Effect of dexmedetomidine on half maximal effective concentration of epidural analgesia by ropivacaine for labor

  Objective  To observe effect of dexmedetomidine on half maximal effective concentration(EC₅₀) of epidural analgesia by ropivacaine for labor.

  Methods  A total of 90 full-term pregnant women with labor analgesia were selected as study objects, and were randomly divided into control group (ropivacaine group) and combined group (dexmedetomidine combined with ropivacaine group), with 45 cases in each group. Epidural pulse analgesia pumps were connected with catheters through epidural puncture (L_2~3). In the control group, the fluid in epidural pulse analgesia pump was formulated as a mixture of ropivacaine hydrochloride and normal saline for 150 mL, while the fluid of epidural pulse analgesia pump in the combined group was formulated as a mixture of ropivacaine hydrochloride, dexmedetomidine for 75 μg and normal saline for 150 mL in total. Blood pressure, heart rate, blood oxygen saturation (SpO₂), Visual Analogue Scale (VAS) scores and body temperature of pregnant women of two groups before administration in epidural space for the first time (T₀) and 15 min after drug injection (T₁), 30 min (T₂), 1 h (T₃), 2 h (T₄), 4 h (T₅) and delivery of the placenta (T₆) were compared. Cold sensation of block plane after first administration of epidural space, drug response time, cervix opening time, the second labor time, use of oxytocin, and adverse events were compared.

  Results  The EC₅₀ of labor analgesia by ropivacaine in the control group was 0.078%(95%CI, 0.074% to 0.082%), and was 0.062% in the combined group(95%CI, 0.057% to 0.068%). The level of epidural cold sensory block was from T₈ to T₉ in both groups. The onset time of the combined group was significantly shorter than that in the control group (P < 0.05). The VAS scores from time points of T₁ to T₆ in both groups were significantly lower than that at T₀ (P < 0.05). There were no differences in VAS scores at different time points between the two groups (P>0.05). At time points from T₃ to T₅, body temperature and hear rate in the combined group were significantly lower than those of control group (P < 0.05). The incidence of shivering in the control group was significantly higher than that in the combined group (P < 0.05).

  Conclusion  Dexmedetomidine can significantly reduce EC₅₀ of epidural analgesia by ropivacaine for labor, and correspondingly reduce the incidence of shivering and intrapartum fever in pregnant women.