Comparison of Preoperative Ultrasound Guided Pectoralis Nerve Block Placement Versus Intra-operative Placement: A Prospective Randomized Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Preoperative Ultrasound Guided Pectoralis Nerve Block Placement Versus Intra-operative Placement: A Prospective Randomized Trial (NCT03201809), a randomized na study. The primary outcome is Post-operative Narcotic Usage.

2. Clinical Question

The practical statistical question is whether the recorded mean amount of narcotic used differed between the two randomized groups during the stated follow-up period. The posted summaries give a mean and standard deviation for each group, but the registry record does not report an inferential estimate of the between-group contrast, a confidence interval, or a p-value. The available summary therefore describes the observed groups; it does not establish how compatible the difference in their means is with chance variation under a specified statistical model.

The registry names post-operative self-reported pain scores and post-operative anti-emetic usage as secondary outcomes. Results for those outcomes are not reported in the registry record. The clinical question should therefore be kept focused on the reported primary endpoint rather than broadened to conclusions about pain relief, anti-emetic use, or other aspects of recovery.

3. Trial Design

This was a randomized, parallel-group trial with no masking reported. The registry lists the study as not applicable for phase, an enrollment of 12, and a terminated status. The start date is 2016-09-01, and the primary completion date is 2020-03-23. The reason for termination is not reported in the registry record.

The two groups were the On-Q Catheter arm and the Ultrasound Guided Pectoral Nerve Block arm. Each arm has a posted sample size of 6. The On-Q description specifies a catheter within the implant pocket and an infusion of 0.2% Ropivacaine at 4 mL/h, for a total of 400 mL, described as about 4 days. The block description specifies single-shot pre-operative injections, with separate volumes and concentrations for the Pecs 1 and pecs 2 injections. The registry title refers to pre-operative versus intra-operative placement, while the arm descriptions provide the details above; further detail about the operative timing of catheter placement is not reported in the registry record.

Randomization is reported, but the sequence-generation method, allocation concealment, and any stratification factors are not reported in the registry record. Because masking is listed as none, the study is described as unmasked. The record does not specify which participants or study staff, if any, were aware of group assignment at each stage.

The primary outcome was post-operative narcotic usage, measured as a mean amount in mg from the operation through up to 2 days, with standard deviation as the dispersion measure. The record lists two secondary outcomes: post-operative anti-emetic usage and post-operative self-reported pain scores. Further details about their measurement, timing, and analysis are not reported in the registry record. No sample-size justification or detailed statistical analysis plan is 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

Reasons for not completing this period:

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 Post-operative Narcotic Usage, measured over post operation up to 2 days.

The primary endpoint is the amount of narcotic used after the operation, measured in mg over a period described as post operation up to 2 days. It is reported as a mean for each group, with a standard deviation to describe variability among participants. This is a continuous outcome: individual observations can take a range of numerical values, rather than being limited to a yes-or-no event.

Use of narcotics is a recorded measure of post-operative medication consumption. In general, an outcome of this kind can describe how much medication participants used during a specified period. Its interpretation depends on the measurement and recording procedures, and on what medication use represents in the study context. The registry describes the endpoint as the amount of narcotic used but does not report the specific drugs included, the rules for converting use to mg, or how use was recorded.

The posted mean is a group-level summary, not an individual participant’s outcome. The standard deviation gives information about the spread of participant values around that group’s mean; it is not the standard error of the mean and is not a confidence interval. In the On-Q Catheter arm, the mean was 23.95 mg with a standard deviation of 24.32. In the Ultrasound Guided Pectoral Nerve Block arm, the mean was 6.43 mg with a standard deviation of 5.95.

The endpoint is time-bounded, but additional details about the measurement window and collection procedures are not reported in the registry record. The record also does not report an adjusted comparison or an inferential estimate for the difference between groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous measure summarized by an arithmetic mean and standard deviation for each arm. The registry reports the number of participants, mean, and standard deviation for both groups. It does not report a statistical test or an estimated contrast between the group means. The distinction between descriptive summaries and inferential analysis is central to interpreting these results.

What do the mean and standard deviation describe?

General statistical context: the mean is the arithmetic average of observed values in a group. It gives a compact description of the group’s central level, but it does not show the individual values or their pattern. The standard deviation describes how dispersed observations are around the mean. A larger standard deviation indicates greater spread on the outcome’s measurement scale. It is not the uncertainty in the mean itself, and it does not indicate whether two group means differ statistically.

For this endpoint, the registry reports the mean and standard deviation in mg for each group. The means are 23.95 and 6.43, and the standard deviations are 24.32 and 5.95, respectively. Those summaries do not show whether values were symmetric, skewed, clustered, or influenced by a small number of observations. Individual-level data or additional distributional summaries would be needed to examine those features.

What would a comparison of means add?

General statistical context: a two-group comparison of means estimates a contrast between the groups and quantifies uncertainty around that estimate. A confidence interval can indicate the range of contrasts compatible with the observed data and the analysis method. A hypothesis test can assess compatibility with a null hypothesis, under its assumptions. These methods require a defined analysis and suitable data. The registry record does not post the comparison estimate, confidence interval, or p-value for this endpoint, so the descriptive summaries cannot be substituted for those inferential results.

Different analysis methods can make different assumptions. A conventional model-based comparison may rely on features such as independent observations and an appropriate model for the outcome distribution. With small groups, checking distributional assumptions is difficult from summary statistics alone. If outcomes are strongly skewed or contain influential values, a mean-based comparison may require particular care. The record does not report distribution checks, a transformation, a robust method, or any other approach to handling such issues.

How should variability affect the reading?

General statistical context: variability describes differences among participants, while precision describes uncertainty in an estimate. The standard deviation is a measure of the former. The standard error and confidence interval are examples of measures related to the latter. A group can have a mean that appears distinct from another group while the uncertainty around the contrast remains substantial, especially when the groups are small or the observations are variable. No confidence interval or standard error for the contrast is reported in the registry record.

Over-dispersion is a general concern when observed variability is greater than a statistical model expects. If a model fails to account for excess variation, its standard errors may be too small and its confidence intervals too narrow. This is a general principle, not a finding about this trial: the registry record does not report a model or an assessment of over-dispersion. It also does not provide enough participant-level information to assess whether a particular variance model would be appropriate.

What do the sample-size illustrations represent?

General statistical context: a planning calculation estimates the number of participants that might be needed under chosen assumptions; it is not a measure of the evidence generated by a completed study. The record describes planning illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. For these illustrations, the effect to detect is a stated fraction of the observed effect. The record specifies that non-time-to-event planning quantities are expressed as participants per arm.

These assumptions describe planning illustrations, not the trial’s original design or a documented sample-size justification. No sample-size justification is reported in the registry record. A calculation based on an observed effect is especially sensitive to the estimate used as its starting point, and with only 6 participants per arm that estimate may be uncertain. Such planning quantities must not be interpreted as observed power or as evidence that the study had a particular probability of detecting an effect. The record does not provide a trial-specific design calculation that can be distinguished from those illustrations.

What is missing from the inferential record?

The registry lists no analyses for the outcome and indicates that values are missing or not estimable for a two-arm comparison of the continuous endpoint. As a result, there is no reported model specification, test statistic, confidence interval, or p-value to interpret. The record does not report whether any adjustment for baseline characteristics or other covariates was planned or performed. It also does not describe any interim analysis, stopping rule, or multiplicity adjustment.

General statistical context: a complete analysis description ordinarily identifies the analysis population, the outcome definition, the contrast of interest, the model or test, and the handling of missing data. Those details help readers assess whether the analysis corresponds to the trial question and whether its assumptions are reasonable. Most of these details are not reported in the registry record. This limits assessment of how the posted group summaries relate to the randomized comparison, but it does not change the descriptive values that are posted.

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("On-Q Catheter", "Ultrasound Guided Pectoral Nerve Block")
n   <- c(6, 6)
m   <- c(23.95, 6.43)
sp  <- c(24.32, 5.95)
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  On-Q Catheter  6  23.950  24.320  -1.572  49.472
CARM  Ultrasound Guided Pectoral Nerve Block  6  6.430  5.950  0.186  12.674

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome, post-operative narcotic usage, and two secondary outcomes: post-operative anti-emetic usage and post-operative self-reported pain scores. Results for the secondary outcomes are not reported in the registry record. The record does not report a multiplicity plan describing whether or how the analyses of multiple outcomes would be considered together. Without such a plan and without posted secondary results, the secondary outcomes cannot be used to broaden interpretation of the primary summaries.

The record lists no analyses for the continuous primary endpoint and says values are missing or not estimable for a two-arm comparison. This does not mean that the arm-level means and standard deviations are absent; those descriptive results are posted. It means that an inferential comparison is not reported. The registry does not provide an analysis population, a description of which participants contributed to each outcome summary, or a participant flow accounting for missing outcomes.

Missing-data methods, if any, are not reported in the registry record. It is not reported whether all randomized participants contributed primary-outcome data, whether any observations were excluded, or how incomplete follow-up was handled. The record also does not say whether the analysis followed an intention-to-treat principle or another population definition. These omissions prevent assessment of how missing observations or exclusions might affect the comparison.

General statistical context: missing-data handling can affect estimates if the likelihood or reason for missingness is related to outcomes or group assignment. An analysis population definition clarifies which randomized participants are included and why. These are general considerations, not claims that missing data or exclusions occurred in this trial. The registry record does not provide enough information to determine whether they did.

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.

The posted safety figures report 0 serious adverse events among 6 participants at risk in the On-Q Catheter arm and 0 among 6 at risk in the Ultrasound Guided Pectoral Nerve Block arm. Other adverse events are also reported as 0 among 6 participants at risk in each arm. Deaths are reported as 0 in both groups. No serious adverse-event terms are listed.

These counts describe events reported in the registry record; they do not show that the possibility of an adverse event is absent. With a small number of participants in each group, an event that was not observed in this trial could still occur in a larger or different group. General statistical context: when event counts are small or zero, the data provide limited precision for estimating event frequency, and a zero count should not be read as proof of zero risk.

The registry does not report the safety observation period, definitions used for serious or other adverse events, or details of event ascertainment. It is not possible to tell from the record whether the figures cover the same time window as the primary outcome. The counts should therefore be read as the posted event summaries, not as a comprehensive characterization of safety or as a comparison demonstrating a difference between the groups.

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

The registry’s primary-outcome summaries show mean post-operative narcotic usage of 23.95 mg in the On-Q Catheter arm and 6.43 mg in the Ultrasound Guided Pectoral Nerve Block arm. Each arm includes 6 participants in the posted summary. The standard deviations, 24.32 and 5.95 respectively, describe substantial variation in observed values, particularly in the catheter arm. These are descriptive results for the period from the operation through up to 2 days.

The summaries do not establish that the groups differ beyond what might be attributable to sampling variability. No inferential comparison, confidence interval, or p-value is reported, and the registry notes that a two-arm comparison of the continuous endpoint is missing or not estimable. Without an uncertainty estimate and analysis details, the size and precision of a group contrast cannot be fully assessed from the registry record.

The results also do not establish that either approach changes pain, recovery, or other outcomes. The registry lists post-operative self-reported pain scores and anti-emetic usage as secondary outcomes, but their results are not reported. Narcotic use is the primary measure described in the record; it should not be treated as interchangeable with a direct pain score or with a complete account of patient experience.

The reported safety counts show no serious adverse events, other adverse events, or deaths in either group among the participants listed as at risk. Those observations do not demonstrate that either approach is free of risk. The small groups and the absence of detail about the safety observation period and event definitions limit what can be concluded from the counts.

General statistical context: a randomized design can help make groups comparable in expectation, but a small enrolled sample may still have chance imbalances, and randomization does not remove uncertainty. The registry reports randomized allocation, but does not report the method of sequence generation, allocation concealment, or an analysis population. The terminated status is recorded, while the reason for termination is not reported. These registry entries are important context, but they do not explain why the study ended or establish that its results are biased.

In short, the posted means describe the observed groups, while the registry record does not report the inferential analysis needed to quantify the uncertainty in their comparison. No conclusion about efficacy, lack of efficacy, or comparative safety follows from these summaries alone.

14. Why This Trial Matters Statistically

This trial illustrates the distinction between reporting group summaries and reporting a statistical comparison. A mean and standard deviation for each arm can describe the observed outcome values, but they do not by themselves quantify uncertainty in the contrast between arms. For the primary endpoint, the registry posts group means and standard deviations but no comparative estimate, confidence interval, or p-value. Readers can see the descriptive pattern, but cannot assess the precision of a modeled or tested contrast from the registry record.

The small enrollment makes that distinction especially important. The reported group sizes are 6 participants each. General statistical context: small samples often produce imprecise estimates, and individual observations can have substantial influence on the mean. The displayed standard deviations also show that the observed values were not identical within either group. A formal analysis would need to communicate both the estimated contrast and its uncertainty, alongside enough detail for readers to understand the method used.

The record also highlights the value of documenting analysis populations, missing-data handling, and endpoint methods. Those details let readers distinguish an outcome summary from a prespecified analysis and judge how incomplete observations or exclusions were treated. Such information is not reported for this trial’s primary comparison. Similarly, the secondary outcomes are listed without posted results, and no multiplicity plan is reported.

Finally, a terminated status without a reported reason illustrates why enrollment and status alone should not be used to infer a study’s history. The registry reports an enrollment of 12, but not an enrollment target or the reason for termination. Statistical interpretation is strongest when descriptive results, inferential estimates, uncertainty, and study conduct are all documented. The available record offers a limited descriptive account and leaves those other elements 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 main limitation for interpretation is the absence of a reported inferential comparison for the primary continuous endpoint. The registry provides arm-level means, standard deviations, and sample sizes, but no estimate of the between-group contrast, confidence interval, p-value, or analysis method. The record also states that values are missing or not estimable for a two-arm comparison. The observed summaries therefore cannot establish the precision of the contrast.

Each arm has 6 participants. This small sample means that the group means may be sensitive to individual observations, while the posted standard deviations indicate variability within both groups. Participant-level data and distributional summaries are not reported, so the data shape and potential influence of unusual values cannot be assessed. The reason the trial was terminated is not reported in the registry record, and no intended enrollment target is given; the reported enrollment alone cannot explain the study’s completion.

Several design and conduct details are not reported in the registry record: eligibility criteria, participant characteristics, randomization sequence methods, allocation concealment, outcome recording procedures, analysis population, and missing-data handling. The record does not explain which narcotics counted toward the endpoint or how use was represented in mg. It specifies the outcome timeframe as post operation up to 2 days, but further collection details are not reported.

The registry lists two secondary outcomes but does not report their results, and it does not report a multiplicity plan. The safety summaries do not include event definitions, ascertainment methods, or a safety observation period. These gaps limit assessment of the full set of outcomes and safety reporting. They do not show that any particular procedure was or was not used; those details are simply not reported in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Comparison of Preoperative Ultrasound Guided Pectoralis Nerve Block Placement Versus Intra-operative Placement: A Prospective Randomized Trial — NCT03201809.
• Registry record last updated 2021-10-15; status last verified 2021-10.
• Results first posted 2021-10-15.
• 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 describes a randomized, parallel-group trial with no masking, comparing an On-Q Catheter arm with an Ultrasound Guided Pectoral Nerve Block arm. It lists post-operative narcotic usage in mg, from the operation through up to 2 days, as the primary outcome. The reported mean and standard deviation are 23.95 and 24.32 for the catheter arm, and 6.43 and 5.95 for the block arm; each posted arm summary includes 6 participants.

The registry lists post-operative anti-emetic usage and post-operative self-reported pain scores as secondary outcomes, but their results are not reported in the registry record. No inferential analysis of the primary outcome is posted. Safety counts report no serious or other adverse events and no deaths in either group among 6 participants at risk per group. The study is listed as terminated, with enrollment of 12; the reason for termination is not reported.