6.7 Fluid & Electrolyte Therapy Across the Ages: Maintenance, Dehydration, Fluid Overload & Electrolyte Emergencies

Fluid & Electrolyte Therapy Across the Ages

Transport patients range from 500-gram preterm infants to adolescents. Fluid errors in either direction are common and dangerous: under-resuscitation in dehydration and shock, and over-resuscitation in cardiac disease, capillary leak, and prolonged transports where infusions keep running. This section brings together the rules used throughout the clinical chapters.

Body Water by Age

Newborns also have a larger extracellular fraction, immature renal concentrating ability, and a limited ability to excrete a sodium load. Neonatal fluid orders therefore change day by day.

Maintenance Fluids

Children beyond the newborn period

• Holliday-Segar (daily): 100 mL/kg for the first 10 kg + 50 mL/kg for the next 10 kg + 20 mL/kg for each kg above 20 kg.
• 4-2-1 rule (hourly): 4 mL/kg/h for the first 10 kg + 2 mL/kg/h for the next 10 kg + 1 mL/kg/h for each kg above 20 kg. A 25 kg child needs 40 + 20 + 5 = 65 mL/h.
• Fluid choice: The AAP 2018 clinical practice guideline recommends isotonic solutions with appropriate potassium chloride and dextrose for most patients aged 28 days to 18 years. Hypotonic maintenance fluids cause hospital-acquired hyponatremia, especially when ADH is elevated by pain, nausea, meningitis, pneumonia, bronchiolitis, or surgery.

Neonates

• Term infants usually start around 60–80 mL/kg/day on day 1 as D10W, with no sodium or potassium until diuresis begins and urine output is established. Totals are advanced by about 10–20 mL/kg/day toward 120–150 mL/kg/day.
• Preterm and ELBW infants often need higher initial volumes because of transepidermal water loss, adjusted by weight, sodium, and urine output.
• Always recalculate the glucose infusion rate when changing rate or dextrose concentration (Section 9.3).

Dehydration (see also Section 12.2)

• Estimate severity from weight change (the best measure), then heart rate, capillary refill, mucous membranes, tears, fontanelle, and urine output.
• Shock: Give isotonic boluses (10–20 mL/kg) with reassessment. Hypotension is a late sign.
• Deficit replacement: Replace the deficit (% dehydration × weight in kg × 10 mL) plus maintenance over 24–48 hours, more slowly for hypernatremic dehydration.
• Special cases: DKA (Section 14.2) and hypernatremic dehydration need slower, carefully calculated correction.

Fluid Overload

Percent fluid overload (%FO) = [(total fluid in − total fluid out) in liters ÷ admission weight in kg] × 100.

• Overload above about 10–20% is associated with longer ventilation and higher mortality in critically ill children.
• Signs: Edema, hepatomegaly, crackles, rising oxygen needs, weight gain, and gallop rhythm.
• Transport contributors: Carrier and flush volumes, antibiotic dilutions, boluses given at both hospitals, and maintenance fluids that keep running unchanged.
• Management: Stop or reduce maintenance fluids, concentrate infusions, give diuretics (for example, furosemide about 1 mg/kg IV when perfusion allows), and discuss renal replacement therapy with the receiving team in refractory cases.

Electrolyte Emergencies

Sodium

Potassium

• Hypokalemia: Causes weakness, ileus, and arrhythmias. It worsens with insulin, albuterol, alkalosis, and diuretics. IV replacement is typically 0.5–1 mEq/kg (maximum dose per protocol) infused over 1–2 hours with continuous ECG monitoring. Never give potassium by IV push. Concentrated solutions require central access.
• Hyperkalemia: Peaked T waves progress to PR prolongation, QRS widening, and a sine-wave rhythm (Section 9.3). Treatment follows three steps:
  1. Stabilize the myocardium: Calcium gluconate 10% (about 100 mg/kg = 1 mL/kg; maximum per protocol) or calcium chloride 10% (about 20 mg/kg via central or IO access).
  2. Shift potassium into cells: Regular insulin 0.1 unit/kg with glucose about 0.5 g/kg, inhaled albuterol, and sodium bicarbonate if acidotic.
  3. Remove potassium: Loop diuretics if the kidneys work, binders, or dialysis. Stop potassium-containing fluids, and consider causes such as AKI, tumor lysis (Section 15.2), hemolysis, and adrenal crisis.

Calcium and magnesium

• Hypocalcemia: Tetany, stridor, prolonged QT, seizures, and hypotension. It is common after massive transfusion (citrate), in sepsis, in DiGeorge syndrome, and in neonates (Section 9.3). Treat symptomatic cases with calcium gluconate 10% about 50–100 mg/kg IV slowly with ECG monitoring. Check magnesium, because hypomagnesemia makes hypocalcemia resistant to treatment.
• Hypomagnesemia: Arrhythmias (including torsades de pointes), seizures, and refractory hypocalcemia or hypokalemia. Give magnesium sulfate about 25–50 mg/kg IV (maximum 2 g) over 20–30 minutes, or faster for torsades.

Fluid Dynamics in the Transport Environment

• Use infusion pumps for all fluids. Gravity drips change with vehicle acceleration, altitude, and bag height (Section 3.3).
• Air in glass or rigid containers and in pressure-bag bladders expands with altitude (Boyle's law), which changes delivered pressures. Vent bags and recheck pressure bags after climb and descent.
• Keep a running intake and output total, including flushes, and hand it off.

Transport Scenario

A 9-month-old with bronchiolitis has been on D5 0.2% saline at full maintenance for two days and now has a seizure. Sodium is 121 mEq/L. The team gives 3% saline 3 mL/kg over 15 minutes, and the seizure stops. The team then switches maintenance to an isotonic solution at a restricted rate and rechecks sodium after the bolus, aiming for no more than 8–10 mEq/L of total rise over the first 24 hours. The handoff highlights the likely cause: hypotonic fluid plus ADH release from the respiratory illness.