Determination of the Minimum Local Analgesic Concentration of Ropivacaine Combined with Different dose Sufentanil for Labor Analgesia

Objective: To determine the effective concentration of epidural sufentanil combined with ropivacaine for analgesiai in the first stage of labor.Methods:Ninety-three ASA Ⅰ～Ⅱ nulliparous women over 38～42 week gestation,with 3～4 cm cervical dilatation were randomly assigned to three groups.Group C serves as control group using plain ropivacaine.The patients in group A and B were given sufentanil 0.4 mg/L and 0.6 mg/L respectively.Fifteen milliliter of different concentration of sufentanil combined with ropivacaine was given epidurally.The concentration of ropivacaine was determined by the response of the previous parturient to a higher or lower concentration using double-blind,up-and-down sequential allocation.The initial concentration of epidural ropivacaine in each group was 0.12%.If VAS score was less than 3 within 30 min,analgesia was defined as effective.Results:Among the 93 parturients recruited,three were excluded from the study because of prolapse of cord.The results showed that EC50 of epidural ropivacaine for labor analgesia was 0.056%(95%CI0.048%～0.066%)in group A(n=29),and 0.042%(95%CI0.034%～0.052%)in group B(n=30),0.115%(95%CI0.112%～0.128%)in group C(n=31).Conclusion:The addition of sufentanil resulted in dose-dependent reduction in EC50 of ropivacaine during epidural labor analgesia.The minimum effective concentration of ropivacaine for epidural labor analgesia combined with 0.4 mg/L and 0.6 mg/L sufentanil are 0.056%and 0.042% respectively.