Effects of a low concentration of ropivacaine on maternal labor force during labor analgesia

Objective To investigate the effects of a low concentration of ropivacaine on the contraction of the uterine and abdominal muscles during labor analgesia. Methods One hundred and fifty primiparous women who expected to have a natural birth were selected. Then, 100 primiparous women were divided into two groups according to the random number table method: a 0.062 5% ropivacaine group (group ropivacaine, n=50) and a 0.062 5% levobupivacaine group (group levobupivacaine, n=50). Meanwhile, 50 primiparous women who did not take analgesic measures during vaginal delivery were set as a control group. Their age, body mass index(BMI), gestational age, cesarean section rate, forceps delivery rate, the duration of the first and second stages of labor, the rate of oxytocin use, and blood loss 2 h after delivery were recorded. The maternal pain was evaluated on the basis of Visual Analogue Scale (VAS) scores at the beginning of labor analgesia (T1), 15 min after labor analgesia (T2), 30 min after labor analgesia (T3) and 45 min after labor analgesia (T4). Then, the parameters of electromyography (EMG) burst wave energy were recorded, including the number and duration of burst waves, root mean square (RMS), and power and peak frequency, so as to comprehensively evaluate the contraction of the uterine and abdominal muscles. Results There was no significant difference in age, BMI, gestational age, cesarean section rate, forceps delivery rate, and blood loss 2 h after delivery among the three groups (P>0.05). Compared with groups control and ropivacaine, group levobupivacaine presented significantly extended duration of the first and second stages of labor, and marked increases in the rate of oxytocin use (P<0.05). Compared with group control, groups ropivacaine and levobupivacaine showed obviously decreased maternal VAS scores at T2, T3, and T4 (P<0.05). In the first stage of labor, compared with group control, the RMS of uterine muscle EMG in groups ropivacaine and levobupivacaine significantly reduced (P<0.05), compared with groups control and ropivacaine, the maternal power of group levobupivacaine significantly reduced (P<0.05). In the second stage of labor, compared with groups control and ropivacaine, group levobupivacaine presented significantly extended duration of EMG burst wave in the uterine muscle (P<0.05), compared with group control, groups ropivacaine and levobupivacaine showed significantly reduced RMS (P<0.05). Conclusions The use of 0.062 5% ropivacaine for epidural analgesia can achieve good effects, without significant impacts on maternal labor force, and does not prolong labor stage. Key words: Ropivacaine; Levobupivacaine; Labor analgesia; Electromyography; Labor stage