11.1 The newborn infant

stabilization and examination

Dr Neil Campbell began this Chapter in the fifth edition of this book, thus:

‘Most babies are born at term gestation (37–42 weeks), following normal pregnancy and labour, and are healthy. Having a baby is for most people one of life’s most joyous and enriching experiences. Health professionals should keep these matters in mind and be as unobtrusive as possible with medical interventions, remembering we are, in a way, privileged to share in this special experience.’

Introduction

Currently, annually, there are approximately 295 000 babies born in Australia and 64 000 born in New Zealand. In both countries the average age of a mother having her first baby has been increasing in recent years and is now around 30 years. Approximately 92% of all births are at term (at least 37 completed weeks of gestation). Around 25% of all births are now by caesarean section, although in many other countries this figure is much lower.

It is worth being aware that the outcome from pregnancy in developed countries does not always conform to parental expectations:

• around 1 in 5 pregnancies ends in an early miscarriage

• about 6%–8% of infants are born preterm (less than 37 completed weeks)

• 1% of infants still die around the time of birth

• up to 5% of infants will have some form of birth defect.

Neonatal transition

Much of the adaptation of the fetus to life ex utero takes place over a few days and may bring to light congenital disorders. If the process is disrupted, serious disease may result.

Circulation

In utero there is high pulmonary vascular resistance such that only 10–15% of the cardiac output goes through the pulmonary circulation. Most of the cardiac output bypasses the lungs by flowing right-to-left across the foramen ovale or through the ductus arteriosus (Fig. 11.1.1). With the infant’s first breath the pulmonary vascular resistance falls and blood flows to the lungs; with cord clamping the peripheral vascular resistance rises and the foramen ovale is kept shut; and with the rise in partial pressure of oxygen (P_ao₂) and withdrawal of prostaglandins produced by the fetoplacental unit, the ductus closes. In some babies with persistent pulmonary hypertension, these changes do not occur and there continues to be a right-to-left shunt at the atrium and ductus. Such infants are tachypnoeic and remain cyanosed.

Fig. 11.1.1 The normal fetal circulation. Pul. A, pulmonary artery; Pul.V, pulmonary vein.

Respiration

The fetal lungs are filled with fluid that has been secreted by the pulmonary epithelium. There is a net outward movement of this fluid into the amniotic fluid with breathing movements during fetal life. Hormonal changes, including a rise in catecholamines, occurring with the onset of labour, lead to the reabsorption of some of this fluid from the alveolar sacs. Most remaining fluid is squeezed out of the lungs during passage of the chest through the birth canal (and can be seen as clear fluid around the nose and mouth at birth). With normal chest recoil the infant’s lungs fill with air, surfactant is released from the type II pneumocytes, lowering surface tension in the alveoli, and the residual lung volume is established with the first few breaths. Infants born by caesarean section, prior to labour, are more likely to have retained lung fluid (transient tachypnoea of the newborn; see Chapter 11.3).

Temperature control

Newborn infants have a larger surface area compared to their weight than do adults and can become cold rapidly. They are wet at birth and lose heat through water evaporation, as well as via radiation, conduction and convection if not clothed. After birth, hormonal changes lead to heat production from non-shivering thermogenesis in the brown adipose tissue. Core temperature is normally maintained at 36.5–37°C. Hypothermia will increase oxygen consumption required for basal metabolism and is a not uncommon cause of tachypnoea (see Chapter 11.3). Hypothermia may also occur in conditions such as sepsis.

Metabolism

The fetus is dependent on the maternal supply of glucose via the placenta, and glycogen stores are laid down in the liver, muscle and heart as gestation increases. At birth the maternal glucose supply ceases and the infant’s glucose levels fall over the next 1–2 hours before hormonal mechanisms bring about a rise from mobilized stores. Infants who have delay in feeding, preterm, growth retarded and sick infants, as well as infants of diabetic mothers, are all at increased risk of significant hypoglycaemia (see Chapter 11.2).

Fluid balance

Fetal urine contributes significantly to the amniotic fluid volume. The fetal urine is dilute and the placenta is responsible for fluid and electrolyte haemostasis. After birth a transition is made to water and salt conservation by the kidneys. In the first 2–3 days there is a negative sodium and fluid balance, contributing to much of the infant’s weight loss, as well as a shift in fluid from the extracellular to the intracellular compartments.

Gastrointestinal

The fetus swallows amniotic fluid, which is rich in growth factors. After birth, coordination of sucking and swallowing is readily established on day 1, and healthy term infants demand to feed from the breast eight or more times a day. Meconium should be passed by all infants by 48 hours of age. Before birth, unconjugated bilirubin is excreted by the placenta. During the transition to hepatic conjugation and excretion of bilirubin, all infants have raised serum bilirubin levels to some degree (see Chapter 11.2). All newborn infants have low levels of vitamin K-dependent clotting factors. Intrinsic vitamin K production follows bacterial colonization of the gut. This occurs in the first few days, but the vitamin K deficiency state carries with it a risk of haemorrhage (see below).

Neonatal stabilization and resuscitation

More than 5 million neonatal deaths occur worldwide every year, with the World Health Organization estimating that 19% of these are from birth asphyxia. In developing countries, nearly 1 in 4 infants who fail to initiate and sustain breathing at birth will die, yet easily acquired skills and simple equipment can help the majority of these babies.

It is estimated that 5–10% of newborns need some stimulation to breathe at birth. However, population-based surveys in developed countries suggest only 1–2% of term or near-term infants need active resuscitation with inflation breaths from a bag and mask. Only 20% of these (2 per 1000 births) progress to intubation.

Resuscitation of the newborn infant follows the same principles as resuscitation at other times (A, B, C, D: Airway, Breathing, Cardiac, Drugs). At the same time there are important differences resulting from the unique physiological changes associated with the infant’s transition from in utero to ex utero existence, as well as pathological states presenting at birth. In most cases it is better to talk of neonatal stabilization rather than resuscitation, and delayed onset of respiration rather than birth asphyxia.

Advanced resuscitation skills can be learned readily with the aid of mannequins and teaching scenarios. There are a number of different neonatal resuscitation guidelines and courses. Because neonatal resuscitation demands a team approach, it is essential to be familiar with local equipment and protocols.

Animal experiments carried out in the 1960s looked at the effects of acute, total asphyxia on heart rate (HR) and breathing (Fig. 11.1.2). At delivery by caesarean section (simply to control the situation), air breathing was prevented totally by occlusion of the airway. There was an initial period of gasping followed by cessation of breathing (primary apnoea), then a further period of gasping and finally no breathing (terminal apnoea).

Fig. 11.1.2 Physiological changes after acute asphyxia in a newborn monkey.

Primary apnoea usually lasted for 1–2 min, with HR maintained at 80–120 bpm. It could be prolonged by commonly used obstetric analgesic or anaesthetic agents. Simple tactile stimulation shortened the time to further gasping. In terminal apnoea, the time from the start of active resuscitation (ventilation) to further gasping and regular breathing reflected the degree of acidosis from asphyxia.

In the human situation there is always a chance acute total asphyxia may occur, although it is uncommon, for example with shoulder dystocia and a tight cord around the neck (nuchal cord), placental abruption or cord accidents. However, most peripartum hypoxia is in the context of prolonged, partial insults, and many of these can be predicted by the obstetric situation and fetal monitoring. At birth, most such infants will not have progressed to terminal apnoea and will respond promptly to resuscitation.

Because the extent of the asphyxial insult will be reflected by the pH and lactate in the arterial cord blood, resulting from anaerobic metabolism, a segment of cord can be clamped at each end and sampled up to 20 min later.

Apgar scores

Since the 1950s the Apgar score (Table 11.1.1) has been used to assess the infant’s condition at birth and to differentiate those who are vigorous or depressed. Many health jurisdictions require the Apgar score at 1 and 5 minutes to be recorded.

Table 11.1.1 The Apgar score

Historical note

Virginia Apgar was an American obstetric anaesthetist. Her score, based on the five signs typically used by anaesthetists to monitor their patients, was first published in 1953 as a method of assessing the effect of obstetrical and maternal anaesthetic management on the newborn.

There are many problems with the Apgar score:

• Different observers will record slightly different scores.

• There are clearly many routes to a score of 5 or 6 (for example), and both this and the infant’s condition should be fully described.

• Vigorous infants should not be suctioned (as this may lead to vagus-induced bradycardia or even vocal cord occlusion) and so a score of 2 is awarded for ‘reflex irritability’ by inference. Such infants will all have scores of 9–10.

• The score is much less satisfactory in very preterm or ventilated infants.

• For an individual infant there is little correlation between the Apgar score and pH or lactate values, and unfortunately neither is good at predicting the long-term outcome.

However, the 1-minute Apgar, if low, does indicate the need for stimulation, and the 5-minute Apgar indicates the response to earlier resuscitation.

Which births to attend?

All births do need someone capable of looking after the mother and a separate person capable of looking after the infant. Anyone involved in the practice of childbirth has a duty to be competent in neonatal resuscitation and a responsibility to see that the appropriate equipment is available and in working order.

Resuscitators should become familiar with their equipment, or that provided in the health facility in which they practise. The main tools to deliver positive pressure ventilation, short of intubation, are self-inflating bags (Laerdal) or T-piece resuscitators (Neopuff), and appropriately sized face masks. The wearing of gloves is recommended.

Basic care and stabilization (Fig. 11.1.3)

• Check the maternal and obstetric history.

• Anticipate problems.

• Check the equipment: infant overhead warmer, air and oxygen supply, suction apparatus, self-inflating bag and appropriately sized masks and/or pressure device and T-piece, intubation equipment, umbilical catheter, drugs.

• Start stopwatch when infant’s body is free from the mother.

• Assess the infant rapidly, particularly tone, breathing and HR (use stethoscope on chest):

1. The infant is vigorous and crying. Leave alone (but dry and wrap, or place in skin to skin contact with mother).

2. Infant cyanosed, irregular respirations, HR > 100. Gentle stimulation, check head in neutral position (avoid neck flexion and hyperextension) to open the airway, gentle oropharyngeal suction if obvious obstruction. Most respond.

3. Still inadequate respirations or apnoea, or HR < 100: (30 seconds from birth). Three to five slow (3 seconds) breaths then bag and mask at 40–60 per minute. Have pop-off valve or manometer set at 30 cmH₂O, but lower pressures are probably adequate. Check the response: should be visible chest movement and increase in HR.

4. HR < 60 and not increasing, inadequate respirations or apnoea. Proceed to ADVANCED resuscitation. Call for help. Intubate, if skilled. Otherwise continue with bag and mask, check head in neutral position with jaw thrust, check chest movement and air entry. Give 3 cardiac compressions (see below) to 1 breath. Consider drugs: IV adrenaline (epinephrine).

• Call for help at any time

• Assessment of colour is considered unreliable so oxygenation should be assessed by pulse oximetry. Applying the probe to the right hand or wrist before connecting to the instrument produces faster readings.

Studies have shown the appropriate technique to achieve the most effective use of a face mask during neonatal resuscitation (Fig. 11.1.4).

• Hold the newborn head in a neutral position (A).

• Gently roll the mask on to the face from the tip of the chin (B, C).

• Hold the mask with thumb and index finger at the top where the silicone is thickest (D).

Fig. 11.1.3 Newborn resuscitation algorithm. CPAP, continuous positive airway pressure; LMA, laryngeal mask airway; SpO₂, peripheral oxygen saturation Australian Resuscitation Council 2010.

Fig. 11.1.4 Technique for using face mask in neonatal resuscitation.

(From Schilleman K, Witlox RS, Lopriore E et al 2010 Leak and obstruction with mask ventilation during simulated neonatal resuscitation. Arch Dis Child Fetal Neonatal Ed 2010;95:F398–F402, with permission.)