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 Comparison of Pre-op and Post-op Pectoralis Nerve Block (NCT03653988), a randomized na study. The primary outcome is Pain Score Assessment Using a Visual Analog Scale-Immediately Post-surgery.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03653988 |
| Phase | NA |
| Condition | Breast Cancer, Postoperative Pain, Anesthesia |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 34 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Melinda Seering |
| Results posted | Yes |
2. Clinical Question
Population
The registry describes patients undergoing mastectomy with reconstruction. It lists breast cancer, postoperative pain, anesthesia, and nerve block among the conditions associated with the study. The enrolled group is reported as 34 participants, with 17 in each arm for the primary outcome. Further eligibility details and a fuller description of the study population are not reported in the registry record.
Intervention
The pre-operative group received a PEC I/II block from an anesthesiologist after induction of general anesthesia and before surgery. The registry describes this as the current standard of care at the University of Iowa. The intervention is a difference in when and by whom the block was administered, rather than a comparison of block with no block.
Comparator
The intra-operative group received the block from the surgeon after mastectomy and before reconstruction. Both arms therefore involved a PEC I/II block in the surgical care pathway; the timing and administering clinician distinguish the groups. Further details about block technique or other aspects of care are not reported in the registry record.
Primary question
The primary question is whether mean visual analog scale pain scores upon arrival in the recovery room differ between pre-operative and intra-operative block administration. The registry reports means with 95% confidence intervals for each arm, but no posted between-group estimate or inferential test. The reported arm summaries describe the outcome; on their own, they do not establish whether the difference between timing strategies is statistically distinguishable from chance or clinically important.
3. Trial Design
The registry describes a randomized, double-masked, parallel-group trial. The study is marked completed, with enrollment of 34. The recorded start date is 2019-03-12 and the primary completion date is 2021-10-31. The phase is listed as not applicable. Further information about the randomization procedure, allocation concealment, or which people were masked is not reported in the registry record.
The comparison is between two ways of scheduling a PEC I/II block for mastectomy with reconstruction. In the pre-operative arm, the anesthesiologist administered the block after induction of general anesthesia and before surgery. In the intra-operative arm, the surgeon administered it after mastectomy and before reconstruction. The registry describes pre-operative block use as the current standard of care at the study site. It does not describe a no-block arm, so the principal contrast concerns timing and provider within a pathway in which both groups receive a block.
The primary outcome is a continuous pain score assessed upon arrival in the recovery room after leaving the operating room. The registry reports an arm mean and a 95% confidence interval for each group. Each arm has 17 participants in the posted primary outcome summary. The registry also lists seven secondary outcomes relating to postoperative pain scores and narcotic use. Specific outcome results for those secondary measures are not included in the posted results summarized by the registry data for this comparison.
Although the record identifies the design as randomized and double-masked, it does not report the planned analysis methods, analysis populations, or how missing observations were handled. The primary outcome comparison is therefore best read as a randomized design accompanied by arm-level descriptive summaries, rather than as a complete report of the intended statistical comparison.
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 | PEC I/II Block - Pre-operative | PEC I/II Block - Intra-operative |
|---|---|---|
| STARTED | 17 | 17 |
| COMPLETED | 17 | 17 |
| NOT COMPLETED | 0 | 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 | PEC I/II Block - Pre-operative | PEC I/II Block - Intra-operative | Total |
|---|---|---|---|---|
| Participants analysed | 17 | 17 | 34 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 16 | 16 | 32 |
| Age, Categorical: >=65 years | Participants | 1 | 1 | 2 |
| Age, Continuous | years | 44 (32 to 74) | 44 (44 to 69) | 44 (32 to 74) |
| Sex: Female, Male: Female | Participants | 17 | 17 | 34 |
| Sex: Female, Male: Male | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 | 1 | 1 |
| Race (NIH/OMB): White | Participants | 17 | 15 | 32 |
| Race (NIH/OMB): More than one race | Participants | 0 | 1 | 1 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Region of Enrollment: United States | participants | 17 | 17 | 34 |
6. Primary Endpoint
The registry lists the primary outcome as Pain Score Assessment Using a Visual Analog Scale-Immediately Post-surgery, measured over upon arrival to the recovery room after leaving the operating room.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | units on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is pain measured with a visual analog scale immediately after surgery, upon arrival in the recovery room after leaving the operating room. The registry describes the scale as a continuous measure from 0 to 10, with 0 indicating no pain, 5 moderate pain, and 10 intense pain. The outcome is summarized as a mean and a 95% confidence interval for each arm.
A continuous score can preserve gradations in reported pain rather than reducing the outcome to a yes-or-no category. Comparing means can therefore describe the average level of the measured score in the two groups. The confidence interval conveys uncertainty around each arm’s estimated mean, given the observed data and the assumptions behind the interval. It is not itself a measure of the range of individual participants’ scores.
The timing makes this an immediate postoperative endpoint, not a measure of pain across the entire recovery period. The registry separately lists pain assessments on postoperative days 1, 3, and 7, a surgical recheck assessment, and measures of narcotic use. These are distinct outcomes and should not be treated as interchangeable with the immediate recovery-room score. Details of the visual analog scale’s administration, including who recorded the score and whether the same procedure was used in both arms, are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome means are 1.6 units on the scale for the pre-operative arm and 2.3 for the intra-operative arm. The 95% confidence interval for the pre-operative mean is 0.3 to 3.0; for the intra-operative mean it is 1.1 to 3.6. These figures describe the mean score in each arm and the uncertainty around those arm-specific estimates. They are not a reported estimate of the difference between arms.
Numerically, the pre-operative arm’s mean is lower than the intra-operative arm’s mean. That descriptive ordering should not be converted into a claim that the timing strategies differ reliably. The registry does not post a between-group estimate, confidence interval for the contrast, or p-value for this primary outcome. It also lists zero posted analyses. Without an inferential comparison, the precision of the arm means does not answer whether the observed separation between them is compatible with random variation under a no-difference comparison.
A confidence interval around each mean concerns that mean, not the difference between means. Even when arm-specific intervals overlap or do not overlap, that visual relationship is not a substitute for a directly estimated contrast and its uncertainty. The appropriate statistical object for the trial question would be a comparison of the randomized groups, with an estimate and uncertainty interval, interpreted in light of the analysis plan. Those results are not reported in the registry record.
The arm summaries also do not show how pain scores varied among individual participants. The reported confidence intervals should not be read as containing a specified proportion of individual scores. Nor do the means describe later pain or medication use. The registry lists those as secondary outcomes, but their results and the corresponding estimates are not reported in the record summarized for this comparison.
The study’s randomized parallel design is relevant because random allocation is intended to support a fair comparison of groups, subject to the conduct of the trial and the analysis. However, the record does not explain the randomization method, the masking procedures, or the analysis population. Those omissions limit assessment of how the design was implemented and how the posted summaries relate to all randomized participants.
These results therefore support a narrow description: the registry reports mean immediate postoperative pain scores of 1.6 and 2.3 for the pre-operative and intra-operative groups, respectively, with the stated arm-specific confidence intervals. The registry does not report an inferential result for the contrast. The posted summaries do not establish whether a difference exists, its precise size, or whether any difference would matter to patients or clinical practice.
9. Statistical Methods Explained
Statistical methods are only partly described in the registry record. The design is identified as randomized, double-masked, and parallel, and the primary endpoint is described as a continuous measure summarized by its mean and 95% confidence interval. A detailed statistical analysis plan, including the method used for the primary between-group comparison, is not reported in the registry record.
What does a mean summarize?
General explanation: a mean is the arithmetic average of the observations included in an analysis. For a continuous endpoint such as a visual analog scale score, it provides a compact description of the group’s central level. It does not show the full distribution: groups with the same mean can have different variability, skewness, or concentrations of scores. The registry gives the arm means but does not report a measure of spread for individual scores.
The mean is also sensitive to the set of observations included. If scores are missing, or if some participants are excluded from an analysis, the analyzed mean may not represent the full randomized group in the same way. The handling of missing scores and the analysis population are not reported in the registry record. It is therefore not possible to determine from the posted summary how these issues were handled.
What does a confidence interval convey?
General explanation: a confidence interval expresses uncertainty in an estimate under a statistical procedure and its assumptions. A narrower interval indicates greater precision under that procedure; a wider interval indicates less precision. The reported 95% confidence intervals apply to each arm’s mean. They do not directly quantify uncertainty in the difference between the two randomized groups.
To answer a comparative question, an analysis would ordinarily report a between-group contrast, its confidence interval, and possibly a test statistic or p-value. The contrast’s uncertainty depends on information from both arms and on the analysis method. The registry reports none of those comparative statistics for the primary endpoint. Comparing the arm-specific intervals by eye is not an equivalent method: the intervals were reported for separate means, not for the difference that the trial question asks about.
Why does the randomized design matter?
General explanation: random allocation is used to reduce systematic differences between groups at assignment, so that an outcome contrast can be interpreted as a comparison of assigned strategies, subject to trial conduct, follow-up, and analysis. The record identifies the study as randomized but does not describe the sequence generation, allocation concealment, or implementation. It also identifies double masking without stating which roles were masked or how masking was maintained. These details are not reported in the registry record.
A parallel-group design assigns participants to one group for the comparison rather than describing a crossover between interventions. Here, the arms differ in timing and in the clinician administering the block. Because both arms receive a block, the trial’s stated comparison is not block versus no block. The results should be interpreted as relating to this particular contrast, not as a test of whether a PEC I/II block is beneficial compared with no block.
What can be said about planning illustrations?
General explanation: sample-size planning uses assumptions about the effect to detect, variability, allocation, and the chosen error rate. A planning illustration is not an outcome of the trial and does not show the probability that the completed trial detected an effect. The registry’s planning description states a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the target effect expressed as a stated fraction of the observed effect. These are planning assumptions, not a reported analysis of the primary endpoint. No sample-size justification for the trial’s original design is reported in the registry record.
These illustrations must not be interpreted as observed power. Observed power is not a replacement for the effect estimate and its confidence interval, and it cannot fill in the missing comparative analysis. The trial’s reported arm sizes and means alone do not establish what the original design was intended to detect.
Why can multiple outcomes complicate interpretation?
General explanation: when a study examines multiple outcomes or multiple comparisons, the chance of at least one apparently notable result can increase if each is tested separately without an appropriate plan. A prespecified hierarchy, adjustment procedure, or clear distinction between primary and secondary outcomes can help readers understand how findings should be interpreted. The registry identifies one primary outcome and seven secondary outcomes, but multiplicity procedures and the planned handling of secondary analyses are not reported in the registry record. The record lists no posted analyses, so there are no reported secondary inferential results to interpret.
In short, the posted mean and confidence interval for each arm are descriptive summaries. The trial’s design and endpoint are recorded, but key details needed to assess a formal comparison—including the between-group estimate, analysis method, missing-data handling, and analysis population—are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry identifies a primary outcome and seven secondary outcomes. The secondary outcomes include pain assessments on postoperative days 1, 3, and 7, a visual analog scale assessment at surgical recheck, and measures of narcotic use. The record lists eight outcome measures in total. It does not report a multiplicity strategy, such as an adjustment procedure or a hierarchy for interpreting secondary outcomes. This matters because repeated testing across outcomes can complicate interpretation of isolated results. No secondary inferential analyses are posted in the registry record.
Missing-data methods are not reported in the registry record. The record does not state whether any primary outcome scores were missing, how missing values were handled, or whether sensitivity analyses were conducted. It also does not identify the analysis population used for the primary outcome, such as whether the analysis followed randomized assignment or included only participants with an observed score. Although the outcome summary reports 17 participants in each arm, this alone does not establish the complete analysis process or resolve whether missingness was relevant.
These omissions limit assessment of whether the posted summaries include all randomized participants and whether the results could be affected by missing observations. They also prevent evaluation of how the secondary outcomes were intended to complement the primary question. No assumptions about the missing-data pattern or analysis plan can be made from the registry record.
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 |
|---|---|---|---|
| PEC I/II Block - Pre-operative | 0 | 17 | 0.0% |
| PEC I/II Block - Intra-operative | 0 | 17 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| PEC I/II Block - Pre-operative | 17 of 17 |
| PEC I/II Block - Intra-operative | 17 of 17 |
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 |
|---|---|
| PEC I/II Block - Pre-operative | 6 of 17 |
| PEC I/II Block - Intra-operative | 3 of 17 |
Most frequent serious adverse event terms
| Event term | Organ system | PEC I/II Block - Pre-operative | PEC I/II Block - Intra-operative |
|---|---|---|---|
| Local Anesthetic Toxicity | Injury, poisoning and procedural complications | 0 of 17 | 0 of 17 |
Most frequent non-serious adverse event terms
| Event term | Organ system | PEC I/II Block - Pre-operative | PEC I/II Block - Intra-operative |
|---|---|---|---|
| Vomiting | Surgical and medical procedures | 6 of 17 | 3 of 17 |
Serious events with the highest arm-level rate: local anesthetic toxicity (0.0%).
The registry’s adverse-event summary reports zero participants with serious adverse events among 17 at risk in each arm. It lists local anesthetic toxicity as a serious adverse-event term at 0.0%. The summary also reports other adverse events affecting 6 participants in the pre-operative group and 3 in the intra-operative group, with 17 at risk in each group. These are counts in the posted safety record; the summary does not provide detail about the nature, timing, severity, or relationship of the other events to the block.
The death entries require particular caution. The registry record lists 17 deaths in each group, while also listing 17 participants at risk in each group. It provides no clarification of these entries or explanation of how they relate to the adverse-event summaries. They should not be interpreted as a verified count of deaths without clarification from the registry record or another authoritative study source. The record’s serious-event and death fields therefore cannot be reconciled from the posted information alone.
Safety summaries describe what is entered in the registry; they do not by themselves establish comparative safety. The record does not report a statistical comparison of adverse events. The small group counts and the unexplained death entries further limit what can be concluded from these figures.
12. What the Result Does, and Does Not, Mean
The result directly reported for the primary endpoint is an arm-level summary of immediate postoperative pain scores. The pre-operative group has a mean of 1.6 units, with a 95% confidence interval of 0.3 to 3.0. The intra-operative group has a mean of 2.3 units, with a 95% confidence interval of 1.1 to 3.6. Those summaries indicate the observed means in the posted data and the reported uncertainty around each mean.
They do not provide a formal estimate of the difference between the groups. No contrast, confidence interval for the contrast, or p-value is posted for the primary outcome. Consequently, the summaries do not show whether the apparent difference in means is statistically distinguishable from chance, how precisely any between-group difference is estimated, or whether it is clinically important. The arm-level confidence intervals cannot be substituted for a confidence interval around the comparison.
The result is also specific to the timing comparison recorded: an anesthesiologist-administered block after induction and before surgery versus a surgeon-administered block after mastectomy and before reconstruction. It does not compare a block with no block, and it does not answer questions about other block techniques, patient groups, or care settings. The registry does not report further details needed to judge how broadly the result might apply.
The primary endpoint concerns pain upon arrival in the recovery room. It does not establish the pattern of pain later in recovery or the amount of narcotic use. Although the registry lists later pain assessments and narcotic-use outcomes, their results are not reported in the record for this comparison. The available primary outcome summary should not be generalized to those unreported outcomes.
The completed randomized design is relevant to the intended comparison, but details about randomization, masking, missing observations, analysis populations, and statistical methods are not reported. The adverse-event record also contains unexplained death entries. Taken together, the registry supports a careful description of the posted outcome summaries, not a broad claim about efficacy, clinical importance, or safety.
13. Why This Trial Matters Statistically
This trial addresses a statistical question about timing within a shared procedural approach. Both groups received a PEC I/II block, while the timing and administering clinician differed. That distinction matters for interpretation: an arm comparison concerns these two recorded strategies, not the general question of block versus no block. Keeping the estimand—the specific comparison the study seeks to quantify—clear prevents results from being extended beyond what the design addresses.
The endpoint also illustrates why reporting the comparative estimate matters. Separate group means show the observed average score in each arm, but the research question is about the difference between randomized groups. A direct estimate of that difference, with its uncertainty, would make the comparison easier to assess. Without it, readers cannot judge the precision of the contrast or distinguish a descriptive separation of means from an inferential result.
The registry identifies several additional pain and narcotic-use outcomes. These outcomes may describe different parts of postoperative recovery, but multiplicity and outcome-specific analysis plans affect how a collection of results should be read. The record does not report the planned multiplicity approach or inferential results for the secondary outcomes. The distinction between a registered outcome and a posted result is therefore important.
Finally, the record demonstrates the value of complete, internally interpretable reporting. Details of the statistical plan, missing-data handling, analysis population, and masking are not reported. The safety summary includes death entries that are not explained alongside the at-risk counts. These gaps do not erase the descriptive endpoint data, but they constrain the conclusions that can be drawn from the registry alone. Statistically, a transparent between-group analysis and clarified safety reporting would be needed for a fuller reading of this trial.
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 results is the absence of a reported between-group analysis for the primary endpoint. Arm means and their confidence intervals are available, but a direct contrast and its uncertainty are not. The registry lists zero analyses. As a result, the primary comparison cannot be assessed through a reported inferential estimate.
The registry does not report the statistical analysis plan, the randomization procedure, allocation concealment, or which people were masked. It identifies the trial as double-masked but does not explain how masking was implemented. The analysis population and handling of missing observations are also not reported. These details are important for assessing whether the analysis corresponds to randomized assignment and how robust the results are to incomplete outcome data.
The primary outcome is a single immediate recovery-room assessment. Later pain scores and narcotic-use outcomes are listed, but their results are not reported in the record for this comparison. The registered outcomes therefore cannot be used to characterize the full postoperative course based on the information available. The registry also does not provide further detail about visual analog scale administration.
The two arms differ in both timing and provider: the anesthesiologist administered the pre-operative block, while the surgeon administered the intra-operative block. The design therefore compares the recorded care strategies as a package; it cannot isolate timing from provider effects based on the posted information. No additional procedural detail is reported that would support broader comparisons.
Finally, the safety record lists 17 deaths in each group while also listing 17 participants at risk in each group, without explaining the entries. This internal ambiguity prevents a confident interpretation of the death figures. These limitations are specific to what the registry record reports and should be kept separate from any information available in other study documents.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Comparison of Pre-op and Post-op Pectoralis Nerve Block — NCT03653988.
- Registry record last updated 2024-08-16; status last verified 2024-08.
- Results first posted 2024-08-16.
- 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.
18. Record Summary
The registry record describes a completed randomized, double-masked, parallel-group comparison of pre-operative and intra-operative PEC I/II block administration for mastectomy with reconstruction. Enrollment is reported as 34. The pre-operative block was administered by an anesthesiologist after induction of general anesthesia; the intra-operative block was administered by a surgeon after mastectomy and before reconstruction.
The primary outcome is a continuous visual analog scale pain score upon arrival in the recovery room. The registry reports a mean of 1.6, with a 95% confidence interval of 0.3 to 3.0, for the pre-operative group and a mean of 2.3, with a 95% confidence interval of 1.1 to 3.6, for the intra-operative group. A between-group estimate and inferential test are not reported. Seven secondary outcomes are listed, but their results are not reported in the registry record.
The registry does not report the detailed analysis plan, missing-data methods, or analysis population. Its adverse-event record lists zero serious adverse events in each group, other adverse events affecting 6 and 3 participants, and unexplained death entries of 17 in each group. These safety entries require clarification before interpretation.