A double-blind comparison of the abdominal wall relaxation produced by epidural 0.75% ropivacaine and 0.75% bupivacaine in gynecologic surgery.

BACKGROUND AND OBJECTIVES: Ropivacaine is a long-acting local anesthetic agent with similar potency to that of bupivacaine when administered for epidural anesthesia. Ropivacaine, however, may be less cardiotoxic than bupivacaine. Epidural bupivacaine and ropivacaine have been shown to be equally effective in providing sensory block for lower extremity surgery, but they have not been compared for their ability to produce abdominal wall relaxation.

METHODS: Sixty-six American Society of Anesthesiologists I-III women, 18-70 years old undergoing elective gynecologic surgery were studied in a randomized, double-blind manner after giving informed consent in an institutionally approved protocol. Thirty-four patients received a single epidural injection of 20 ml 0.75% bupivacaine at the L2-L3-L4 interspace and 32 patients received 20 ml 0.75% ropivacaine in a similar manner. Sensory block was tested with pinprick; motor block with a modified Bromage scale, rectus abdominis muscle (RAM) test and surgeon satisfaction. Statistical analysis was performed using the SigmaStat for Windows computer software. Parametric data were analyzed with Student's t-test, while nonparametric data was analyzed using the Mann-Whitney rank sum test.

RESULTS: Results are expressed as mean +/- SD. Times to maximal sensory block and peak sensory level achieved were similar in both groups. However, time to complete sensory regression was significantly longer with bupivacaine than ropivacaine (458 +/- 77 vs. 404 +/- 62 minutes, P < .03). Bupivacaine lower extremity motor block onset was significantly faster than ropivacaine (9 +/- 3 vs. 12 +/- 3 minutes, P < .0013). Time to maximum lower extremity motor block was significantly shorter with bupivacaine than ropivacaine (28 +/- 12 vs. 40 +/- 15 minutes, P < .0234). Duration of lower extremity motor block was significantly longer with bupivacaine than ropivacaine (371 +/- 97 vs. 310 +/- 65 minutes P < .069). There was no significant difference between the two groups for changes in RAM scores or the time to achieve those changes. Maximum motor block scores using the modified Bromage score and surgeon satisfaction with operating conditions also did not demonstrate a significant difference between the two groups. In one instance (with ropivacaine), anesthesia was judged clinically inadequate despite evidence of bilateral epidural anesthesia.

CONCLUSIONS: Both 0.75% ropivacaine and 0.75% bupivacaine provide adequate surgical anesthesia for lower abdominal surgery when administered epidurally. However, lower extremity motor block with ropivacaine is significantly shorter and of slower onset and sensory block shorter at these concentrations.