Pregnancy is associated with many anatomical and physiologic changes that affect the presentation and management of various illnesses. This article deals with several respiratory issues that one may encounter in the gravid patient, including asthma, pneumonia, tuberculosis and acute respiratory distress in pregnancy. Approach to dyspnoea in pregnancy and smoking cessation is also discussed.
Respiratory disorders during pregnancy may be encountered and may have an effect on pregnancy outcomes. An understanding of how pregnancy affects the disease presentation and vice versa, will help the clinician provide better care for the gravid patient.
Respiratory diseases are an important cause of morbidity and mortality in pregnant women. Chronic lung diseases such as asthma and cystic fibrosis may present unique management problems in pregnancy, and others such as pneumonia and tuberculosis can target pregnant women just as they target non-pregnant women. Some diseases, such as pulmonary embolism, may be more likely because of the pregnancy itself. Physiologic dyspnea and hyperventilation are common symptoms of pregnancy, but they are usually benign and not reflective of serious underlying pathology.
A number of the physiological changes which occur during pregnancy affect the lungs and this may alter pulmonary function. Ventilation increases by 20–50% at the end of the first trimester and this is sustained throughout pregnancy, causing a mild compensated respiratory alkalosis with PCO2 slightly lower and PO2 slightly higher than normal. Diaphragmatic excursion, vital capacity, and total lung volume are unchanged. These alterations are of little consequence to a normal woman during pregnancy but, in a patient with diminished respiratory reserve, they can contribute to pulmonary decompensation.
Foetal oxygen delivery is dependent on maternal blood oxygen content and uterine blood flow. Uterine blood flow decreases with maternal hypotension, low maternal cardiac output, uterine artery vasoconstriction secondary to increased levels of exogenous or endogenous catecholamines, and maternal alkalosis. Maternal alkalosis also affects oxygen unloading at the tissue level because of a shift in the oxygen-haemoglobin dissociation relation with greater binding affinity.
Physiologic dyspnea usually occurs early in pregnancy and improves closer to term. Patients are able to perform daily activities and are usually not dyspneic with rest. Pathologic dyspnea, however, usually worsens with time. The pregnant patient may occasionally complain of paroxysmal nocturnal dyspnea, orthopnea, and chest discomfort during late pregnancy. Although this may suggest cardiac disease, it is often due to an upward displacement of the diaphragm.
Pneumonia, although infrequent, is the most common non-obstetric infection to cause complications as well as maternal and foetal mortality in the peripartum period. The microorganisms that cause pneumonia in the pregnant patient are not unique; however, pregnant women may be more susceptible to organisms that are controlled by cell-mediated immune processes, such as viruses, fungi, and mycobacteria.
Although in the majority cases of Respiratory disorders in pregnancy the treatment should follow standard guidelines, there are some important exceptions such as the use of warfarin in pulmonary embolism. There are often concerns about the use of a number of drugs in pregnancy due to potential problems with placental transfer to the foetus.
Several serious pulmonary complications of pregnancy may occur, however, and because they can adversely affect outcomes for both mother and foetus, physicians should be aware of their occurrence and familiar with prevention and treatment strategies.