External respiration is the means by which the body gains oxygen (inspiration) and excretes carbon dioxide (expiration). Assessment of respiration includes observation of the rate (number per minute), depth and regularity of breaths and any associated signs (e.g. skin colour). Breath sounds may also be heard, or the chest felt to rise and fall, as well as being visually observed.

There is some debate as to the normal respiratory rate for a healthy adult at rest. Mooney (2007) suggests this is 12–18 times per minute; Docherty & Coote (2006) state the rate is 10–20 breaths per minute whereas Bailey et al (2008) propose the respiratory rate to be 14–18 per minute.

Tachypnoea is an increased respiratory rate, above 20 breaths per minute. It can be due to pain or fever (Bailey et al., 2008 and Nelson and Schell, 2006), although Docherty & Coote (2006) suggest that tachypnoea occurs with respiratory rates above 30 breaths per minute.

Bradypnoea refers to a decreased but regular respiratory rate of below 8 (Docherty & Coote 2006) or, more commonly, 10 breaths per minute (Nelson & Schell 2006). Dyspnoea refers to difficulty with breathing and the woman may be seen to use some accessory muscles of respiration, e.g. shoulder or neck, have nasal flaring and/or pursed lips.

The newborn baby may breathe irregularly with a respiration rate of 40–60 breaths per minute (Michaelides 2004). Due to the weakness of the intercostal muscles, the baby may appear to be breathing abdominally, as the diaphragm is extensively used (Blackburn 2007). Tachypnoea in the newborn (above 60 breaths per minute) is often an early sign of illness, particularly cardiac, respiratory, metabolic or infection (Gardner & Johnson 2006). The baby may show other signs of respiratory difficulty when tachypnoeic, such as nasal flaring (where the nares increase in size to decrease the airway resistance up to 40%), grunting (from forced expiration through a partially closed glottis) and using accessory muscles of respiration (the thin chest walls are pulled inwards on inspiration – recession/retraction, usually seen around the sternum, intercostal, subcostal and supracostal muscles).

When supporting both the fetus and the woman, the body’s oxygen demands are high. The function and anatomy of the respiratory tract changes. Breathing is largely diaphragmatic, with the diaphragm being displaced upwards as the lower ribs flare. Progesterone relaxes the smooth muscle of the alveoli and despite the gravid uterus splinting the diaphragm from below, each breath is deeper. The rate of respiration is unchanged.

The number and strength of contractions affect the pattern and depth of respiration during labour. Breath holding should be discouraged and deep breathing between contractions should be encouraged to maintain oxygenation amidst considerable muscular activity. Breathing exercises can assist the woman both physically and psychologically. Maternal hyperventilation can lead to decreased fetal oxygenation (Blackburn 2007).

Respiration returns swiftly to its pre-pregnant rate, volume and pattern once labour is completed. This is due to the decrease in intra-abdominal pressure that allows increased movement of the diaphragm. The effects of progesterone on the respiratory tract, for example, rib cage elasticity, take 1–3 weeks to resolve completely (Blackburn 2007).

Respiration is initiated as the baby is born and the fetal circulation adapts to the extrauterine circulation. A mature, patent respiratory tract is needed for oxygenation of the lungs. The first breath requires high negative intrathoracic pressure (30–40 cmH ₂O) but thereafter, due to the action of surfactant, a pressure of only 5 cmH ₂O is required. Respiration is established by a number of factors:

• stimulation (light, tactile and temperature)

• compression and decompression of the chest as it passes through the vagina

• reflex stimulus of the respiratory centre from the chemoreceptors

• changes within the cardiovascular system to perfuse the lungs.