The author was afraid of fetal damage, looking at fetal bradycardia in manually controlled oxytocin infusion in 1960s-1970s, and invented automatic and safe induction with oxytocin infusion.
As the sensitivity of pregnant uterus to oxytocin was broad, someone was very sensitive, while insensitive in the other case, it is unable to predict the sensitivity to oxytocin in the non-selected pregnant woman, who received labor induction with oxytocin infusion. The past experience of oxytocin induction developed excessive uterine contraction and fetal heart rate (FHR) bradycardia under 100 bpm in oxytocin sensitive case, where fetal damage or demise was concerned (Figure 1). Thus, it was necessary to start from very low dose oxytocin testing the sensitivity level looking for suitable oxytocin dose to develop normal contraction, thus, oxytocin was gradually increased studying the reaction of myometrium with uterine contraction curve in this study. Oxytocin increasing stopped when normal contraction curve appeared, then the contraction is induced by appropriate dose oxytocin until delivery, while whole oxytocin infusion stopped automatically, if the contraction is too strong, or fetal monitor detects abnormal FHR.
Five U oxytocin was mixed to 500 ml 5% glucose solution preparing the induction material. The liquid volume was determined by a checker set at the fluid bottle. The infusion tube was passed through the injection pump. and air bubble was detected by bubble checker set at the injection tube. Fluid infusion was stopped when the low volume of injection fluid or by the presence of air buble in the tube. An external FHR monitor probe and tocodynamometer probes were set at maternal abdomen and connected the fetal monitor (Figure 2).
The infusion started from 0.2 ml/min (2 ｍU oxytocin) and increased to twice level every 10 min automatically, checking the contraction curve automatically at the fetal monitor, Injection volume increased until the contraction duration was 1 min and its interval was 2.5 min, then kept the same infusion until fetal delivery (Figure 3).
The infusion fully stopped automatically, when
1) Contraction duration was more than 2 min.
2) Peak to peak contraction interval was less than 1 min. 1 and 2 were the sign of hyper contraction of uterus.
3) FHR monitor sound alarms abnormal FHR (bradycardia etc.), which was
Figure 1. Fetal bradycardia below 100 bpm (lower line) in uterine hyper-contraction (upper lne) due to 40mU/ml manually controlled oxytocin infusion in 1966.
Figure 2. Automatic oxytocin infusion labor induction system programmed by Maeda and provided by T0ITU (Tokyo).
Figure 3. A case of automatic oxytocin labor induction. Fetal heart rate (upper line) and external uterine contraction (lower line). Left, middle and right parts are the progress of labor induction  .
the sign of fetal asphyxia.
4) No contraction was detected by the infusion until the lowest level of injection fluid that was the sign of no sensitivity of the pregnant uterus, where the induction was stopped, and it is tried again another day.
Thirty three non-selected pregnant women received the automatic labor induction, then 28 cases (85%) achieved normal vaginal delivery, that was favorable result because 65% of manually controlled oxytocin labor induction achieved normal vaginal delivery. There was significant difference (p = 0.048) between automatic and manual control inductions  .
Unselected pregnant women received favorable oxytocin induction without hyper-uterine contraction nor fetal hypoxia. Significant difference was found in the comparison to manually controlled oxytocin labor induction, which can be risky due to hyper-contraction and fetal hypoxia, namely, some cases of manually controlled oxytocin induction was sued by the ominous outcomes after termination of the present study. Thus, the abnormalities would be avoided by the automatically controlled oxytocin induction, because the induction stopped by the hyper-uterine contraction and abnormal FHR in our study.
Automatically controlled oxytocin induction, which induced normal uterine contraction, avoiding hyper-uterine contraction followed by fetal hypoxia, which was safe to the fetus under oxytocin infusion labor induction.
Grant of Japanese Ministry.
The author expresses sincere gratitude for the Grant of Japanese Ministry of Health & Welfare, and TOITU (Tokyo) for their production of the automatic system.