What is the best next step for a 30-year-old pregnant woman at 32 weeks gestation with asthma exacerbation and oxygen saturation of 92% on room air?

Management of Asthma Exacerbation in a Pregnant Woman

Begin oxygen therapy aiming for saturation greater than 95% as the best next step for this pregnant woman with asthma exacerbation and oxygen saturation of 92% on room air.

Rationale for Oxygen Therapy

For pregnant women with acute illness or hypoxemia, the British Thoracic Society guidelines specifically recommend a target oxygen saturation of 94-98% 1. This is particularly important in pregnancy where maternal hypoxemia can lead to fetal compromise. The patient's current oxygen saturation of 92% is below the recommended target for pregnant women.

The National Asthma Education and Prevention Program guidelines also support this approach, stating that oxygen administration through nasal cannulae or mask is recommended to maintain oxygen saturation greater than 90% in general, but specifically greater than 95% in pregnant women 1.

Management Algorithm for Asthma Exacerbation in Pregnancy

1. Initial Assessment:

   • Current presentation: Oxygen saturation 92%, respiratory rate 24/min, diffuse wheezing, able to speak in full sentences
   • Severity classification: Moderate exacerbation based on symptoms and vital signs

2. Immediate Interventions:

   • Oxygen therapy: Begin supplemental oxygen to achieve saturation >95% 1
   • Continue bronchodilator therapy (albuterol) and systemic corticosteroids (methylprednisolone) that have already been initiated
   • Position patient appropriately (avoid supine position)

3. Monitoring:

   • Continuous pulse oximetry until clear response to bronchodilator therapy
   • Fetal monitoring (already initiated)
   • Monitor for signs of worsening respiratory status

Positioning Considerations

While proper positioning is important, having the patient lie supine (option A) would be contraindicated. For pregnant women beyond 20 weeks gestation (patient is at 32 weeks), the British Thoracic Society recommends using left lateral tilt or full left lateral position to avoid aortocaval compression 1. This improves cardiac output and oxygen delivery to both mother and fetus.

Diagnostic Testing Considerations

Regarding chest radiography (option B), this is not routinely recommended in asthma exacerbations unless there is suspicion of pneumothorax, pneumonia, or other complications 1. There is no indication of these complications in this patient's presentation, and radiation exposure should be minimized during pregnancy when possible.

Medication Considerations

Starting a long-acting beta-adrenergic agent (option C) is not appropriate during an acute exacerbation. These medications are for maintenance therapy, not acute management.

Intravenous theophylline (option D) is not recommended as first-line therapy for asthma exacerbations. It has a narrow therapeutic window and potential for significant adverse effects, especially during pregnancy 2.

Special Considerations in Pregnancy

Asthma exacerbations during pregnancy require prompt treatment as maternal hypoxemia can adversely affect the fetus. Most asthma medications are considered safe during pregnancy, and uncontrolled asthma poses a greater risk than the medications used to treat it 2.

Pitfalls to Avoid

1. Delaying oxygen supplementation in a pregnant woman with hypoxemia
2. Underestimating the severity of asthma exacerbation during pregnancy
3. Using inappropriate positioning (supine) that could compromise maternal-fetal circulation
4. Ordering unnecessary radiographic studies that expose the fetus to radiation
5. Using medications with unfavorable risk profiles (like theophylline) when safer alternatives are available

By following these evidence-based guidelines, the management of asthma exacerbation in this pregnant patient can be optimized to ensure the best outcomes for both mother and fetus.