Lungs in Pregnancy

Lungs in Pregnancy


Pregnancy induces a number of alterations in anatomy and Physiology which have got important pulmonary and cardiovascular consequences. Some of the changes that occur during pregnancy are briefly described below. Airways: There occurs hyperemia, edema and hypersecretion in the upper airways during pregnancy. These changes can induce or aggravate nasal obstruction and obstructive sleep apnea syndrome. Respiratory Muscles & Rib Cage: Diaphragm is displaced upward but the excursion remains the same. The tone of the abdominal muscle decreases. Physiological Changes: The expiratory reserve volume decreases by 8-40% and residual volume reducers by 7-22%. The functional residual capacity therefore decreases by 10-25%. There is no change in vital capacity, total lung capacity and lung compliance. The total pulmonary resistance falls by 50% during pregnancy. There is rise in tidal volume by about 20% which causes an increase in minute ventilation.

Cardiovascular Changes:

There is an increase in the heart rate and stroke volume, as a result the cardiac output increases. There is fall in the systemic and pulmonary vascular resistances during second trimester of pregnancy. Due to this fall in systemic vascular resistance, there is an increase in the level of aldosterone which induces an increase in plasma volume compared to red cell mass (This is responsible for physiological anaemia of pregnancy).

Dyspnoea during Pregnancy:

About 40-60% of pregnant females complain of dyspnoea during pregnancy. Physiological hyperventilation of pregnancy is caused by altered chest wall muscle proprioception due to an increase in respiratory stimulation, physiological dyspnoea occurs early in the pregnancy and improves during labour and does not occur at rest. The important common pulmonary causes of dyspnoea during pregnancy are asthma, aspiration, pulmonary thromboembolism, pneumonia, amniotic fluid embolism and air embolism etc.

  1. Asthma in pregnancy: If asthma is not controlled during pregnancy, it can increase the incidence of preterm labour and growth retardation. In various studies, it was shown that about 35% of cases of asthma will worsen, 30% will improve and rest will remain unaltered during pregnancy. Therapy of asthma during pregnancy does not differ from that in a non pregnant patient. If the patient is on oral or inhaled steroids, she should be started on parental hydrocortisone before labour.
  2. Restructive lung disease during pregnancy: Most of the restrictive lung diseases constitute relative contraindications to pregnancy. However, if FVC is less than 1L, pregnancy should be avoided. The clinical course of sarcoidosis is not altered by pregnancy. However, pregnant patient of sarcoidosis who have stage IV disease, or have advanced age will have poor prognosis. In progressive systemic sclerosis with renal failure, the pregnancy should be avoided. Worsening of systemic lupus erythematosus is uncommon during pregnancy.
  3. Deep venous and pulmonary thromboembolism: Pregnancy is a hypercoagulable state (venous stasis, increased clotting factors and decreased fibrinolytic activity. Heparin is the drug of choice for anticoagulation. Warfarin is given between 6-12 week’s can produce embryopathy (stippled epiphyses, nasal hypoplasia).
  4. Amniotic Fluid Embolism: It presents as a sudden, unexpected shock during or after labour followed by respiratory distress. About 10-15% patients develop seizures and disseminated intravascular coagulation. The diagnosis is made on clinical grounds and confirmed by taking a sample from pulmonary artery and showing fat globules. Pathophysiologically, there is mechanical obstruction of pulmonary vasculature, increased alveolar capillary leakage and anaphylaxis due to foetal antigens. Management is largely supportive. Mechanical ventilation and diuresis may be required.
  5. Pleural Diseases: During pregnancy due to increased blood volume, there is increased incidence of benign pleural effusion. Choriocarcinoma may metastasize to the lung or pleura producing haemorrhagic pleural effusion.
  6. Pneumonia complicating pregnancy: The incidence of pneumonia is not increased during pregnancy. However, if pneumonia occurs, it can have progressive course. Mortality is increased due to : reduced lymphocyte proliferation, reduced cell mediated cytotoxicity and reduced lymphokine response.

Tuberculosis and Pregnancy:

Some studies have shown an increased incidence of relapse of tuberculosis during post partum period. In preantibiotic era, there was increased maternal mortality from untreated tuberculosis. Treatment of tuberculosis is similar to that of non pregnant patient. Streptomycin is contraindicated for fear of ototoxicity. Some studies have shown that use of Rifampicin during pregnancy can produce limb reduction, central nervous system abnormality and decreased prothrombin levels. But Rifampicin continues to be given during pregnancy.

Prof. S.K.Jindal
Dept. of Pulmonary Medicine, PGI Chandigarh

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