Chapter 15. Fluids, Electrolytes, and Acid–Base Balance

Daily Fluid Requirements

Kilograms of Body Weight–Based Method (Pediatrics. 1957;19:823)

• 1–10 kg: 100 mL/kg/d and
• 10–20 kg: 50 mL/kg/d and
• >20 kg: 20 mL/kg/d

BSA-Based Method (Pediatrics. 1960;25:496)

• See “BSA Nomogram and Calculations” in Chapter 1 for BSA calculation.
  • BSA (m2) × 1500–1600 mL/m2/d = Daily requirement

• Examples (22-kg child):
  • Daily (body weight–based method): (100 mL/kg/d × 10 kg) + (50 mL/kg/d × 10 kg) + 20 mL/kg/d × 2 kg) = 1540 mL/d (divide by 24 for hourly rate = 64 mL/h)
  • Daily (BSA-based method): 0.84 m2 × 1600 mL/m2/d = 1344 mL/d (divide by 24 for hourly rate = 56 mL/h)

Glucose

• Included in IV fluids to prevent protein catabolism, 3–4 mg/kg/min (not calorically adequate; see TPN section in Chapter 4 for parenteral nutrition).
  • D5W = 5% glucose solution = 5 g glucose/dL = 5 g glucose/100 mL = 50 mg/mL water

Sodium (Na)

• Maintenance: 2–3 mEq/kg/d
  • Normal saline (NS) = 0.9% saline = 154 mEq/L; ½ NS = 0.45% saline = 77 mEq/L; ¼ NS = 0.225% saline = 38 mEq/L
• For 1x MIVF, the following saline concentrations approximate maintenance Na: D1/4NS for 0–20 kg and D1/2NS for >20 kg

Potassium (K)

• Maintenance is age dependant.
  • Infant; 2–3 mEq/kg/d
  • Child: 1–2 mEq/kg/d
  • Adolescent: 1 mEq/kg/d
  • Adult: 0.5–1.0 mEq/kg/d
  • K should always be added if anticipated duration of IVF greater than 24 h
  • When providing 1x MIVF, adding KCl 20 mEq/L to IVF will approximate daily maintenance for all ages

Modifications to Maintenance Daily Fluid Requirements:

• Calculations above are for 1x MIVF, assuming an average, hospitalized patient with caloric demands 20% to 30% above resting energy expenditure.
• Any perturbation affecting fluid intake or output or energy demand or /utilization directly affects daily MIVF needs

Increased Mivf Needs

• ↑ Fluid losses: Renal (renal tubular injury, hyperglycemia, diuretic administration, mannitol administration, diabetes insipidus), GI (vomiting, diarrhea, NG suction, burns (see Critical Care chapter)
• ↑ Energy expenditure: Fever (↑ 12% for each °C over 37°C), radiant warmer, hyperthyroidism, hypermetabolic states

Decreased Mivf Needs

• ↓ Fluid losses: Anuric or oliguric renal failure, SIADH, ventilation with humidified air (decreases insensible loss)
• ↓ Energy expenditure: Coma, sedation, paralysis, hypothermia, hypothyroidism

• All calculations are based on the condition at the time of initiation of fluids; ongoing losses must be addressed as observed.
• End points to follow in all patients: Clinical improvement, weight gain, urine output.
• Bicarbonate administration should be avoided for initial replacement and then utilized only in extreme cases (serum HCO3 <8).
  • [Desired HCO3 (24 mEq/L) – current ...