Respiratory infection during pregnancy and peripartum period is a complex condition with specialized concerns in terms of risks, diagnosis, and management. Although the pathogens are often similar to those seen in the general population, pregnant patients compose a unique group because of altered physiology and differences in immunologic response, leading to singular risk profile. The chances of associated morbidity and mortality, not only for the patient but also the fetus, are increased and require clinicians to adjust their management as needed. In fact, pneumonia is an independent risk factor for preterm labor and delivery, cesarean delivery, smaller size for gestational age, lower birth weights, lower Apgar scores, and preeclampsia/eclampsia.1,2,3,4
This chapter introduces normal maternal pulmonary physiology, diagnosis and management of respiratory infections, and special therapeutic considerations in the pregnant patient. Although obstetric patients may have significant respiratory and systemic symptoms related to upper respiratory tract infections, such as bronchitis and sinusitis, we focus on pneumonia and tuberculosis (TB).
NORMAL MATERNAL PULMONARY PHYSIOLOGY
In general, pregnant patients are deemed to be an at-risk population, primarily because of fetal considerations. However, pregnancy-induced adaptations to the immune system may also confer some degree of vulnerability to certain pathogens, although pregnancy is not traditionally considered a profound immunosuppressed state. Physiologically, maternal cellular immunity adapts to tolerate the presence of the fetus, with changes including decreased lymphocyte proliferative response, smaller number of helper T cells, decreased natural killer cell activity, reduced lymphocyte cytotoxic activity, as well as hormonally triggered inhibition of cell-mediated immunity.5,6 Humoral immunity is not compromised. In particular, pregnant patients seem to have an increased susceptibility to viral infections, which may be related to changes in innate interferon (IFN) responses during pregnancy.7,8
In addition to changes in immunity, there are significant adaptations of maternal pulmonary and systemic physiology. Table 9-1 describes the relevant anatomical and physiological changes seen in pregnant patients.9 Fetal metabolic demands on material circulation result in an increase in oxygen consumption by almost 20% during pregnancy. Increases in thoracic diameter and diaphragmatic excursion, despite restriction caused from the growing gravid uterus, allow pregnant patients to increase tidal volumes to meet the oxygen needs. Consequently, minute ventilation increases by almost 50%, without significant changes in respiratory rate. Pulmonary function tests show decreased functional residual capacity (decreased expiratory reserve volume and residual volume) but no impairment of inspiratory function.
TABLE 9-1Anatomical and Physiologic Changes of Respiratory System in Pregnancya ||Download (.pdf) TABLE 9-1 Anatomical and Physiologic Changes of Respiratory System in Pregnancya
|Type of Change ||Description ||Cause ||Impact on Risk or Management of Respiratory Failure |
|Anatomical ||Increase in subcostal angle from 60 to 130 degrees || ||Decreased chest compliance may affect mechanical ventilation |
| ||Rise in diaphragm ||To accommodate enlarging uterus || |
| ||Rise in intra-abdominal ...|