Asthma is one of the most common diseases in the UK, with a prevalence of 15% in children and 10% in adults. Its incidence is increasing. Asthma is both the most common respiratory condition and one of the most common medical conditions seen in pregnancy, occurring in approximately 10% of pregnant women. Of these, around 10% will need hospital admission for an acute exacerbation.
Anaesthetists may be involved in looking after women who have an exacerbation of their asthma during pregnancy or when on the delivery suite.
Problems and special considerations
In pregnancy, asthma remains stable in approximately one-third of patients, worsens in one-third, and improves in another third of patients, an effect thought to be caused by progesterone and cortisol. If symptoms do deteriorate, this is related to both the altered respiratory physiology of pregnancy and increased prostaglandin (PG) F2a secretion, which has bronchoconstrictor effects; this tends to occur in the second and third trimester, with peak deterioration occurring in the sixth month.
In severe cases, patients may be taking a number of bronchodilator and antiinflammatory drugs, including steroids. If high-dose steroids are being taken (> 7.5 mg prednisolone), steroid replacement should be considered during labour and delivery.
Stress, especially pain and anxiety, may precipitate an acute exacerbation, although viral infections are thought to be the most common cause of an acute exacerbation.
The increased demands of pregnancy make mothers more vulnerable to acute exacerbations of asthma. During an acute attack, physicians not accustomed to the assessment of pregnant patients may misinterpret blood gas results, for example by not appreciating that an arterial partial pressure of carbon dioxide of 5.5-6.0 kPa is grossly abnormal.
Both maternal (hypertensive disorders, haemorrhage and complicated labour) and neonatal (low birth weight, fetal growth restriction, preterm labour) complications are more common in mothers with asthma, especially if poorly controlled.
Pethidine has been implicated in worsening asthma because of its histamine-releasing action, though it is thought to be better than other opioids as it has a smooth muscle relaxant effect.
General anaesthesia in an asthmatic pregnant patient may provoke severe bronchospasm, especially when the airway is instrumented. Thiopental has been implicated in causing bronchospasm, although this is disputed; propofol or ketamine may be considered for induction of anaesthesia. Non-steroidal anti-inflammatory drugs are well known to induce bronchospasm in susceptible patients.
Carboprost (Hemabate) is a PGF2a analogue and should be used with extreme caution in women with asthma. Beta-agonists are usually best avoided when managing hypertensive disorders of pregnancy.
Management options
Ideally, women with moderate or severe asthma should be counselled in the antenatal period and a plan set out for their management in labour. The primary aim of treatment is the maintenance of oxygenation. As asthma sufferers often play down their symptoms, direct questioning about their exercise tolerance and their current treatment, including steroids, is required for the antenatal record. Acute exacerbations should be treated aggressively. Current advice is that influenza vaccinations should not be given until after 12 weeks’ gestation.
Caesarean delivery is reserved for obstetric reasons. Induction of labour using prostaglandins is usually avoided. Basic techniques for analgesia and anaesthesia are as for nonasthmatic mothers, bearing the above points in mind. Acute asthma attacks are rare in labour. However, bronchospasm in labour may interfere with effective self-administration of Entonox. The woman should be fully alert and in control during her labour as much as possible, and therefore able to manage her asthma treatment with her inhalers. Epidural analgesia should be recommended generally.
Regional anaesthesia is indicated for operative deliveries, although a high block may reduce the ability to cough. In a woman with unstable asthma, neuraxial techniques may impede use of accessory muscles of respiration, and extreme care is required.
There is no contraindication to the standard treatments for an asthmatic attack in pregnancy or labour, including the use of inhaled or systemic steroids, intravenous theophyllines and magnesium. It is important to remember that peak flow measurements are useful for monitoring the condition, and that respiratory reserve is less during pregnancy, particularly if the mother’s attack is precipitated by a respiratory tract infection. Chest radiography and arterial blood sampling may both be needed in the investigation of an acute asthma attack.
Key points
• Both maternal and neonatal complications are more common in mothers with asthma, especially if poorly controlled.
• Epidural analgesia should be encouraged in labour.
• Regional anaesthesia is indicated for operative delivery.
• Acute exacerbations should be treated as for non-pregnant patients.
Further reading
Bonham CA, Patterson KC, Strek ME. Asthma outcomes and management during pregnancy. Chest 2018; 153: 515-27.
British Thoracic Society, Scottish Intercollegiate Guidelines Network. British Guideline on the Management of Asthma: a National Clinical Guideline. London: BTS; Edinburgh: SIGN, 2016. www .sign.ac.uk/assets/sign153.pdf (accessed December 2018).