EXTREMELY LOW BIRTH WEIGHT INFANT
Category: Child Health
Abstract : Extremely Low Birth Weight Infant Thermoregulation As a result of a
high body surface area–to–body weight ratio, decreased brown fat stores, and
decreased glycogen supply, ELBW infants are particularly susceptible to heat
loss immediately after birth. Hypothermia may result in hypoglycemia, apnea, and
metabolic acidosis. ELBW infants can lose heat in 4 ways, namely, via r
Extremely Low Birth Weight Infant
Thermoregulation
As a result of a
high body surface area–to–body weight ratio, decreased brown fat stores, and
decreased glycogen supply, ELBW infants are particularly susceptible to heat
loss immediately after birth. Hypothermia may result in hypoglycemia, apnea, and
metabolic acidosis.
ELBW infants can lose heat in 4 ways, namely, via radiation,
conduction, convection, and evaporation. Radiation occurs when the infant loses
heat to a colder object, conduction occurs when the infant loses heat through
contact with a surface, convection occurs when the infant loses heat to the
surrounding air, and evaporation occurs when heat is lost through water
dissipation. Temperature control is paramount to survival and typically is
achieved with use of radiant warmers or double-walled incubators. Immediately
after birth, the infant should be dried and placed on a radiant warmer and a hat
or another covering should be placed on its head. Hypothermia (<35°C) has
been associated with poor outcome, including chronic oxygen
dependency.
During transport from the delivery room to the neonatal
intensive care unit, care should be taken to cover the baby, either with warmed
blankets or with cellophane wrap, to help the infant retain body heat. The
infant should be placed in a double-walled heated incubator during transport.
The delivery room and the neonatal intensive care unit also should be kept warm
to prevent hypothermia in the infant. Future architectural designs should
facilitate adjacent location of delivery rooms and neonatal intensive care units
or at least provide separately heated resuscitation
rooms.
Hypoglycemia
Fetal euglycemia is maintained during pregnancy by
the mother via the placenta. However, ELBW infants have difficulty maintaining
glucose levels within reference range after birth, at which time the maternal
source of glucose is lost. In addition, ELBW infants are usually under stress
and have insufficient levels of glycogen stores. In the preterm infant,
hypoglycemia usually is diagnosed when whole blood glucose levels are lower than
20-40 mg/dL. In a recent review, Cornblath et al also recommended that a glucose
concentration of less than 45 mg/dL be used as a screening or treating level in
preterms infants. Symptoms may be present but may not be as obvious as those in
a more mature infant (seizures, jitteriness, lethargy, apnea, poor feeding).
Thus, hypoglycemia often may be discovered only after routine serum dextrose
sampling. One form of accepted treatment consists of an immediate intravenous
glucose infusion of 2 mL/kg of 10% dextrose-in-water solution (200 mg/kg)
followed by a continuous infusion of dextrose at 6-8 mg/kg/min to maintain a
constant supply of glucose for metabolic needs and to avoid
hypoglycemia.
Fluids and electrolytes
Fluid and electrolyte management
must be closely controlled because disturbances may result in or exacerbate
morbidities, such as patent ductus arteriosus (PDA), intraventricular hemorrhage
(IVH), and chronic lung disease (CLD) or bronchopulmonary dysplasia (BPD).
Compared to full-term newborns, ELBW infants have proportionally more fluid in
the extracellular fluid compartment than the intracellular compartment. They
also have a larger proportion of total body weight composed of water. During the
early days after birth, diuresis may result in a 10-20% weight loss, which can
be exacerbated by iatrogenic causes, such as radiant warmers and
phototherapy.
ELBW infants also have compromised renal function stemming
from a decreased glomerular filtration rate; a decreased ability to reabsorb
bicarbonate, secrete potassium, and other ions; and a relative inability to
concentrate urine. In addition, they reabsorb creatinine via the tubules
following birth and, thus, serum creatinine levels are elevated for at least the
first 48 hours of life, especially in ELBW infants, and do not reflect renal
function for the first few days following birth. Fluid status is commonly
monitored with daily (or sometimes twice daily) body weights and strict
recording of fluid intake and output.
Electrolytes are monitored
frequently to maintain homeostasis. ELBW infants are prone to nonoliguric
hyperkalemia, defined as a serum potassium level greater than 6.5 mmol/L, which
has been associated with cardiac arrhythmias and death. Omar et al concluded
that prenatal administration of steroids prevented nonoliguric hyperkalemia in
ELBW infants, and they speculated that prenatal use of steroids induced
up-regulation of cell membrane sodium-potassium-ATP activity in the
fetus.
Nutrition
Initiating and maintaining growth of ELBW infants is
a continuing challenge. Infants commonly are weighed daily, and body length and
head circumference usually are measured weekly to track growth. The growth rate
often lags because of complications such as hypoxia and sepsis. Concern that
early feeding may be a risk factor for necrotizing enterocolitis (NEC) often
deters initiation of enteral feeding. Parenteral nutrition may provide the
greater source of energy in ELBW infants in the first few weeks after
birth.
ELBW infants have high energy requirements because of their
greater growth rate. Heat loss from the skin also raises energy needs. ELBW
infants expend 60-75 kcal/kg/d and need at least 120 kcal/kg/d to achieve the
desired growth rate of 15 g/kg/d. Current common practice in the early days
after birth calls for most energy to be provided in the form of parenteral
glucose and lipids. ELBW infants may tolerate a glucose infusion rate of 6-8
mg/kg/min, but hyperglycemia may be a common and serious complication early
after birth.
Lipid intake may vary from 1-4 g/kg/d of 20% lipid emulsion,
as tolerated. Since ELBW infants lose at least 1.2 g/kg/d of endogenous protein,
they require at least that amount of amino acids and 30 kcal/kg/d to maintain
protein homeostasis. They also need such essential amino acids as cysteine and
may require glutamine, found in human breast milk but not always present in
parenteral nutrition mixtures. Trace minerals, such as iron, iodine, zinc,
copper, selenium, and fluorine, are beneficial as well. Early evidence suggests
that chromium, molybdenum, manganese, and cobalt may need to be added to the
nutritional regimen, especially in ELBW infants who require long-term parenteral
nutrition.
Enteral feeding often is begun when the infant is medically
stable, using small-volume trophic feeding (approximately 10 mL/kg/d) to
stimulate the gastrointestinal tract and prevent mucosal atrophy. Prolonged use
of parenteral nutrition may result in cholestasis and elevated triglyceride
levels. To reduce these complications, weekly laboratory tests usually are
obtained to evaluate liver function, alkaline phosphatase, and triglyceride
levels. Bolus feedings every 2-4 hours may begin as early as day 1. If
tolerated, as evidenced by minimal gastric residuals and clinical stability,
feeding may increase to 10-20 mL/kg/d, although feeding practices vary widely.
Although bolus feeding may appear to be more physiologically appropriate,
infants who do not tolerate the volume of the bolus may be fed
continuously.
Breast milk is considered by some to be the best choice for
enteral feeding and has been suggested to have protective effects against NEC.
Breast milk must be fortified with calcium and phosphorus to promote proper bone
growth. Low birth weight infants have a high need for macronutrients and
micronutrients that approaches intrauterine needs; at the same time, the
functionally immature gastrointestinal tract precludes adequate enteral intake.
Despite its many immunologic and nutritional advantages, an exclusive diet of
unsupplemented breast milk may provide insufficient quantities of energy,
protein, calcium, and phosphorous to support the goals of intrauterine bone
mineralization and growth rates in small premature infants.
Human milk
may be supplemented by adding liquid or powder commercially available
fortifiers, premature infant formulas, modular supplements, or vitamin/mineral
supplements. Commercially available multinutrient fortifiers include Enfamil
Human Milk Fortifier (Mead Johnson Nutritionals; Evansville, Indiana) or Similac
Human Milk Fortifier (Ross Products, Abbott Laboratories; Columbus, Ohio), both
of which are powders. Similac Natural Care Liquid Fortifier (Ross Products),
which is a liquid, is also available.
Comparisons of the nutrient content
and source of macronutrients of these fortifiers have been published. Potential
complications of human milk fortifiers include nutrient imbalance, increased
osmolarity, and bacterial contamination. A number of specially formulated
preterm formulas are available that have been shown to promote proper growth, as
well. Caloric density usually is increased when a full feeding volume is
achieved and the infant is no longer on intravenous supplementation.
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