The incidence of pneumonia in pregnant women overall is thought to be similar to that in the non-obstetric population, although it is more common in women with underlying respiratory disease, anaemia or immunosuppression (e.g. HIV infection, corticosteroids), and in advanced pregnancy. Pneumonia is the commonest cause of sepsis necessitating critical care admission in the obstetric population in the UK, but it is a relatively uncommon cause of death in the Confidential Enquiries into Maternal Deaths reports. However, during the H1N1 influenza (‘swine flu’) pandemic of 2009-10, the deaths of 32 pregnant women were attributed to H1N1.
The increased mortality from certain pneumonias in pregnancy, compared with nonpregnant women, is thought to arise from the altered immune responses, combined with the decreased functional residual capacity, decreased residual volume and increased oxygen consumption, that are part of the normal physiological changes of pregnancy. Anaesthetists are likely to be involved in the care of women with chest infection through the need for analgesia/ anaesthesia around delivery, or for supportive/intensive care should a parturient become critically ill.
Problems and special considerations
Signs and symptoms may be similar to the changes of respiratory physiology in pregnancy and may be non-specific, e.g. fever, rigors, nausea/vomiting, chest discomfort/pain and shortness of breath. Thus, diagnosis may be delayed.
Medical staff are often reluctant to perform a chest x-ray to confirm a diagnosis in a pregnant woman, because of anxiety over fetal exposure to radiation. However, the risks from a single x-ray are small and usually considered to be outweighed by the advantages if pneumonia is suspected.
Sputum and blood cultures should be taken, although their usefulness has been debated, and in a significant proportion of patients the aetiological agent may not be identified.
Pneumonia in the mother is associated with significant fetal morbidity, for example premature labour, fetal growth restriction and premature birth.
Viral pneumonia may be associated with a high risk of infecting staff, increasing spread and hampering the ability of healthcare services to cope in an epidemic or pandemic. The severe acute respiratory syndrome (SARS) epidemic of 2002-03 and the H1N1 pandemic of 2009-10, in particular, carried significant risk to staff.
Bacterial pneumonia
This is usually community-acquired. Common bacterial agents include Streptococcus pneumoniae and Haemophilus influenzae, but others such as Mycoplasma, Staphylococcus,
Legionella, Klebsiella and Pseudomonas may also be responsible. Management involves supportive therapy with the appropriate antibiotics. Guidelines from the American Thoracic Society suggest administering a macrolide antibiotic for mild disease and adding a ^-lactam if the pneumonia is more severe. These antibiotics are safe for use in pregnancy and have coverage for most of the microorganisms associated with bacterial pneumonia in pregnancy.
Viral pneumonia
The most common causative agents in pregnancy are the influenza A (the strain most commonly affecting humans) and varicella (chickenpox) viruses. Viral pneumonia may lead to severe acute respiratory failure, secondary bacterial infection and acute lung injury.
Influenza
Seasonal flu is more likely to cause severe illness in pregnant women than in non-pregnant women, and annual vaccination is recommended unless there are contraindications. Recently, a number of newer influenza viral strains have been identified, all of which have been associated with significant maternal and perinatal morbidity. In 2009, the World Health Organization declared a pandemic when H1N1 caused over 18,000 deaths worldwide (over 450 in the UK). Severe disease was notably more common in young people, unlike seasonal influenza, with other risk factors being diabetes, obesity, immunosuppression and particularly pregnancy, with an estimated increased mortality risk of 4-6 times that in the non-pregnant population.
Signs and symptoms are similar to those in non-obstetric women and range from mild illness, typically with high fever, to severe and progressive hypoxaemia. Diagnosis is by nasal/pharyngeal swabs. The mortality rate for those admitted to the intensive care unit is approximately 20-25%, and is thought to be greater in those not receiving antiviral therapy within 2 days of the onset of symptoms. There is an increased risk of premature delivery (times three) and stillbirth/early neonatal death (times five) in pregnant women admitted to hospital.
Varicella
Chickenpox is an illness usually seen in childhood, but primary varicella may also occur in adults, 16% of whom develop complications - one of which is varicella pneumonia. The diagnosis is usually clinical, based on the history, rash and/or previous contact, but may be helped by the presence of granular infiltrates seen on chest x-ray combined with the presence of serum antibodies, although these may not be seen for 2 weeks. Pneumonia occurs in up to 10% of pregnant women with chickenpox; risk factors include smoking, preexisting lung disease, immunosuppression (e.g. with steroid therapy) and late pregnancy. With appropriate modern therapy (antiviral drugs and intensive care), mortality is thought to be under 1% (approximately five times the rate in non-pregnant adults), though historical rates of up to 45% have been reported.
Fungal pneumonia
This is not commonly seen in pregnancy, but if it is, it may be associated with immunosuppression. Signs and symptoms are as in the non-obstetric population, but, as for viral infection, severe respiratory disease may ensue. The diagnosis may be made with sputum culture or serum antigens and chest x-ray changes (usually a nodular pattern is seen on the x-ray). Treatment is with intravenous amphotericin in the peripartum period and flucano- zole in the postpartum period, as there has been an association with flucanozole and fetal malformations.
Management options
Several strategies exist to prevent pneumonia in this high-risk population. Risk factors should be identified and modified where possible; if the mother has a coexisting respiratory disease, this should be optimised. Vaccinations are available for influenza, varicella and pneumococcus and are associated with fewer complications, including pneumonia and mortality. The influenza vaccination in pregnancy has been shown to reduce maternal morbidity and mortality, and improve fetal outcomes including risk of perinatal death, prematurity and low birth weight.
Management of pneumonia in pregnancy includes admission, appropriate investigation (including white blood cell count, C-reactive protein, arterial blood gas analysis and chest x-ray), initiation of antimicrobial/antiviral/antifungal therapy, fetal evaluation and respiratory support when required. Supplemental oxygen is usually required, to improve both maternal and fetal oxygenation.
In swine flu, antivirals such as oseltamivir and zanamivir have been used in pregnancy with success, particularly when administered within the first 48 hours of symptoms; treatment should be administered on clinical grounds rather than on diagnostic testing, owing to the latter’s low sensitivity. In chickenpox, aciclovir is usually the treatment of choice. Delivery during varicella viraemia may be associated with maternal coagulopathy and hepatitis and severe neonatal infection, and should be delayed if possible. Respiratory failure may require tracheal intubation and ventilation, although non-invasive methods (e.g. mask- delivered continuous positive airway pressure) may be effective, at least in the short term. Respiratory failure is a result of intrapulmonary shunting rather than hypoventilation, and so ventilation with positive end-expiratory pressure (PEEP) may be beneficial. Hypoxia may not be responsive to therapies such as PEEP, nitric oxide or use of the prone position. High- frequency ventilation/oscillation, extracorporeal membrane oxygenation (ECMO) and intravenacaval membrane oxygenation have been described for refractory cases, and experience in pregnancy is increasing. Early referral to a specialist centre capable of ECMO has been shown to be of benefit to survival in non-obstetric patients with severe respiratory failure. However, consideration must be given to whether obstetric services are available on site.
Delivery of the fetus may be necessary to improve the functional status of the mother, but whether improvement in clinical status really results is debatable; some advocate that delivery should be only for obstetric reasons. If caesarean section is required, the choice of regional or general anaesthesia requires careful consideration of the relative risks and benefits, including the likelihood that the mother’s condition may worsen after delivery.
Units should have a clear policy on caring for women with potentially contagious respiratory infections, including the provision of protective masks and training in their use.
Key points
• The effects of pneumonia may be exacerbated by the physiological changes of pregnancy and the increased demands of the fetus.
• Careful antenatal assessment is important.
• Regional analgesia and anaesthesia are usually indicated.
Further reading
Brito V, Niederman MS. Pneumonia complicating pregnancy. Clin Chest Med 2011; 32: 121-32.
Knight M, Kenyon S, Brocklehurst P, et al.; MBRRACE-UK. Saving Lives, Improving Mothers’ Care: Lessons learned to inform future maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2009-12. Oxford: National Perinatal Epidemiology Unit, University of Oxford, 2014.
Lamont RF, Sobel JD, Carrington D, et al. Varicella-zoster virus (chickenpox) infection in pregnancy. BJOG 2011; 118: 1155-62.
Rasmussen S, Jamieson D. 2009 H1N1 influenza and pregnancy: 5 years later. N Engl J Med 2014; 371: 1373-5.