Asthma in Pregnancy

It is a common obstructive pulmonary disease

Affects millions of people worldwide and complicates about 8% of pregnancies

May be the most common potentially serious medical complication of pregnancy

It is a chronic disease

Can be life-threatening in severe or poorly controlled cases

Episodic; symptom free periods and acute exacerbations

Characterized by increased responsiveness of the tracheobronchial tree to multiple stimuli.

Definitions

Total lung capacity: maximum volume of air present in the lungs at end of maximal inspiration

Functional residual capacity: volume of air present at end of passive expiration

Tidal volume: amount of air inhaled or exhaled normally at rest

Forced vital capacity: amount of air that can be expelled from the lungs after taking the deepest possible breath

Peak expiratory flow rate (PEFR): lung function test that measures how fast a person can exhale

Forced expiratory volume in 1 second (FEV₁): measures how much a person can exhale during a forced breath in the 1st second.

Characterized by chronic inflammation, swelling and narrowing of bronchial tubes resulting in difficulty in breathing

The bronchial narrowing may be partially or completely reversible with or without treatment

Chronically inflamed bronchial tubes may become overly sensitive to and remain in a state of heightened sensitivity called bronchial hyperactivity.

Potential risks from maternal asthma

Maternal complications

• Pre-eclampsia
• Hypertension
• Toxemia
• C-section placenta previa
• Hyperemesis gravidarum

Risk factors for exacerbations of asthma during pregnancy

• Non-adherence with controller therapy
• Viral infections
• Diaphragmatic elevation of up to 4 cm
• Increased prostaglandin F2α may promote bronchoconstriction
• Asthma triggers
• Gastroedophageal reflux
• Imcreased emotional stress
• Increased progesterone levels result in centrally mediated hyperventilation, manifested as ‘dyspnea of pregnancy’

Results in higher O₂ and lower PCO₂

Diaphragm elevated by 4 cm

Increased transverse diameter (2cm) and chest circumference (5-7cm)

Decrease in

• Total lung capacity
• Functional residual capacity

Increased tidal volume; (amount of air inhaled or exhaled normally at rest); progesterone effect

No clinically significant change in

• Forced vital capacity (amount of air that can be expelled from the lungs after taking the deepest possible breath)
• Peak expiratory flow rate (PEFR)
• Forced expiratory volume in 1 second (FEV₁)

Airway resistance is reduced due to the progesterone-mediated bronchial and tracheal smooth muscle relaxation.

Hypersensitivity to CO₂ increases the respiratory rate by 15%.

Alveolar ventilation is about 70% higher at the end of gestation.

Fall in arterial and alveolar carbon dioxide tensions.

The development of alkalosis is forestalled by compensatory decreases in serum bicarbonate.

Oxygen consumption and carbon dioxide production are increased by 60%.

Effects of pregnancy on asthma

• Variable effect: rule of thirds; 1/3rd improved, 1/3rd became worse, 1/3rd remains the same
• Worsening symptoms may be due to cessation of drugs because of fear of adverse effects
• Improvement in symptoms may be due to progesterone effect; smooth muscle relaxation
• The higher the severity of asthma, the worse the exacerbation

Effects of asthma on pregnancy

• No consensus but mild asthma/good control less likely to have complications and vice versa
• Effects on mother: pre-eclampsia, respiratory failure, death
• Effects on fetus: preterm birth, low birth weight, IUGR, increased perinatal morbidity and mortality,
• Exacerbations in first trimester is associated with increased risk of congenital malformations
• Lower FEV₁ during pregnancy is associated with increased risk of prematurity and low birth weight

Same as in non-pregnant state

Symptoms: include wheezing, shortness of breath, chest tightness, cough

May be worse at nights

Exposure to triggers may be identified; these may be allergens or irritants

• Allergens e.g. pollen, dustmites, molds, fish, peanuts, latex, infections, exercise
• Irritants e.g. respiratory infections, smoke, NSAIDS, petrol fumes, insecticides, exhaust from cars, generators

Symptoms and signs

• Shortness of breath
• Wheezing
• Chest tightness
• Use of accessory muscles
• Tachypnea
• Rhonchi

Pulmonary function tests

• FEV₁ (forced expiratory volume in 1 second; maximal amount of air that can be forcefully exhaled in the first second of a forced exhalation; requires a spirometer)
• PEFR (maximal rate at which a person can exhale during a short maximal expiratory effort after a full inspiration)

FEV₁

Best measure of pulmonary function

Is converted to a percentage of normal based on the patient’s height, weight and race.

It is a marker of the degree of obstruction in asthma patients

Classification

1. Normal: FEV₁ greater 80% of predicted
2. Mild obstruction: FEV₁ 60% to 79% of predicted
3. Moderate obstruction: FEV₁ 40% to 59% of predicted
4. Severe obstruction: FEV₁ less than 40% of predicted

In asthma, the FEV₁ is usually decreased because of an increased airway resistance to expiratory flow.

PEFR

Correlates well with FEV₁

Easily measured with peak flow meter

To perform a peak flow:

• Stand up straight.
• Make sure the indicator is at the bottom of the meter.
• Take a deep breath, filling your lungs completely.
• Place the mouthpiece in your mouth; lightly bite with your teeth, and close your lips on it.
• Blast the air out as hard and as fast as possible in a single blow. Repeat 3 times and record the highest value obtained
• Keep a chart

The Peak Exploratory Flow Rate (PEFR) correlates with the FEV₁

Measured reliably with inexpensive, disposable, portable peak flow meters

Insight to course of asthma throughout the day

Help detect early signs of deterioration

Twice daily- upon awakening and after 12hr.

National Asthma Education and prevention program (NAEPP classification)

1. Mild intermittent
2. Mild persistent
3. Moderate persistent
4. Severe persistent

Mild intermittent Asthma

• Attacks occur ≤ twice per week
• Nocturnal attacks ≤ twice per month
• Normal PEFR or FEV₁ (≥ 80% predicted), variability < 20%

Mild persistent

• Attacks occur >twice a week but not every day
• Nocturnal attacks > twice a month
• Attacks are sometimes severe enough to affect regular activities
• Normal PEFR or FEV₁ (>80%)

Moderate persistent

• Attacks occur daily
• Nocturnal attacks occur > twice a week
• PEFR OR FEV₁ >60% to <80% predicted; variability >30%
• Regular medications necessary to control symptoms

Severe persistent

• Attacks occur frequently; continuous daytime symptoms/frequent exacerbations
• Frequent nocturnal symptoms
• Symptoms limit daily activity
• PEFR or FEV₁ ≤60% predicted, variability >30%
• Regular oral corticosteroids necessary to control symptoms

• Acute respiratory distress in pregnancy
• Physiologic dyspnea of pregnancy
• Asthma
• Pneumonia
• Peripartum cardiomyopathy
• COPD
• Amniotic fluid embolism

• Maintaining adequate oxygenation of the fetus by preventing hypoxic episodes in mother
• Achieving minimal or no maternal symptoms at day or night
• Minimal or no exacerbations
• No limitation of activity
• Maintenance of normal or near normal pulmonary function
• Minimal or no adverse effects from medications

Components of effective management

• Objective assessment and monitoring
• Patient education
• Avoidance or control of asthma triggers
• Drug therapy

Objective measures for assessment and monitoring

• Gold standard: FEV₁ following maximal inspiration
• Mean FEV₁ < 80% predicted is associated with increased preterm delivery < 37 and birth weight <2500g
• PEFR correlates well with FEV₁ and can be easily measured with peak flow meters
• Typical PEFR in pregnancy is 380-550 L/min
• Pregnant woman should determine her personal best and calculate her PEFR zones: green > 80%; yellow 50-80%; red < 50%

Patient education

• Importance of good control
• Identification and avoidance of triggers
• Medical management
• Self-monitoring of PEFR

Educational topics for asthmatic pregnant women:

• Stop smoking
• Use of inhaler devices
• Adherence to treatment
• Environmental control
• Self-treatment action plan

Avoidance or control of triggers

• Common association between asthma and allergy; 75-85% asthma patients have positive skin test to common allergens e.g. animal dander, household mite, cockroach antigen

Drug therapy

• Minimum drugs that control symptoms
• 2 groups; rescue and maintenance

Rescue agents

• Used to treat acute bronchospasm and provide symptomatic relief
• Does not treat the underlying inflammation
• E.g. beta-2 agonists, anti-cholinergics

Maintenance agents

• Treat underlying inflammation
• E.g. steroids, leukotriene antagonists, cromolyn

Asthma in pregnancy is an increasingly common problem

Excellent maternal and perinatal outcome can be obtained particularly for mild-moderate cases

Severe cases may be associated with increased maternal and perinatal morbidity and mortality