Metabolism and nutritional considerations

Infants have relatively greater nutritional requirements than do adults for minimizing loss of body protein. The resting metabolic rate of an infant is two to three times that of an adult, which results in rapid metabolic imbalances in infants. The potential for complications increases proportionately with the duration of fluid restriction because infants are prone to hypovolemia and dehydration.

The neonate’s body weight represents 70% to 80% fluid. Fluid weight is directly related to body fat content. Preterm infants have less body fat and consequently lose fluids easily. Other fluid losses are associated with urinary loss, gastrointestinal loss, insensible loss through respiration, and surgical loss by evaporation via the skin and drains. Fluid replacement for babies is calculated according to body weight as follows:

Procedures performed on infants and toddlers should have priority on the surgical schedule so that these patients can return to a normal fluid and feeding routine as quickly as possible.

Infants may be given regular formula or a varied diet up to 6 hours before anesthesia and clear liquids, usually dextrose in water, up to 2 hours before the surgical procedure. A satisfactory state of hydration is thus maintained, and milk curds are absent from the stomach. Infants may be breastfed up to 4 hours before the surgical procedure. Breast milk has less or no curd and empties faster from the stomach than does formula. Infants should not miss more than one or two feedings. Oral intake is resumed promptly after the infant recovers from anesthesia.

Toddlers and preschool children may be permitted clear liquids up to 2 to 4 hours preoperatively. Intake of clear oral fluids in small amounts decreases the level of gastric acid contents by stimulating gastric emptying and diminishes the hunger-deprivation response.

Children older than 5 years may have nothing by mouth (NPO) after midnight or 6 hours before induction of anesthesia. Exceptions may be necessary for children with fever, diabetes, or other special problems. For these children, clear liquids with supplemental glucose may be ordered to be given orally up to 2 hours preoperatively.

Older children may require slower progression of oral dietary intake postoperatively and are maintained with supplemental intravenous (IV) therapy that includes protein and vitamins. Vitamins K and C may be given to patients of any age-group.

Fluid and electrolyte balance considerations

The newborn is not dehydrated and withstands major surgical procedures within the first 4 days of life without extensive fluid and electrolyte replacement. The renal system is easily overloaded with the administration of IV fluids. The newborn has a lower glomerular filtration rate and less efficient renal tubular function than does an adult. (Renal function improves during the first 2 months of life and approaches adult levels by age 2 years.) During the time of an average surgical procedure on a newborn, a total of 10 to 30 mL of fluid may be administered. Usually 5% dextrose in half-strength normal saline solution is infused.

Administration of excessive IV dextrose solution is avoided in infants younger than 1 year because they maintain lower glycogen stores. During physiologic stress, the patient easily becomes hyperglycemic. Hyperglycemia acts as an osmotic diuretic and causes increased urinary output and dilutional hyponatremia. The increased urine volume can be a false indicator of renal and hemodynamic status. Seizures and neurologic damage may result. Seizures may be clinically undetected while the infant is under general anesthesia because the pharmacologic agents act as anticonvulsants.

Infants have a relatively larger body surface area to body mass ratio than do adults. When they become dehydrated, which can occur rapidly, bodily functions are disturbed, as is the acid-base balance. Plasma proteins differ in concentration from those of an adult. Fluid and electrolyte replacements are necessary. In children older than 1 year, isotonic solutions, such as normal saline or Ringer’s lactate, are given IV per kilogram of body weight.

Urinary output is directly related to body size and age. Neonates can concentrate 400 mOsm/L initially and 500 mOsm/L progressively over the first few days compared with 1200 mOsm/L in the average size adult. This concentration and excretion of the solute load result in 2 to 4 mL/kg/hr urinary output. Older children (toddlers and preschoolers) produce 1 to 2 mL/kg/hr of urine when adequately hydrated. Urine measurement in children is difficult to monitor without a Foley catheter.

The hemoglobin level is lowest at 2 to 3 months of age (Table 8-2). The blood volume of the average newborn is 250 mL, approximately 75 to 80 mL/kg of body weight (Table 8-3). A subtle sign of blood loss is a narrowed pulse pressure less than 20 beats per minute. Significant blood loss requires replacement. Blood is typed and crossmatched in readiness. Although blood loss is small in most cases, a loss of 30 mL may represent 10% to 20% of circulating blood volume in an infant. The small margin of safety indicates the need for replacement of blood loss exceeding 10% of circulating blood volume. When replacement exceeds 50% of the estimated blood volume, sodium bicarbonate is infused to minimize metabolic acidosis.

Hypotension in an infant is not apparent until 50% of the circulating volume is lost. Hypotension is usually caused by myocardial depression from anesthetic agents, primarily inhalation anesthesia. The infant’s myocardium has fewer contractile muscle fibers and more noncontractile connective tissue than in an older child or adult and therefore lacks myocardial force to maintain cardiac output. The cardiac output depends on the heart rate. Any decrease in heart rate directly affects blood pressure and body tissue perfusion.

IV infusions should be administered with the following precautions:

If venous access cannot be quickly established, intraosseous infusion may be indicated for fluid replacement (Fig. 8-1). A cutdown on an extremity vein, usually the saphenous vein, may be necessary for toddlers and older children. An extremity should be splinted to immobilize it. A 150-mL or 250-mL solution drip chamber, sometimes referred to as Burette, Buritrol, Metriset, or Soluset, is used to help avoid the danger of overhydration. This chamber is available in sizes that range from 50 to 250 mL from manufacturers such as Abbott, Braun, and Baxter. Adapters are set for accurate control of the desired flow rate.

Body temperature considerations

Temperature regulation is controlled in the anterior hypothalamus. Cooling causes vasoconstriction for the conservation of body heat. Extremes of cooling cause shivering in infants older than 3 months that generates body heat and increases metabolic needs, causing a 200% to 500% increase in oxygen consumption.

Neonates (especially preterm), infants, and children have wider average body temperature variations than do adults. Infants younger than 3 months do not have a shiver response because of immature neurologic development. Body temperature in the newborn tends to range from as low as 97° F to 100° F (36.1° C to 37.7° C). Temperature begins to stabilize within this range 12 to 24 hours after birth if the environment is controlled. The relatively high rate of heat loss in proportion to heat production in the infant results from an incompletely developed thermoregulatory mechanism and from a body fat to lean mass ratio with only a thin layer of subcutaneous brown fat for insulation.

Extensive extracorporeal circulation (ECMO) also causes rapid dissipation of heat from the body. A hypothermic newborn or infant metabolizes anesthetic agents more slowly and is susceptible to postoperative respiratory depression and delayed emergence from anesthesia. The first signs of significant hypothermia in a pediatric patient younger than 1 year are a heart rate less than 100 beats per minute, metabolic acidosis, hypoglycemia, hyperkalemia, elevated blood urea nitrogen (BUN) levels, and oliguria.

Oxygen consumption is at a minimum when abdominal skin temperature is 97° F (36.1° C). A room temperature 5° F (15° C) cooler than that of abdominal skin produces a 50% increase in oxygen consumption, creating the hazard of acidosis. These factors account for the pediatric patient’s susceptibility to environmental changes. The following can result in heat loss:

Neonates, infants, and children are kept warm during the surgical procedure to minimize heat loss and to prevent hypothermia. Body temperature tends to decrease in the OR because of cooling from air conditioning and open body cavities. Room temperature should be maintained as warm as 85° F (29.4° C). Continuous core body temperature monitoring should be performed (skin temperature sensors may be sufficient for short procedures). Other precautions should also be taken as follows:

The scrub person moistens sponges in warm saline solution before handing them to the surgeon. Irrigant for urologic procedures should be warmed to body temperature except where contraindicated. Room temperature solutions may be indicated where heated solutions may increase bleeding by vasodilation.

Indicators of thermoregulatory status

Hyperthermia (i.e., core temperature of the body over 104° F [40° C]) during the surgical procedure can be caused by fever, dehydration, decrease in sweating from atropine administration, excessive drapes, and drugs that disturb temperature regulation, such as general anesthetics and barbiturates. If the patient is febrile preoperatively, the surgical procedure may be delayed to allow reduction in temperature and to permit fluid administration. If an immediate surgical procedure is necessary and fever persists, anesthesia is induced and external cooling is used. IV fluids may be given at room temperature instead of warmed during administration.

Beginning signs of hypothermia include initial tachycardia and tachypnea as the body tries to compensate by circulating warmed blood throughout the body. As chilling progresses, the pediatric patient becomes bradycardic with shallow respirations because metabolic processes have slowed.

A sudden rise in temperature during the surgical procedure may indicate malignant hyperthermia. Immediate cooling with ice and cool fluids is necessary. More detailed information about malignant hyperthermia is described in Chapter 31.

Cardiopulmonary status considerations

The heart rate fluctuates widely among infants, toddlers, and preschool children and varies during activity and at rest (Table 8-4). Infants younger than 1 year tolerate a heart rate between 200 and 250 beats per minute without hemodynamic consequence. Heart rhythm disturbance is uncommon unless a cardiac anomaly is present. Cardiopulmonary complications manifest as respiratory compromise more frequently than as cardiac dysfunction. After age 5 years, cardiopulmonary response to stress resembles that of a young adult.

Cardiac and respiratory rates and sounds are continually monitored in all age-groups with precordial or esophageal stethoscopy. Blood pressure, vital signs, electrocardiogram (ECG) results, and other parameters as indicated also are monitored throughout the surgical procedure (see Table 8-4). A pulse oximeter can be placed on the palm of the hand or on the midfoot of a newborn or small infant. Smaller patients experience oxygen desaturation easily. A disadvantage of pulse oximetry is that it cannot detect instantaneous drops in oxygen saturation. It gives readouts of levels that have already occurred. Because of increased carboxyhemoglobin levels, it may be ineffective for patients who have had smoke inhalation or carbon monoxide poisoning. A pulse oximeter reading of 80% is clinically diagnostic of central cyanosis. Hypoxemia can cause bradycardia to decrease oxygen consumption of the myocardium.

Infants are particularly susceptible to respiratory obstruction because of their anatomic structure. They are primarily obligate nasal breathers. They have small nares, a relatively large tongue, lymphoid tissue present, and a small-diameter trachea, which causes disproportionate narrowing of the airway. The pharynx is funnel-shaped and allows secretions to pool and obstruct the airway. A cylindric thorax, poorly developed accessory respiratory muscles, and increased volume of abdominal contents limit diaphragmatic movement. The chest is more compliant and collapses easily.

Pediatric infection risk considerations

Newborns and infants are susceptible to nosocomial infection. Many preterm infants who have respiratory distress and circulatory problems survive because of advances in perinatal medicine, which has increased the population of infants who are at high risk and debilitated with reduced humoral and cellular defenses to infection. Aseptic technique is essential in handling neonates and all other pediatric patients.

An elective surgical procedure should be delayed in the presence of respiratory infection because of the risk of airway obstruction. Intubation of inflamed tissues may cause laryngeal edema. Coryza, inflammation of mucous membranes of the nose, is often a sign of an infectious respiratory disease.

Frequent use of antibiotics may lead to antibiotic resistance in some microorganisms. Many types of antibiotics are used to treat infection; however, prevention via aseptic and sterile techniques is more beneficial to the patient.

Pediatric pain management considerations

Infants and children are sensitive to pain with the same intensity as adults. Their pain may be intense, but infants, toddlers, and preschool children are unable to describe its location and nature with specific terms, although they have some limited pain descriptive vocabulary around the age of 18 months.

Neonates and infants can be assessed for pain with physiologic parameters such as heart rate and oxygen saturation and with facial expressions such as brow bulge, eye squeeze, and nasolabial furrow and body movements.

Another method of measuring pain is the FLACC behavioral pain assessment scale (Face, Legs, Activity, Cry, and Consolability) developed by nurses and physicians at C. S. Mott Children’s Hospital at the University of Michigan Health System in Ann Arbor. The chart measures and scores five categories of behavior in pediatric patients ages 2 months to 7 years in relationship to pain (Table 8-5).

School-age children may refer pain to a part of the body not involved in the disease process. Figure 8-2 describes the Wong-Baker FACES pain rating scale that can be used to determine the severity of pain experienced by a pediatric patient. Insecurity and fear in an older child may be more traumatic than the pain itself. Children should be observed for signs of pain (i.e., vocalizations, facial expressions, crying, body movements, physiologic parameters). Children also differ from adults in their response to pharmacologic agents; their tolerance to analgesic drugs is altered (Table 8-6).

Most pediatric medication errors occur because children vary significantly in body weight. The number of near-misses is nearly seven times greater in children than in adults. Many errors are as high as 10 times the usual dose because of decimal placement mistakes in calculation. Considerations in pediatric medication should include the following:

Prevention of pediatric medication errors should include, but is not limited to, the following activities: