rapid fluid administration in pediatric DKA, as initial reexpansion should not exceed 50 mL/kg over the first 4 hours to minimize cerebral edema risk 1