Contributor: Bill Mabie, MD; Amy Picklesimer, MD
Last Update: 5/1/2011
Definition: Asthma is a lung disease with the following characteristics:
- Airway obstruction that is partially or completely reversible, either spontaneously or with treatment.
- Airway inflammation
- Increased airway responsiveness to a variety of stimuli
Incidence: The incidence of asthma in pregnancy is 4% – 8%.
Pathogenesis: Genetic predisposition and environmental risk factors (allergens, viral, bacterial) interact to produce bronchospasm, acute inflammation, persistent inflammation, and remodeling of the tracheobronchial tree. The asthma disease process is located in all parts of the bronchial tree from the trachea to the alveolar tissue.
- Airway obstruction
- Abnormal gas exchange
- Cardiovascular dysfunction
Fetal oxygenation may be threatened in 3 ways relevant to asthma.
- Maternal hypoxia
- Reduced uterine blood flow
In the clinic, patients typically present with physician-diagnosed asthma and are already using inhaled bronchodilators. However, if one were required to make the diagnosis of asthma during pregnancy one would perform 1) a history and physical and 2) spirometry before and after a bronchodilator.
The history is characterized by episodic wheeze, cough and dyspnea. There are characteristic triggers such as house dust mites, mold, cat and dog dander, cockroaches, pollen, cigarette smoke, changes in the weather, airborne chemicals, dust and viral sensitivity. Triad asthma consists of nasal polyps, aspirin sensitivity, and asthma. There is often a history of childhood asthma which the patient did not outgrow.
On physical exam one looks for wheezes, tachypnea, tachycardia, prolonged expiratory phase, tripod position, use of accessory muscles, and pulsus paradoxus. Inspect the nose for nasal polyps. Subcutaneous emphysema suggests pneumothorax. Absence of wheezing can be a bad sign since the patient is not moving any air. The potential workup for asthma is show below:
Peak expiratory flow rate (PEFR)
Spirometry (FEV1, FVC, FEV1/FVC)
Exhaled nitric oxide
Blood tests – CBC with differential, Alpha 1 – antitrypsin level
Tests of allergy – serum total lgE(>1000 IU/ml), skin tests (RAST), in vitro blood test panels (lgE antibody to specific antigens)
If spirometry is not available and the patient has a classic history and response to therapy, one can make the diagnosis of asthma. With a less typical presentation, a formal approach to the diagnosis is needed. It is important to emphasize that asthma is variable. The spirometry may be normal in which case a repeat examination can be done when the patient is symptomatic. Serial assessment over time possibly with a therapeutic trial of bronchodilator is a second option. Thirdly, bronchoprovocative testing (methacholine) can be used.
- Increase in FEV1 by 12% after inhaled bronchodilator
- Greater than 20% variability in PEFR over time that corresponds to symptoms
- Bronchoprovocative testing with inhaled methacholine or histamine. Dose required to drop the FEV1 by 20%
The differential diagnosis is as follows:
- Post-nasal drip
- Vocal cord dysfunction
- Endobronchial disease
- Pulmonary embolism
- Congestive heart failure
- Bronchopulmonary aspergillosis
- Cough secondary to drugs
- Panic disorder
Referral to a consultant could be considered for the following reasons:
Pulmonologist – Diagnosis uncertain, alternate pulmonary diagnosis suspected, further PFTs needed, patient not doing well on polypharmacy
Allergist – Allergic triggers prominent, blood tests suggest atopy, immunotherapy being considered
Profile of patients with potentially fatal asthma
- Previous mechanical ventilation
- Requires chronic oral corticosteroid therapy
- Severe disease with multiple hospital admissions for asthma
- Wide clinical variations in peak expiratory flow rate
- Fails to appreciate the significance of the airflow obstruction until quite severe
- Overreliant on short-acting bronchodilator therapy
- Inadequate long-term care
The antenatal management of asthma includes assessing severity, assessing control, and using step-care to tailor asthma therapy to the individual patient. Moderate and severe persistent asthma is considered high risk. At the first visit, one should obtain a history and physical, comorbidity, smoking, daytime symptoms, nighttime symptoms, days of work missed, emergency care visits, medication, allergy history, and immunotherapy history. With moderate and severe persistent asthma, one should schedule visits on clinical judgment. Intermittent and mild persistent asthmatics can be seen monthly.
At each visit obtain the history of emergency room visits, hospitalizations, or unscheduled clinc visits, daytime or nighttime symptom frequency, medication dosages, and compliance. Check the asthma diary and assess peak expiratory flow rate at each visit of patients with moderate and severe persistent disease. Daily PEFR should be considered for moderate and severe persistent asthma. Moderate and severe persistent asthmatics may need fetal surveillance with ultrasound and NST’s.
Management of acute asthma in pregnancy is summarized below:
- History and physical
- Patient in seated position rather than supine
- O2 sat on room air
- Peak Expiratory Flow Rate (PEFR )
- Fetal monitoring and/or BPP if fetus potentially viable
- Oxygen by nasal cannula at 3-4 L/min
- Maintain O2 sat > 95%
- Intravenous fluid containing glucose at a rate of at least 100 ml/hr
- Chest radiograph
- Antibiotics – usually not required
- Bad signs – PEFR < 50% of predicted, PaCO2 > 42 mmHg, patient confused or exhausted
Pharmacologic management of acute asthma in pregnancy is summarized below:
- Beta-agonist bronchodilator (metered-dose inhaler or nebulizer) up to 3 doses in first 60 minutes
- Nebulized ipratropium (Atrovent)
- Intravenous methylprednisolone (with initial therapy in patients on regular corticosteroids or with poor response during the first hour of treatment) 1 mg/kg every 6 hours. Taper as patient improves
- Consider intravenous magnesium sulfate (Not for routine use. Does not confer much benefit beyond that achieved with inhaled beta-agonists and systemic corticosteroids. Suggested for life-threatening exacerbations.) 2 grams infused over 20 minutes
- Consider subcutaneous terbutaline 0.25 mg if patient not responding to the above therapy.
Labor and delivery management is summarized below:
- Continue asthma medications
- Consider PEFR on admission and q 12 hours if acute exacerbation
- Avoid dehydration
- Provide adequate analgesia
- Prevent adrenal crisis
- Postpone elective delivery during asthma exacerbation
- Occasionally delivery may improve unstable asthma
- Cervical ripening – PGE1 or E2
- Hemabate and methergine may cause bronchospasm
- Magnesium sulfate or calcium channel blocker for tocolysis
- Avoid indomethacin
- Epidural anesthesia is encouraged
- Fentanyl is the preferred intravenous narcotic
- Ketamine and halogenated anesthetics are the preferred general anesthetics
Asthma Action Plan and How to Control Things That Make Your Asthma Worse
- National Heart Lung and Blood Institute Guidelines for the Diagnosis and Treatment of Asthma. www.nhlbi.nih.gov/guidelines/asthma. Accessed 2-28-08.
- Dombrowski MP, Schatz M; ACOG Committee on Practice Bulletins. ACOG practice bulletin: Clinical management guidelines for obstetricians and gynecologists. Number 90, February 2008: Asthma in pregnancy. Obstet Gynecol 2008;111:457-64.
- Dombrowski MP. Asthma and pregnancy. Obstet Gynecol 2006;108:667-81.