Acid–base

Before labour the normal fetus has a pH around 7.3, pCO₂ about 35 mmHg and pO₂ between 35 and 40 mmHg. At the end of labour repeated episodes of hypoxia associated with uterine contractions result in the normal newborn having a pH of 7.22–7.26, pCO₂ of 50 mmHg, pO₂ of 20 mmHg and a base excess of −5 to −8. This change equates with subjecting a normal fetus to 2 minutes of total anoxia. After 8–10 minutes of total anoxia, permanent brain damage would result.

Cardiovascular system

The fetal lungs in utero receive only 10% of the fetal right ventricular output. At birth the newborn’s first breath expands the lungs and reduces pulmonary vascular resistance, thus allowing increased pulmonary flow. At the same time systemic vascular resistance rises when the umbilical cord is clamped. These changes and rising pO₂ result in closure of the shunts, foramen ovale and ductus arteriosus, establishing the pulmonary and systemic circulation. Hypoxia, acidosis and pulmonary atelectasis increase pulmonary vascular resistance and hence prevent closure of the shunts, thus limiting oxygenation of the blood. Prompt resuscitation will:

Breathing is stimulated by exposure to the extrauterine environment and by the increasing fetal plasma carbon dioxide (pCO₂). Air is drawn in during the first breath. However, this air is expelled again through a partly closed glottis to effect the cry we hear from a healthy baby. During the first few minutes, breathing may be irregular or even intermittent but this is followed by more regular breathing at 40–60 breaths a minute. Regular breathing lowers pCO₂ and raises pO₂.

Normal acid–base status is only achieved at the end of 1 or 2 hours. Any complication which depresses the newborn prolongs this recovery period.

Lung liquid

In utero the fetus secretes fluid continuously from its lungs. Compression of the thorax during labour helps to expel this lung fluid. It is thought that raised fetal plasma adrenaline following the stress of labour is important in switching off the mechanism for lung fluid production and thus preparing the fetus for extrauterine existence. The residual lung liquid at birth is usually rapidly absorbed into the capillaries or lymphatics. Infants delivered electively by caesarean section have less opportunity for removing this lung fluid and therefore may develop some respiratory distress (transient tachypnoea) due to retention of lung liquid. Spontaneous resolution is expected and, while an increased oxygen concentration may be needed for a time, artificial ventilation is seldom necessary.

Body temperature

Keeping the baby warm is essential. The newborn’s large surface area to body volume ratio, especially if preterm or of low birthweight, allows rapid cooling. A rapid drop in body temperature increases the need for oxygenation and exacerbates metabolic acidosis. Maintenance of body temperature is therefore particularly important in depressed infants. Failure to maintain adequate body temperature in preterm neonates is a major contributory factor to mortality due to respiratory distress syndrome. All neonates should be dried quickly, wrapped in a prewarmed towel and placed in a warm environment. Most resuscitation trolleys now incorporate an overhead radiant heater which should be switched on well in advance (Figure 12.1).

Figure 12.1 A resuscitation trolley.

Preparation

Whenever there is time before the baby is born, obtain the obstetric history and check the resuscitation trolley and the equipment. Switch on the overhead heater. Request additional help if appropriate, e.g. for babies of less than 34 weeks’ gestation or for multiple births. Introduce yourself to the parents.

Procedure at delivery

At the moment of birth start the clock, and dry and cover the baby in the warm towel. Assessment at birth is commonly by the Apgar score which documents five criteria (Table 12.1). Each criterion is scored from 0 to 2 to describe the spectrum from poor to good. The maximum score is 10 points. The infant is examined at 1 minute and again at 5 minutes after birth, scores being allocated at these two intervals. The score does not predict the outcome for the baby, and it is not useful in the management of individual babies, but it can be repeated again at regular intervals to document the response to resuscitation.

Table 12.1 The Apgar score

Decide on the baby’s need for resuscitation by assessing four of the Apgar score signs – breathing, colour, heart rate and tone. The baby will then be in one of four groups and the appropriate management is followed (Table 12.2) proceeding in the order ABCD:

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