UMEM Educational Pearls

Category: Critical Care

Title: Changes in pulmonary physiology during pregnancy

Keywords: pulmonary physiology, critical care, respiratory alkalosis (PubMed Search)

Posted: 3/15/2011 by Haney Mallemat, MD
Click here to contact Haney Mallemat, MD

Many changes in pulmonary physiology occur during pregnancy. These changes are generally well tolerated but can become problematic when pathologic states arise.

Here are a few examples of the normal changes and potential consequences:

Progesterone increases tidal volume and respiratory rate.

  • “Normally" a mild respiratory alkalosis pH 7.4-7.47, PaCO2 28-32, and bicarbonate 17-22 (renal compensation).

  • Low metabolic reserve with systemic illness.

Weight gain, anasarca, and breast size reduces chest wall elasticity.

  • Potential for restrictive physiology and reduced lung volumes.

  • Can be challenging to to mechanically ventilate due to decreased compliance and intra-thoracic pressure 

Mechanical displacement of abdominal and thoracic contents by growing uterus.

  • Reduced lung volumes leading to reduced oxygen reserve and decreased apnea time.

  • Aim higher if placing chest tube (avoid abdominal contents)

  • Uterine pressure on stomach can increase aspiration risk and pulmonary injury. 


Chestnutt, A. Physiology of Normal Pregnancy. Crit Care Clinic 20 (2004) 609-615