This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Minimum Effective Concentration of Ropivacaine for Brachial Plexus Block Via the Supraclavicular and Infraclavicular Approach, Femoral Nerve Block, Sciatic Nerve Block Via the Popliteal and Parasacral Approach (NCT01452126), a na phase 2 study. The primary outcome is Effective Concentration of Ropivacaine to Produce Surgical Anesthesia in 50% of Population.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01452126 |
| Phase | Phase 2 |
| Condition | Surgical Anesthesia |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | Triple |
| Enrollment | 49 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of New Mexico |
| Results posted | Yes |
2. Clinical Question
Population
Adults undergoing regional nerve blocks for surgical anesthesia. The registry record lists surgical anesthesia as the condition and gives an enrollment of 49.
Intervention
Ropivacaine at concentrations assigned sequentially. The concentration for a patient depended on whether the previous patient's block produced successful surgical anesthesia.
Comparator
There was no concurrent control group or randomized comparison. The registry identifies a single-group model and allocation as not applicable.
Primary question
What ropivacaine concentration produces surgical anesthesia in 50% of the population for the nerve-block procedures under study?
The registered study aimed to identify the minimum effective anesthetic concentration, or MEAC, for regional blocks. The title identifies supraclavicular and infraclavicular brachial plexus blocks, femoral nerve block, and sciatic nerve block using popliteal and parasacral approaches. The brief summary also includes transversus abdominis plane blocks. The record does not clarify how these procedures were distributed among participants or whether each procedure had a separate concentration estimate.
The core question is about a concentration associated with a specified probability of successful surgical anesthesia, not a comparison of ropivacaine with another drug or treatment. Because the study uses sequential allocation in a single group, the previous patient's success or failure informs the next concentration. The registry record does not report the concentration estimate or the observed response data needed to assess the primary question.
3. Trial Design
This was a Phase 2, single-group dose-finding study sponsored by the University of New Mexico. The registry lists enrollment as 49 and status as terminated. The recorded start was 2011-06, and primary completion was recorded as 2011-09. The reason for termination and the relationship between registered enrollment and the number of participants who completed the study are not reported in the registry record.
The intervention was ropivacaine concentration. According to the arm description, each patient's concentration was assigned sequentially, depending on success or failure of surgical anesthesia in the previous patient. This is not a randomized comparison of parallel treatment arms: allocation is listed as not applicable, and the model is single group. Accordingly, an arm-to-arm treatment contrast should not be read into the design.
Masking is recorded as triple. The registry record does not explain which people were masked, what information was concealed, or how masking was maintained while concentrations were assigned in sequence. It also does not report the dose-finding algorithm, concentration starting point, permitted concentration changes, or stopping rule.
The study title and brief summary do not describe the block procedures identically. The title names the brachial plexus, femoral, and sciatic approaches; the brief summary additionally names transversus abdominis plane blocks. The record does not explain whether the procedures were analyzed together or separately. This matters because the target concentration may be specific to a block approach, while the registered primary endpoint refers broadly to the concentration producing surgical anesthesia in 50% of the population.
No analysis results are reported, and the registry lists no analyses. The design description therefore supports an account of how concentration assignment was intended to proceed, but not a conclusion about the estimated MEAC or the precision of that estimate.
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.
Overall Study
| Stage | Ropivacaine |
|---|---|
| STARTED | 49 |
| COMPLETED | 49 |
| NOT COMPLETED | 0 |
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.
| Characteristic | Unit | Ropivacaine |
|---|---|---|
| Participants analysed | 49 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 49 |
| Age, Categorical: >=65 years | Participants | 0 |
| Gender: Female | Participants | 19 |
| Gender: Male | Participants | 30 |
6. Primary Endpoint
The registry lists the primary outcome as Effective Concentration of Ropivacaine to Produce Surgical Anesthesia in 50% of Population, measured over 1 day.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | percentage concentration, ropivacaine |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled as the effective concentration of ropivacaine to produce surgical anesthesia in 50% of the population. It is expressed as percentage concentration of ropivacaine, with a timeframe of 1 day. The description says that each patient's nerve-block injection concentration was determined according to protocol.
In general, a concentration tied to a target response probability is a dose-finding quantity. It aims to identify a concentration at which the desired response is expected in a specified share of a target population. The specified target in this endpoint is 50%. This differs from reporting only whether a particular participant experienced successful anesthesia: an estimated population concentration requires a method that relates concentrations to response outcomes.
The registry record does not report the endpoint value, the response definition, the number of successful blocks, or the method used to estimate the concentration. The phrase “surgical anesthesia” indicates the intended clinical response, but the criteria used to classify success and failure are not described in the record. The multiple block approaches also leave unclear whether the endpoint was intended as a pooled estimate or as separate estimates by procedure.
Without the estimate and its uncertainty, the posted record does not establish how precisely the target concentration was identified. Nor does the endpoint title alone show how frequently anesthesia was achieved at any particular concentration.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes a sequential dose-finding study, but it does not report the primary endpoint result. No estimated concentration for producing surgical anesthesia in 50% of the population is available in the record. It also does not report a confidence interval, response counts by concentration, or a statistical test for the primary outcome. As a result, the main scientific question cannot be answered from the posted results.
The sequence-based allocation is important for interpreting the design. Each patient's concentration depended on the preceding patient's success or failure, rather than on random assignment to a concurrent control group. The registry therefore does not support a direct comparison between ropivacaine and another treatment, or between independently randomized concentration groups. The sequence could have been used to guide dose finding, but the specific estimation procedure and its assumptions are not reported.
The record lists 49 as enrollment, but this does not itself show how many participants contributed evaluable primary endpoint data. The registry gives no analysis population, missing outcome information, or participant flow. It would therefore be inappropriate to treat the enrollment figure as the denominator for the primary endpoint or to infer the number of successful blocks.
Safety information is limited to the recorded adverse-event counts: the ropivacaine group lists 0 serious events among 49 at risk and 11 in the other-event count among 49 at risk. These counts do not describe event types, timing, severity for the other events, or attribution to the drug or procedure. The absence of a reported serious event count is not evidence that no risk exists, especially when the record does not provide detailed event definitions or follow-up information.
The registry marks the study as terminated. It does not report the reason, whether termination affected the planned dose-finding procedure, or whether the primary analysis was completed. The status alone cannot establish that the study stopped because of safety, futility, recruitment, or any other cause.
Overall, the posted record is informative about the intended research question and the sequential single-group structure, but not about the efficacy endpoint's observed result. Any numerical sample-size illustrations associated with the posted material should be interpreted as planning calculations, not evidence of observed power or a substitute for an unreported primary analysis.
9. Statistical Methods Explained
What does a MEAC target represent?
In general, a minimum effective anesthetic concentration is a dose-finding target linked to a response probability. Here, the stated target is the concentration expected to produce surgical anesthesia in 50% of the population. The term describes a population-level estimate, not a claim that every participant receives the same benefit or that the response is certain at the estimated concentration. The registry record does not report the estimate or the observed outcomes needed to evaluate it.
How does sequential allocation work?
In general, a sequential dose-finding design uses information from earlier participants to guide the dose or concentration given to later participants. In this study, the arm description says the next ropivacaine concentration depended on whether the previous patient's surgical anesthesia was successful. This differs from random assignment to fixed parallel groups. It can concentrate observations around a dose-finding target, but the interpretation depends on the exact escalation or de-escalation rules and the analysis method. Those details are not reported in the registry record.
The registry does not state the first concentration used, possible concentration levels, size of concentration changes, or conditions for stopping allocation. It also does not state whether the procedure-specific blocks followed separate sequences. Without those details, readers cannot reconstruct the assignment process or determine how well the observed sequence would identify the target concentration.
Why does uncertainty matter?
In general, a point estimate gives a single best estimate under a statistical method, while a confidence interval communicates uncertainty around that estimate. A narrow interval indicates greater precision under the method's assumptions; a wide interval indicates less precision. Neither the point estimate nor an interval is reported for the primary endpoint in the registry record. Consequently, the numerical precision of the proposed MEAC cannot be assessed.
For sequential dose finding, uncertainty can depend on the number and pattern of responses across concentrations, the allocation rule, and the model used to connect concentration with response. These considerations are general; the registry record does not identify a particular model, response curve, or interval method. No model-based assumptions should be attributed to the study without those details.
What does over-dispersion mean in general?
Over-dispersion occurs when outcome variability is greater than a statistical model expects. If it is ignored, a model may express more precision than the data warrant. This concept can matter in analyses of clustered or heterogeneous responses, but the registry does not report an over-dispersion assessment or even the fitted model. It is therefore a general methodological consideration, not a finding about this study.
How should the planning calculations be read?
The sample-size assumptions describe planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is expressed as a stated fraction of the observed effect. These are planning assumptions, not a description of this trial's single-group sequential allocation. The record does not report that the study used those assumptions to choose enrollment, and the illustrations are not observed power.
In general, power is a property of a specified design and assumed effect, variability, and analysis procedure. It is not a retrospective measure of whether a completed study established its result. Here, the primary estimate and analysis are absent, so no observed-power conclusion is supported. The assumptions for a two-arm planning comparison also do not turn the study into a randomized two-arm trial.
What analysis is actually reported?
The registry lists no analyses. It does not identify a statistical estimator, adjustment variables, hypothesis tests, confidence interval procedure, or analysis population. A design description and an endpoint title are not enough to infer these methods. The result therefore cannot be reconstructed from the registry information, and a simple recalculation from summary statistics is not possible because the relevant outcome summaries are absent.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists a primary endpoint and a secondary outcome concerning the number of patients with complications. It reports two outcome measures but lists no analyses. No multiplicity strategy is reported in the registry record. It is therefore unknown whether the investigators planned any adjustment for examining multiple outcomes, procedures, or concentration estimates. The record also does not indicate whether there were additional prespecified endpoints beyond those listed.
Missing-data handling is not reported in the registry record. There is no account of participants excluded from the primary analysis, missing response classifications, incomplete follow-up, or how such observations might have been handled. The recorded enrollment of 49 cannot be assumed to equal the primary endpoint analysis population, because no analysis population or participant flow is given.
The registry does not identify an intention-to-treat, per-protocol, or other analysis population. Nor does it state how protocol deviations, failed blocks, or unavailable endpoint assessments were handled. In a sequential design, missing responses could also affect how subsequent concentrations are assigned, but the record does not say whether this occurred or how it was addressed.
Because the title names several block approaches and the brief summary includes an additional approach, the scope of the primary analysis is unclear. The registry does not say whether concentrations were estimated separately by procedure, whether observations were pooled, or how multiple procedure-specific questions were handled. These omissions limit interpretation of both the primary endpoint and the secondary complication outcome.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Ropivacaine | 0 | 49 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Ropivacaine | 11 of 49 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Ropivacaine |
|---|---|---|
| Failure of regional anesthesia | Surgical and medical procedures | 11 of 49 |
The registry lists the ropivacaine group with 49 at risk for serious adverse events and 0 serious events. It also lists 49 at risk for other adverse events and 11 in the other-event count. The record does not provide the terms for the reported other events; the serious adverse-event terms list is empty.
These are descriptive counts, not a comparison with a control group. Since the design is single group and no like-for-like comparator is listed, the counts cannot establish whether events were more or less frequent than under another treatment. The record also does not report event severity beyond the serious versus other categorization, timing, duration, relationship to ropivacaine, or how events were collected.
A zero serious-event count in the registry is not proof that serious harm is impossible. The available record does not provide enough detail about follow-up or event ascertainment to interpret the count beyond what it reports. Likewise, the other-event count does not identify which complications occurred or whether they were related to the block, the drug, the underlying procedure, or another cause.
12. What the Result Does, and Does Not, Mean
The registry record establishes that investigators planned a Phase 2 dose-finding study of ropivacaine for regional anesthesia. It describes sequential concentration assignment based on the preceding patient's success or failure and specifies a primary target: the concentration expected to produce surgical anesthesia in 50% of the population. Those details clarify the intended question and the broad design.
The record does not establish the primary result. It gives no estimated concentration, response data by concentration, uncertainty interval, or statistical analysis. It therefore cannot show how close the study came to identifying its intended target, how precise an estimate might have been, or whether results differed across block approaches.
The enrollment entry and adverse-event counts should not be treated as substitutes for missing outcome results. Enrollment does not show how many participants contributed endpoint data, and safety counts do not reveal the probability of successful anesthesia. The record's terminated status also does not explain why the study ended or whether its planned analyses were completed.
In general, a dose-finding estimate applies to the studied population, intervention, procedure, outcome definition, and analysis assumptions. The registry record does not provide enough detail to define all of those elements, particularly the separate or pooled handling of the different block approaches. The stated 50% target is an endpoint definition, not an observed success rate.
Accordingly, the sound interpretation is limited: the study was designed to investigate ropivacaine concentrations for surgical anesthesia, but the posted registry information does not report the result needed to answer its main question. It does not support a treatment recommendation or a conclusion that a particular concentration is effective or ineffective.
13. Why This Trial Matters Statistically
This trial is statistically interesting because it uses a sequential concentration assignment rather than a conventional randomized comparison. In general, such designs can use response information as it accumulates to guide later assignments. That makes the allocation process central to interpretation: the concentration given to a participant is connected to outcomes observed earlier in the sequence.
The study also poses a dose-finding question rather than a simple comparison of treatment groups. Its primary endpoint targets the concentration associated with surgical anesthesia in 50% of the population. This type of target requires an estimate of the relationship between concentration and response, together with uncertainty about that estimate. The registry record reports neither.
The breadth of procedures makes clarity about analysis particularly important. The title names several nerve-block approaches, while the brief summary also includes transversus abdominis plane blocks. Whether the study sought separate estimates or a pooled result is not reported. Different procedures may represent distinct dose-finding questions; the registry does not explain how that issue was addressed.
The record is also a useful example of why design details and results need to be distinguished. Sequential allocation is described, but the dose rules and statistical estimator are not. Enrollment and safety counts are reported, but the primary outcome result is not. A study's endpoint definition alone cannot substitute for the estimate, response data, and precision needed to judge what was learned.
14. 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 of the registry record is the absence of primary endpoint results. The effective concentration estimate, participant response data, and uncertainty around the estimate are not reported in the registry record. The registry also lists no analyses, so the method used to derive the intended dose-finding result cannot be evaluated.
The sequential allocation is only briefly described. The starting concentration, allowable changes, escalation or de-escalation rules, stopping rule, and estimator are not reported. Without them, the allocation sequence and statistical properties of the procedure cannot be assessed. Masking is labeled triple, but who was masked and how masking operated are not specified.
The population and procedure scope are also unclear. The brief summary describes adults and several types of blocks; the title and summary do not list precisely the same set of procedures. The record does not clarify whether each block had a separate sequence or estimate, whether the data were pooled, or how the endpoint was defined for each procedure.
Although enrollment is recorded as 49, the record does not report the analysis population, participant flow, missing outcomes, or protocol deviations. It also does not explain why the study was terminated. These gaps prevent assessment of how termination and incomplete or unavailable data may have affected the primary result.
Safety reporting is limited to counts and does not include event terms, timing, attribution, or detailed follow-up. Finally, the planning assumptions describe a two-arm illustration, which does not match the registered single-group sequential design. The illustrations should not be mistaken for the trial's original design rationale or for observed power.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Minimum Effective Concentration of Ropivacaine for Brachial Plexus Block Via the Supraclavicular and Infraclavicular Approach, Femoral Nerve Block, Sciatic Nerve Block Via the Popliteal and Parasacral Approach — NCT01452126.
- Registry record last updated 2016-12-19; status last verified 2016-10.
- Results first posted 2016-12-19.
- 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.
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18. Record Summary
NCT01452126 is a University of New Mexico Phase 2, single-group study of ropivacaine concentration for regional nerve blocks. The registry lists sequential allocation based on the previous patient's success or failure, triple masking, enrollment of 49, and terminated status. The recorded study start was 2011-06, with primary completion in 2011-09.
The primary endpoint asks for the concentration that produces surgical anesthesia in 50% of the population, with a timeframe of 1 day. The title and brief summary describe multiple block approaches, but the record does not clarify whether outcomes were analyzed separately or together. The primary result and statistical analyses are not reported in the registry record.
For safety, the ropivacaine group lists 0 serious events among 49 at risk and 11 in the other-event count among 49 at risk. Event details and the reason for termination are not reported in the registry record.