Definition

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. Respiration can be consciously controlled (e.g. for swimming, singing, etc.) but is unconsciously determined by definite and precise mechanisms. During quiet, normal breathing (eupnoea) the diaphragm flattens during inspiration and the intercostal muscles pull the ribs upwards and outwards increasing the intra-thoracic volume and pulling 500–800 mL of air into the lungs (Higginson & Jones 2009). Expiration generally lasts twice as long as inspiration allowing a conversation to be held. A quick assessment of respiratory impairment is to ask the woman a question – if she can only speak in short sentences, there is a degree of respiratory distress. Abnormal posture, e.g. sitting up, leaning forwards, may be a compensatory posture designed to improve the mechanics of breathing and should be noted (Massey & Meredith 2010).

Normal values

Automatic control of breathing occurs within the respiratory centres in the brainstem which regulate breathing according to reflex responses and chemical signals (mainly carbon dioxide in the blood), e.g. an excessive carbon dioxide level in the blood (hypercapnia) will cause respirations to increase until it returns to a normal level (Dearsley 2013). There is some debate as to the normal respiratory rate for a healthy adult at rest. Higginson & Jones (2009) and Mooney (2007) suggest this is 12–18 times per minute; Dearsley (2013) and Jevon (2010) prefer 12–20 and Docherty & Coote (2006) propose 10–20. Edmunds et al (2011) advise that when a woman’s respiratory rate is greater than 24 breaths per minute, more frequent observations should be performed, and if they are above 27, prompt referral is indicated.

Tachypnoea is an increased respiratory rate above 20 breaths per minute (Churchill et al 2014) although Docherty & Coote (2006) suggest that tachypnoea does not occur until the respiratory rate is above 30 breaths per minute. Tachypnoea is often rapid, shallow breathing and can occur in response to metabolic acidosis, exercise, fear, fever (the rate rises approximately four breaths/minute for each degree the temperature increases), pain and is the most sensitive indicator of an impending adverse event. The UK Sepsis Trust (2014) advise that a respiratory rate >20 is a red flag and when combined with another red flag, action should be taken. However, if the rate is >25, action is taken regardless of the other observations as is it indicative of sepsis until proved otherwise.

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 denotes difficulty with breathing and the woman may be seen to use some accessory muscles of respiration, e.g. sternomastoid, scalene, abdominal, have nasal flaring and/or pursed lips – typically seen with obstructed lung disease. Pursed lips acts as a physiological positive end expiratory pressure (PEEP) and helps increase intra-airway pressure and prevent expiratory airway closure thus maximizing perfusion by decreasing the respiratory rate and increasing arterial oxygenation. About 60–70% of women experience physiological dyspnoea during pregnancy that can occur at rest or with mild exertion (Blackburn 2013).

Breathing is usually silent; when sounds are present, they are usually the result of narrowed airways or moisture within, or inflammation of, the lungs or pleura:

The newborn baby has an erratic periodic breathing pattern that is interspersed with periods of apnoea (10–15 seconds) with a respiratory rate of 30–40 breaths per minute that can increase to 60 (England 2014), although Cameron (2011) suggests the rate is 20–40. Due to the weakness of the intercostal muscles, the baby may appear to be breathing abdominally as the diaphragm is used extensively used (Blackburn 2013). Tachypnoea in the newborn (above 60 breaths per minute) is the earliest sign of respiratory disease and may also indicate other illnesses, e.g. cardiac, metabolic or infectious (Gardner et al 2011). 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). Grunting acts as a compensatory mechanism to stabilize the alveoli by increasing transpulmonary pressure and delaying expiration which will increase gaseous exchange (Gardner et al 2011).

Babies are mainly diaphragmatic breathers which means their diaphragm moves symmetrically with each breath. Asymmetrical breathing should be investigated particularly following shoulder dystocia as damage to the baby’s phrenic nerve may have resulted which is a cause of asymmetrical breathing movement.

Labour

Oxygen consumption increases 40–60% and inadequate oxygenation can increase the severity of pain which in turn can result in hyperventilation. The number and strength of contractions affect the pattern and depth of respiration during labour. Breath holding should be discouraged as it increases PaCO₂ levels which in turn results in compensatory hyperventilation in an effort to lower PaCO₂ levels. Maternal hyperventilation can also lead to dizziness, tingling and decreased fetal oxygenation (Blackburn 2013). Deep slow breathing between contractions should be encouraged to maintain oxygenation amidst considerable muscular activity.

Postnatal period: maternal

Respiration returns swiftly to its prepregnant 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 and the decrease in progesterone. Anatomical changes revert to their prepregnant state by 24 weeks post-delivery (Blackburn 2013).

Postnatal period: baby

Lung development and growth occurs throughout pregnancy and continues for the first 2–3 years of life. Although terminal air sacs appear by 24–26 weeks, blood vessels, lung surface area and volume do not increase sharply until 30 weeks. The number of air spaces increases from 240 000 at 24 weeks, to four million at 32–36 weeks and 50–150 million at term. The alveolar develop further from 36 weeks with about 20% formed by term. Surfactant levels also increase significantly towards term. Thus a baby born preterm is likely to experience respiratory difficulties. Additionally the baby’s lungs are fluid-filled, and the fluid has to be removed at birth and replaced with air for effective ventilation to occur.

Respiration is initiated as the baby is born and the fetal circulation adapts to the extrauterine circulation, but the process begins before birth. Lung fluid absorption begins during early labour and fluid is expelled through the baby’s nose and mouth as the thorax is squeezed during the baby’s journey through the birth canal. At birth there is approximately 35% of the original lung fluid volume remaining that has to be removed (Blackburn 2013).

The first diaphragmatic breath occurs within 9 seconds of delivery and generates high positive intra-thoracic pressures (70 cmH₂O). As the pressure begins to decrease (30–40 cmH₂O), air enters the lungs. Subsequent breaths require less pressure as the smaller airways and alveoli remain open due to the action of surfactant.

Respiration is initiated by a number of factors: