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 HCO3] × 0.5 × [wt in kg] = HCO3 to administer slowly over hours to days

Weight-Based Determination of Degree of Dehydration

• Percentage of total body weight lost acutely is attributable to loss of body fluid Infant (<15 kg): ≤5% mild, 6–10% moderate, ≥11% severeOlder child (≥15 kg): ≤3% mild, 6% moderate, ≥9% severe
  
• Example (child with pre-illness weight of 20 kg who now weighs 19 kg):
  
• Weight loss 1 kg = 1-L fluid loss/20 kg body wt = 5% dehydration

Biochemical Classification of Dehydration

• Clinical parameters determine the degree of dehydration, and biochemical parameters (primarily serum sodium) guide the choice of rehydration fluids.

Correction of Hypernatremic and Hyponatremic Dehydration

• See “Hypernatremia” and “Hyponatremia” in this chapter.

Correction of Isonatremic Dehydration (Most Common Type of Dehydration)

Oral Rehydration for Mild to Moderate Isonatremic Dehydration

• Oral rehydration is as efficacious as IV rehydration for acute gastroenteritis and may result in shorter hospitalization; this is best with one-on-one care from adult caregiver (Cochrane Database 2006(3):CD004390, Pediatrics 1996;97(3):424).

Oral Rehydration Strategies

• Resume normal diet as soon as tolerated; do not restrict diet (eg, BRAT diet).
  
• Encourage breastfeeding; do not dilute or change from standard formula.
  
• Generally, a lower osmolality and lower carbohydrate content are tolerated better. Avoid antibiotics, antidiarrheals, and anticholinergics (hyoscyamine).
  
• IV ondansetron may ↓ emesis (Pediatrics 2002;109:e62).
  
• Oral zinc (15–30 mg/d) ↓ duration of acute or persistent diarrhea in children older than age 6 mo, especially in developing countries, where malnutrition is prevalent (Cochrane Database Syst Rev 2008(3):CD005436, Morbid Mortal Wkly Rep 2003;52 (RR-16):1).
  
• Oral rehydration solution (ORS) should be WHO oral rehydration solution or a solution similar in composition.

Composition of Selected Enteral Products

IV Rehydration

• This is for patients with severe isonatremic dehydration, or oral rehydration failure and those unable to tolerate PO.
  
• It is divided into the initial emergent rehydration phase and the subsequent second fluid hydration phase.
  
  
  
  • Initial rehydration phase (correction of hypovolemia, mental status, perfusion)
    
    
    
    • Done over initial 2–4 h using NS or LR (20 cc/kg boluses).
      
    • There is no benefit of using colloid over crystalloid fluids for resuscitation (Cochrane Database Syst Rev 2000(2):CD000567).
    
    
  • Second phase of rehydration
    
    
    
    • Administration of maintenance fluid needs (based on weight), replacement of any additional deficits not replaced in the initial rehydration phase (estimated by weight loss or clinical evaluation at presentation), replacement of continuing losses (strict input and output recording), correction of electrolyte imbalances.
      
    • Choice of fluids is based on the status of the patient’s sodium and potassium levels and the need to correct electrolyte imbalances.
      
      
      
      • NS to correct any residual volume deficits.
        
      • 1/2 NS or NS for maintenance fluids and continued loss replacement. NS is not usually maintenance fluid; however, it may be beneficial in preventing hyponatremia from hypotonic fluids in hospitalized dehydrated pts (due to ADH in this population).

Composition of Commonly Used IV Fluids