| Background: Labor pain relief remained the main concern of obstetricians and parturients through centuries. A number of techniques have evolved to maintain the level of analgesia throughout labour. Epidural analgesia, commonly recognized as the most effective way of providing pain relief in labour, was introduced into common clinical practice in the 1980s. To infuse Sufentanil or Fentanil into epidural catheter could diminish the amount of local anaesthetics and additives reduce the dense motor block in the lower extremities, which made parturients walk during the first stage of labor process. Ambulatory labor analgesia has attained wide spread popularity in obstetric anesthesia worldwide in that its onset of analgesia is rapid and reliable, and maternal satisfaction is high. However, the impact of ambulatory labor analgesia on duration of labor, bleeding amount during labor, application of ocytocic and incidence of caesarean section remains disputable. Moreover, although it is widely thought that ambulatory labor analgesia has no negative effects on fetus heart rate, Apgar points and newborn asphyxia, more sensitive index are expected to evaluate the use of this new technique. Fetal pulse oximetry emerged 15 years ago as a promising new technology intended to improve assessment of fetal condition during labor. A large amount of physiologic data and one large randomized clinical trial have brought this technology into clinical practice.Objectives: To undertake clinical controlled trials of ambulatory labor analgesia and to analyze its effect on labor, fetal pulse oximetry was used to monitor the fetaloxygen saturation during labor process continuously and pH value of umbilical blood after labor. Furthermore, the relationship between the changes of fetal oxygen saturation during labor process and the pH value of umbilical blood was explored and observed in order to provide evidence for clinical diagnosis of fetal and newborn asphyxia, and for expanding application of this technique.Methods: 76 parturients with uncomplicated term pregnancies were randomized, among which 20 patients who asked for pain relief were allocated to ambulated position group with combined spinal-epidural labor analgesia technique, when the other 56 were taken as trial control. All parturients enrolled in ambulatory labor analgesia received Sufentanil 4 microg in epidural catheter after which was passed through a 17-gauge Tuohy needle and left in the lumbar epidural space (insertion level L3-4 or L2-3) at cervical dilatation >/= 3 cm. Then 0.1% ropivacaine 100 mL + Sufentanil 0.25 microg was provided with intermittent administrations with doses 5ml/h. Fetal oxygen saturation was monitored continuously during uterine contraction intermittence, while Fetal oxygen saturation values were recorded every 5 minutes and mean Fetal oxygen saturation values was calculated. Umbilical blood was analyzed within 30 minutes after fetal delivery and pH, BE value were recorded.Results: 1. Baseline analysis of both groups: There was no significant difference between the ambulatory labor analgesia group and the control in labor duration and newborn weight, except that the mean age of parturients in control group was younger than that of the trial group. 2. Comparing of the trial factors: There was no statistical difference between the trial group and the control in the mean and lowest values of Fetal oxygen saturation during the first and second labor stage, and the same statistical results was also observed in the pH value and BE value of newborn umbilical blood between both groups. However, although no significant correlation was found between BE value and pH value or the lowest fetal oxygen saturation value, the umbilical pH value did correlate with the lowest fetal oxygen saturation value positively. 3.effects of labor analgesia: The application of ocytocic and the incidence of caesarean section in the trial group were not differed from the control. The latency in the first labor stage of ambulatory analgesia group was a little longer than that ofthe control group, whereas the same significance was not shown in the active stage and the second labor stage. The bleeding amount at 2h and 24h after delivery was not different between the ambulatory analgesia group and the control. 4. Relative studies on fetal oxygen saturation: the mean Fetal oxygen saturation value in the second labor stage was lower than that in the first labor stage, but no significant correlation was demonstrated between the labor process and the lowest Fetal oxygen saturation value. 5. Asphyxia analysis: one mild asphyxia case was found in the trial group while there were two in the control group, one of which the caesarean section was adopted. As to this case, the amniotic fluid was clear and the prognosis of this newborn baby was not bad. 6. Reason analysis of caesarean section: the reason of the two cases in the trial group undergone was because of the existing of the dystocia indices. Among the 6 cases who also received caesarean section, 4 was due to the appearing of dystocia, while the other two was found amniotic fluid contaminated with fetus stool and fetus tachycardia during the first latency stage. Therefore, umbilical blood analysis and fetal oxygen saturation monitoring was not administered on them.Conclusion: Ambulatory labor analgesia did not influence the fetal oxygen saturation of the total labor duration significantly. Meanwhile, it did not affect the labor development, bleeding amount after delivery, pregnancy outcome and fetus outcome as well. Thus, it might be an ideal labor analgesia method for labor with expanding application future. Moreover, our exploration on the changes of fetal oxygen saturation during labor process and its correlation with pH value of umbilical blood confirmed the declining model of fetal oxygen saturation during labor process, and the line correlation between Fetal oxygen saturation and pH value of umbilical blood after delivery. With high sensitivity and specificity, to monitor labor process with fetal oxygen saturation is a necessary index.
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