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A Randomized Comparison of Ropivacaine 0.1% and 0.2% for Continuous Interscalene Block After Shoulder Surgery

Yang, Chun Woo, MD*; Jung, Sung Mee, MD; Kang, Po Soon, MD, PhD; Kwon, Hee Uk, MD, PhD; Cho, Choon Kyu, MD; Lee, Younsuk, MD, PhD§; Kim, Chul Woung, MD, PhD; Kim, Su Young, PhD

doi: 10.1213/ANE.0b013e318280e109
Regional Anesthesia: Brief Report
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BACKGROUND: The optimal concentration of ropivacaine for continuous interscalene block after shoulder surgery is currently unknown.

METHODS: Fifty-six patients received a perineural infusion of either ropivacaine 0.1% or 0.2% for 48 hours after shoulder surgery. We assessed pain scores as primary end points and supplemental analgesia, ropivacaine consumption, motor block, side effects, and patient satisfaction as secondary end points.

RESULTS: Pain scores were not statistically different during the infusion periods; however, supplemental analgesia consumption was higher in the group receiving ropivacaine 0.1% during the first 24 hours (64% vs 28%, P = 0.022). Other secondary end points were statistically inconclusive.

CONCLUSIONS: These results suggest that ropivacaine 0.2% provides more effective analgesia than ropivacaine 0.1% during the first 24 hours for continuous interscalene block after shoulder surgery.

From the *Department of Anesthesiology and Pain Medicine, Cheju Halla General Hospital, Jeju-si, Jeju Special Self-Governing Province; Department of Anesthesiology and Pain Medicine, Yeungnam University School of Medicine, Daegu; Department of Anesthesiology and Pain Medicine, Konyang University Hospital, Daejeon; §Department of Anesthesiology and Pain Medicine, Dongguk University Ilsan Hospital, Goyang; Department of Preventive Medicine, School of Medicine, Chungnam National University, Daejeon; and Department of Preventive Medicine, Colledge of Medicine, Jeju National University, Jeju-si, Jeju Special Self-Governing Province, South Korea.

Accepted for publication November 27, 2012.

The authors declare no conflicts of interest.

Reprints will not be available from the authors.

Address correspondence to Chun Woo Yang, MD, Department of Anesthesiology and Pain Medicine, Cheju Halla General Hospital, Doreongno 65, Jeju-si, Jeju, South Korea. Address e-mail to everycw@daum.net.

Continuous interscalene block provides effective postoperative analgesia after shoulder surgery.1 Due to the superior or equivalent analgesia and greater patient satisfaction, compared with higher concentrations, ropivacaine 0.2% is commonly infused.2,3 However, few studies have evaluated lower ropivacaine concentrations. Although decreasing the concentration of ropivacaine from 0.2% to 0.1% for continuous interscalene block could theoretically result in a decrease of unwanted motor block and paresthesia, as well as the risk of local anesthetic toxicity, it might provide inferior analgesia.

Therefore, we compared the analgesic efficacy of ropivacaine 0.1% vs 0.2% for continuous interscalene block after shoulder surgery. The primary end point was pain score. Secondary end points included supplemental analgesia at 24 hours, ropivacaine consumption, motor block, side effects, and patient satisfaction.

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METHODS

With IRB approval and written informed consent, 56 ASA physical status I to III patients scheduled to undergo shoulder surgery under interscalene block performed by a single surgeon were enrolled in this prospective randomized study. Exclusion criteria included severe respiratory disease, preexisting neuropathy, coagulopathy, or allergy to study medications. Using sealed envelopes, patients were randomly assigned to receive either ropivacaine 0.1% or 0.2% for continuous interscalene block.

All patients received standard monitoring and sufentanil 0.1 µg/kg IV before the block. Using a nerve stimulator (Stimuplex HNS12, B. Braun, Melsungen, Germany) initially set at 1.0 mA, 0.1 milliseconds, and 1 Hz, an end-hole catheter (Contiplex A, B. Braun) was inserted with a technique similar to one previously described using a sustained contraction end point of the deltoid, pectoralis, biceps, or triceps muscles at 0.6 mA.4 Ropivacaine 0.5% 30 mL was injected through the catheter. The catheter was subcutaneously tunneled over 3 to 4 cm through an 18-gauge IV needle and was fixed to the skin with a suture.

Surgical anesthesia was defined as the loss of cold sensation in the C5-6 dermatomes and loss of shoulder abduction. Supplemental sedation with propofol infusion was administered intraoperatively, according to patient preference. If the patient complained of pain during surgery, rescue analgesia was provided with IV administration of sufentanil 5 to 10 µg. If this proved to be ineffective, general anesthesia was given.

On arrival at the postanesthesia care unit, a continuous infusion was started and continued for 48 hours (5 mL/h basal; 3 mL bolus; 20 minutes lockout). Rescue analgesia with 75 mg of IM diclofenac was available on demand.

Assessment of pain scores, ropivacaine consumption, and motor block was performed in the postanesthesia care unit, 6, 12, 18, 24, and 48 hours after surgery. Pain was assessed while at rest and during passive shoulder abduction using the visual analog scale (0–10). Motor block of the operated arm was assessed by a blinded observer who asked the patient to squeeze with both hands, and this was scored using a 3-point scale (0 = no, 1 = partial, 2 = complete). Supplemental analgesia and side effects (nausea, vomiting, dyspnea, and paresthesia in the fingers) for 24 and 48 hours were also recorded. At 48 hours, patient satisfaction was evaluated with a 2-point score (1 = satisfied, if necessary, I will repeat it; 2 = unsatisfied, I will never repeat it again). Data collection was performed by a research nurse who was blinded to the study drug concentration.

According to our null hypothesis, ropivacaine 0.2% is superior to ropivacaine 0.1% on either pain score or supplemental analgesia at 24 hours. Twenty-two patients per group were required to detect a difference of 2 in the pain score between the groups (α = 0.05, β = 0.1, estimated SD = 2). Six extra patients were included to allow for possible dropouts.

In this study, we assessed multiple correlated end points. For clear interpretation, we performed joint hypothesis testing for analysis of the primary end points and gatekeeping procedures were used for analysis of secondary end points.5 Data are presented as mean (SD), median (range), or percentage of patients. The Mann–Whitney U test with Bonferroni correction for multiple repeated measurements was used for analysis of pain scores and ropivacaine consumption. Analysis of supplemental analgesia, motor block, side effects, and patient satisfaction was performed using either χ2 or the Fisher exact test, where appropriate. A 2-sided P <0.05 was considered significant.

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RESULTS

Of the 56 enrolled patients, 50 completed the study. Patients’ demographics were similar in both groups (Table 1). Although more patients required supplemental analgesia in the group receiving ropivacaine 0.1% during the first 24 hours (64% vs 28%, 95% confidence interval of difference 0.08–0.57, P = 0.022; Table 2), pain scores did not differ statistically significantly at 24 hours (95% confidence interval of median difference –1 to 1, P = 0.862) or at any other time point (Fig. 1). Other secondary end points are comparable in both groups (Figs. 2 and 3, and Table 2).

Table 2

Table 2

Table 1

Table 1

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

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DISCUSSION

The results of this study demonstrate that continuous interscalene block using ropivacaine 0.1% produces a similar pain score, but more supplemental analgesia compared with ropivacaine 0.2% during the first 24 hours after shoulder surgery. This suggests that ropivacaine 0.2% provides superior analgesia compared with ropivacaine 0.1% during the first 24 hours for continuous interscalene block after shoulder surgery. However, during the next 24 hours, both concentrations provided similar analgesia.

Consistent with findings from a previous study on continuous femoral nerve blockade,8 our results suggest that for continuous interscalene block after shoulder surgery, decreasing a ropivacaine concentration from 0.2% to 0.1% reduces the analgesic effectiveness of the technique. A possible explanation for this finding is that the minimal effective concentration for postoperative analgesia after this surgery may be >0.1%. Another explanation is that total drug mass may be the primary determinant of continuous interscalene block effects. Therefore, a higher basal infusion rate may be required to overcome the reduction of concentration.

We expected that a lower concentration of ropivacaine would result in a reduction in motor block and paresthesia. However, there was no difference in motor block between the 2 different concentrations, and this could be explained by subjective assessments of the motor function and/or inadequate power for these outcome measures.

In conclusion, results of this study demonstrated that ropivacaine 0.2% provided more effective analgesia compared with ropivacaine 0.1% during only the first 24 hours for continuous interscalene block after shoulder surgery. Therefore, ropivacaine 0.2% is recommended in the first 24 hours when the pain is probably more severe.

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DISCLOSURES

Name: Chun Woo Yang, MD.

Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.

Attestation: Chun Woo Yang has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Sung Mee Jung, MD.

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: Sung Mee Jung has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Po Soon Kang, MD, PhD.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Po Soon Kang has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Hee Uk Kwon, MD, PhD.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Hee Uk Kwon has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Choon Kyu Cho, MD.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Choon Kyu Cho has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Younsuk Lee, MD, PhD.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Younsuk Lee has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Chul Woung Kim, MD, PhD.

Contribution: This author helped analyze the data.

Attestation: Chul Woung Kim has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Su Young Kim, PhD.

Contribution: This author helped analyze the data.

Attestation: Su Young Kim has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

This manuscript was handled by: Terese T. Horlocker, MD.

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