Fluid and Electrolyte Balance in Pediatric Surgery

Fluid and Electrolyte Balance in Pediatric Surgical Patients

• Critical understanding of fluid and electrolyte balance is essential in pediatric surgical patients, particularly in infants, due to their limited reserve and high risk of dehydration or fluid overload.
• Certain surgical diagnoses, such as gastroschisis or short-gut syndrome, are prone to fluid loss, while others, like congenital diaphragmatic hernia, require careful restoration of intravascular volume to prevent cardiac failure.

Infant Physiologic Day and Fluid Balance Assessment

• An infant's physiologic day is approximately eight hours in duration, making regular assessment of fluid balance crucial.
• Assessment should include fluid intake and output for the previous eight hours to prevent dehydration or fluid overload.

Clinical Signs of Dehydration and Fluid Overload

• Clinical signs of dehydration: tachycardia, decreased urine output, reduced skin turgor, depressed fontanelle, absent tears, lethargy, and poor feeding.
• Clinical signs of fluid overload: new oxygen requirement, respiratory distress, tachypnea, and tachycardia.

Physical Assessment of Fluid Status

• A complete head-to-toe evaluation is necessary to determine whether perturbations in normal physiology are present.

Total Body Water and Extracellular Fluid

• At 12 weeks' gestation, the total body water of a fetus is approximately 94 cc/kg, decreasing to around 80 cc/kg at full term.
• Total body water drops an additional 5% within the first week of life, reaching adult levels (60-65 cc/kg) by 1 year of life.
• Extracellular fluid reduces parallel to the drop in total body water, with accelerated changes in preterm infants.

Daily Maintenance Fluid Requirements

• Formula for estimating daily maintenance fluids: 100 mL/kg for the first 10 kg, plus 50 mL/kg for 11-20 kg, plus 25 mL/kg for each additional kilogram of body weight thereafter.
• Conversion to IV fluid orders: 4 mL/kg/h up to 10 kg, add 2 mL/kg/h for 11-20 kg, and add 1 mL/kg/h for each additional kilogram body weight thereafter.

Neonatal Fluid Management

• Newborn infants with gastroschisis may require fluid requirements of 150-180 cc/kg/day due to evaporative losses from the exposed bowel.
• Precise management of a neonate's fluid status requires understanding of changes in glomerular filtration rate (GFR) and tubular function of the kidney.

Glomerular Filtration Rate (GFR) and Tubular Function

• Term newborn's GFR is approximately 21 mL/min/1.73 m2, increasing to 60 mL/min/1.73 m2 within the first 2 weeks of life and reaching adult levels by 2 years of age.
• Capacity to concentrate urine is limited in preterm and term infants, with a maximum concentration of 600 mOsm/kg compared to 1200 mOsm/kg in adults.

Sodium and Potassium Requirements

• Sodium requirements: 2 mEq/kg per day in term infants, up to 5 mEq/kg per day in critically ill preterm infants due to salt wasting.
• Potassium requirements: 1-2 mEq/kg per day.

Understanding fluid and electrolyte balance is crucial in pediatric surgery, especially in infants who have little reserve. Meticulous attention to hydration status is necessary to prevent fluid overload or dehydration.