The Study of the Effect of Maternal FiO2 on the Umbilical Blood Gas Analysis and Maternal Awareness in Cesarean Section under General Anesthesia

Kim, Yu Hee; Kim, Jong Hak; Im, Keum Ah; Lee, Choon Hi

Abstract

General anesthesia for cesarean section usually includes 50% oxygen and nitrous oxide, supplemented by a low concentration of a volatile agent. This is based upon data demonstrating that an increase in maternal FiO2(inspired oxygen concentration) to more than 0.6 did not improve fetal oxygenation, But the use of 100% oxygen supplemented only by volatile anesthetics probably is safe in the case of emergency operation or fetal distress and advantageous in prevention of maternal awareness during cesarean section. The present study was designed to compare the effect of increasing FiO2 upon fetal oxygenation. It was also proposed to determine awareness, by questioning patients as well about dreams or other manifestations of inadequate depth of anesthesia. 30 patients undergoing cesarean section under general anesthesia were selected and they were allocated randomly into three groups according to FiO2 as follows; Group 1(n=10): FiO2 0.33 with 0.75 vo1% isoflurane, Group 2(n=10): FiO2 0.66 with 0.75vo1% isoflurane, Group 3(n= 10): FiO2 1.0 with 0.75 vo1% isoflurane. For the induction of anesthesia, thiopental 4 mg/kg was administered, followed by succinylcholine 1.5 mg/kg. After intubation, the lung was ventilated with different FiO2 and maternal arterial blood was sampled just before delivery and umbilical arterial and venous blood were sampled immediately after delivery. Induction to delivery time(IDT), uterine incision to delivery time(IDT), neonatal birth weight and Apgar score were measured. The patient was interviewed to evaluate the incidence of awareness three days after operation. Our results were as follows; There were statistically significant differences between three groups in maternal PaO2, but there were no statistically significant differences between three groups in umbilical arterial and venous oxygenation. Induction to delivery time(IDT) in group 1 was significantly short, compared to group 2 and 3, but uterine incision to delivery time(UDT) was not statistically difference between three groups. The condition of the neonates at birth was generally good except one in group 2. But, this neonate recovered as 5-min Apgar score of 9 after aspiration of amnionic fluid and oxygen administration. Two patients reported dreaming, pain recall or fact recall and one of them refused to be administrated the same anesthesia once again, respectively in three groups. In conclusion, the use of FiO2 0.33 is probably safe in no fetal distress while the use of FiO2 1.0 results in no increase of oxygen partial pressure of umbilical artery and vein, but it guarantees the safe method in the case of suspecting fetal depression. Our anesthetic method was not enough to prevent the awareness. So, further study about not only deep, but also safe anesthetic method is justified.