Structural Differences in Respiratory System and Airway of Parturients

Oxygen consumption increases with increased alveolar ventilation and respiratory alkalosis occurs. Thus, PaCO2 becomes 28-32 mmHg in pregnant women, and this amount is compensated with renal bicarbonate absorption. Preoxygenation can be made slower by inhalation of 100% oxygen for 2-5 minutes. Denitrogenation of the lungs occurs after three minutes [1]. Another method can be applied quickly with 4-8 deep breaths of 100% oxygen [2]. However, for pregnant women who will have a cesarean section under general anesthesia, an oxygen fraction of 1 has been shown to increase fetal oxygenation more compared with the 0.3 or 0.5 FiO2 [3]. As this may lead to free oxygen radicals and apsorbtion atalectesia, 80 % oxygen is recommended.