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Randomized Controlled Trial
. 2008 Nov-Dec;33(6):518-25.
doi: 10.1016/j.rapm.2008.05.006.

Effects of local anesthetic concentration and dose on continuous interscalene nerve blocks: a dual-center, randomized, observer-masked, controlled study

Affiliations
Randomized Controlled Trial

Effects of local anesthetic concentration and dose on continuous interscalene nerve blocks: a dual-center, randomized, observer-masked, controlled study

Linda T Le et al. Reg Anesth Pain Med. 2008 Nov-Dec.

Abstract

Background and objectives: It is currently unknown if the primary determinant of continuous peripheral nerve block effects is simply total drug dose, or whether local anesthetic concentration and/or volume have an influence. We therefore tested the null hypothesis that providing ropivacaine at different concentrations and rates--but at an equal total basal dose--produces similar effects when used in a continuous interscalene nerve block.

Methods: Preoperatively, an anterolateral interscalene perineural catheter was inserted using the anterolateral approach in patients undergoing moderately painful shoulder surgery. Subjects were randomly assigned to receive a postoperative perineural infusion of either 0.2% ropivacaine (basal 8 mL/h, bolus 4 mL) or 0.4% ropivacaine (basal 4 mL/h, bolus 2 mL) through the second postoperative day. Our primary endpoint was the incidence of an insensate hand/finger during the 24 hours beginning the morning following surgery.

Results: The incidence of an insensate hand/finger did not differ between the treatment groups (n = 50) to a statistically significant degree (0.2% ropivacaine, mean [SD] of 0.8 [1.3] times; 0.4% ropivacaine, mean 0.3 [0.6] times; estimated difference = 0.5 episodes, 95% confidence interval, -0.1 to 1.1 episodes; P = .080). However, this is statistically inconclusive given the confidence interval. In contrast, pain (P = .020) and dissatisfaction (P = .011) were greater in patients given 0.4% ropivacaine.

Conclusions: For continuous interscalene nerve blocks, given the statistically inconclusive primary endpoint results and design limitations of the current study, further research on this topic is warranted. In contrast, providing a lower concentration of local anesthetic at a higher basal rate provided superior analgesia.

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Figures

Figure 1
Figure 1
Effects of interscalene perineural ropivacaine concentration on postoperative pain following moderately-painful surgery of the shoulder. Pain severity indicated using a Numeric Rating Scale (NRS) of 0-10, with 0 equal to no pain and 10 being the worst imaginable pain. Data are expressed as median (horizontal bar) with 25th-75th (box) and 10th-90th (whiskers) percentiles for patients randomly assigned to group 0.2% (0.2% ropivacaine, 8 mL/h basal, 4 mL bolus) or group 0.4% (0.4% ropivacaine, 4 mL/h basal, 2 mL bolus). Because each comparison dilutes all other P-values, we restricted our analysis to 4 comparisons among secondary end points. P-values are provided where statistical comparisons were applied.
Figure 1
Figure 1
Effects of interscalene perineural ropivacaine concentration on postoperative pain following moderately-painful surgery of the shoulder. Pain severity indicated using a Numeric Rating Scale (NRS) of 0-10, with 0 equal to no pain and 10 being the worst imaginable pain. Data are expressed as median (horizontal bar) with 25th-75th (box) and 10th-90th (whiskers) percentiles for patients randomly assigned to group 0.2% (0.2% ropivacaine, 8 mL/h basal, 4 mL bolus) or group 0.4% (0.4% ropivacaine, 4 mL/h basal, 2 mL bolus). Because each comparison dilutes all other P-values, we restricted our analysis to 4 comparisons among secondary end points. P-values are provided where statistical comparisons were applied.

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