Supplementary Oxygen for Caesarean Section.

摘要

Women undergoing Caesarean sections (CS) are commonly given supplementary oxygen even though the benefit of administering supplementary oxygen during CS is unclear if not, controversial. The rationale for providing supplementary oxygen to the mother is to increase oxygen delivery to the fetus and hence improve neonatal oxygenation and outcome. However, recent publications have shown that formation of oxygen free radicals are enhanced in the presence of hyperoxia, which may directly injure or aggravate ischaemia-reperfusion injury and adversely affect the fetus. There are also theoretical concerns that hyperoxia in the umbilical vein may lead to vasoconstriction in the uteroplacental unit or early closure of the ductus arteriosus.;Hypothesis 2: Breathing supplementary oxygen during elective Caesarean section under regional anaesthesia does not improve fetal oxygenation in the event of a prolonged uterine incision-to-delivery (U-D) interval. Conclusions 2: The results showed no differences in UV or UA blood gases, oxygen content or Apgar scores between cases with and without prolonged U-D interval.;Hypothesis 3: There are no effects on fetal oxygenation and lipid peroxidation in the mother and fetus from breathing supplementary oxygen during regional anaesthesia for emergency Caesarean section. Conclusion 3: The findings rejected hypothesis 3. Breathing 60% supplementary oxygen during emergency CS performed under regional anaesthesia significantly increased fetal oxygenation. Overall, UV oxygen partial pressure and content increased by 19% and 24% respectively. Sub-group analysis showed that the improvement in fetal oxygen content was greatest in the relatively hypoxic fetus where fetal compromise was considered to be present. In this subgroup, oxygen partial pressure and content increased by 17% and 32% respectively. The improvement in fetal oxygenation was not associated with an increase in lipid-peroxidation in the mother or fetus.;Hypothesis 4: There are no differences in fetal oxygenation from using an inspiratory oxygen percentage of 30%, 50% or 100% oxygen during general anaesthesia for elective Caesarean section. Conclusion 4: The findings rejected hypothesis 4. There was an increase in UV and UA oxygen content by 27% and 54% respectively, when patients were given 100% oxygen.;Many studies have explored the relationship between fetal oxygen indices and inspired maternal oxygen fraction during regional and general anaesthesia for CS. However, limitations in these studies have left a gap in the knowledge, and currently it remains unclear 'if', 'when' or 'how much' supplementary oxygen should be given to the mother during elective and emergency CS. The thesis was designed to address these issues by testing the following hypotheses: Hypothesis 1: There are no effects from breathing supplementary oxygen on the mother and fetus during spinal anaesthesia for elective Caesarean section. Conclusion 1: The findings rejected hypothesis 1. Maternal arterial and umbilical venous partial pressure of oxygen was increased by 100% and 20% respectively, when mothers breathed 60% oxygen compared with 21% oxygen. However, the improvement in maternal and fetal oxygenation was associated with an increase in lipid peroxidation in the mother and fetus by 58% and 93% respectively.;Hypothesis 5: There are no differences in lipid peroxidation in the mother and fetus from using an inspiratory oxygen percentage of 30%, 50% or 100% oxygen during general anaesthesia for elective Caesarean section. Conclusion 5: The findings accepted hypothesis 5 that there are no differences in lipid peroxidation from using an inspiratory oxygen percentage of 30%, 50% or 100% oxygen. Surprisingly, increased lipid peroxidation were observed in the maternal, UA and UV blood of all three groups, by 104%, 240% and 230% respectively, which probably resulted from the preoxygenation before induction of anaesthesia. No increase in lipid peroxidation in the fetus was measured even though there was a very significant increase in UV oxygen content by 40% from using an inspiratory oxygen percentage of 100% oxygen compared to 30% or 50% oxygen.;Summary This thesis has shown that breathing a very high fraction of inspired oxygen is required during elective CS under regional anaesthesia before a small increase in fetal oxygenation can be detected. This is because oxygenation of the fetus is already quite high when mothers breathe room air, and breathing supplementary oxygen could only marginally increase the partial pressure of oxygen to above the normal physiological level. However, this modest increase in fetal oxygenation was associated with an increase in lipid peroxidation in both the mother and fetus, raising the question on the necessity for supplementary oxygen. Despite the previous concerns of the adverse effects from a prolonged U-D interval, there was no deterioration in the UA and UV blood gases, oxygen content or Apgar scores, regardless of whether supplementary oxygen was used. Overall, it can be concluded that supplementary oxygen is not necessary for elective CS. (Abstract shortened by UMI.).