Abstract
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 [11. Baraka AS, Taha SK, Aouad MT, El-Khatib MF, Kawkabani NI (1999) Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques. Anesthesiology 91: 612-616.]. Another method can be applied quickly with 4-8 deep breaths of 100% oxygen [22. Benumof JL (1999) Preoxygenation: best method for both efficacy and efficiency. Anesthesiology 91: 603-605.]. 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 [33. Khaw KS, Ngan Kee WD, Chu CY, Ng FF, Tam WH, et al. (2010) Effects of different inspired oxygen fractions on lipid peroxidation during general anaesthesia for elective Caesarean section. Br J Anaesth 105: 355-360. ]. As this may lead to free oxygen radicals and apsorbtion atalectesia, 80 % oxygen is recommended.
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