Fluid management is straightforward when executed correctly and has severe consequences when errors occur. The approach requires accurate calculation of baseline maintenance requirements, precise assessment of dehydration severity, and appropriate replacement of ongoing losses without excessive rehydration.
Holliday-Segar: Still the Standard
Most of us still use Holliday-Segar, even though it was cooked up in 1957. For NPO kids:
- First 10 kg: 100 mL/kg/day
- Next 10 kg: 50 mL/kg/day
- >20 kg: 20 mL/kg/day
So a 25 kg kid needs (10 × 100) + (10 × 50) + (5 × 20) = 1600 mL/day, roughly 67 mL/hr.
Fever increases metabolic rate and fluid requirements. Add approximately 10–12% of calculated maintenance per degree Celsius above 38°C. Use the Maintenance Fluids calculator to ensure accurate computation rather than mental calculation, which is prone to error.
Isotonic Versus Hypotonic Fluids
Historically, hypotonic fluids (0.2% saline) were used routinely for hospitalized children. This practice resulted in iatrogenic hyponatremia, seizures, and mortality; it is now recognized as inappropriate. Current standard practice employs isotonic fluids: 0.9% normal saline or balanced crystalloid solutions. These solutions match plasma osmolality and avoid inducing hyponatremia. Isotonic fluids are the standard for maintenance fluid therapy.
Hypotonic fluids have limited specific indications: documented hypernatremia requiring gradual correction, severe syndrome of inappropriate antidiuretic hormone (SIADH), or specific cardiac conditions. These are specialized situations, not routine practice.
Clinical Assessment of Dehydration
Physical examination remains the cornerstone of dehydration assessment. Mild dehydration (3-5%) presents with dry lips, slightly decreased skin turgor, and normal mental status. Moderate dehydration (6-9%) manifests as visibly dry mucous membranes, reduced skin turgor, and compensatory tachycardia. Severe dehydration (10% or greater) shows skin tenting, altered mental status, weak pulses, cool extremities, and possibly hypotension.
Assessment requires systematic evaluation of multiple clinical parameters: capillary refill time, mucous membrane moisture, skin turgor, heart rate, blood pressure, and mental status. Use the Gorelick Dehydration Scale to ensure objective, standardized assessment.
The Math
Deficit = Weight (kg) × Dehydration (%) × 10
So a 10 kg kid who's 8% dehydrated has an 800 mL hole to fill.
For mild to moderate dehydration without shock, oral rehydration therapy using low-osmolarity solutions is the preferred initial approach, with success rates exceeding 90% over several hours.
For children unable to tolerate oral intake, those in shock, or with severe dehydration, intravenous fluid therapy is required. Administer a 20 mL/kg isotonic crystalloid bolus for shock; more gradual replacement (4-6 hours) is appropriate for stable children with moderate dehydration.
Use the Fluid Deficit calculator to ensure accurate deficit calculations rather than relying on mental computation.
DKA Fluid Management: The Two-Bag Approach
Children with diabetic ketoacidosis typically have 5–10% dehydration, metabolic acidosis, and total body potassium depletion (serum potassium may be normal or high initially due to extracellular shift from acidosis and insulin deficiency).
The two-bag system uses two premixed IV bags at different dextrose concentrations, allowing rapid titration of glucose delivery without changing the overall fluid rate:
Bag 1: 0.9% NS (or 0.45% NS) with potassium, no dextrose. Bag 2: Same base fluid with 10% dextrose and potassium.
By adjusting the relative rates of the two bags (total rate stays constant), you can titrate dextrose delivery to keep blood glucose declining at 50–100 mg/dL/hour without interrupting insulin. This avoids the repeated bag changes required with traditional single-bag protocols.
Insulin infusion: 0.05–0.1 units/kg/hour (do not bolus). Start potassium replacement (20–40 mEq/L in fluids) once serum potassium is <5.5 mEq/L and urine output is established. Replace deficit evenly over 24–48 hours.
Use the DKA Two-Bag calculator to determine patient-specific fluid and electrolyte requirements.
Replacement of Ongoing Losses
Gastrointestinal losses require consideration: vomiting and nasogastric tubes deplete potassium and chloride, while diarrhea causes bicarbonate losses. Replace ongoing losses milliliter-for-milliliter with appropriate electrolyte composition.
Fever and tachypnea increase insensible fluid losses. Add approximately 10–12% of calculated maintenance requirements per degree Celsius above 38°C.
Assess adequacy of resuscitation via urine output: target 1-2 mL/kg/hour in young children and 0.5-1 mL/kg/hour in older children. Lower output suggests inadequate perfusion or renal dysfunction.
Summary
Current fluid management principles include: use isotonic solutions for maintenance therapy; employ oral rehydration therapy when feasible; utilize intravenous therapy for children unable to tolerate enteral rehydration. Calculate deficits accurately, replace ongoing losses appropriately, and avoid excessive rehydration.