Abstract ID: A39
Abstract Title: Prospective Randomized Double-Blind Comparison of Bupivacaine 0.125% versus Ropivacaine 0.2% for Continuous Femoral Analgesia
Poster Type: Either
ABSTRACT BODY
Introduction
Ropivacaine is a commonly used local anesthetic for postoperative continuous femoral nerve block (CFNB) due to a presumed better sensory/motor blocking profile compared to bupivacaine. Previous studies have shown less motor block with a faster recovery with ropivacaine. Yet, these studies did not compare equipotent concentrations of ropivacaine and bupivacaine, and failed to use a rigorous quantitative evaluation of motor block. The objective of this study is to quantitatively evaluate the degree of quadriceps motor weakness and sensory analgesia by comparing “equipotent doses” of ropivacaine 0.2% to bupivacaine 0.125% for CFNB.
Methods
12 volunteers were recruited after local IRB approval and written informed consent. Each subject received CFNBs via bilateral femoral perineural catheters.
Femoral nerves were localized with a PNS(0.1ms, 2Hz) and a stimulating catheter. Final catheter position was accepted only when quadriceps contraction was elicited at ≤0.5mA. Each subject then received an infusion of ropivacaine 0.2% in one catheter and bupivacaine 0.125% in the contralateral catheter. The subjects and investigators were blinded to the infusions. Each infusion ran at 5ml/hr for 6 hours after a 10ml loading dose.
Evaluation of the femoral nerve functions was assessed by force dynamometry of quadriceps strength and tolerance to transcutaneous electrical stimulation (TES) over the lower anterior thigh. Testing was done every 30 minutes until 12 hours after the infusions were stopped.
To detect a 25% (std dev 20%) difference in motor block between the two local anesthetics, a minimum of 10 CFNB per group were needed for α=0.05 and β=0.2. Peak analgesia to TES and peak motor block with regression were analyzed using unpaired T-tests and repeated measures analysis of variance.
Results
10 CFNB were successful in each group. There was no difference in peak quadriceps motor block (100%) or peak tolerance to TES (57±9mA vs. 56±9mA, P=0.8) between ropivacaine 0.2% and bupivacaine 0.125% (Figure 1).
After stopping the infusion, ropivacaine had a shorter and more predictable return to ≥90% of baseline quadriceps strength (P≤0.0001). 12 hours post infusion, the ropivacaine group had regained 94±14% versus only 55±46% in the bupivacaine group, P=0.02.
Conclusions
This study shows no significant difference in either peak motor block or peak sensory analgesia between continuous femoral perineural infusions of bupivacaine 0.125% vs. ropivacaine 0.2%. Ropivacaine did have a shorter and more predictable return to baseline motor function after stopping the infusion.
Femoral nerve catheter infusions are intended to provide postoperative analgesia without inhibiting the patient’s ability to perform physical therapy. These results indicate little advantage in using ropivacaine over bupivacaine for CFNB. Presently, the higher cost of ropivacaine may make its use less desirable in clinical practice.
References
1. Anesth Analg 2002; 95:204-208
2. Anesth Analg 2001; 92:218-223
3. Anesth Analg 2003; 96:253-259
Figure 1. Hourly comparison of quadriceps motor block during local anesthetic infusion (hours B-I5) and regression (hours I5-P12). I = infusion and P = post infusion.
ATTACHED FILES
A39_Figure 1.TIF
Reg Anesth Pain Med 2004; 29(2):A39