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CHAPTER 2

Neonatal Physiology and Transport

Larry Hadley
Kokila Lakhoo

Introduction
It is perhaps trite to emphasize that the child is not merely a small adult,
but nowhere is this distinction more apparent than in the neonate.
The transition from intrauterine to extrauterine life requires
fundamental changes in the circulatory, respiratory, metabolic, and
immune functions of the newborn. When a surgical pathology is added
to the mix, these essential adaptations can be compromised, leading to Birth Weight (gm)
organ dysfunction. Single organ dysfunction is frequently the start of a
cascade that rapidly results in failure of the entire organism. Thus, the
emphasis in neonatal care is on the prevention of problems rather than
on the management of disasters once they have occurred. In order to
prevent dysfunction, it is important to recognise patients at particular
risk but also to have in place general principles of care and to train
nursing staff and paramedical personnel in their application. Neonatal Preterm Postterm
care is a team effort. Whenever possible, the team should include the
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mother and other family members, if culturally appropriate. Gestation (weeks)
Neonatal physiology is not defined by geography or politics, but
our ability to recognise and respond to system dysfunction is a factor Figure 2.1: Neonatal classification (LGA = large for gestational age; AGA =
of the human and material resources available. In a developing country appropriate for gestational age; SGA = small for gestational age).
where scarce resources must be utilised for the maximum benefit of
numerous constituencies, imaginative alternatives to standard Western maternal infections and poor nutrition, placental insufficiency, maternal
care are required. It is in just this environment that maternal ill health cigarette smoking, and maternal substance abuse such as drugs and
and deficient antenatal care add to the considerable difficulties faced by alcohol. Frequently, polyhydramnios complicates a pregnancy in
neonates during the perinatal period. which the foetus has an intestinal abnormality due to the inability to
Many of the neonate’s survival mechanisms are installed during ingest and recycle amniotic fluid, stimulating early labour. Such babies
the third trimester of pregnancy, and preterm delivery can additionally are therefore exposed to the risks of prematurity and its associated
challenge the successful transition to independent life, the difficulties problems as well as the morbidity of a surgical pathology. Recognition
being directly proportional to the degree of prematurity. of a neonate’s status allows prediction of potential clinical problems,
Occasionally, the uterus proves to be a hostile environment for thus allowing preventive steps to be taken. Table 2.1 outlines the
the developing foetus and, in conjunction with obstetric colleagues, traditional risks faced by SGA and preterm infants.
pregnancy management will need to take account of the interests of The risks associated with prematurity are reflected in the mortality
both the foetus and the mother. Certainly, the antenatal recognition of preterm babies without surgical disease and depend upon the degree
of surgical disease calls for skilled management of the pregnancy and of prematurity and body weight (Figure 2.2). This risk of mortality
delivery and provides the surgeon with an unborn patient for whom must be weighed against the available resources and the nature of the
diagnosis, prognosis, investigation, and management are difficult. surgical problem before a decision on management can be taken. Such
A few specific anomalies can be ascribed to genetic, teratogenic, or considerations are particularly germane to the practice of neonatal
infectious causes, but the pathogenesis of most congenital malformations surgery in a developing country where both human and material
remains unknown. It is improbable, however, that any insult that results resource limitations may be extreme.
in a congenital abnormality will affect a single system or structure
without affecting other structures that are developing at the same time. Temperature Control
Thus, multiple abnormalities should be suspected and sought in every The neonate is designed as a radiator with a large surface area relative
neonate presenting for surgery. to its mass. Heat is lost through convection, conduction, radiation,
Neonatal Classification and the latent heat of evaporation of transdermal fluid loss. In the term
neonate, heat loss is reduced by a layer of insulating subcutaneous fat
Neonates come in a variety of sizes and degrees of maturity. It is impor-
and a thick skin that reduces transdermal fluid loss. Heat production
tant to recognise risk factors in any patient presenting for surgery, but
comes from hepatic glycogenolysis and the metabolism of brown fat, a
particularly so in the neonate, in whom body weight and prematurity
metabolic response termed “nonshivering thermogenesis”. All of these
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are easily assessed and critical to defining the likely co-morbidities and
defences against heat loss are weakened in the preterm infant, who has
risk factors and help to determine appropriate management (Figure 2.1).
a thin skin, increased transdermal water loss, no subcutaneous fat, and
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Many “surgical” babies are born before term; in addition, they are
who has been born before having the opportunity to lay down any brown
often small for their gestational age (SGA). Causative factors include