Effects of Local Anesthetic Concentration and Dose on Continuous Interscalene Nerve Blocks: A Dual-Center, Randomized, Observer-Masked, Controlled Study
Bibliographic record
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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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.003 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".