Respiratory System Changes During Pregnancy

Respiratory Tract . Hormonal changes to the mucosal vasculature of the respiratory tract lead to capillary engorgement and swelling of the lining in the nose, oropharynx, larynx, and trachea. Symptoms of nasal congestion, voice change and upper respiratory tract infection may prevail throughout gestation. These symptoms can be exacerbated by fluid overload or oedema associated with pregnancy-induced hypertension (PIH) or pre-eclampsia . In such cases, manipulation of the airway can result in profuse bleeding from the nose or oropharynx; endotracheal intubation can be difficult; and only a smaller than usual endotracheal tube may fit through the larynx. Airway resistance is reduced, probably due to the progesterone-mediated relaxation of the bronchial musculature.

Lung Volumes . Upward displacement by the uterus causes a 4 cm elevation of the diaphragm, but total lung capacity decreases only slightly because of compensatory increases in the diameters of the chest, as well as flaring of the ribs. These changes are brought about by hormonal effects that loosen ligaments.
From the middle of the second trimester, expiratory reserve volume, residual volume and functional residual volume are progressively decreased, by approximately 20% at term.

Oxygen consumption increases gradually in response to the needs of the growing foetus, culminating in a rise of at least 20% at term. During labour, oxygen consumption is further increased (up to and over 60%) as a result of the exaggerated cardiac and respiratory work load.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. World Anaesthesia & the World Federation of Societies of Anaesthesiologists : http://www.nda.ox.ac.uk/wfsa/index.htm