A Comparison of Ropivacaine Alone Versus Combination of Dexamethasone and Clonidine for Block: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Comparison of Ropivacaine Alone Versus Combination of Dexamethasone and Clonidine for Block (NCT02151487), a registered phase not stated study. The primary outcome is Duration of the Sensorial Supraclavicular Block.

2. Clinical Question

3. Trial Design

The registry describes a prospective, observer-blinded study of supraclavicular brachial plexus block using ultrasound. Its title and brief description characterize the study as randomized. At the same time, the registry record does not state the allocation method and cautions that the arms are not a like-for-like control comparison. The available record therefore does not establish how participants were assigned or whether the listed groups can be interpreted as randomized comparisons.

Four intervention groups are listed. One received ropivacaine 0.5% 25 ml alone. The other groups received that ropivacaine regimen with 4 mg dexamethasone, with 100 mcg clonidine, or with both 4 mg dexamethasone and 100 mcg clonidine. The study aim was to evaluate postoperative analgesic efficacy, and the stated hypothesis was that adding both adjuvants would prolong analgesia compared with ropivacaine alone.

The registry reports enrollment of 97 and a COMPLETED status. The recorded start is 2014-03 and primary completion is 2016-04. These details describe the trial record but do not establish how many participants contributed data to each outcome or analysis. The registry lists Postoperative Analgesia as a secondary outcome and reports 2 outcome measures, but it lists 0 analyses. The protocol, allocation details, analysis populations, and statistical analysis plan are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Study takes place in routine clinical context. Subjects who received supraclavicular nerve block with ropivacaine alone or ropivacaine with adjuvants enrolled to the study.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Participants received supraclavicular nerve block with ropivacaine alone and ropivacaine with adjuvants.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Duration of the Sensorial Supraclavicular Block, measured over within 24-hr after surgery.

The primary endpoint is Duration of the Sensorial Supraclavicular Block, measured in hours. The registry defines it as the interval from admission to the Post-Anesthesia Care Unit until the first pain medication is taken at home. The timeframe is within 24-hr after surgery. The endpoint is described as a continuous measure summarized by a mean and standard deviation.

As a general statistical concept, duration is useful when the research question concerns how long a block or its associated analgesia persists. A continuous time measure can retain more information than reducing follow-up to a simple yes-or-no outcome at a single time point. The chosen definition also sets a specific operational endpoint: it depends on the recorded time of admission to the Post-Anesthesia Care Unit and the time of first pain medication at home. It should not automatically be interpreted as a direct measure of every aspect of pain or block function.

The registry record does not report group means, standard deviations, differences, confidence intervals, or tests for this endpoint. It therefore does not permit a numerical assessment of the size or precision of any group contrast. The timing definition and summary measure are described, but the numerical primary-outcome findings are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary endpoint as a continuous measure summarized by its mean and standard deviation. These summaries have distinct roles. The mean represents the arithmetic average of measured durations, while the standard deviation describes how spread out individual measurements are around that average. Neither summary alone gives the uncertainty in a comparison between groups. A confidence interval for a contrast would help convey the range of effect sizes compatible with the data and the analysis assumptions.

What does a confidence interval add?

As a general statistical concept, a confidence interval expresses uncertainty around an estimated effect. A narrow interval indicates greater precision than a wide interval, although interpretation still depends on the design, measurement, and analysis. The registry record does not report an effect estimate or confidence interval for the primary endpoint, so the precision of any group comparison cannot be evaluated. A p-value, even if it were reported, would not by itself indicate the size or clinical meaning of an effect.

How should the four groups be compared?

The listed regimens form four groups: ropivacaine alone, ropivacaine with dexamethasone, ropivacaine with clonidine, and ropivacaine with both adjuvants. A complete analysis could define specific contrasts of interest, such as each adjuvant regimen compared with ropivacaine alone, or a comparison of the combination with each single-adjuvant regimen. These are general possibilities, not analyses confirmed by the registry. The record reports 0 analyses and does not specify a contrast hierarchy, a model, adjustment variables, or the statistical plan.

Because allocation is not stated and the record cautions that the arms are not a like-for-like control comparison, interpretation of any potential contrast would need to account for how the groups were formed. In a randomized design with appropriate conduct, random allocation can support causal comparisons by balancing factors on average. That general principle cannot establish that the groups in this record were allocated in that way. The title's description of randomization does not replace the missing allocation details.

Why can variation affect a comparison?

As a general statistical concept, greater variability in measured durations can make a group mean less precise and can make differences harder to distinguish from random variation. The standard deviation is relevant to describing this variation. If the distribution of durations is strongly skewed or includes unusual long durations, a mean and standard deviation may not fully communicate its shape. The registry does not report distributional summaries or diagnostic checks, so the suitability of any particular model cannot be assessed.

Over-dispersion is a general concern when observed variability exceeds what a chosen statistical model assumes. In that situation, standard errors may be too small if the model does not accommodate the extra variability, making confidence intervals too narrow and tests too optimistic. Whether over-dispersion is relevant depends on the data and model. The registry record does not identify a model or report diagnostics, and no conclusion about over-dispersion in this study is possible.

The endpoint is described as elapsed time between two events, but it is also summarized as a mean with standard deviation. General time-to-event methods can be useful when some participants do not experience the event during follow-up or when observation ends before the event occurs; such methods can account for incomplete event times under stated assumptions. The registry does not report censoring, follow-up completeness, or a time-to-event analysis. It is therefore not possible to determine whether these issues arose or how they were handled.

The sample-size assumptions describe planning illustrations: a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect expressed as a stated fraction of the observed effect. These are illustrative assumptions, not evidence about the original design. Sample-size illustrations answer a planning question under chosen assumptions; they are not observed power and do not replace the trial's actual estimates or uncertainty. The registry does not report its own sample-size justification.

Finally, the numerical outcome analysis is absent from the registry record. Without group summaries, contrasts, uncertainty intervals, and a stated analysis method, statistical interpretation must remain limited to the design and endpoint description rather than claims about an estimated effect.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Ropivacaine", "Ropivacaine and Dexamethasone", "Ropivacaine and Clonidine", "Ropivacaine, Dexamethasone and Clonidine")
n   <- c(25, 22, 16, 20)
m   <- c(13.4, 14, 17.4, 18.8)
sp  <- c(6, 6.6, 6, 6.2)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Ropivacaine  25  13.400  6.000  10.923  15.877
CARM  Ropivacaine and Dexamethasone  22  14.000  6.600  11.074  16.926
CARM  Ropivacaine and Clonidine  16  17.400  6.000  14.203  20.597
CARM  Ropivacaine, Dexamethasone and Clonidine  20  18.800  6.200  15.898  21.702

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when more than one outcome, group contrast, or statistical test is examined. As a general statistical concept, making several comparisons can increase the chance that at least one result appears statistically notable by chance. A prespecified testing strategy can clarify which contrasts are primary and whether any adjustment is planned. The registry lists four treatment groups and identifies a primary endpoint, but the analysis plan, contrast hierarchy, and any multiplicity procedure are not reported in the registry record. The number of outcome measures is reported as 2, and Postoperative Analgesia is listed as a secondary outcome; the record does not explain how results across outcomes would be interpreted together.

The registry does not report how missing endpoint measurements were handled, whether all enrolled participants were included in each analysis, or whether any imputation or sensitivity analysis was used. It also does not describe the analysis populations, such as an intention-to-treat population or a population defined by treatment received. These omissions make it impossible to assess whether missingness or exclusions could have affected the primary comparison.

The record reports enrollment of 97, but enrollment alone does not show how many participants had usable primary-outcome data or contributed to each group analysis. The listed adverse-event denominators are specific to the safety entries and should not be assumed to be the primary-endpoint analysis counts. No interim analyses or stopping rules are reported in the registry record. Consequently, the treatment of multiplicity, missing data, analysis populations, and interim monitoring cannot be evaluated from the posted record.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events, other adverse events, and deaths by intervention group. For serious adverse events, the recorded count is 0 in each group: ropivacaine, with 27 at risk; ropivacaine and dexamethasone, with 27 at risk; ropivacaine and clonidine, with 20 at risk; and ropivacaine, dexamethasone and clonidine, with 23 at risk. The recorded death count is 0 in each group.

For other adverse events, the registry records 0 among 27 at risk in the ropivacaine group, 1 among 27 at risk in the ropivacaine-and-dexamethasone group, 0 among 20 at risk in the ropivacaine-and-clonidine group, and 0 among 23 at risk in the group receiving all three drugs. The record does not identify the event's nature, timing, severity, or assessed relationship to treatment.

These are reported counts for the listed groups, not estimates of comparative risk. The registry record does not give additional safety-analysis details or uncertainty measures. A zero count in a trial record does not establish that an event cannot occur, and these entries alone do not support broader conclusions about safety.

13. What the Result Does, and Does Not, Mean

The registry record establishes the question the investigators intended to study: whether adding dexamethasone, clonidine, or both to ropivacaine changes the duration of sensorial supraclavicular block. It also describes the four regimens, the endpoint's timing definition, and the study's completed status. These are useful details for understanding the study's scope.

What the record does not establish is the size or direction of any primary-outcome difference. Numerical group results and statistical analyses are not reported. Without those, there is no estimate to interpret, no confidence interval to assess precision, and no statistical test to discuss. The investigators' stated hypothesis is not evidence that the expected difference occurred.

The design description also needs qualification. The title and brief summary call the study randomized and observer-blinded, while the registry does not state allocation and flags that the arms are not a like-for-like control comparison. The reader therefore cannot use the available record alone to verify how treatment groups were formed or how comparable they were. That uncertainty limits causal interpretation even if numerical group results were available.

The adverse-event counts provide a separate, limited description of events recorded by group. They should not be used to infer efficacy or to make broad claims about treatment safety. The record does not report event details or a fuller comparative safety analysis.

Accordingly, the defensible interpretation is about what was planned and registered, not about a demonstrated treatment effect. The record does not show that an adjuvant prolonged block duration, nor does it show that it failed to do so. Answering that question requires outcome estimates and an analysis whose methods and population are clear.

14. Why This Trial Matters Statistically

This trial is statistically interesting because it sets out a multi-arm comparison of a base regimen with two individual adjuvants and their combination. Such a structure can raise several distinct questions: whether each adjuvant regimen differs from ropivacaine alone, whether the combination differs from either single-adjuvant regimen, and whether the combined regimen has an effect beyond the individual components. Those questions require clearly defined comparisons; the registry record does not report which contrasts were analyzed.

The endpoint also illustrates the importance of operational definitions. Duration is defined through two specific recorded events, from admission to the Post-Anesthesia Care Unit to first pain medication at home. Clear definitions allow readers to understand what a measured duration represents, while reminding them that a defined endpoint captures only a particular aspect of the broader clinical question.

The record highlights the distinction between a study description and a result. It identifies a prospective, observer-blinded study and states the investigators' hypothesis, but it does not report outcome estimates or analyses. Statistical interpretation depends on those results, along with adequate information about allocation, missing data, and the analysis population.

It also illustrates why planning calculations must be distinguished from observed findings. The stated sample-size assumptions describe planning illustrations based on an observed effect, not the study's own design and not observed power. Without the trial's effect estimates and analysis details, such calculations cannot answer the clinical question. The key statistical contribution of a registry record is therefore not only its stated aim, but also the transparency and completeness of its posted outcome reporting.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitation for interpreting this trial record is the absence of numerical primary-outcome results and analyses. The record gives the endpoint definition but not group means, standard deviations, contrasts, confidence intervals, or p-values. It is therefore not possible to estimate the effect or its precision.

Allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. Although the title and brief description call the study randomized, the available record does not explain how allocation was carried out or resolve the comparability concern. The observer-blinded description does not clarify which people were blinded or how blinding was maintained.

Other design and analysis details are also not reported in the registry record: eligibility criteria, participant characteristics, the original sample-size justification, the primary analysis method, the analysis populations, missing-data handling, multiplicity procedures, and interim analyses. Without those details, the risk of bias and robustness of any unposted result cannot be assessed.

The endpoint relies on the time to first pain medication at home following admission to the Post-Anesthesia Care Unit. The record does not describe how those times were collected, whether follow-up was complete, or how participants without a recorded event were handled. The adverse-event entries likewise lack event descriptions and do not establish comparative safety. These limitations concern what can be learned from the registry record; they are not evidence that a particular result or bias occurred.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Comparison of Ropivacaine Alone Versus Combination of Dexamethasone and Clonidine for Block — NCT02151487.
• Registry record last updated 2019-07-05; status last verified 2019-04.
• Results first posted 2019-07-05.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry record concerns a prospective, observer-blinded study of four supraclavicular block regimens for upper extremity surgery: ropivacaine alone, ropivacaine with dexamethasone, ropivacaine with clonidine, and ropivacaine with both adjuvants. It records enrollment of 97, a COMPLETED status, a start of 2014-03, and primary completion in 2016-04.

The primary endpoint is duration of sensorial supraclavicular block, defined as the interval from Post-Anesthesia Care Unit admission to first pain medication at home and summarized as a mean with standard deviation. Numerical primary-outcome results and analyses are not reported in the registry record. Allocation details, the statistical plan, missing-data methods, and analysis populations are also not reported. Safety entries record 0 serious adverse events and 0 deaths in each group, with 1 other adverse event in the ropivacaine-and-dexamethasone group.