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11. Bronchial Asthma in Pregnancy
Asthma is reportedly the most common potentially serious yet treatable medical problem to complicate pregnancy occurring in about 3–8% of pregnant women.
The control of maternal asthma is directly proportional to better outcomes in both maternal and fetal.
Large recent studies seem to point to us that asthma follows a rule of thirds during pregnancy—1/third of the pregnant women get better, 1/third of the pregnant women remain the same, and in 1/third of the pregnant women, the symptoms worsen.
It has also been noted that in most pregnant asthmatic women, the same disease course during the first pregnancy is followed during the latest pregnancies.
In a large study, most acute exacerbations of asthma occur between 24th and 36th weeks of gestation, and such acute flare-ups are rare during the last month of gestation.
Ninety percent of pregnant women with adequately controlled asthma have no symptoms during labor, delivery, and puerperium, and most of them will go back to their prepregnancy status within 12 weeks.
11.1 Pregnancy-Induced Physiological Changes
Alterations of the cardiorespiratory physiology that occur during pregnancy contribute to the exacerbation of many respiratory problems in women during their pregnancy.
11.1.1 Respiratory System Changes
11.1.1.1 Anatomical Changes
- 1.
Changes in chest wall conformation.
- 2.
Elevation of the diaphragm.
- 3.
Respiratory center stimulation due to the effect of progesterone.
11.1.1.2 Physiological Changes
- 1.
Increase in tidal volume and minute volume.
- 2.
Lung volumes and capacities:
- (a)
Inspiratory capacity and tidal volume increased (due to progesterone).
- (b)
FRC, ERV, and RV decrease (due to elevation of diaphragm).
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- (c)
TLC (total lung capacity)—mild decrease or unchanged.
- (a)
In summary, though pulmonary functions are altered in pregnancy, it only induces stress on respiratory function of the pregnant women in the presence of any respiratory disease like asthma.
11.1.1.3 ABG
Because of increased minute ventilation, alveolar ventilation is increased leading to respiratory alkalosis. This gets partially compensated by a metabolic acidosis generated by the kidney.
As a result of this, the gravida’s normal ABG may appear abnormal, i.e., show features s/o respiratory alkalosis. Therefore we must keep in mind that for a pregnant woman:
Normal pH: 7.4–7.47.
Normal pCO2: 25 mm of Hg–32 mm of Hg.
11.1.2 Cardiovascular System Changes
- 1.
Increased blood volume (20–100% above preconception levels) due to increased plasma volume and increased red cell mass.
- 2.
Cardiac output rises by 30–60%.
- 3.
Heart rate rises by 10–20 bpm.
- 4.
Decreased vascular resistance (progesterone-induced relaxation of smooth muscles) leads to a minor fall in both diastolic blood pressure and systolic blood pressure.
11.2 Effects of Asthma on Pregnancy
- 1.
Preterm birth.
- 2.
Small for gestational age infants.
- 3.
Intrauterine growth restriction.
- 4.
Stillbirth.
- 5.
Congenital malformations (e.g., spina bifida, VSD and ASD (ventricular/atrial septal defects).
- 6.
Chorioamnionitis.
- 7.
Gestational diabetes.
- 8.
Low APGAR scores.
Fetal hypoxia as a result of poor asthmatic control of the gravida can even lead to neonatal respiratory difficulties, fetal brain ischemia, and cerebral palsy. In contrast if asthma is well controlled throughout pregnancy, there is little or no increased risk of adverse maternal and fetal outcomes.
Therefore pregnancy should call for optimizing therapy and maximizing lung function in order to decrease the possibility of acute exacerbation.
11.3 Effects of Pregnancy on Asthma
Worsening of asthma during pregnancy may be due to multiple contributory factors—allergen exposure; upper respiratory tract infection, especially rhinitis; gastroesophageal reflux poor compliance of medication, continue smoking illicit drug use; etc.
High-risk patients are those who have history of severe preconception asthma and those whose asthma has worsened in earlier pregnancies (Table 11.1).
Risk factors and triggers involved in asthma
Endogenous factors | Environmental factors |
|---|---|
Genetic predisposition | Indoor allergens |
Atopy | Outdoor allergens |
Airway hyperresponsiveness | Occupational sensitizers |
Gender | Passive smoking |
Ethnicity | Respiratory infections |
Obesity | Diet |
Early viral infections | Acetaminophen (paracetamol) |
Triggers | |
Allergens | |
Upper respiratory tract viral infections | |
Exercise and hyperventilation | |
Cold air | |
Sulfur dioxide and irritant gases | |
Drugs (β blockers, aspirin) stress | |
Irritants (household sprays, paint fumes) | |
Apart from these factors, in pregnancy GERD (gastroesophageal reflux disease) and allergic rhinitis are common triggers.
11.4 Differential Diagnosis for Acute Dyspnea in Pregnancy
Physiological dyspnea of pregnancy which is a benign symptom.
Pulmonary edema.
Pulmonary embolism.
Pneumothorax.
Pneumonia.
Worsening asthma.
Severe asthma.
Pregnant patients can also suffer from various hematological and cardiac diseases which can produce anemia and lead to dyspnea.
Airway obstruction.
Amniotic fluid embolism.
Acute congestive heart failure (CHF).
11.4.1 Management of the Asthmatic Gravida
- 1.
Prevention of chronic day and night symptoms.
- 2.
Maintenance of optimal pulmonary function and normal activities using therapies with minimal or no adverse side effects.
- 3.
Maintain fetal oxygenation by preventing episodes of maternal hypoxia (Table 11.2).
Asthma control
Characteristic | Controlled (all of the following) | Partly controlled | Uncontrolled |
|---|---|---|---|
Daytime symptoms | None (≤2/week) | >2/week | Three or more features of partly controlled |
Limitation of activities | None | Any | |
Nocturnal symptoms/awakening | None | Any | |
Need for reliever/rescue treatment | None (≤2/week) | >2/week | |
Lung function (PEF or FEV1) | Normal | 80% Predicted |
The best way to achieve these goals is by a multidisciplinary approach that incorporates regular monitoring of clinical symptoms, self-management education, and the correct use of pharmacotherapies.
The British Thoracic Society (BTS) and Global Initiative for Asthma (GINA) recommend continuing pregnant women on the same asthma therapy used prior to the pregnancy, if their asthma is well controlled.
11.5 Clinical Presentation
Cough.
Shortness of breath.
Tightness in the chest.
Noisy, sometimes shallow, breathing.
Nocturnal awakenings.
Recurrent episodes of symptom complex.
Exacerbations possibly provoked by nonspecific stimuli.
Personal or family history of other atopic disease (like hay fever, eczema).
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