Maintenance fluids

Reliance on the method of Holliday and Segar continues despite concern regarding its relevance to the perioperative care of young children. In their seminal 1957 paper, the authors provided a simplified method for estimating maintenance fluids and electrolytes based on energy requirements: 1-kg to 10-kg infants need about 100 cal·kg⁻¹·24 h⁻¹; each kilogram over 10 kg and up to 20 kg requires an additional 50 cal·kg⁻¹·24 h⁻¹; after 20 kg, each additional kilogram requires 20 cal·kg⁻¹·24 h⁻¹. Approximately 1 mL of water is needed for each calorie expended. This method can be simplified (Table 194-1). These recommendations were intended to guide maintainence fluid therapy for hospitalized children, however, and not for intraoperative care.

Fluid replacement

The fluid deficit in a patient receiving nothing by mouth can be calculated by multiplying the number of hours that the patient is not receiving anything by mouth by the maintenance fluid requirement. Although a scientific basis for the following recommendation is lacking, common practice is to not only provide maintenance requirements, but also replace half of the fluid deficit in 1 h, one fourth of the deficit in the second hour, and the final one fourth of the deficit in the third hour. Likewise, limited data exist to support the practice of replacing third-space losses, as has been described in most standard texts of pediatric anesthesia (Table 194-2). Many factors may influence fluid requirements in the very young, making the use of simplified formulas problematic and potentially dangerous. In the neonate, insensible water loss is increased by fever, crying, sweating, hyperventilation, bilirubin lights, and radiant heaters. Adequacy of fluid therapy is best monitored by clinical signs (heart rate, blood pressure, urine output, capillary refill, central venous pressure) rather than by blind adherence to a poorly validated formula. A few simple rules that will help to avoid problems occasionaly encountered in fluid management:

Blood replacement

In the first 3 months of life, infants experience a physiologic anemia, decreasing their mean hemoglobin of 16.8 g/dL at term to a nadir of 10.5 to 11.5 g/dL at age 8 to 12 weeks. In premature infants, this decrease may be even more profound and may occur around week 6 post partum. Infants undergoing surgical interventions during this time do not require transfusion therapy unless they have clinical indications to do so. There are only two accepted indications for the transfusion of red blood cells: (1) to increase O₂-carrying capacity (O₂ delivery = cardiac output × hemoglobin × O₂ saturation) or to avoid an impending inadequate O₂-carrying state and (2) to suppress production, or dilute the amount, of endogenous hemoglobin in selected patients with thalassemia or sickle cell disease.

In 1996, the American Society of Anesthesiologists Task Force on Blood Component Therapy published transfusion practice guidelines that are probably applicable to pediatric patients without cardiopulmonary disease. The points regarding red blood cell transfusions are summarized here. Guidelines specific to pediatric patients older than 4 months of age have been published (Box 194-1).

A number of calculations have been presented for the evaluation of transfusion thresholds. One such formula proposes that the maximum allowable blood loss should equal the estimated blood volume multiplied by the hematocrit minus the target hematocrit divided by the hematocrit. In clinical practice, these calculations have limited utility as they are dependent on estimates of blood loss that have been repeatedly shown to be inaccurate. In children, transfusion is best guided by close monitoring of hemodynamic parameters and frequent determination of hemoglobin concentration. Estimated blood volume for various ages is shown in Table 194-4.

Red blood cell products

The transfusion of fresh whole blood (≤5 days old) would appear to be the obvious choice for resuscitation of a bleeding child because it replaces all of the components being lost. If fresh whole blood is not obtainable but its use is required, stored red blood cells can be reconstituted with fresh frozen plasma. It may be appropriate to ask the blood bank to split units to limit donor exposure and waste. For neonates, it is recommended that red blood cells be cytomegalovirus negative and leukocyte reduced via filtration or irradiated to prevent infection and graft-versus-host disease.

Glucose management

Much controversy exists over the need for the administration of supplemental glucose in infants and children. Some recommend the use of glucose-containing fluids for all children under anesthesia, whereas others suggest that only infants and younger children need intraoperative glucose supplementation. A third option is to measure the patient’s glucose concentration during the operation and to supplement only when needed. Any of these options is acceptable as long as care is taken to prevent hyperglycemia and, more importantly, hypoglycemia. The simplest means of preventing either is to use a solution of 2.5% dextrose in lactated Ringer’s solution infused at a maintenance rate. This solution should be used in all infants and young children and may be sufficient for those at risk for developing hypoglycemia (those with metabolic or liver disease). Premature infants and neonates, however, may require a solution containing 5% dextrose, as their glucose consumption may be as high as 8 mg·kg⁻¹·min⁻¹. Infants receiving concentrated glucose solutions preoperatively should continue to receive at least half the rate intraoperatively. When in doubt, the serum glucose concentration should be measured at regular intervals. No data exist to support tight intraoperative glucose control in children, as has been advocated for adults. The risk of profound neurologic injury resulting from hypoglycemia must be weighed against the uncertain benefit of tight glucose control.