Asthma in pregnancy

Overview
Asthma is one of the most common pulmonary conditions occurring during pregnancy with a prevalence rate of 3.7% to 8.4% in United States during the period 1997-2001.

Pathophysiology

 * During pregnancy, due to high levels of progesterone, minute ventilatory rate is increased causing compensated respiratory alkalosis.
 * The arterial blood gases may reveal a higher PO2 and lower PCO2 with mild alkalotic PH. Normal PCO2 during pregnancy is suggestive of impending respiratory failure.
 * Asthma is characterized by broncho-constriction or inflammation of airways with production of thick mucoid secretions. In a small prospective study involving 16 asthmatic pregnant women, hyper-reactivity was seen to be lower as evidenced by a reduction in minimum medication requirements.

Natural History, Complications and Prognosis
Severe or poorly controlled asthma cause maternal hypoxia, hypercapnia and respiratory alkalosis which may impair fetal oxygenation and uteroplacental blood flow. Asthma during pregnancy may have negative impact on both mother and the child especially in severe or poorly controlled cases. Complications include:
 * Complications during labor
 * Congenital anomalies
 * Complications of corticosteroid use
 * Cesarean delivery
 * Hyperemesis
 * Hypertensive conditions
 * Low birth weight infants
 * Neonatal hypoglycemia
 * Neonatal mortality
 * Neonatal seizures
 * Preterm labor and premature delivery
 * Preeclampsia
 * Respiratory failure
 * Uterine hemorrhage

History and Symptoms

 * The majority of patients have personal or family history of other atopic diseases.
 * The clinical presentation of asthma in pregnancy varies with individuals both spontaneously and with therapy.
 * In some cases, asthma is characterized by chronic respiratory impairment and others experience episodic attacks secondary to a number of triggering events including upper respiratory tract infection, stress, cold air, exercise, exposure to allergen (such as pets, dust, mites, pollen) or air pollutants (such as smoke or traffic fumes).
 * The cardinal symptoms of asthma include:
 * Loud expiratory wheeze
 * Nocturnal cough
 * Dyspnea
 * Chest tightness
 * Stridor in the absence of a wheeze may be confused with a COPD-type of disease and hence it is difficult to diagnose asthma based upon the history alone.

General appearance

 * Anxious and agitated
 * Altered consciousness, fatigue and lethargy in patients with acidosis

Vitals

 * Tachypnea
 * Tachycardia
 * Pulsus paradoxicus
 * Fever in presence of respiratory infection

Inspection

 * Retraction of accessory muscles of respiration such as sternocleidomastoid, abdominal and pectoralis muscles with each breath

Percussion

 * Hyper-resonant in all lung fields.

Auscultation

 * Long, high-pitched expiratory wheeze
 * Ronchi
 * Bronchovesicular breath sounds
 * Silent chest among patients in distress is a sign of severe and complicated asthma

Cardiology Examination

 * Jugular venous distension secondary to increased intrathoracic pressure in presence of pneumothorax
 * Tachycardia

Extremities
Clubbing

Lab Tests

 * Blood tests: Leukocytosis may be noted as a physiologic response to pregnancy or corticosteroid therapy
 * Arterial blood gases: Low PCO2 and elevated PO2 may be noted initially secondary to hyperventilation resulting in respiratory alkalosis. Elevated PCO2 may be noted in patients with severe asthma with impending respiratory failure.
 * Compensated respiratory alkalosis is the physiologic change noted in pregnancy secondary to hyperventilation due to high levels of progesterone. Asthma causes overlapping of respiratory acidosis over physiologic respiratory alkalosis and hence a modest elevation in PCO2 may be noted.

Pulmonary Function Testing

 * In normal pregnancy, FEV1, vital capacity, total lung capacity, FEV1/FVC remains unchanged while functional residual capacity, residual volume decreases with increase in tidal volume. FEV1 may decrease when pregnant women lie in supine position.
 * Pregnant women with acute asthma should rest in seated position rather than lying down.
 * As with non-pregnant asthmatics, pregnant asthmatics have reduced FEV1 and increased residual volume, functional residual capacity, and total lung capacity which can be reversed with bronchodilators.

Methacholine Challenge Test

 * Methacholine challenge test is usually not recommended in pregnancy as it can have teratogenic effects (Pregnancy Category C).

==Treatment ==
 * Monitor asthma control during all prenatal visits.
 * Asthmatic symptoms worsen in about a third during pregnancy and improve in a third; hence, medications should be adjusted accordingly.
 * Patients should rest in seated position rather than lying down
 * Oxygen supplementation should be provided to maintain PO2 over 70mm Hg
 * Regular monitoring and maintenance of lung function to ensure adequate oxygen supply to the fetus.
 * It is safer to treat asthma with medications than to have poorly-controlled asthma.

Treatment of chronic asthma in pregnancy

 * Albuterol is the preferred short-acting β2-agonist (SABA)
 * Inhaled corticosteroid such as budesonide alone or in combination with a long acting beta agonist such as salmeterol are recommended for the initial management of moderate persistent asthma.
 * Montelukast or zafirlukast can be considered as an alternative therapy.

Treatment of acute exacerbation of asthma in pregnancy

 * Oral or intravenous glucocorticoids is recommended for acute exacerbation of asthma similar to non-pregnant asthmatics.
 * Use of methylxanthines is not recommended in emergency setting as they do not provide additional benefit when compared to beta adrenergics and IV glucocorticoids.
 * Magnesium sulfate which is usually given during hypertensive conditions in pregnancy or preterm labor also have a beneficial effect on asthma by relaxing airway muscles.
 * Use of epinephrine should be avoided in pregnancy as it can lead to congenital malformations, fetal tachycardia, and vasoconstriction of the uteroplacental circulation.

Peripartum Management

 * Peripartum pain control can be managed with butorphanol or fentanyl. Morphine and meperidine should be avoided as they can induce release of histamine and possibly cause bronchoconstriction.
 * Epidural anesthesia is preferred for pain control during labor in the gestational asthmatics. In case general anesthesia is required, ketamine and halogenated anesthetics are preferred as they have bronchodilatory effects.
 * Use of oxytocin is recommended in induction of labor and control of postpartum hemorrhage.
 * Use of prostaglandin E1 and E2 analogs are shown to be safe in pregnancy However, prostaglandin F2 alpha analogs should be avoided as they can induce bronchospasm. Ergot derivatives have similar property and therefore should also be avoided.