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.