During the course of their pregnancy, studies show that 20% of asthma patients have exacerbations severe enough to seek urgent medical care. Approximately 6% require hospital admissions. Severe exacerbations such as those requiring hospital admission, urgent physician visits, or systemic corticosteroids are significantly more likely to occur with severe asthma.
Exacerbations are most common in the late second trimester to early third trimester. The most common reasons for exacerbations are viral infections and non-compliance of inhaled corticosteroid treatment. The importance of regular usage of inhaled corticosteroids for persistent asthma cannot be overemphasized. Studies show that for patients using inhaled corticosteroids before pregnancy, the rate of asthma-related physician visits decreased and the number of emergency department visits was unchanged after pregnancy.
Management of Exacerbations
The management of the pregnant woman having an asthma exacerbation is set forth in the NAEPP Guidelines. Treatment depends on the severity of the exacerbation with nebulized albuterol and oral steroids used as the primary treatment, particularly at home. For pregnant women with severe exacerbations in the emergency department, nebulized ipratropium can be added to the nebulized albuterol.
The usual Pco2 in pregnancy is in the range of 26 to 30 mm Hg. For pregnant women presenting with a severe acute asthma exacerbation, a Pco2 of 40 signifies impending respiratory arrest.
Fortunately, it is rare for a pregnant woman to require intubation and mechanical ventilation. If needed, intubation should be oral instead of nasal due to airway narrowing. Preoxygenation with 100% oxygen prior to intubation is important to avoid a precipitous drop in oxygen that may occur after even a short period of apnea. Studies show that it is important to maintain cricoid pressure before and after intubation to avoid aspiration and gastric insufflation.
Studies show that patients should be ventilated with respiratory rates of 8 to 12 breaths per minute, tidal volumes of 6 to 8 ml/kg, and high-inspiratory flow rates of 100 to 120 per minute. Hyperventilation should be avoided because a respiratory alkalosis may decrease uterine blood flow and impair oxygenation of the fetus. In addition, it is important to avoid volutrauma and barotrauma.