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 Impact of the Serratus Plane Block in Pain and the Use of Opioids in Breast Surgery (NCT02905149), a randomized phase 4 study. The primary outcome is Total Opioid Usage.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02905149 |
| Phase | Phase 4 |
| Condition | Surgery, Breast Reconstruction |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 60 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Instituto de Investigacion Sanitaria La Fe |
| Results posted | Yes |
2. Clinical Question
Population
People undergoing breast surgery, including a registry condition of breast reconstruction. The registry record does not report further eligibility details or describe the enrolled participants in greater detail.
Intervention
Standard anesthesia plus a serratus plane block, listed in the record under the arm name Serrato. The registry describes the block as an interfascial block at the serratus muscle.
Comparator
Standard anesthesia alone, listed under the arm name Control. Further details of the anesthesia regimens are not reported in the registry record.
Primary question
Did the groups differ in total opioid use, converted to morphine milligrams, during the first 24 hours after surgery, including intraoperative and postoperative use? The registry reports group medians and a sponsor analysis comparing final values.
The clinical question focuses on opioid consumption over a defined postoperative period rather than on a single pain rating. The registry also lists pain at rest and while coughing, time to first opioid administration on the ward, and opioid-related complications as secondary outcomes. These outcomes address other aspects of postoperative analgesia, but the posted primary result concerns opioid use.
The trial record identifies surgery and breast reconstruction as conditions, but does not report the specific operations, participant characteristics, or clinical circumstances that might affect opioid requirements. It also does not report the criteria used to select participants or details of any co-interventions beyond the stated anesthesia approaches. Those omissions limit how specifically the clinical question can be applied to particular surgical settings.
3. Trial Design
The registry describes a Phase 4, randomized, double-blind, parallel-group trial with enrollment of 60. The study status is completed. The recorded start date is 2016-08-02, and the primary completion date is 2017-06-08. The sponsor is Instituto de Investigacion Sanitaria La Fe.
The intervention arm, called Serrato, received standard anesthesia plus a serratus plane block. The Control arm received standard anesthesia. Random allocation is reported, but the registry record does not describe the sequence-generation method, allocation concealment, or who was blinded. It also does not explain how blinding was maintained or assessed. The parallel design means the registry presents outcomes by assigned arm rather than as a within-participant comparison.
The primary outcome was total opioid use during the first 24 hours after surgery, including intraoperative and postoperative use. The listed opioids were fentanyl and morphine, with fentanyl converted to morphine milligram equivalents using the recorded conversion of 10 mcgs/1mg. The primary outcome description says that 2 participants were lost to follow-up because of malfunctioning of the electronic device administering postoperative opioid.
The posted primary outcome results include 28 participants in the Serrato arm and 30 in the Control arm. The safety results report 30 participants at risk in each arm. The registry record does not explain the difference between the analysis counts and the safety counts, or give additional details about analysis populations. The record lists 4 outcome measures and 1 analysis. Further operational details, including the study setting and the exact timing or conduct of assessments, 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.
Overall Study
| Stage | Serrato | Control |
|---|---|---|
| STARTED | 30 | 30 |
| COMPLETED | 28 | 30 |
| NOT COMPLETED | 2 | 0 |
Reasons for not completing this period:
| Reason | Serrato | Control |
|---|---|---|
| Lost to Follow-up | 2 | 0 |
Analysis population for the primary outcome, as defined in the registry: 2 participants were lost to follow up because of malfunctioning of the electronic device administering the potoperative opioid
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 | Serrato | Control | Total |
|---|---|---|---|---|
| Participants analysed | 30 | 30 | 60 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 17 | 18 | 35 |
| Age, Categorical: >=65 years | Participants | 13 | 12 | 25 |
| Sex: Female, Male: Female | Participants | 30 | 30 | 60 |
| Sex: Female, Male: Male | Participants | 0 | 0 | 0 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| Region of Enrollment: Spain | participants | 30 | 30 | 60 |
6. Primary Endpoint
The registry lists the primary outcome as Total Opioid Usage, measured over First 24 hours after surgery.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | 95% Confidence Interval |
| Unit | milligrams |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is total opioid use in the first 24 hours after surgery, combining intraoperative and postoperative use. The registry reports the measure in morphine milligrams. Because fentanyl and morphine were both used, fentanyl was converted to morphine milligram equivalents using the recorded conversion of 10 mcgs/1mg. This creates a common scale for summarizing use of the two listed opioids.
Opioid consumption is a medication-use outcome. In general, it can complement pain ratings because it records administered medication rather than a participant’s reported pain intensity. It does not, by itself, describe pain, comfort, function, or the reasons a clinician or participant may have chosen a particular dose. Those outcomes need to be interpreted separately.
The registry specifies a median and a 95% confidence interval for each arm. The reported median was 18.5 milligrams in the Serrato arm, with a 95% confidence interval of 17.0 to 24.0, and 30.0 milligrams in the Control arm, with a 95% confidence interval of 26.0 to 35.0. The primary outcome description identifies device malfunction as the reason 2 participants were lost to follow-up. Further information about how missing opioid-use measurements were handled is not reported in the registry record.
As a general statistical point, the median describes the middle of an ordered set of observations and can be less affected by unusually high values than the mean. The confidence interval conveys uncertainty around an estimate; it is not a range that contains every participant’s opioid use.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome results show a lower observed median opioid use in the Serrato arm than in the Control arm during the first 24 hours after surgery. The medians were 18.5 and 30.0 morphine milligrams, respectively. Their reported 95% confidence intervals were 17.0 to 24.0 and 26.0 to 35.0. These are descriptive summaries of the analyzed groups and should be read alongside the sponsor’s comparison, rather than as a complete account of every participant’s values.
The sponsor reports a Wilcoxon (Mann-Whitney) analysis, with the parameter described as a median difference in final values. The reported estimate is 9, its 95% confidence interval is 4 to 14.5, and the reported p-value is < 0.05. The registry does not make the subtraction order explicit in the listed analysis result, so the estimate is best quoted as reported rather than assigned a direction from its sign. The group medians themselves show which arm had the lower observed median.
In general, a confidence interval gives a range of values compatible with the data and the method’s assumptions. It communicates uncertainty around an estimate, not certainty about the true effect. A p-value below the reported threshold is evidence against the test’s null hypothesis under its assumptions; it is not the probability that the null hypothesis is true, nor a measure of clinical importance. The exact p-value is not reported in the registry record.
The analysis uses a rank-based method. In general, rank tests compare the ordering of observations across groups and can be useful when outcomes are skewed or contain influential values. A rank-test result is not automatically a test of medians alone: interpreting it specifically as a median difference depends on additional distributional conditions. The registry reports the comparison as a median difference but does not provide distribution plots or further assumptions that would clarify that interpretation.
The reported results are limited to the primary opioid-use outcome. The registry lists secondary outcomes concerning pain, time to first opioid administration on the ward, and opioid-related complications, but their results are not included among the reported analyses described in the record. The record also identifies values as missing or not estimable for a two-arm comparison for another endpoint. Consequently, the primary finding does not establish what happened on those secondary measures.
The difference in group summaries is an observed trial result, not a guarantee that the same pattern would occur in other settings or populations. Participant characteristics, surgical procedures, opioid protocols, and other contextual details are not reported in the registry record. The result should therefore be read as evidence about the recorded groups and outcome, with uncertainty and reporting limits kept in view, rather than as a universal estimate.
9. Statistical Methods Explained
The registry reports a Wilcoxon (Mann-Whitney) comparison of final values and describes its parameter as a median difference. The following statistical notes are general explanations of the method and its interpretation; they do not add unreported details about how the trial was conducted.
What does a rank-based comparison do?
In general, the Mann-Whitney approach uses the ordering of observations rather than relying directly on group means. Values from both groups are ranked together, and the test evaluates whether observations in one group tend to rank higher or lower than observations in the other. This makes the method applicable to outcomes that may not be well represented by a normal distribution. It does not require the outcome to be reduced to a mean and standard deviation.
A rank test can detect a difference in distributions even when the group medians do not tell the whole story. If the distributions have similar shapes and differ mainly in location, a location shift and a median difference may be a reasonable way to describe the comparison. If shapes or spreads differ, a rank-test result can reflect more than a difference between medians. The registry record does not report distributional diagnostics, so the reported median-difference label should be read together with this general qualification.
How should the confidence intervals be read?
In general, a confidence interval describes uncertainty around an estimated quantity under a specified statistical method. The primary outcome reports a 95% confidence interval for each arm’s median and the sponsor comparison reports a 95% confidence interval for the median difference. Wider intervals indicate less precision than narrower intervals in the same measurement context. An interval is not a statement that a fixed proportion of individual participant values lie inside it, and it does not eliminate uncertainty about the estimate.
The reported arm intervals are 17.0 to 24.0 for Serrato and 26.0 to 35.0 for Control. The comparison interval is 4 to 14.5. These quantities describe different estimates: the first pair concerns each arm’s median, while the latter concerns the sponsor’s stated between-arm parameter. The registry record does not give additional information about the confidence-interval construction.
What does the p-value contribute?
The reported p-value is < 0.05. In general, a p-value measures how unusual data at least as incompatible with a null hypothesis would be if that hypothesis and the test assumptions were true. It does not measure the size or importance of a difference, and it is not the probability that the result occurred by chance. Because the record reports only a threshold, the exact p-value is not reported in the registry record.
The interpretation of a p-value also depends on which outcome and analysis were planned, whether other analyses were conducted, and how results were selected for reporting. The registry lists 4 outcome measures and 1 analysis, but a multiplicity plan is not reported in the registry record. The record therefore does not establish whether the reported test was adjusted for other possible comparisons.
Why can over-dispersion matter?
In general, over-dispersion means that observed variability is greater than a statistical model expects. A model that understates variability can produce confidence intervals that are too narrow and tests that appear more decisive than the data warrant. The Mann-Whitney test is rank-based and does not model opioid-use counts using a simple count-distribution assumption, but variability and distribution shape still matter when interpreting a group comparison or a median difference. The registry does not report an over-dispersion assessment, and no claim about one is warranted.
How do planning illustrations differ from observed results?
General sample-size planning uses assumptions about the effect to detect, the significance level, allocation, and statistical method. The record describes planning illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. For non-time-to-event outcomes, such illustrations are expressed as participants per arm; time-to-event illustrations use a total event count. Such planning figures are not observed trial outcomes and are not observed power. The trial’s own sample-size justification is not reported in the registry record, and no planning count should be mistaken for the number analyzed.
The registry’s outcome counts, analysis description, and group summaries do not supply all details needed to reconstruct the statistical procedure. The exact software, confidence-interval method, handling of ties, and any covariate adjustment are not reported in the registry record. General explanations of the test therefore clarify how to think about the result, but do not establish unreported implementation choices.
10. Analyses Reported by the Sponsor
| Method | Estimate | 95% CI | P-value |
|---|---|---|---|
| Wilcoxon (Mann-Whitney) | Median Difference (Final Values) 9 | 4 to 14.5 | < 0.050 |
The registry reports the sponsor’s own analysis as a Wilcoxon (Mann-Whitney) comparison of final values. It gives a median-difference estimate of 9, a 95% confidence interval of 4 to 14.5, and p < 0.05. The same record reports group medians of 18.5 for Serrato and 30.0 for Control. The estimate is quoted as recorded because the listed analysis does not specify the subtraction order.
No separate recalculated estimate is reported in the registry record. The sponsor’s result is therefore the available inferential comparison, while the arm medians and their confidence intervals provide descriptive context. The record does not flag a discrepancy between a sponsor analysis and a recalculation.
In general, a recalculation from summary statistics may not reproduce an analysis based on participant-level observations, particularly for a rank-based test. Group medians and confidence intervals alone do not contain all the information needed to recreate that test or its p-value. The sponsor’s reported analysis should be distinguished from any simple unadjusted recalculation, and neither should be treated as proof of a broader clinical conclusion.
11. Multiplicity, Missing Data and Analysis Populations
The registry lists 4 outcome measures, including the primary outcome of total opioid use and secondary outcomes of pain at rest and while coughing, time to first opioid administration on the ward, and opioid-related complications. It reports 1 analysis. The multiplicity plan—whether and how the analysis accounted for assessing more than one outcome or conducting other comparisons—is not reported in the registry record.
Multiplicity matters in general because making several statistical comparisons can increase the chance that at least one result appears notable even when there is no underlying difference. Whether an adjustment is appropriate depends on the study’s questions and analysis plan. The record does not give enough detail to determine whether the reported p-value was intended as a single primary test, whether other tests were performed, or whether any adjustment was used. The listed analysis count alone does not establish a complete multiplicity strategy.
The primary outcome description says that 2 participants were lost to follow-up because of malfunctioning of the electronic device administering postoperative opioid. The primary analysis counts are 28 for Serrato and 30 for Control. The registry record does not describe the method used to handle the missing measurements, whether the analysis followed randomized assignment, or whether any imputation or sensitivity analysis was performed. The analysis population and missing-data assumptions are not reported in the registry record.
Missing outcome data can affect estimates when the probability of missingness is related to the outcome or differs across groups. In general, a reason related to measurement equipment explains why values were unavailable, but it does not by itself show whether the missingness could influence the comparison. No further assessment is reported. The record also does not explain the relation between the outcome analysis counts and the safety counts.
Although the three secondary outcomes are named, their result estimates are not reported in the registry record. For another endpoint, the record indicates that values are missing or not estimable for a two-arm comparison. This lack of posted results prevents assessment of those outcomes and should not be interpreted as evidence that no events or differences occurred.
12. 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 |
|---|---|---|---|
| Serrato | 0 | 30 | 0.0% |
| Control | 0 | 30 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Serrato | 0 of 30 |
| Control | 0 of 30 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Serrato | 0 of 30 |
| Control | 0 of 30 |
The registry reports 0 serious adverse events, 0 other adverse events, and 0 deaths in each arm. Each arm has 30 participants listed as at risk for serious and other adverse events. These figures describe what the registry reports; they do not establish that no adverse events occurred outside the recorded categories or observation period.
The record does not report the definitions used for serious or other adverse events, how actively events were sought, the safety follow-up period, or whether the categories include all events experienced by participants. The listed safety counts also do not explain the difference between the safety group counts and the primary outcome analysis counts.
In general, zero reported events in a trial does not prove that an event is impossible or that a treatment has no safety risk. A trial’s ability to characterize uncommon harms depends on its size, follow-up, event ascertainment, and reporting. The safety data should therefore be read as a limited record of reported events in this study, not as a comprehensive safety estimate or a basis for treatment decisions.
13. What the Result Does, and Does Not, Mean
The primary result describes total opioid use during the first 24 hours after surgery in the randomized Serrato and Control groups. The recorded median was lower in the Serrato arm than in the Control arm. The sponsor’s reported rank-based comparison gives a median-difference estimate of 9, with a 95% confidence interval of 4 to 14.5 and p < 0.05. The group summaries and inferential result offer evidence about this measured outcome in the trial, with uncertainty reflected in the confidence intervals.
The result does not by itself establish how participants felt, whether pain was controlled, or whether they experienced better recovery. Opioid use is one measure and can be influenced by clinical practice and other factors. The registry lists pain ratings and other secondary outcomes, but their results are not reported in the registry record. The primary finding therefore cannot stand in for those outcomes.
Nor does the result show that the same difference would occur in every breast operation, care setting, or participant group. The registry does not report detailed participant characteristics, surgical procedures, or the anesthesia protocols beyond the brief arm descriptions. Those omissions constrain judgments about generalizability.
The reported absence of recorded serious adverse events, other adverse events, and deaths should not be interpreted as proof of no risk. Event definitions and safety follow-up details are not reported in the registry record. In general, a study’s estimates are most informative when its outcome measurement, analysis population, missing-data handling, and safety ascertainment are clearly described.
Overall, the posted data document a between-arm difference in the primary opioid-use summaries and a sponsor-reported statistical comparison. They do not establish a complete account of the trial’s secondary outcomes, long-term results, or broader clinical effects. Statistical evidence and clinical meaning are related but distinct: the size, precision, relevance, and limitations of the measured outcome all matter.
14. Why This Trial Matters Statistically
This trial illustrates how a clinical question can be expressed as a quantitative outcome: total opioid use over a defined postoperative period, converted to a common morphine-milligram scale. That definition makes the target of the primary comparison more specific than a general question about pain relief. It also highlights why endpoint details matter: the outcome combines intraoperative and postoperative use and includes a conversion between the listed opioids.
The result offers a useful setting for distinguishing descriptive summaries from inferential comparisons. The arm medians describe observed group outcomes, while the sponsor’s rank-based analysis addresses a between-group comparison. Confidence intervals communicate uncertainty in both the arm summaries and the reported comparison. A p-value alone would not convey the magnitude or precision of the estimate.
It also demonstrates limits of registry reporting. The record describes randomization and double masking, but does not explain the procedures used to implement them. It notes device-related missing outcome data, but does not report the analysis population or missing-data method. It names secondary outcomes without reporting their results. These details affect how confidently readers can interpret and contextualize the primary result.
Finally, the safety results show why zero recorded events need careful interpretation. Without event definitions and follow-up details, the absence of reported events is not equivalent to evidence that risk is absent. The trial is statistically informative about its specified primary outcome, while the record leaves important questions about conduct, secondary outcomes, and applicability unresolved.
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 registry record gives only brief intervention descriptions: standard anesthesia plus a serratus plane block versus standard anesthesia. It does not report the detailed anesthesia protocols, surgical procedures, participant characteristics, or study setting. These missing details make it difficult to judge how similar other clinical contexts would be to the trial.
Although the study is described as randomized and double-blind, the sequence-generation procedure, allocation concealment, identities of blinded groups, and maintenance of masking are not reported in the registry record. The record also does not describe the statistical analysis plan, the basis for the trial’s planned enrollment, or whether interim analyses were conducted. These points should remain unknown rather than inferred from the design labels.
The primary endpoint has device-related missing data: 2 participants were lost to follow-up because of malfunctioning of the electronic opioid-administration device. The method for handling those data and the analysis population are not reported. Primary outcome analysis counts differ from the safety counts, but the registry does not explain the difference. This limits assessment of how the reported estimates relate to all participants enrolled.
The registry names secondary outcomes but does not report their estimates. It also indicates missing or not estimable values for a two-arm comparison for another endpoint. The multiplicity plan is not reported, and details of the confidence-interval construction are not given. The exact p-value is also not reported beyond the threshold.
Safety interpretation is constrained by absent definitions and follow-up details. The record reports no serious adverse events, other adverse events, or deaths in the listed groups, but does not explain how events were collected or categorized. Together, these reporting limits mean that the posted primary result can be interpreted, but a fuller appraisal of trial conduct, other outcomes, and safety is not possible from the registry record alone.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: Impact of the Serratus Plane Block in Pain and the Use of Opioids in Breast Surgery — NCT02905149.
- Registry record last updated 2020-03-02; status last verified 2017-08.
- Results first posted 2020-03-02.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
19. Record Summary
NCT02905149 is a completed Phase 4, randomized, double-blind, parallel-group trial sponsored by Instituto de Investigacion Sanitaria La Fe. It enrolled 60 and compared standard anesthesia plus a serratus plane block with standard anesthesia alone in breast surgery.
The primary outcome was total opioid use in the first 24 hours after surgery, converted to morphine milligrams. The reported medians were 18.5 in the Serrato arm and 30.0 in the Control arm. The sponsor reported a median-difference estimate of 9, with a 95% confidence interval of 4 to 14.5 and p < 0.05.
The record lists secondary outcomes related to pain, opioid timing, and opioid-related complications, but their results are not reported in the registry record. It reports 0 serious adverse events, 0 other adverse events, and 0 deaths in each arm. Further detail on analysis populations, missing-data handling, and safety definitions is not reported.