DETERMINATION OF DOSE RESPONSE FOR INTRATHECAL ROPIVACINE IN LABORING PARTURIENTS

Abstract

S268 INTRODUCTION: Using the combined spinal epidural (CSE) technique, intrathecal injections of low doses of local anesthetics and/or opioids are being increasingly used for labor analgesia. Ropivacaine, a newly introduced amide local anesthetic, has been shown to be minimally cardiotoxic and results in less motor block than the traditional bupivacaine, [1,2] when used epidurally. Intrathecal ropivacaine has been recently used for general surgery [3] and labor analgesia. [4] The purpose of this study was to determine the ideal intrathecal dose of ropivacaine which would provide adequate labor analgesia with minimal or no motor blockade, and without adversely affecting the mother, fetus, or progress of labor. METHODS: Following institutional approval and written informed consent, twenty healthy, term parturients aged 15-35 years who requested analgesia for labor, participated in the study. All parturients received pulmonary aspiration prophylaxis and 200 cc bolus of lactated Ringer's solution intravenously. The parturients were randomized into five groups in a double blinded manner: Group A - fentanyl 15 mcg (n = 4), Group B - ropivacaine (ropi) 0.5 mg + fentanyl 15 mcg (n = 3), Group C - ropi 1.0 mg + fentanyl 15mcg (n = 6), Group D - ropi 1.5 mg + fentanyl 15mcg (n = 4), Group E - ropi 2.0 mg + fentanyl 15mcg (n = 3). Using the needle through needle technique {Tuohy 17 gauge and Whitacre 27 gauge (11.9cm)}, all parturients received fentanyl 15 mcg intrathecally (with or without ropivacaine), followed by epidural catheter insertion. The epidural block was maintained with ropivacaine 0.1 % and fentanyl 2 mcg/ml infusion after patient's request for further analgesia. Visual analog pain scores (VAS) were assessed before and after the intrathecal dose, and epidural block. Sensory and motor blockade were assessed by pinprick and modified Bromage scale, respectively. Hemodynamic parameters, onset and duration of analgesia, duration of first and second stages of labor, and neonatal Apgar scores were recorded. Parturients were assessed twenty-four hours postpartum for satisfaction with analgesia, and for side effects. RESULTS: There were no demographic differences in the five study groups. All subjects had satisfactory analgesia at 5 minutes after the block. The mean duration of analgesia with intrathecal fentanyl was 80 +/- 10.8 minutes, while in combination with ropivacaine, it was 151.93 +/- 34.45 minutes (p = 0.001), which is statistically significant according to the independent sample T-test. One way ANOVA on the five treatment groups showed significant difference in duration of analgesia across groups (p = 0.001), while multiple comparison analysis determined a significant difference between groups A and C (p = 0.004). The mean duration of the first and second stages of labor were 458.10 +/- 169.77 minutes (p = 0.614) and 35.35 +/- 8.76 minutes (p = 0.328), respectively, with no significant difference across groups. Average time interval between intrathecal injection and delivery was 302.75 +/- 130.61 minutes. Neither the VAS pain scores at 1 and 5 min (p = 0.107, 0.835) nor the changes in VAS pain scores at 1 and 5 min (p = 0.349, 0.883) were significantly different across groups. Fisher's exact test showed no significant difference in motor blockade (detectable weakness of hip flexion) between fentanyl and fentanyl/ropivacaine groups (p = 0.587). Sensory blockade to pin prick was not discernible in 50% of subjects. No significant differences in hemodynamic parameters, umbilical cord gases, or neonatal Apgar scores were noted between the five groups. Two parturients {group C, n=1, group E, n=1} required cesarean section for failure at progression of labor. All patients were satisfied with labor analgesia. None of the parturients experienced postpartum headache, neurological problems, or urinary retention. CONCLUSION: In this ongoing study, our findings suggest that intrathecal ropivacaine (0.5 to 2.0 mg) with fentanyl 15 mcg provides instantaneous analgesia for laboring parturients, without compromising maternal or fetal safety. Our preliminary data, statistically and clinically, suggests that the combination of fentanyl and low dose ropivacaine prolongs the duration of labor analgesia. The addition of ropivacaine does not produce any motor block and may allow ambulation. We recommend the use of low dose ropivacaine and fentanyl 15 mcg intrathecally in the combined spinal epidural technique for labor analgesia.