The total body water of a newborn is 75%–80% and decreases gradually as fat and muscle content increase with age to the adult level of approximately 60%. The extracellular fluid (ECF) fluid represents 45% of body weight in term neonates and 30% by the age of 1 year, compared with 20% in adults. The term infant can compensate more than the preterm infant, but newborns with a large surface-to-weight ratio, higher total water content, limited renal ability to concentrate, greater insensible water loss from thin skin, and high blood flow can become clinically dehydrated in a very short period of time.
INTRAOPERATIVE FLUID MANAGEMENT
Intraoperative fluid therapy is aimed at providing basal metabolic requirements (maintenance fluids), compensating for preoperative deficits and replacing losses from surgical field.
Holliday and Segar in 1957 first presented a practical method to prescribe intravenous (IV) fluids, best known as the “4/2/1 rule.” Under normal conditions, 1 mL of water is required to metabolize 1 kcal. The calorie expenditure calculated was 100 kcal/kg for infants weighing 3–10 kg (fluid requirement of 4 mL/kg), 1000 kcal +50 kcal/kg for each kilogram between 10 kg but <20 kg (fluid requirement of 40 mL + 2 mL/kg for each kg between 11 and 20 kg), and 1500 kcal +20 kcal/kg for each kilogram over 20 kg (fluid requirement of 60 mL + 1 mL/kg for each kg > 20 kg). The electrolyte composition was considered the same as human milk and cow’s milk and was recommended at 2 mEq/100 kcal/d of both potassium and chloride and 3 mEq/100 kcal/d of sodium. For many decades, the fluid given to children by pediatricians was 5% dextrose (D5) with 0.25%–0.33% strength saline based on this concept.
Recent studies have shown that use of hypotonic solutions along with stress-induced increased secretion of antidiuretic hormone (ADH) perioperatively can lead to hyponatremic encephalopathy, permanent neurological damage, and even death in children. For these reasons, intraoperative estimation of fluid deficits, maintenance fluids, surgical losses, and postoperative fluid management is typically replaced using an isotonic solution such as Ringer’s lactate (LR).
Considerable debate has recently occurred regarding the amount of deficit generated by shorter nil per oral (NPO) status (2 h for clear liquids) and the existence of “third-space losses.” In 1975, Furman proposed calculating the preoperative deficits by multiplying the hourly rate, as per 4/2/1 rule method, by the number of hours NPO. They then suggested replacing half of this volume during the first hour of surgery, followed by the other half over the next 2 hours. In infants and young children who have been starved for excessive periods, addition of 1% or 2% dextrose to LR is appropriate. Conversely, Holliday and Segar have changed their recommendations for maintenance fluid therapy, especially for surgical patients. They recommend to correct first fluid deficit with 20–40 mL/kg, then to give half of the average maintenance for the first 24 hours (2/1/0.5 rule) and to monitor daily sodium plasma concentrations. This fluid deficit is typically replaced using D5LR in the early postoperative period.