TRANSITION TO EXTRA-UTERINE LIFE

Following birth the neonate undergoes several physiological changes so that it can adapt to extra-uterine life. Two main changes affect respiration and cardiovascular function.

Changes in the pattern of blood circulation

The second change is the redirection of the blood flow following the cessation of the high blood flow through the umbilical arteries that perfused the placental villi, and a lowering of the large volume of blood returning through the umbilical vein and the vena cava. The venous pressure in the vena cava falls and the ductus venosus closes. The lungs expand with the first breath and the pulmonary vascular resistance falls abruptly. The infant’s systemic blood pressure rises slightly at the same time, which results in a temporary reversal in the direction of the blood flowing through the ductus arteriosus. As the infant breathes, the oxygen tension in the blood rises and the muscular walls of the ductus contract, the passage of blood through it ceasing. At the same time, the pressure in the right atrium falls. There is a simultaneous increase in the blood flow through the lungs. This blood enters and increases the pressure in the left atrium. Because of the changes in pressure between the two atria, the foramen ovale closes.

With the closure of the ductus venosus, the foramen ovale and the ductus arteriosus, the adult pattern of circulation of the blood is established (Fig. 26.1; compare with Fig. 4.1, p. 29).

Fig. 26.1 Normal circulation in the newborn.

PERINATAL HYPOXIA

Any condition occurring during late pregnancy or labour that reduces the oxygen available to the fetus will predispose it to cardiorespiratory and neurological depression at birth. These conditions have been mentioned when discussing the at-risk fetus in pregnancy and labour (see p. 152).

If severe fetal hypoxia develops in pregnancy, the fetus may die in utero or may be born with acidaemia and hypercapnia as well as hypoxia (asphyxia). A blood pH of less than 7.10 may lead to pulmonary vasoconstriction, which further impairs gas exchange. Hypoxia increases the base deficit and blood lactate level. Both of these changes increase the risk to the fetus of neurological damage. In such cases, resuscitation is urgently needed at birth.

The severity of cardiorespiratory and neurological depression around the time of birth can be assessed by the Apgar scoring system (Table 26.1) or by the pH and/or blood lactate of umbilical artery blood. Both are useful in managing the immediate problem but are relatively poor indicators of long-term outcome.

The basic resuscitation of the newborn is described on page 77 (see Fig. 8.15). The most important step in resuscitation is to initiate ventilation with intermittent positive-pressure respiration; current evidence suggests that ventilation using air (21% oxygen) should be the initial step for term babies, with oxygen being added only if hypoxia persists despite adequate ventilation. Initial ventilation should be with a mask and inflating device; failure to initiate spontaneous breathing within 2–5 minutes may require endotracheal intubation – but only if a person skilled in this technique is present. If the infant remains bradycardic (HR <60) despite adequate ventilation, the circulation should be supported by external cardiac massage (Fig. 26.2) and, possibly, endotracheal 1: 10 000 adrenaline 0.3–1.0 mL/kg. Once the umbilical vein is cannulated a further 0.1–0.3 mL/kg dose of adrenaline is given, and if there is no response further doses of adrenaline 0.1– 0.3 mL/kg can be given at 3–5-minute intervals.

Fig. 26.2 Closed cardiac massage. Intermittent pressure is applied over the middle third of the sternum (which is pressed down about half an inch) with two fingers or thumbs. The heart is compressed between the rib cage and the vertebral column, and blood is expelled into the great vessel. For clarity, the endotracheal tube has been omitted in the drawing.

A 5-minute Apgar of less than 6 should be followed by measurements of arterial blood gases and pH, and treatment given to adjust the findings if necessary.

Infants who have required advanced resuscitation or have prolonged cardiorespiratory depression should be closely observed in a special care nursery until it is clear that they have recovered or need continuing specialist care.

BIRTH INJURIES

With increasingly good obstetric care during childbirth, birth injuries are becoming less common and less severe. Only those injuries most likely to occur will be discussed. In all cases, the injury must be explained to the parents and the treatment and prognosis discussed.

Cranial injuries (Fig. 26.3)

Fig. 26.3 Location of extracranial and extradural haemorrhages.

Caput succedaneum

Caput succedaneum is caused by pressure on the fetal scalp when the head is being pushed deeply into the pelvis and the venous return from the scalp is impeded. The oedematous swelling and bruising is subcutaneous and can cover a large area of scalp. Treatment is not required; the swelling of the caput disappears rapidly and the bruising within a few days.

Cephalhaematoma

Cephalhaematomas may occur after a spontaneous vaginal delivery or following trauma from the obstetric forceps or the ventouse. The periosteum is sheared from the underlying parietal bone and subperiosteal haemorrhage occurs. The swelling is limited to the outline of the bone; initially it is tense, subsequently it is fluctuant and the rim may calcify. The haematoma remains for 2 weeks to 3 months and is slowly absorbed.

Subaponeurotic (subgaleal) haemorrhage

Subaponeurotic haemorrhage, while rare, occurs most commonly after a traumatic vacuum extraction (see p. 195–197) and may result in significant blood loss from the infant’s circulation. Occasionally the bleeding is very rapid and life-threatening and requires urgent blood transfusion. Frequent observation for diffuse head swelling following vacuum extraction is mandatory.

Intracranial haemorrhage

Intracranial haemorrhage may be subarachnoid, subdural or intraventricular. Subarachnoid haemorrhage is common and may cause irritability and even convulsions over the first 2 days; it rarely has longstanding effects. Subdural haemorrhage can follow the misapplication of forceps; in severe cases the infant may be shocked and show little response to resuscitation. Intraventricular haemorrhage is found most often in preterm infants; it is diagnosed by ultrasound examinations, which should be performed routinely on very preterm infants.

RESPIRATORY DISORDERS

NEONATAL INFECTIONS

Infections occurring during pregnancy that affect the fetus are discussed in Chapter 17. Infection may be acquired during labour, particularly if the membranes have been ruptured for a long time, or from vaginal colonisation by group B streptococci (GBS) (see p. 137). Acquired GBS infection may cause rapid onset of septicaemia, pneumonia ± meningitis within hours of birth.

Infections occurring after birth include:

The signs of neonatal infection may be non-specific, with lethargy, poor temperature control (including hypothermia as well as fever), poor feeding, vomiting and/or compromised perfusion. Any infant suspected of having infection requires a blood culture, blood picture examination and possibly non-specific infection marker (e.g. C-reactive protein); if the diagnosis remains unclear collection of a urine specimen (by suprapubic aspiration), a chest X-ray and a lumbar puncture to exclude meningitis should be performed.

Treatment consists of giving the appropriate antibiotic, depending on local bacterial sensitivities and experience. Early treatment is of the utmost importance to minimize the risk of death or long-term sequelae. Care must be taken to prevent cross-infection by ensuring that the staff practise infection control measures, especially hand hygiene.

JAUNDICE

Over half (50–60%) of all babies will have visibly detectable jaundice, but most will be physiological in origin requiring neither investigation nor treatment. Any doubts about the severity of the jaundice requires a serum bilirubin (SBR) estimation. In a term baby an SBR of >250 μmol/L requires further investigation and possible treatment. Likewise for any jaundice appearing in the first 24 hours of life.

Jaundice is further considered on page 216.

INFANTS OF DIABETIC MOTHERS

Babies born to mothers with diabetes have a range of special issues, and are discussed on pages 132–134.

CONGENITAL MALFORMATIONS

Congenital malformations affect up to 3.5% of all infants. In about 2% of all infants such defects are major (Table 26.2). Many of the more severe structural abnormalities are now diagnosed antenatally during the 18-week morphology ultrasound scan, which gives the opportunity for counselling and discussion of the likely prognosis. When the diagnosis has been established the doctor should talk with the parents, explaining the malformation and the prognosis calmly and sympathetically. Most parents go through a grieving period. They may express anger and guilt, questioning whether anything they did or did not do during the pregnancy caused the malformation. Most appreciate counselling sessions.

Table 26.2 Order of prevalence of 28 selected birth defects: Victoria, Australia 2005–6

* Per male babies. From Riley M & Halliday J, Birth Defects in Victoria 2005–2006, Victorian Perinatal Data Collection Unit, Victorian Government Department of Human Services, Melbourne, 2008, with permission.

† Terminations of pregnancies.

The major malformations are described below.

Central nervous system defects

Anencephaly (Fig. 26.4) and spina bifida (Fig. 26.5) can be diagnosed in pregnancy, as described on page 43. Hydrocephalus can be diagnosed in the second half of pregnancy by ultrasound scanning, but may only be noticed when delivery is difficult.

Fig. 26.4 Anencephaly.

Fig. 26.5 Spina bifida.

Down syndrome (Trisomy 21)

Down syndrome is the most common genetic defect. The infant may have slanting eyes with epicanthic folds, short hands, small fingers, simian creases of the palms and increased spacing between the first and second toes; the head is flattened at the back, the neck short and webbed, (Fig. 26.6). Generalized hypotonia is a characteristic finding. Most Down syndrome children have a lower than average cognitive ability, often ranging from mild to moderate impairment; a small number have severe to profound mental disability. There may be associated congenital anomalies – most commonly cardiac or gastrointestinal, but any system may be involved.

Fig. 26.6 Down syndrome.

The incidence of Down syndrome increases with the age of the mother (Fig. 26.7). As mentioned in Chapter 6 (p. 42), Down syndrome can now be diagnosed by routine screening in over 80% of cases in early pregnancy, and termination offered.

Fig. 26.7 The rate of Down syndrome in live births in relation to maternal age.

Open and honest communication with the parents from the outset is vital. Most communities have active Down syndrome support groups and specialist health professional programmes. Early referral should be made.

METABOLIC DISORDERS

Cystic fibrosis, affecting one baby in 2000; congenital hypothyroidism (1 in 6000), and phenylketonuria (1 in 10 000) can be detected by filter paper tests on blood samples taken at 48–72 hours of life. Following the introduction of tandem mass spectrometry (TMS), the pattern of biochemical markers may help identify over 20 additional metabolic conditions, for example, medium chain acyl-coenzyme A dehydrogenase (MCAD) deficiency, homocystinuria and maple syrup urine disease.

MATERNAL INGESTION OF DRUGS AFFECTING THE FETUS

Pregnant women should avoid taking medications as far as possible, as many pharmaceutical agents cross the placenta and may affect the fetus adversely. If a drug is required, the doctor should read the product information document before prescribing it. In some countries, lists of drugs that should be avoided during pregnancy are obtainable from the health authorities.

CIRCUMCISION

Current advice in most developed regions is that this is not required for medical reasons. There is evidence of a small increased risk of urinary tract infection in uncircumcised boys, and acquisition of HIV infection has been shown to be more likely in uncircumcised male adults. Thus in regions with a high prevalence of HIV circumcision may be indicated. Unless required for cultural or religious reasons it should be delayed until the infant is 6 months old and should be performed under a local or a general anaesthetic.