The postoperative analgesic efficacy of wound instillation with ropivacaine 0.1% versus ropivacaine 0.2%

STUDY OBJECTIVES: To assess the influence of ropivacaine concentration on wound instillation-induced postoperative analgesia following total abdominal hysterectomy with bilateral salpingo-oophorectomy. DESIGN: Prospective, randomized, double-blind study. SETTING: Large referral hospital. PATIENTS: 40 ASA physical status I and II patients undergoing total abdominal hysterectomy with bilateral salpingo-oophorectomy. INTERVENTIONS: A standard general anesthetic was administered. In all cases surgery was performed via a Pfannenstiel incision. On completion of the surgery, a multi-orifice, 20-gauge epidural catheter was placed above the fascia such that the tip was sited at the point that demarcated 50% of the length of the surgical wound. Thereafter, the catheter was connected to an electronic patient-controlled analgesia (PCA) device programmed to deliver 9 mL of drug, with a lockout time of 60 minutes and no basal infusion. Patients were randomized to receive PCA with ropivacaine 0.1% (Group 0.1) or ropivacaine 0.2% (Group 0.2). During the first 6 postoperative hours, a co-investigator administered "rescue" morphine (2 mg IV). Thereafter, "rescue" meperidine 1 mg/kg was administered on patient request. MEASUREMENTS AND MAIN RESULTS: The number of attempts to activate the PCA device and actual PCA instillations during the 24 hour study period were similar between the groups. The number of 2 mg "rescue" morphine dosages administered was 4.3 +/- 1.7 versus 4.4 +/- 2.5 for the Group 0.1 and Group 0.2, respectively. For Group 0.1 and Group 0.2, the total dose of "rescue" morphine administered during the first 6 postoperative hours was 8.7 mg +/- 3.6 versus 9.1 mg +/- 5, respectively. "Rescue" meperidine administration during the subsequent 18 hours was similar between the groups. Throughout the study period, pain scores were similar between the groups. CONCLUSION: With a pre-set volume, varying the concentration of ropivacaine (0.1% versus 0.2%) does not affect the analgesic efficacy of wound instillation following total abdominal hysterectomy with bilateral salpingo-oophorectomy.