AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Background

Asthma is a chronic inflammatory disease of the airways that is characterized by increased responsiveness of the tracheobronchial tree to multiple stimuli. 

Asthma is an episodic disease of acute exacerbations intermingled with symptom-free periods. Most attacks prove to be short-lived, lasting minutes to hours. Although patients appear to recover completely clinically, evidence suggests that patients with asthma develop chronic airflow limitations.

Asthma is classically divided into 2 distinct types: allergic (extrinsic) and idiosyncratic (intrinsic).

Allergic asthma is frequently associated with a personal and/or familial history of allergic diseases and high serum levels of immunoglobin E (IgE). Patients with this type of asthma often have positive skin reactions to intradermal airborne antigen injections and have a positive response to provocation tests involving inhalation of specific antigens.

In contrast, idiosyncratic asthma often has normal IgE levels and no familial or personal history of allergy.

Asthma is the most common chronic condition in pregnancy. Despite the frequently held notion that it is harmless, asthma can cause tremendous morbidity to both the fetus and the mother. In fact, severe and/or poorly controlled asthma has been associated with numerous adverse perinatal outcomes, including preeclampsia, pregnancy-induced hypertension, uterine hemorrhage, premature birth, congenital anomalies, fetal growth restriction, and low birth weight.

Pathophysiology

Pregnancy has a significant effect on the respiratory physiology of a woman. While the respiratory rate and vital capacity does not change in pregnancy, there is an increase in tidal volume, minute ventilation (40%), and minute oxygen uptake (20%) with resultant decrease in functional residual capacity and residual volume of air as a consequence of the elevated diaphragm. In addition, airway conductance is increased and total pulmonary resistance is reduced, possibly as a result of progesterone. 

The result of all of these physiologic changes is a hyperventilatory picture as a normal state of affairs in the later half of pregnancy. This results in the picture of a chronic respiratory alkalosis during pregnancy with a decreased pCO₂, decreased bicarbonate, and increased pH. A normal pCO₂ in a pregnant patient may signal impending respiratory failure. The increased minute ventilation and improved pulmonary function in pregnancy promote more efficient gas exchange from the maternal lungs to the blood. Therefore, changes in respiratory status occur more rapidly in pregnancy than in the nonpregnant patient.

Asthma is characterized by inflammation of the airways, with an abnormal accumulation of eosinophils, lymphocytes, mast cells, macrophages, dendritic cells, and myofibroblasts. This leads to a reduction in airway diameter caused by smooth muscle contraction, vascular congestion, bronchial wall edema, and thick secretions.

Frequency

United States

Prevalence of asthma in the general population is 4-5%. In pregnancy, the prevalence ranges from 1-4%.

International

Statistics are the same as in the United States.

Mortality/Morbidity

• Morbidity and mortality rates of pregnant women with asthma are comparable to the general population.
• The mortality rate from asthma in the United States is currently 2.1 per 100,000.
• Death rates in the United States have been increasing from 0.8 per 100,000 in the general population in the late 1970s to 2.1 per 100,000 in 1994.¹

Race

Prevalence and mortality rates are significantly higher in African Americans and Hispanics when compared with whites.

Sex

The male-to-female ratio in childhood is 2:1. That ratio decreases to 1:1 by 30 years.

Age

The prevalence of asthma is the same in all women of childbearing age.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

History

• Cough
• Shortness of breath
• Chest tightness
• Noisy breathing
• Nocturnal awakenings
• Recurrent episodes of symptom complex
• Exacerbations possibly provoked by nonspecific stimuli
• Personal or family history of other atopic disease (eg, hay fever, eczema)

Physical

• Physical examination may be completely normal during remission.
• Tachypnea
• Retraction (sternomastoid, abdominal, pectoralis muscles)
• Agitation, usually a sign of hypoxia or respiratory distress
• Pulsus paradoxicus  (>20 mm Hg)
• Pulmonary findings
• • Diffuse wheezes (long, high-pitched sounds on expiration and, occasionally, on inspiration)
  • Diffuse rhonchi (short, high- or low-pitched squeaks or gurgles on inspiration, expiration, or both)
  • Bronchovesicular sounds
  • Expiratory phase of respiration equal or more prominent than inspiratory phase
• Signs of fatigue and near respiratory arrest
• • Alteration in the level of consciousness, such as lethargy, which is a sign of respiratory acidosis and fatigue
• • Abdominal breathing
  • Inability to speak in complete sentences
• Signs of complicated asthma
• • Check for equality of breath sounds (pneumonia, mucous plugs, barotrauma). The amount of wheezing does not always correlate with the severity of the attack. A silent chest in someone in distress is more worrisome.
  • Jugular venous distension from increased intrathoracic pressure (from a coexistent pneumothorax)
  • Hypotension and tachycardia (think tension pneumothorax)
  • Fever, a sign of upper or lower respiratory infections

Causes

• A complex and poorly defined interaction of genetic predisposition and environmental stimulation causes the asthma.
• The basic mechanism for nonspecific bronchial hyper-responsiveness is unknown.
• Airway inflammation is the most popular hypothesis.
• Implicated environmental stimuli include the following:  
• • Allergens, including pollens, house-dust mites, cockroach antigen, animal dander, molds, and Hymenopteran stings
  • Irritants, including cigarette smoke, wood smoke, air pollution, strong odors, occupational dust, and chemicals
  • Medical conditions, including viral upper respiratory infections, sinusitis, esophageal reflux, and Ascaris infestations
  • Drugs and chemicals, including aspirin, nonsteroidal anti-inflammatory drugs, beta-blockers, radiocontrast media, and sulfites
• Exercise
• Cold air
• Menses
• Emotional stress

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Other Problems to be Considered

Airway obstruction
Amniotic fluid embolism
Acute congestive heart failure (CHF), secondary to peripartum cardiomyopathy
Physiologic dyspnea of pregnancy

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Lab Studies

• Complete blood cell count (CBC) with differential  
• • This is performed to assess the degree of nonspecific inflammation and the possibility of a comorbid anemia or thrombocytopenia.
  • Leukocytosis may be the result of a physiologic response to pregnancy, steroid therapy, upper respiratory tract infections, or the stress of an asthma attack.
• Arterial blood gas level  
• • Arterial blood gas (ABG) analysis indicates the level of oxygenation and respiratory compensation.
  • PaCO₂ is generally low in early stages of exacerbation as a result of hyperventilation.
  • An increase in PaCO₂ can be a sign of impending respiratory failure.
  • ABG results often show a decrease in PaO₂.
  • Physiologic changes that accompany pregnancy in the pulmonary system slightly alter normal ABG values: pH 7.4-7.45, pO₂ 95-105 mm Hg, pCO₂ 28-32, and bicarbonate 18-31 mEq/L.
• Blood cultures must be obtained in patients in whom pneumonia is found or reasonably suggested.

Imaging Studies

• Chest radiography
• • A normal chest radiograph in late pregnancy typically reveals an enlarged heart and some prominent lung markings from elevation of the diaphragm.
  • Chest radiography is indicated when the other coexistent conditions such as pneumonia, barotrauma, CHF, or chronic obstructive pulmonary disease are likely.
  • Chest radiographs (2 views) with a shielded maternal abdomen provides the fetus of approximately 0.00005 rad.

Other Tests

• Pulmonary function tests  
• • Hand-held peak flow meters are available in most EDs. If the patient’s baseline is known, clinicians can use measurement to assess severity of attack and its response to medications.
  • Reversible airflow obstruction is central to the diagnosis and assessment of asthma.
  • Changes in pulmonary function during acute asthma include the following:
  • • Decreased peak expiratory flow rate (PEFR) and forced expiratory volume in one second (FEV1)
    • Mild reduction in the forced vital capacity (FVC)
    • An increased residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC)
    • Normal diffusing capacity
  • Patients with asthma usually demonstrate a greater than 15% increase in FEV1, FVC, and PEFR when treated with bronchodilators.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Prehospital Care

• Address the airway status as needed.
• Provide early institution of beta-agonist inhalational therapy.
• Provide supplemental oxygen.

Emergency Department Care

Pregnant patients who present with typical mild exacerbations of asthma may be treated like regular asthmatics with bronchodilator therapy and steroids. However, special attention must be given to pregnant patients who present with severe asthma exacerbations because the resulting maternal hypoxia can have devastating consequences on the fetus.

As always in the ED, address the ABCs. The patient should be placed on a cardiac monitor and pulse oximetry. The threshold of intubation should be low to prevent/limit hypoxic episodes to the fetus. Intubate and mechanically ventilate the following patients:

• Those in or near respiratory arrest
• Those failing to respond to treatment as evidenced by  
• • Hypoxemia despite supplemental oxygen
  • Increasing CO₂ retention
  • Persistent/worsening level of consciousness
  • Hemodynamic instability

The key to treating asthma in the pregnant patient is to frequently assess the patient, the severity of the attack, and the patient’s response to treatment.

• Hypoxia, acidosis, unequal breath sounds, pneumothorax, and atypical features serve as warning signs of severe exacerbations.
• Inhaled beta2-agonists are the mainstay of treatment.
• Beta2-agonist, inhaled and/or subcutaneous, is typically given 3 doses over 60-90 minutes.
• Beta-adrenergic blocking agents should be avoided due to bronchospastic effect.
• Early use of systemic steroids has been shown to reduce the length of stay in the ED and the admission rate; the effect of steroids is seen within 4-6 hours of the institution of therapy.
• Supply supplemental oxygen to maintain oxygen saturation higher than 95%.
• Intravenous fluids can help loosen and clear secretions.
• Fetal monitoring becomes important after 20 weeks of gestation in severe cases.
• Tranquilizers and sedatives should be avoided because of their respiratory depressant effect.
• Antihistamines are not useful in the treatment of asthma.
• Mucolytic agents increase bronchospasm.
• Mechanical ventilation  
• • Less than 1% of all asthmatics require mechanical ventilation.
  • Asthmatics have higher complication rates from mechanical ventilation.
  • Increased airway resistance may result in extremely high peak airway pressures, barotraumas, and hemodynamic impairment.
  • Mucus plugging is common, increasing airway resistance, atelectasis, and the incidence of secondary pneumonia.
  • Paradoxical increases in bronchospasm from aggravation by the endotracheal tube may occur.
  • Ventilation setting
  • • Typical ventilator settings may lead to stacked breaths and increased airway pressures.
    • Decrease the I:E ratio and set low respiratory rate to allow for adequate expiration.

Consultations

Consult an obstetrician.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Almost all antiasthma drugs are safe to use in pregnancy and during breastfeeding. In fact, undertreating is a frequent occurrence for the pregnant patient because patients are worried about the medication effects on the fetus.

Outpatient management of asthma is similar for the pregnant patient as it is for the nonpregnant patient. Beta-adrenergic agonists remain the mainstay of treating exacerbations and handling mild forms of asthma. For moderate-persistent asthma, a beta-adrenergic agonist combined with an inhaled anti-inflammatory agent or inhaled corticosteroid is recommended for treatment. In severe asthma, oral corticosteroids and beta-agonists are recommended.

Corticosteroids can be used in the acute and outpatient setting and have been shown to be relatively safe in pregnancy. The intravenous, intramuscular, and oral preparations can be used for the acute exacerbation, whereas the inhaled preparations are reserved for outpatient maintenance therapy.

A longer-acting beta2-adrenoreceptor agonist (eg, salmeterol), whose bronchodilator effects last at least 12 hours, is an effective treatment of nocturnal asthma.

Historically, methylxanthines and oral beta-agonists have been used to treat asthma. Both have been shown to be safe in pregnancy but have fallen out of favor for newer medicines and the inhaled forms, respectively. 

Magnesium sulfate is another medication that is safe to use in pregnancy. It works as a smooth muscle relaxant of the airway.

Drug Category: Bronchodilators

Achieve short-term relief most effectively, increasing airway caliber by relaxing airway smooth muscle. Beta2-receptor agonists are widely used and have less systemic effects than nonselective agonists. They are effective after an inhaled or oral dose and have a long duration of action. Albuterol, terbutaline, metaproterenol, and bitolterol are available as metered-dose inhalers. Salmeterol, also a beta2-adrenoreceptor agonist, has a long duration of action (at least 12 h). Therefore, it is an effective agent for the treatment of nocturnal asthma.

Drug Category: Beta2-adrenergic agonist agents

These agents are used in the acute severe asthmatic attack.

Drug Category: Anticholinergic

These agents are particularly beneficial for patients with coexistent heart disease in whom beta-adrenergic stimulation may be dangerous.

Drug Category: Methylxanthine

Importance of theophylline as an antiasthmatic agent is decreasing because adrenoreceptor agonists and anti-inflammatory drugs are successful. Theophylline has a very narrow therapeutic window.

Drug Category: Corticosteroids

This category includes the oral corticosteroids (eg, prednisone), inhaled corticosteroids (eg, beclomethasone, flunisolide, triamcinolone), and cromolyn and nedocromil. Clinical studies have consistently shown the efficacy of corticosteroid use.

Aerosol use is the most effective way to decrease the systemic effects of corticosteroid therapy. Their chronic use reduces symptoms and improves pulmonary function in patients with mild asthma. If bronchodilator therapy is not sufficient, inhaled corticosteroids should be started.

Systemic corticosteroids are reserved for patients who require more urgent treatment. Conversely, cromolyn and nedocromil inhibit antigen- and exercise-induced asthma. They can be indicated as the first-line anti-inflammatory medication for the treatment of asthma.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Further Inpatient Care

• Criteria for hospital admission
• • Inadequate response to ED therapy
• • pO₂ less than 70 mm Hg
  • Signs of fetal distress (eg, decreased movement, abnormal cardio tocodynamometry, uterine contractions)
• • Multiple medication use (ie, requiring 3 or more medications simultaneously)
• • A protracted course with poor response to outpatient therapy thus far instituted or history of severe asthma requiring intubation or ICU admission and inadequate home conditions and transport/access to ED care
• Criteria for ICU admission
• • Altered level of consciousness
• • Poor air flow
• • Signs of fatigue, downhill course, or need for mechanical ventilation
• • PEFR/FEV1 less than 25% of predicted or pCO₂ greater than 35 mm Hg

Further Outpatient Care

• Criteria for home discharge
• • Symptoms and physical examination greatly improve
  • Patient able to walk out of ED without obvious distress
  • PEFR/FEV1 greater than 70% baseline
  • No fetal distress
  • Good follow-up and access to ED in case of relapse
• Follow-up appointment 2-4 days following the ED visit is recommended.
• Consider referral to an asthma specialist.

In/Out Patient Meds

• Glucocorticoids at the time of discharge have proven to be useful and reduce the incidence of ED visits.

Complications

• Respiratory failure and need for mechanical ventilation
• Barotrauma
• Complications of (parenteral) steroid use
• Death

Prognosis

• Women with mild disease are unlikely to have problems.
• Patients with severe asthma are at greater risk of deterioration.
• The risk of deterioration is greatest in the last portion of a pregnancy.
• There is inconsistent evidence in mothers with asthma, with an increased incidence of the following: 
• • Pregnancy-induced hypertension (PIH)
  • Neonatal hypoglycemia, seizures, tachypnea, and NICU admissions
  • Small and preterm infants (This appears to be small and may be minimized by good control of asthma.)
  • Studies shows that low birth weight infants were more common in women with daily symptoms or low expiratory flow than in women without asthma.
  • Preterm labor

Patient Education

• Most complications of asthma during pregnancy are from undermedication; thus, the goal is to emphasize the importance and safety of therapy. Education should cover the following aspects of asthma and pregnancy:
• • Signs and symptoms of asthma
  • Importance and safety of the medication to the fetus and to the mother
  • Warning signs that indicate they should go to the ED
  • Potential harm to their fetus and increased risk to themselves with undertreatment or unnecessary delays in seeking additional care
  • Prevention and avoidance of known triggers
  • Home use of metered-dose inhalers and peak flow meters
  • Medication adverse effects
  • Use of written diaries to record PEFR
  • Use of written guidelines for managing an exacerbation and for prudently using the ED
• For excellent patient education resources, see eMedicine's Asthma Center. Also, visit eMedicine's patient education articles, Asthma and Asthma in Pregnancy.

ACKNOWLEDGMENTS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors, A Antoine Kazzi, MD, and Araz Marachelian, MD, to the development and writing of this article.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

1. Sly RM, O'Donnell R. Stabilization of asthma mortality. Ann Allergy Asthma Immunol. Apr 1997;78(4):347-54. [Medline].
2. Hornby PJ, Abrahams TP. Pulmonary pharmacology. Clin Obstet Gynecol. Mar 1996;39(1):17-35. [Medline].
3. Mabie WC. Asthma in pregnancy. Clin Obstet Gynecol. Mar 1996;39(1):56-69. [Medline].
4. Mays M, Leiner S. Asthma. A comprehensive review. J Nurse Midwifery. May-Jun 1995;40(3):256-68. [Medline].
5. Nelson-Piercy C, Moore-Gillon J. Asthma in pregnancy. Br J Hosp Med. Feb 7-20 1996;55(3):115-7. [Medline].
6. Rey E, Boulet LP. Asthma in pregnancy. BMJ. Mar 17 2007;334(7593):582-5. [Medline].

Article Last Updated: Aug 20, 2008