Introduction

A number of significant physiological changes occur within the maternal respiratory system throughout pregnancy, either as a result of hormonal or neonatal effects. Chapter 1 details these changes.

Asthma

Asthma is a common condition characterized by intermittent reversible airways obstruction, chronic inflammation of the airways and bronchospasm. It affects approximately 5% of the population in the UK and is more common in women than men.

Asthma may be affected by pregnancy. Meta-analysis has shown approximately one-third of women will have improved symptoms, one-third will worsen and one-third will see no changes. Any worsening of symptoms will typically peak at six months gestation. There is often an improvement of symptoms during labour, perhaps due to endogenous corticosteroid production, with acute asthma being very rare at this stage.

Well-controlled asthma is unlikely to have any impact on the pregnancy. Uncontrolled asthma is associated with a variety of complications, including hyperemesis, hypertension, pre-eclampsia, vaginal haemorrhage, complicated labour, fetal growth restriction, preterm birth, increased perinatal mortality and neonatal hypoxia. Large cohort studies have shown an increased caesarean section rate in those with moderate and severe asthma.

Treatment should be optimized during pregnancy. A large case-controlled study showed no increased risk of congenital malformations in mothers being treated for asthma. There is good evidence that the older therapies have no teratogenic effects and no evidence to show the newer agents cause any harm. The risk of uncontrolled asthma is far greater than the theoretical risk of therapy.

Acute asthma should be managed in the standard way. Poor management is associated with poor outcomes for mother and fetus; there is no known risk to the fetus with standard treatment.

Asthma is not a contraindication to any form of labour analgesia. Should caesarean section be required, regional anaesthesia is suitable, as those with asthma are less likely to tolerate mechanical ventilation well.

Postpartum haemorrhage can safely be managed with syntometrine and prostaglandin E2. Prostaglandin F2α may cause bronchospasm.

Breastfeeding is not a contraindication to any of the treatments given for asthma, none of which are found in dangerous levels in the milk. Oral steroids may also be given safely to the breastfeeding mother.

Pulmonary hypertension

Pulmonary artery hypertension (PAH) is defined as mean pulmonary artery pressures >25 mmHg at rest or >30 mmHg with exercise. This can arise from a wide variety of disease states leading to a common end pathway of plexogenic pulmonary arteriopathy. It can be sub-classified into:

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  Idiopathic pulmonary arterial hypertension

  
  
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  Associated with left heart disease/congenital heart disease (e.g. Eisenmenger’s)

  
  
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  Associated with lung disease/hypoxaemia

  
  
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  Associated with chronic thrombotic/embolic disease

  
  
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  Miscellaneous (e.g. histiocytosis, lymphangioleiomyomatosis, sarcoidosis).

Idiopathic pulmonary hypertension is a rare disease with prevalence in the region of 10 per million. It is three times more common in women than men. Much more commonly, PAH is associated with cardiac or respiratory disorders giving an overall prevalence of around 100 per million.

The pathophysiology is worsened by physiological changes of pregnancy. Cardiac output fails to rise in response to the normal reduction in systemic vascular resistance. The pulmonary vasculature also fails in its response to an increased circulating volume. Hypercoagulability can lead to thromboembolism and further rises in PA pressures. The situation worsens in labour with further stress and tachycardia. This can lead to fatal pulmonary hypertensive crisis.

Women are often counselled against pregnancy as maternal mortality is between 30% and 50%, depending on the aetiology of PAH. In the event of pregnancy a multidisciplinary team with knowledge of the condition should be consulted.

Parturients are often started on low-molecular-weight heparin during pregnancy. Oxygen and diuretics may reduce the burden on the pulmonary vasculature. Many pulmonary vasoactive compounds are teratogenic, although sildenafil may be safe. There is no consensus on optimum mode of delivery, but this should be with full invasive monitoring and the facility to administer nitric oxide in order to reduce PVR and therefore pulmonary arterial pressure.

Mothers should be monitored closely for at least two weeks, as many deaths are in the postpartum period.

Pulmonary embolism

Pulmonary embolism (PE) is an obstruction to the lung vasculature by a substance that has travelled from elsewhere in the circulation. This is most commonly thrombus, but can be fat, air or amniotic fluid.

The haemostatic changes during pregnancy include increased concentrations of factors I, II, V, VII, VIII, X and XII, as well as reduced effectiveness of activated protein C and reduced levels of protein S. This leads to a hypercoagulable state and increased risk of thromboembolism. Large studies have demonstrated PE in 1–2 of 7000 pregnancies, most of these occurring postpartum. In the 2006–2008 CEMACE report there were 0.79 deaths per 100,000 maternities; this was the lowest level since 1985. Obesity is an independent risk factor with 14 of the 16 women dying from PE having a BMI >25 kg/m². Other predictors of risk are pre-eclampsia, caesarean section and multiple births.

A high index of suspicion should be employed and the clinician alert for dyspnoea or tachypnoea with or without pleuritic chest pain and/or haemoptysis.

Investigations should be as for the non-pregnant population. Those with suspected PE should have CT pulmonary angiography performed. The potential benefits of accurate diagnosis and subsequent treatment should be weighed against an increased lifetime risk of maternal breast cancer and theoretical harm to the fetus.

Current practice is an extrapolation of treatment used in non-pregnant patients and observational studies. Low-molecular-weight heparins are the treatment of choice; warfarin is teratogenic and should be avoided, although can be taken while breastfeeding. Unfractionated heparin is often substituted close to delivery because of the potential for reversal in the event of haemorrhage. Treatment should continue for the longest duration, either three months after the initial diagnosis or six weeks post delivery.

Sarcoidosis

Sarcoidosis is a multisystem disorder, of unknown aetiology, characterized by granulomas, which can be found in most tissues of the body, but are most commonly found in the lungs.

The condition typically presents between the ages of 20 years and 40 years and will affect an estimated 1 in 2000 pregnancies. Although the condition usually has a benign course, fatalities are reported.

Knowledge of sarcoidosis and pregnancy comes primarily from observational studies and case reports. There is often a relapsing remitting course of sarcoidosis; those in remission or with stable disease typically see no changes to their condition during pregnancy. Expectant mothers with active sarcoidosis will often find their symptoms improve as they approach term; radiological improvements are also recorded. Unfortunately there is often rebound exacerbation, potentially with new manifestations, three to six months post delivery.

There does not seem to be a correlation between sarcoidosis and poor outcome from pregnancy. There have been individual reports of preterm labour and low birth weights, but this seems to be in keeping with the background rates.

The condition should be optimized prior to and during pregnancy. Pulmonary function tests may be of use when planning labour strategies. Corticosteroids are the first-line treatment and have not been shown to have major teratogenic effects in large studies of patients with asthma. If right heart hypertrophy and/or dilatation are present due to pulmonary hypertension women should be advised against pregnancy. The second-line agents methotrexate and cyclophosphamide are teratogenic and should be avoided, although some agents may be safe.

Women should be actively followed up post partum in anticipation of potential worsening of their condition.

Cystic fibrosis

Cystic fibrosis (CF) is an autosomal recessive condition affecting chloride channels found throughout the body. It is a multisystem disorder, but morbidity and mortality arise principally from the respiratory system. The resulting thickening of secretions causes blockages, chronic inflammation, recurrent infections and architectural damage to the lungs.

CF occurs in approximately 1 in 2500–3200 live births. The prevalence is ever increasing as median life expectancy is rising with improved care. There are more adults than children with CF in some European countries.

Although all pregnancies in CF patients should be considered high risk, a baseline FEV1 >60% predicted is associated with favourable outcomes. The normal physiological changes of pregnancy can present a significant challenge to these patients. Increasing minute ventilation with little functional reserve and raising cardiac output with existing right heart strain can be problematic. Indeed, as previously mentioned, pulmonary hypertension can present grave risk.

Predictors of increased risk are weight gain <4.5 kg, BMI <20 kg/m², colonization with B. cepacia, frequent infections, diabetes mellitus, pancreatic insufficiency and recurrent infections. These patients have increased frequency of preterm labour.

Treatment should be optimized during pregnancy and multidisciplinary input sought. Mildly impaired mothers may labour normally with epidural analgesia. Should caesarean section be deemed necessary, each patient must be assessed individually, as no robust evidence exists to guide treatment. Regional anaesthesia is often preferable to reduce impact on the respiratory system and avoid mechanical ventilation. High block should be avoided because of dependence on the accessory muscles. A CSE technique seems a reasonable approach to allow epidural analgesia post section and aid compliance with physiotherapy. These patients require meticulous attention to detail in the perioperative period, with senior input from the CF team, physiotherapy and microbiology, as well as obstetrics/midwifery/anaesthesia.