Arterial Oxygen Desaturation Rate Following Obstructive Apnea in Parturients

Suh, In Ok; Choi, Kyu Taek; Cheun, Jae Kyu

Abstract

Preoxygenation is a standard anesthetic technique for preventing a significant hypoxemia during the induction of anesthesia. Complete denitrogenation is especially important in clinical situations of difficult intubation or in patients with decreased functional residual capacity, and in situations where oxygen saturation is critical. Oxygen consumption in pregnancy is markedly increased at term as compaired to the nonpregnant stage. It is important to evaluate how long parturient women can withstand apneic hypoxemia during induction of general anesthesia. This study was carried out to measure the duration of time required to decrease the SaO2 to 90% After written informed consent was obtained from six healthy parturients who were to under go elective Cesarean section and six healthy non-pregnant women who were to have total abdominal hysterectomies. All subjects had a tight fitting anesthesia mask applied and breathed 100% oxygen, and a single isolated apnea was carried out. Arterial oxygen saturation and gas tensions were measured at a time SaO2 decreased to 90%, also blood gas data of 4 minutes after apnea in the non-pregnant women were obtained. From these, arterial oxyhemoglobin content was calculated, and mean desaturation rate from denitrogenation to the time SaO2 decreased to 90% was calculated. The mean time to obtain 90% saturation was 7.5+/-0.9 minutes in the nonpregnant women and 3.6+/-0.8 minutes in the parturient group. The mean slope of desaturation was steeper in the paturient(-3.336) than the nonpregnant (-1.52). The PaO2 inereased over 400mmHg in both the groups after denitrogenatio. After 4 minutes of apnea, the mean PaO2 decreased to 200mmHg in the non-pregnant women. The rate of rise of alveolar PCO2 during apnea were alower in the non-pregnant women(2.8+/-1.2mmHg/minute) than in the parturient women(6.8+/-1.8mmHg/minute). This study demonstrates that the rate of oxygen desaturation is faster in the parturients than the nonpregnant women. It is suggested that those results came out because of pregnancy-in-duced increase of oxygen consumption rate and decrease in FRC. The results of this study show the induction for term parturients should be speeded up with caution after full oxygenation in comparison with non-pregnant patients.