Each of these methods, while providing a reasonable estimate of maintenance fluids, cannot account for the physiologic changes that occur in hospitalized children. There are many mechanisms of determining the maintenance fluid requirements for children. Congenital abdominal wall defects such as omphalocele and gastroschisis can lead to higher evaporative losses before surgical correction, and thus careful attention should be paid to fluid balance and electrolytes. In addition, children, especially infants, have higher respiratory rates, 8 and this equates to higher insensible losses from the respiratory tract ( Table 1).Īdditional factors must be taken into consideration when determining insensible fluid losses.
#Practical guidelines on fluid therapy pdf skin
6 Secondly, children, especially infants, have a much higher body surface area to weight ratio, and this translates into relatively more water loss from skin compared with adults. First, the higher metabolic rate of children requires a greater caloric expenditure, which translates into higher fluid requirements. Requirements for children are higher than those for adults for multiple reasons. Sensible losses, which include urine output and fecal water, make up the majority of ongoing losses, with additional contributions from insensible losses such as respiration and perspiration. 6 Maintenance fluids are frequently given through an intravenous line, but can also be given orally if the patient is able to tolerate oral therapy. Maintenance fluids are given to compensate for ongoing losses and are required for all patients. The interval between doses is longer in premature infants, up to 48 hours, but this is associated with the immaturity of the neonatal kidney, and not total body water. 5 Drugs generally distribute into the extracellular space, thus the larger extracellular component of fluid in neonates also contributes to the need for larger doses. By the time a patient is out of the neonatal period, the usual dose of gentamicin is 2.5 mg/kg. 4 The dose required to achieve the same peak decreases with older neonates, as the total body water decreases with age. Premature babies require large doses, usually 5 mg/kg of gentamicin, in order to achieve adequate peak concentrations (6–10 mg/L) in the blood. Aminoglycosides are a classic example, as the dose varies widely by age. 2 These changes in total body fluid have important implications for drug therapy, particularly for water soluble drugs. 2 Newborn babies have more extracellular water-45% of total body weight-compared with only 35% of total body weight that is intracellular water. In adults, who have about 60% of total body weight as water, about 20% of total body weight is extracellular water and 40% is intracellular water. In addition to total body water differences, the percent of body weight accounted for by intracellular and extracellular water also changes. 2, 3 In fact, if this weight loss does not occur, there is cause for concern for renal dysfunction and sepsis. 2Īfter birth, infants are expected to lose approximately 5%-15% of their body weight, with more being lost in low birth weight infants. 2 Most adults' total body water is between 50% and 60% of total body weight. 1 This slowly decreases until the child is around one year of age, when total body water content is about 60% of total body weight. At 24 weeks gestational age, a baby's total body water content is close to 80% of total body weight.
Total body water content changes drastically from before birth until one year of age. Monitoring fluid and electrolyte therapy is an important role of the pediatric pharmacist. Hydration status can affect the dose needed to achieve therapeutic concentrations, and dehydrated patients may be at risk for toxicity if standard doses of drugs with high volumes of distribution are used.
Fluid therapy can also have an impact on drug therapy.
Maintenance electrolyte requirements must be taken into account, with particular attention paid to sodium requirements, as recent evidence suggests that sodium needs in hospitalized children are higher than originally thought. Accounting for deficits when determining the fluid infusion rate is an important factor in treating dehydrated patients deficit fluid is generally administered over the first 24 hours of hospitalization. The Holliday-Segar equation remains the standard method for calculating maintenance fluid requirements. Fluid therapy is divided into maintenance, deficit, and replacement requirements. Managing fluids and electrolytes in children is an important skill for pharmacists, who can play an important role in monitoring therapy.