The Holliday-Segar equation remains the standard method for calculating maintenance fluid requirements. Accounting for deficits when determining the fluid. Maintenance fluid therapy as defined by Holliday and The formula assumes normal renal function . Holliday/Segar formula of ml/kg body weight (BW). The Maintenance Fluid Calculation for Children helps to determine the daily volume of fluids needed based on the weight of a child. This calculation also.
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Managing fluids and electrolytes in children is an important skill for pharmacists, who can play an important role in monitoring therapy. Fluid therapy is divided into maintenance, deficit, and replacement requirements. The Holliday-Segar equation remains the standard method for calculating maintenance fluid requirements.
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. 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.
Fluid therapy can also have an impact on drug therapy.
Pediatric Fluid and Electrolyte Therapy
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. Monitoring fluid and electrolyte therapy is an important role of the pediatric pharmacist. Fluid and electrolyte therapy is an essential component of the care of hospitalized children, and a thorough understanding of the changing requirements of growing children is fundamental in appreciating the many important pharmacokinetic changes that occur from birth to adulthood.
While there are many factors that contribute to the fluid and electrolyte needs of children, approaching this therapy in a systematic, organized fashion can help pharmacists meet ongoing as well as changing needs of the patient.
Organizing fluid therapy into maintenance, deficit, and replacement requirements, and then monitoring the patient for response to therapy makes fluid therapy manageable.
Total body water content changes drastically from before birth until one year of age.
In addition to total body water differences, the percent of body weight accounted for by intracellular and extracellular water also changes. Aminoglycosides are a classic example, as the dose varies widely by age.
By the time a patient is out of the neonatal period, the usual dose of gentamicin is 2. 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.
Physiologic sdgar also play a role in fluid therapy. The changes that segra place as a child grows have a great effect on fluid requirements, making special attention to fluid therapy essential in pediatric pharmacotherapy. There are three classifications of fluid therapy, maintenance, deficit, and replacement, each of which will be discussed separately. When choosing the type of fluid and volume to be administered, careful consideration should be paid to each component of fluid therapy.
Maintenance fluids are given to compensate for ongoing losses and are required for all patients. 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.
Requirements for children are higher than those for adults for multiple reasons. First, the higher metabolic rate of children requires a greater caloric expenditure, which translates into higher fluid requirements. In addition, children, especially infants, have higher respiratory rates, 8 and this equates to higher insensible losses from the respiratory tract Table 1.
Additional factors must be taken into consideration when determining insensible fluid losses. 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. There are many mechanisms of determining the maintenance fluid requirements for children. Each of these methods, while providing a reasonable estimate of maintenance fluids, cannot account for the physiologic changes that occur in hospitalized children.
For this reason, when calculating maintenance fluids, pharmacists must always keep in mind factors that may affect fluid balance and changed needs. Hospitalized children frequently have elevated fluid requirements due to their illness.
Patients suffering from fever, burn injuries, 9 hypermetabolic states, pain, asthma, and increased intestinal losses may all have elevated maintenance fluid requirements.
Pediatric Fluid and Electrolyte Therapy
Burn patients in particular are a classic example of patients with increased fluid needs due to higher metabolic rates. While insensible losses from ventilation may not account for a large amount of ongoing normal losses, conditions that increase respiratory formu,a e. When considering fluid requirements in hospitalized children, potential increased or decreased needs should always be kept in mind. The most commonly used technique to calculate maintenance fluids for children is the Holliday-Segar method Table 2.
Forumla every kilocalories used during metabolism, roughly mL of fluid is needed to replace losses.
Thus, while the Holliday-Segar method actually estimates kilocalories lost, it is estimated that a loss of 1 kilocalorie requires 1 mL in replacement, so the kilocalorie estimate is an efficient target for fluid requirements. Other methods of estimating maintenance fluid requirements exist, including those using body surface area and basal calorie requirements. Generally these equations involve more calculations, and the basal calorie requirement method requires an indirect calorimeter, which is an expensive piece of equipment.
The Holliday-Segar method is usually preferred due to its ease of calculation; however, the other methods are employed in some instances. The Holliday-Segar method may be simplified by estimating the fluid requirements in rate required per hour.
This equation, also listed in Table 2arrives at similar volumes of fluid as the traditional Holliday-Segar equation. Deficit fluids, like maintenance fluids, are most easily handled by approaching the needs of the patient in a systematic manner. Clinical signs of dehydration should be taken into consideration first, as they can provide useful insight into the fluid needs of the patient. One clinical sign of dehydration which can be of use is weight loss. Most young children visit their pediatricians frequently, and a relatively recent pre-illness weight will be on record.
Other clinical signs include increased thirst, dry mucous membranes, and decreased urine output Table 3. Every 1 kg of weight lost is equivalent to 1 L of fluid loss. The degree of dehydration calculated should always be compared to the clinical signs, which may be better indicators of hydration status and are also especially useful when a pre-illness weight is unknown.
Once the degree of dehydration is established, the type of dehydration, defined by serum sodium concentrations, needs to be determined. Most dehydrated patients have an isotonic dehydration. Patients with mild to moderate dehydration may be rehydrated with oral therapy, even if diarrhea and vomiting continues.
Patients with hypotonic or isotonic dehydration are given fluids using the same technique to calculate fluid amount and rate Table 5. Rehydration is divided into three phases. In phase I, a bolus of fluid is given in order to restore blood volume to ensure adequate perfusion of critical organs, such as the brain.
Bolus fluids should be isotonic; either normal saline or lactated ringers solution is used at a volume of 20 mL per kg, given over 60 minutes. Isotonic fluids are used because they provide rapid volume expansion in the plasma and extracellular fluid.
When determining the amount of fluid to be administered in phases II and III, the fluid volume given during phase I should be subtracted from the deficit fluid. Phase II is given over 8 hours. Phase III is given over 16 hours. The amount of fluid in phase III is equivalent to two thirds of the daily maintenance plus the remaining deficit.
Generally speaking, phases II and III are simply maintenance fluid plus deficit fluid, given over 24 hours, with half of the deficit fluid given in the first 8 hours, and the second half of the deficit fluid given in the last 16 hours Table 6.
The approach to patients with hypertonic dehydration is quite different, due to the hyperos-molar state of their circulating blood. The deficit fluid volume should be added to the maintenance fluid volume needed for 48 hours, and the total should be administered over 48 hours.
Administering the deficit fluid faster causes osmotic fluid shifts, which can result in cerebral edema and convulsions. Replacement fluids are defined as those given to meet ongoing losses due to medical treatment. Examples of clinical situations where replacement fluids are needed include patients with chest tubes in place, uncontrolled vomiting, continuing diarrhea, or externalized cerebrospinal fluid shunts.
Each of these examples demonstrates a situation where there is an ongoing loss which would not be met by administering only maintenance fluids. Replacement fluids differ from deficit fluids in that they are ongoing, as opposed to a loss of fluid that occurred prior to receiving medical treatment. Concentrations of electrolytes are determined in large part by renal function, 7 making consideration of the patient’s clinical status vitally important when considering electrolyte requirements in children.
An anuric patient will recycle sodium and potassium, making supplementation generally unnecessary. Any renal dysfunction requires frequent electrolyte monitoring. Electrolyte replacement in intravenous fluids generally includes sodium, potassium, and chloride.
It is important to consider maintenance electrolyte requirements when choosing a maintenance fluid for a child. For the most part, practitioners can choose from commercially available products to adequately fulfill maintenance needs. However, there has been recent attention in the literature to the potential for causing hyponatremia when using 0. Some even argue the need for isotonic fluid. Recently, two pediatric deaths from hyponatremia have been reported in post-operative situations.
The subsequent symptoms of hyponatremia were mistaken for a dystonic reaction from promethazine, and the child was treated with diphenhydramine. The second case involved a patient who had surgery to repair a coarctation of the aorta.
The patient became hyponatremic after receiving ethacrynic acid, and it was unclear whether the patient received the subsequent order for a sodium chloride infusion. On the second post-operative day, the patient was unarousable, and this was confused for a side effect of receiving hydromorphone. Later, seizures were misperceived as fidgeting from pain. In both of these cases, symptoms of hyponatremia were explained as side effects of drugs. The potential for hyponatremia or hypernatremia emphasizes the need for close monitoring of serum sodium in hospitalized children receiving intravenous fluid therapy, particularly in the post-operative period.
This is generally given over a few hours, with serum sodium checks done throughout in order to avoid hypernatremia. If the blood came from a heel stick, as is frequently done in infants, cell lysis due to the trauma of the needle can cause intracellular potassium to enter the serum locally, leading to falsely elevated serum potassium.
Hyperkalemia can be treated with a variety of medications. There are multiple mechanisms for decreasing serum potassium, and medications are chosen based upon their mechanism and the level of urgency of the clinical situation. In emergencies, agents which cause a rapid influx of potassium intracellularly are useful as they provide an acute decrease in serum levels. These medications include insulin and beta adrenergic agonists such as albuterol. Sodium polystyrene sulfonate is an exchange resin which holljday sodium for potassium in the gut; 19 its use is generally for less emergent situations.
Diuretics such as furosemide can also be used to increase potassium excretion into the urine, however, diuretics should be used cautiously, as the resultant volume depletion can cause decreased potassium excretion. Determining an initial fluid rate for children based upon their needs is essential. However, once therapy is begun, appropriate monitoring is necessary due to the frequently changing needs of a hospitalized patient. The first parameter for monitoring is oral intake Table 6.
Generally speaking, the oral route for providing fluid therapy is preferred as soon as it is clinically indicated, as any intravenous administration brings with it the risk of infection. Patients who hollkday not allowed anything by mouth for a short time, such as for an uncomplicated surgery, and for whom only maintenance fluids are required, may have their fluids decreased and eventually stopped once they tolerate oral hydration.