Pregnancy and the Lung

Pregnant women are prone not only to common pulmonary diseases but also diseases specific to pregnancy, eg, tocolysis-induced pulmonary edema, amniotic fluid embolism, and gestational trophoblastic neoplasms. Carrying a developing fetus poses additional challenges and restricts pharmacologic considerations.

In pregnancy, hyperventilation and respiratory alkalosis occur due to enhanced central sensitivity to CO₂, independent of progesterone levels (García-Rio et al. Chest. 1996;110[2]:446; Cugell et al. Am Rev Tuberc. 1953;67[5]: 568). Paco₂ for a ventilated pregnant woman should be targeted 30-32 mm Hg (normal range), and marked respiratory alkalosis should be avoided as it decreases uterine blood flow. Maternal permissive hypercapnia is also deleterious because of fetal respiratory acidosis. The upper airway may be narrowed as pregnancy progresses due to edema and weight gain (Izci et al. Eur Respir J. 2006;27[2]:321), and endotracheal intubation can be difficult (Munnur et al. Crit Care Med. 2005;33[10 suppl]:S259). Similarly, many pregnant women suffer from obstructive sleep apnea (OSA) and 16% snore (Facco et al. Obstet Gynecol. 2010: 115[1]:77). OSA can be safely treated with CPAP (Guilleminault et al. Sleep Med. 2004;5[1]:43).

Bronchial hyperresponsiveness to methacholine (BHR) peaks at the second trimester and reverts after delivery (Kwon et al. Am J Obstet Gynecol. 2004;190[5]:1). Miscarriage, depression, and caesarean section are more frequent among pregnant women with severe asthma (Tata et al. Am J Respir Crit Care Med. 2007;175[10]:991). Although gestational exposure to beta-agonists and inhaled and oral corticosteroids does not lead to fetal anomalies (Tata et al. Thorax. 2008;63[11]:981), smoking should be discouraged as it worsens asthma and causes intrauterine fetal growth retardation and congenital malformations (Murphy et al. Thorax. 2010; 65[8]:739; Newman et al. Chest. 2010;137[3]:601). Pulmonary embolism remains the major cause of maternal mortality, and venous thromboembolism accounts for 1.3 events per 1,000 deliveries, which represents a 10-fold risk increment compared with age-matched nonpregnant women. Low-molecular-weight heparin is recommended for the remainder of pregnancy until 6 weeks postpartum and stopped for 24 h before elective induction of labor (Bates SM et al. Chest. 2008;133[6 suppl]:844S).

For more information, attend the Clinical Pulmonary Medicine NetWork Highlight, “Clinical Challenges During Pregnancy” at CHEST 2011, scheduled for October 24, 11:00 am – 12:30 pm, Pregnancy and the Lung.

Dr. Kay-Choong See, Dr. Pyng Lee, FCCP
Steering Committee Member