Pediatric surgical patients are not merely small adults. The
surgical care of children differs markedly from that of adults in
many respects, including unique physiologic demands that vary according
to age and development. The neonate’s physiologic development
is closer to that of a fetus, while adolescents’ physiology
is similar to that of adults, and infants and children have problems unique
to their chronologic and developmental age. Infants and children
also suffer from congenital abnormalities and diseases not seen
in adults, and their management requires an intimate understanding
of the relevant embryology and pathogenesis.
The newborn infant with a surgically correctable lesion often
has other disorders that threaten survival. The care of these babies,
particularly for premature and small-for-gestational-age (SGA) babies,
has improved with the emergence of the intensive care nursery. Dramatic
advances have been made in the technology of infant monitoring and
respiratory support. Low-birth-weight infants can now receive ventilatory
support from sophisticated infant respirators for prolonged periods
in a precisely controlled microenvironment. Surfactant therapy and
high-frequency ventilation has allowed a population of extremely
premature infants to survive. Temperature is controlled by servoregulation,
while pulse and blood pressure are continuously recorded. Ventilation
is monitored by transcutaneous O2 and CO2 electrodes
or by indwelling arterial catheters. The metabolic consequences
of prematurity and intrauterine growth retardation are monitored
by frequent measurement of glucose, calcium, electrolytes, and bilirubin
in microliter quantities of blood. Nutritional requirements for
growth and development can be provided by enteral or parenteral routes.
This kind of specialized care of critically ill newborns requires
trained personnel and specialized equipment. The care of such babies
is best accomplished in designated regional centers capable of providing
pediatric surgical and neonatal intensive care.
Phibbs CS et al: The effects of patient volume
and level of care at the hospital of birth on neonatal mortality.
Newborn infants can be classified according to their level of
maturation (weight) and development (gestational age). A normal
full-term infant has a gestational age of 37–42 weeks and
a body weight greater than 2500 g. The gestational age of the infant
is calculated from the date of the last normal menstrual period.
However, clinical assessment of gestational age by morphologic and
neurologic examination of the small infant can be more accurate
than calculation from the menstrual history.
Four signs may be useful in assessing gestational age. Infants
less than 37 weeks’ gestational age have (1) fine fuzzy
hair with thin, semitransparent skin, (2) ears that lack cartilaginous
support, (3) a breast nodule less than 3 mm in diameter, and (4)
few transverse creases on the balls of the feet anteriorly. In males,
the testicles are incompletely descended and reside in the inguinal canal,
and the scrotum is small with few rugae. In females, the labia minora
are relatively enlarged and the labia majora are small.
Preterm infants are those born before 37 weeks’ gestation. Several
physiologic abnormalities may coexist in preterm infants. Apneic
and bradycardic episodes are common and may represent an immature
central nervous system or, conversely, may represent signs of physiologic
instability, most notably with sepsis. The lungs and retinas of
preterm infants are very susceptible to high oxygen levels. Retinopathy
of prematurity from oxygen toxicity may lead to blindness. Relatively
brief exposures to high oxygen concentrations, often coupled with
barotrauma from the mechanical ventilator, may damage the lungs,
resulting in hyaline membrane disease and respiratory distress syndrome.
Shunting across a patent ductus arteriosus is not uncommon and may
lead to pulmonary hemorrhage and congestive heart failure. The preterm
infant has a friable choroids plexus and is thus susceptible to
intraventricular hemorrhage when stressed in the first week of life.
The premature infant may be unable to tolerate oral feeding because
of a weak suck reflex. Tube feeds or total parenteral nutrition
may be required. Preterm infants have increased requirements for
glucose, calcium, and sodium as well as a propensity for hypothermia,
impaired bilirubin metabolism, polycythemia, and metabolic acidosis. These
problems are accentuated in very low-birth-weight infants or “micropremies” (birth
weight less than 1000 g).
A SGA infant is one who is less than the 10th percentile in weight
for their gestational age. An SGA infant is the product of a pregnancy
complicated by any one of several placental, maternal, or fetal abnormalities.
Although body weight is low, body length and head circumference are
age-appropriate. Compared with the premature infant of equivalent
weight, the SGA infant is developmentally more mature and faces
different physiologic problems. Intrauterine malnutrition results
in reduced body fat and decreased glycogen stores. Their relatively
large surface area and high metabolic rate predisposes them to hypothermia
and hypoglycemia. SGA infants also have an increased risk of meconium
aspiration syndrome. Polycythemia (which may lead to complications
of hyperviscosity syndrome) is common and necessitates close monitoring
of their hematocrit. Because of their relatively mature organ development
and function (compared to preterm infants), retinopathy of prematurity,
intraventricular hemorrhage, and hyaline membrane disease are uncommon.
Infants and children are susceptible to heat loss because they
have a relatively greater body surface area and a thinner subcutaneous
fat layer compared with adults. Heat loss occurring by conduction,
convection, evaporation, and radiation may be four times that of
the adult and is further increased in the preterm infant. Infants
are homeotherms and will expend metabolic energy to stay warm at the
cost of other functions. Heat is generated not by shivering but
by metabolizing brown fat reserves (nonshivering thermogenesis)
in response to norepinephrine. This has practical consequences,
since brown fat may be rendered inactive by some medications (pressors
and anesthetic agents) and may be depleted by poor nutrition. Exposure
to cold environments increases metabolic work and caloric consumption.
Due to limited energy reserves and thin skin, ...