Maintenance fluids calculations are an essential part of clinical practice, particularly in pediatrics, anesthesia, and critical care. Maintenance fluids refer to the amount of fluid required to replace ongoing daily physiological losses of water and electrolytes through urine, respiration, sweat, and stool. These calculations are designed to maintain normal hydration and electrolyte balance in patients who cannot take fluids orally, such as those undergoing surgery, in intensive care units, or with gastrointestinal illnesses.

Maintenance fluid therapy differs from resuscitation fluids (used in shock or acute dehydration) and replacement fluids (used to correct specific deficits like diarrhea or vomiting). Correct calculation and administration prevent both underhydration and iatrogenic complications such as fluid overload or electrolyte imbalance.

Principles of Maintenance Fluid Therapy

Maintenance fluid therapy aims to replace the following normal physiological losses:

• Urinary losses: Vary depending on age, renal function, and metabolic activity.
• Insensible losses: Water lost through skin and lungs, typically 10–15 mL/kg/day.
• Stool losses: About 5–10 mL/kg/day in normal conditions.

In children and adults, body size and metabolic rate influence daily fluid requirements, which are estimated using standardized formulas.

Holliday–Segar Method (Pediatric Standard)

The Holliday–Segar formula, also known as the “100/50/20 rule,” is the most widely used method for calculating pediatric maintenance fluids:

• For the first 10 kg of body weight: 100 mL/kg/day
• For the next 10 kg: 50 mL/kg/day
• For each kg above 20 kg: 20 mL/kg/day

Example: A child weighing 25 kg would require: – First 10 kg = 100 × 10 = 1000 mL – Next 10 kg = 50 × 10 = 500 mL – Remaining 5 kg = 20 × 5 = 100 mL
Total = 1600 mL/day

Adult Maintenance Fluid Requirements

In adults, fluid requirements are often estimated more simply:

• 25–30 mL/kg/day of water for most healthy adults.
• Electrolyte requirements: – Sodium: 1–2 mmol/kg/day – Potassium: 0.5–1 mmol/kg/day – Glucose: 50–100 g/day to prevent starvation ketosis.

For example, a 70 kg adult would require about 2100 mL/day (70 × 30) of water, with appropriate electrolytes and dextrose supplementation.

Electrolyte Composition of Maintenance Fluids

The ideal maintenance solution should mimic daily physiological losses:

• Sodium: 30–70 mmol/day
• Potassium: 20–40 mmol/day
• Chloride: Balanced to sodium
• Glucose: To provide ~5% solution for caloric support

Common choices include 5% dextrose with 0.45% NaCl (plus potassium supplementation as needed), although fluid selection varies by age, comorbidities, and institutional protocols.

Clinical Significance

Correct maintenance fluid calculation has several clinical benefits:

• Prevents dehydration: Especially in patients who cannot drink fluids.
• Maintains electrolyte balance: Avoids hypo- or hypernatremia, hypokalemia, and metabolic derangements.
• Supports metabolic needs: Provides glucose to prevent ketosis and protein catabolism.
• Critical care stability: Ensures hemodynamic support in perioperative and intensive care settings.

Indications for Use

Maintenance fluid therapy is indicated in:

• Children with gastroenteritis unable to take oral fluids.
• Perioperative patients who are nil per os (NPO).
• Critically ill patients with impaired oral intake.
• Patients with chronic illnesses requiring prolonged IV support.

Limitations and Risks

While useful, maintenance fluid therapy carries risks if improperly applied:

• Hyponatremia: Hypotonic solutions can cause dangerous sodium dilution, especially in children.
• Fluid overload: Excessive infusion may lead to pulmonary edema or heart failure in susceptible patients.
• Variable requirements: Fever, burns, sepsis, or high-output losses increase fluid needs beyond standard formulas.
• Individual differences: Patients with renal, cardiac, or hepatic disease may require tailored regimens.