Efficacy of Preoperative Pectoral Nerve Block for Intraoperative Opioid Sparing Effect and Postoperative Analgesia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy of Preoperative Pectoral Nerve Block for Intraoperative Opioid Sparing Effect and Postoperative Analgesia (NCT03210220), a randomized na study. The primary outcome is Intraoperative Remifentanil Consumption.

2. Clinical Question

This randomized, parallel-group trial addresses an intraoperative opioid-consumption endpoint in the setting of breast cancer surgery. Its stated purpose also mentions postoperative pain, but the registry record lists one outcome measure, intraoperative remifentanil consumption, and no posted secondary outcomes. The primary question should therefore be read narrowly: it concerns the recorded mean amount of remifentanil per kilogram per hour during surgery, not a complete assessment of postoperative pain, recovery, or other clinical outcomes.

The intervention description specifies the timing and technique of the block, while the comparator description specifies no block. Those details define the contrast represented in the posted result. They do not, by themselves, describe all co-interventions or perioperative management, which are not reported in the registry record. The outcome is a continuous measure summarized by a mean and standard deviation in each group. Its interpretation depends on the units, observation period, group summaries, and uncertainty around the estimated difference—not only on whether a statistical test crosses a threshold.

3. Trial Design

The registry record describes NCT03210220 as a randomized, quadruple-masked, parallel-group trial with an enrollment of 40. Its status is completed. The condition is breast cancer, and the intervention is a Pecs II block. The listed sponsor is Gachon University Gil Medical Center. The record lists the phase as not applicable.

Participants in the Pecs Group were assigned an ultrasound-guided pectoral nerve block after induction and before surgery. The procedural description states that the needle was advanced into the tissue plane between the pectoralis major and pectoralis minor muscles, near the pectoral branch of the acromiothoracic artery, and that 10 mL of 0.5% ropivacaine was deposited. The Control Group description says there was no block. The registry record does not report further details about anesthetic protocols, other perioperative treatments, or whether the control group received a sham procedure.

The primary outcome is intraoperative remifentanil consumption over the whole intraoperative period, expressed in μg/kg/h. Results are reported as group means and standard deviations. The Pecs Group has a reported group size of 19, mean of 6.75, and standard deviation of 2.18. The Control Group has a reported group size of 20, mean of 10.12, and standard deviation of 3.68. These are the group summaries relevant to the posted continuous outcome.

Although the masking level is recorded as quadruple, the identities of the masked roles and the practical masking procedures are not reported in the registry record. The method used to generate the random sequence, how allocation was concealed, and the handling of withdrawals or missing outcome measurements are also not reported in the registry record. The record lists one outcome measure and no analyses. It does not report a detailed statistical analysis plan or the trial’s original sample-size assumptions.

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 Intraoperative Remifentanil Consumption, measured over whole intraoperative period.

The primary endpoint is intraoperative remifentanil consumption during the whole intraoperative period, expressed in μg/kg/h. Remifentanil is an opioid, and the endpoint quantifies its recorded consumption relative to body weight and time during surgery. The registry record’s stated purpose includes assessing intraoperative opioid consumption; this endpoint gives that question a measurable continuous outcome.

For a continuous measure, a group mean describes the average value in that group, while the standard deviation describes how dispersed individual values are around that mean. The posted summaries give a mean of 6.75 with a standard deviation of 2.18 in the Pecs Group, and a mean of 10.12 with a standard deviation of 3.68 in the Control Group. The reported mean difference is -3.37 μg/kg/h, with a 95% confidence interval from -5.257 to -1.483.

General: a rate-like measure in consistent units can make group averages easier to compare when participants differ in body weight or the duration of observation. The interpretation still depends on how the measure was recorded and whether the groups were managed comparably. The registry record does not describe the measurement procedures in detail. The endpoint does not directly measure postoperative pain, and no secondary outcome results are posted in the registry record. It should therefore be interpreted as a finding about intraoperative remifentanil consumption, rather than as a comprehensive measure of analgesia or overall recovery.

7. Results Posted in the Registry

• Pecs Group: mean 6.75 versus 10.12 on control; difference -3.37 (95% CI -5.26 to -1.48), standardized effect d = -1.11; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous, so its reported summaries are group means and standard deviations. The comparison is stated as a mean difference between the Pecs Group and Control Group. The mean difference is -3.37 μg/kg/h, with a 95% confidence interval from -5.257 to -1.483. The calculation is unadjusted and uses the posted group summaries. The registry record does not report an adjusted analysis or a more detailed statistical analysis plan.

What does a mean difference represent?

A mean difference expresses the contrast between two group averages in the original measurement units. Here the units are μg/kg/h, so the estimate can be read directly against the endpoint. Its negative direction reflects a lower reported mean in the Pecs Group than in the Control Group. This is different from a ratio or percentage contrast; neither is reported in the registry record. A mean difference also does not imply that each participant’s value changed by that amount. It summarizes the group-level contrast.

The standard deviations describe the spread of observations within each group. The Pecs Group standard deviation is 2.18, and the Control Group standard deviation is 3.68. Standard deviation is not the same as the uncertainty in a group mean or the uncertainty in the difference between means. The latter also depends on group sizes and the method used to estimate the comparison. Participant-level distributions are not reported in the registry record, so the summaries cannot reveal skewness, clusters, or extreme observations.

How should the confidence interval be read?

General: a confidence interval is a range of values compatible with the observed data and the assumptions of the method used to calculate it. It conveys uncertainty around an estimate, rather than giving a guarantee that the true effect lies within the particular reported range. The interval from -5.257 to -1.483 is expressed in the same units as the mean difference. Since both endpoints are negative, the interval indicates that the unadjusted estimate is consistently in the direction of a lower mean for the Pecs Group within this interval.

The width of an interval is affected by the amount of information in the data and by variability. A narrower interval generally indicates greater precision than a wider interval, all else being equal. General: greater variation tends to make estimates less precise when sample size and other features are held constant. The registry record reports group standard deviations and group sizes, but does not provide participant-level records, missingness details, or diagnostics that would allow independent assessment of distributional assumptions.

What does the p-value add?

The reported unadjusted p-value is <0.001. General: a p-value measures how incompatible the observed data, or more extreme data, are with a specified null model, assuming the model’s assumptions hold. It is not the probability that the null hypothesis is correct, and it is not a measure of the treatment effect’s size. The p-value should be considered alongside the estimated difference and its confidence interval, not as a standalone conclusion.

The record does not report the exact test used to produce the p-value or a complete inferential analysis plan. It is therefore not appropriate to assign a specific test, transformation, or adjustment procedure to the result beyond what is stated. The result is identified as unadjusted, and no adjustment for multiple outcomes or comparisons is reported. Because the registry lists one outcome measure and no analyses, it is not possible to establish from the record whether additional analyses were planned or conducted but not posted.

Why can over-dispersion matter?

General: over-dispersion occurs when observed variability is greater than a model expects. If a method assumes less variation than is present, uncertainty may be understated and statistical evidence may look stronger than warranted. For a continuous outcome, assessing distributional form and variance assumptions can matter when selecting or checking a method. The registry record does not report a model diagnostic, a formal assessment of variance assumptions, or evidence that over-dispersion was assessed. The term is a general statistical consideration, not a reported feature of this trial.

More generally, results from randomized trials depend on the quality of assignment and outcome measurement, appropriate handling of missing data, and faithful reporting of prespecified analyses. The registry record identifies randomization and quadruple masking, but does not report the random-sequence method, concealment, identities of masked roles, or analysis population. It also does not describe missing-data handling or an intention-to-treat analysis. Those omissions limit what can be concluded about the analysis process; they do not change the values reported for the endpoint.

10. Confidence Intervals and Precision

The estimated mean difference is -3.37 μg/kg/h, and its 95% confidence interval runs from -5.257 to -1.483. The interval retains the negative direction across its reported endpoints, so the uncertainty range is compatible with a lower average remifentanil consumption in the Pecs Group for the primary outcome. Its endpoints also show that the estimate is not known with exact precision: a range of differences remains compatible with the calculation.

General: precision describes how tightly an estimate is determined by the data and the statistical method. A confidence interval communicates this by showing a range of plausible values under the method’s assumptions. It does not express the probability that a particular value inside the interval is correct, and it does not include every potential source of error, such as selection, measurement, or reporting bias. The interval should be interpreted together with the design and reporting limitations.

The group summaries include standard deviations of 2.18 for the Pecs Group and 3.68 for the Control Group, with reported group sizes of 19 and 20, respectively. These features contribute to the uncertainty of a mean difference, but a reader cannot assess the raw distributions or missing observations from the summaries alone. The registry record does not report a separate adjusted confidence interval, an interval for a secondary endpoint, or a prespecified threshold for a clinically important difference.

The confidence interval and the unadjusted p-value (<0.001) address statistical uncertainty under the calculation used. They do not answer whether the size of the difference is important in clinical practice, nor do they establish precision for postoperative pain or other outcomes that are not posted. General: the practical interpretation of an interval depends on whether its full range would lead to meaningfully different conclusions. The registry record does not define a clinical benchmark for this endpoint, so that judgment cannot be made from the record alone.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. The registry record describes this as a planning illustration based on the observed effect, rather than the trial’s own original design calculation. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is specified as a fraction of the observed effect. The original trial design assumptions are not reported in the registry record.

For planning to detect 100% of the observed effect, the illustration gives 13 participants per arm for 80% power and 18 participants per arm for 90% power. For 75% of the observed effect, it gives 23 participants per arm for 80% power and 31 participants per arm for 90% power. For 50% of the observed effect, it gives 52 participants per arm for 80% power and 69 participants per arm for 90% power.

General: power is the probability that a statistical procedure will reject its null hypothesis when a specified effect is true, under the assumptions used for planning. The 80% and 90% columns represent two different target probabilities for detecting the stated effect under those planning assumptions. A higher target power requires more participants per arm when the other assumptions are held fixed. Smaller effects need more participants because they are harder to distinguish from random variation.

These values are planning illustrations, not observed power. They are based on the observed effect and the listed assumptions; they do not establish what assumptions guided the trial’s original design. The illustration is also not a guarantee that a future study with those group sizes would achieve the target power, since results depend on whether the assumed effect and variability are appropriate.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -3.370; pooled standard deviation σ = 3.044.
2. n = 2 × (1.96 + 0.842)² × 3.044² / -3.370² = 12.8, rounded up to 13 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -3.37                      # observed difference in means
sigma <- 3.04404070008661                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(3210220)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 13 (80% power), 18 (90% power)
 75% of observed effect: n per arm = 23 (80% power), 31 (90% power)
 50% of observed effect: n per arm = 52 (80% power), 69 (90% power)
power.t.test: 13.8 
Simulated power at n = 13 per arm: 0.776 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure: intraoperative remifentanil consumption during the whole intraoperative period. It lists no analyses and no posted secondary outcomes. This makes it possible to identify the primary endpoint reported in the record, but does not establish that no other outcomes or analyses were considered during the conduct of the trial. Whether the endpoint and analysis were prespecified in a protocol or statistical analysis plan is not reported in the registry record.

Multiplicity arises when multiple statistical tests are performed and affects the interpretation of the chance of false-positive findings across a family of tests. General: when more tests are conducted, the chance that at least one appears statistically significant by chance can increase, unless the analysis plan addresses that issue. The registry record does not report a multiplicity adjustment, a hierarchy of outcomes, or a family of comparisons. The single posted outcome does not allow a determination of whether multiplicity was relevant to analyses that may not be listed.

The analysis population is not reported in the registry record. The record does not say whether all randomized participants were analyzed according to their assigned groups, whether exclusions occurred, or whether the reported group sizes reflect all randomized participants with available outcome data. Missing-data methods, numbers of missing outcome values, and reasons for missingness are also not reported. These details matter because exclusions and missing observations can alter how representative the analyzed group summaries are of the randomized groups.

The registry identifies the trial as randomized and quadruple-masked, but does not report the sequence-generation method, allocation concealment procedures, or which roles were masked. It also does not give a detailed statistical analysis plan or explain whether the analysis was adjusted for any baseline characteristics. The reported comparison is unadjusted. These reporting gaps limit assessment of selective analysis, attrition, and implementation of the design; they do not establish that any such problem occurred.

Because postoperative pain is mentioned in the study purpose but no secondary outcome result is posted, no statistical conclusion about postoperative pain can be drawn from this record. The absence of posted secondary results should be distinguished from evidence that an outcome was measured and found to have no effect. The registry record does not report a result for that question.

14. 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 serious adverse event figures report zero serious adverse events among 19 participants at risk in the Pecs Group and zero among 20 participants at risk in the Control Group. The record also reports zero other adverse events in both groups, with 19 and 20 participants at risk, respectively. Deaths are recorded as zero in each group. No serious adverse event terms are listed.

These figures describe what is recorded for the stated at-risk groups. They are not evidence that adverse events are impossible, nor do they establish that the interventions have equivalent safety. General: a record of zero events can be informative about the observed trial experience, but limited group size and observation periods can restrict how much it can reveal about uncommon events. The registry record does not specify the adverse-event observation window, severity definitions beyond the serious category, or the method used to collect events.

The figures should be read separately from the primary efficacy endpoint. They do not change the mean difference in remifentanil consumption, and the primary endpoint does not summarize safety. The record does not provide event narratives, timing, or further safety analysis. No rates or comparisons beyond the counts are reported.

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

The posted results show a lower mean intraoperative remifentanil consumption in the Pecs Group than in the Control Group for the single primary outcome listed in the registry record. The estimated mean difference is -3.37 μg/kg/h, and the 95% confidence interval is -5.257 to -1.483. The unadjusted p-value is <0.001. Together, these statistics describe the observed group contrast and its uncertainty under the calculation used.

The finding is limited to intraoperative remifentanil consumption during the whole intraoperative period. The record’s broader purpose mentions postoperative pain, but no secondary results are posted. The result therefore does not establish an effect on postoperative pain, recovery, total opioid use outside the measured period, or other clinical outcomes. It also does not identify how the intervention may have influenced the measured outcome.

General: a statistically clear contrast does not, by itself, establish clinical importance. The registry record does not report a threshold for a clinically important difference in μg/kg/h. The reported difference should therefore be understood in its measurement units without labeling it clinically meaningful or unimportant.

The record describes randomized allocation, a parallel-group model, and quadruple masking. However, it does not report how randomization and masking were implemented, who was masked, how missing data were handled, or which analysis population was used. These omissions leave uncertainty about aspects of trial conduct and analysis. The reported result should not be treated as a guarantee that the same contrast would occur in a different setting or population.

The safety record lists zero serious adverse events and zero other adverse events in each group, as well as zero deaths. These are observed counts in the recorded at-risk groups; they do not establish that no adverse events can occur or characterize rare events. Overall, the registry record supports a focused statistical reading of one intraoperative outcome, while leaving important questions about other outcomes, analysis details, clinical importance, and broader applicability unresolved.

16. Why This Trial Matters Statistically

This trial is statistically informative because its primary endpoint is a continuous measure with group means, standard deviations, and an estimated mean difference. That makes the direction and size of the reported contrast interpretable in the outcome’s own units. The confidence interval adds information beyond the p-value by describing the range of differences compatible with the unadjusted calculation.

The reported means are 6.75 in the Pecs Group and 10.12 in the Control Group, and the reported mean difference is -3.37 μg/kg/h. Its 95% confidence interval, from -5.257 to -1.483, stays on the negative side of zero. This lets readers distinguish the direction of the estimate from its precision. The unadjusted p-value (<0.001) adds a test-based measure of compatibility with a zero-difference model, but it does not establish clinical importance or replace interpretation of the interval.

The trial also illustrates why statistical conclusions must remain tied to the endpoint actually reported. The registry record’s purpose refers to postoperative analgesia, but it posts only intraoperative remifentanil consumption as an outcome measure. A result for opioid consumption cannot substitute for a result on postoperative pain, and the absence of a posted secondary result is not evidence of no effect.

Finally, several elements needed to audit the analysis are not reported in the registry record, including the exact statistical test, missing-data handling, analysis population, and detailed randomization and masking procedures. These gaps make transparent reporting important: an effect estimate is most useful when readers can evaluate how the data were collected, which participants were analyzed, and how the analysis was selected. The posted numbers allow a clear description of the primary comparison, while the record leaves those broader assessment questions open.

17. 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 limited detail about trial conduct and analysis. It identifies randomized allocation and quadruple masking, but does not report the sequence-generation method, allocation concealment, or the roles that were masked. The practical masking procedures are also not described. These missing details limit assessment of whether the reported design features were implemented in a way that could reduce bias.

The primary outcome is reported with group means and standard deviations, but the record does not provide participant-level data, distributional summaries, or diagnostic checks. The exact statistical test and a detailed analysis plan are not reported. The analysis population, missing outcome values, exclusions, and missing-data handling are also not reported in the registry record. The posted group sizes are 19 for the Pecs Group and 20 for the Control Group; the record does not explain how those analyzed group sizes relate to the enrolled population.

The registry lists one outcome measure and no analyses, and no secondary outcomes are posted. Although postoperative pain appears in the study purpose, no postoperative pain result is available in the registry record. The record also does not report a clinical-importance threshold for the primary endpoint, so the practical significance of the estimated difference cannot be judged against a stated benchmark.

Finally, the sample-size illustration is based on the observed effect and stated planning assumptions, not the trial’s original design. The original sample-size justification and design assumptions are not reported in the registry record. The safety record reports zero events in the recorded groups, but the adverse-event observation window and collection procedures are not described. These limitations concern reporting and interpretation; they do not establish that any particular bias or protocol deviation occurred.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Efficacy of Preoperative Pectoral Nerve Block for Intraoperative Opioid Sparing Effect and Postoperative Analgesia — NCT03210220.
• Registry record last updated 2019-11-18; status last verified 2019-10.
• Results first posted 2019-11-18.
• 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.

21. Record Summary

NCT03210220 is a completed randomized, quadruple-masked, parallel-group trial concerning patients undergoing surgery for breast cancer. The Pecs Group received an ultrasound-guided Pecs II block after induction and before surgery; the Control Group received no block. The registry lists an enrollment of 40 and one primary outcome measure.

The primary outcome is intraoperative remifentanil consumption during the whole intraoperative period, measured in μg/kg/h. The Pecs Group mean is 6.75 with a standard deviation of 2.18; the Control Group mean is 10.12 with a standard deviation of 3.68. The reported mean difference is -3.37, with a 95% confidence interval from -5.257 to -1.483 and an unadjusted p-value of <0.001.

The record reports zero serious adverse events, other adverse events, and deaths in each group. No secondary outcomes or analyses are posted. Details of the statistical analysis plan, analysis population, missing-data handling, and several design procedures are not reported in the registry record.