PECS II vs. MTP for Analgesia After MRM: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for PECS II vs. MTP for Analgesia After MRM (NCT06187909), a randomized na study. The primary outcome is Post-operative Pain Severity Assessed by VAS at Hour-4.

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked, parallel-group study comparing two regional block procedures for postoperative analgesia after modified radical mastectomy. It lists the study as completed and its phase as not applicable. The sponsor is Ain Shams University. The registry dates the study start to 2024-01-01 and primary completion to 2024-07-01.

The interventions were PECS II and MTP blocks, both ultrasound-guided and described as using 20 mL of 0.25% bupivacaine. The arm descriptions specify 44 female patients in each group, while the outcome summaries report 42 participants per group. The registry reports total enrollment of 88; it does not explain why the outcome summaries contain fewer participants than the arm descriptions.

The primary outcome was postoperative pain severity at hour-4, assessed with the VAS. Other listed outcomes include VAS assessments at PACU admission and several postoperative hours, time to first rescue analgesia, cumulative nalbuphine consumption in the first 24 hours, and postoperative side effects and complications. Numeric results are posted for the primary outcome and for two secondary measures. The registry record does not report the trial's detailed statistical analysis plan, masking procedures, sample-size justification, or the reason for the difference between the arm descriptions and outcome counts.

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.

Before assignment: Out of 112 screened patients, 24 were excluded (17 did not meet inclusion criteria, 7 declined participation), leaving 88 enrolled and randomly allocated to Group A (PECS II block, n=44) and Group B (MTP block, n=44). Four participants withdrew consent during follow-up, resulting in 84 completions (42 per group). All remaining participants were included in the final analysis, with no exclusions

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 Pain Severity Assessed by VAS at Hour-4, measured over will be evaluated at hour-4 postoperatively.

The primary endpoint is postoperative pain severity at hour-4, measured using the Visual Analogue Scale. The registry describes a scale from 0, meaning no pain, to 10, meaning maximum pain; a higher score represents worse pain. The endpoint is reported as a mean with a standard deviation, which gives a group average and an indication of how spread out individual scores were around that average.

Pain intensity is a continuous patient-reported measure. Comparing group means can describe how the average recorded score differed between the two randomized groups at the specified assessment time. The hour-4 assessment is one time point, not a summary of pain throughout the first postoperative day. The registry separately lists pain assessments at PACU admission and at other postoperative hours, but numeric results for those assessments are not reported in the registry record.

At hour-4, the posted mean was 1.4 in the MTP group, with a standard deviation of 0.6, and 2.2 in the PECS II group, with a standard deviation of 0.7. These summaries describe the recorded scores for the analyzed participants. They do not, on their own, establish why the scores differed or whether the same pattern occurred at other times.

7. Results Posted in the Registry

• PECS II Block Group: mean 2.20 versus 1.40 on control; difference 0.80 (95% CI 0.52 to 1.08), standardized effect d = 1.23; z-test p = <0.001.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Time of First Rescue Analgesia

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • PECS II Block Group: mean 7.90 versus 12.80 on control; difference -4.90 (95% CI -5.34 to -4.46), standardized effect d = -4.80; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for PECS II Block Group than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Cumulative Post-operative Nalbuphine Consumption in the First 24 Hours

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • PECS II Block Group: mean 13.30 versus 8.30 on control; difference 5.00 (95% CI 3.66 to 6.34), standardized effect d = 1.59; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for PECS II Block Group than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary results cover two different aspects of postoperative analgesia: the interval until first rescue analgesia and cumulative nalbuphine consumption during the first 24 hours. The reported directions align with the primary hour-4 comparison in the sense that the MTP group had a longer mean time before rescue and lower mean nalbuphine use, while its hour-4 mean VAS score was lower. Taken together, the measures describe a consistent pattern across pain scoring and analgesic use, but they remain separate outcomes with different units and interpretations.

These secondary findings add context rather than replace the primary endpoint. A pain score at a particular time is a reported assessment, whereas rescue timing and medication consumption also reflect the study's rescue-analgesia process and participant care. The registry does not report enough detail to determine how rescue treatment was triggered or whether the same decision rules were applied in both groups. The listed pain assessments at other times, and postoperative side effects and complications, do not have numeric outcome results in the registry record.

The posted secondary p-values are unadjusted. When several outcomes are examined, the chance of at least one apparently strong result can increase; adjustment or a prespecified hierarchy can address that concern, but neither is reported in the registry record. Thus, the secondary estimates are useful descriptive evidence, while their inferential strength is more limited than if multiplicity handling and the analysis plan were available.

There are no reported analyses for the other listed secondary measures in the record. The available results do not show whether every planned assessment was collected, whether any were omitted, or why numeric results are absent. This limits conclusions about the overall course of pain and the full pattern of side effects and complications. Secondary outcomes should be interpreted as supporting context for the primary comparison, not as independent proof of a broader treatment effect.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Post-operative Pain Severity Assessed by VAS on Admission to Postanesthesia Care Unit (PACU), at Hour-2, Hour-8, Hour-12, Hour-18 and Hour-24.
• Time of First Rescue Analgesia
• Cumulative Post-operative Nalbuphine Consumption in the First 24 Hours
• Incidence of Postoperative Side Effects and Complications

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports continuous outcomes as means and standard deviations. A mean gives the arithmetic average of participants' scores or measurements in a group. A standard deviation describes how dispersed individual observations are around that average. These summaries are useful for describing groups, but they do not show the full distribution, whether values were skewed, or whether particular observations strongly influenced the mean.

What does the mean difference represent?

The primary comparison is expressed as a mean difference: the PECS II group mean minus the MTP group mean. For hour-4 VAS, the posted difference is 0.8. Since a higher VAS score means worse pain, a positive difference indicates a higher average score in the PECS II group. The direction depends on the stated group order and the scale definition; it is not a statement about an individual participant's experience.

The same kind of comparison is reported for the two secondary continuous outcomes. The time-to-first-rescue comparison is a difference in average hours, and the nalbuphine comparison is a difference in average milligrams. These summaries answer different questions from the pain score and should be interpreted in their own units. A mean difference in hours cannot be directly compared in size with a mean difference in milligrams or VAS points.

What does a p-value tell the reader?

A p-value describes how compatible the observed data are with a statistical model in which there is no group difference, under the assumptions of the test. A small p-value is not the probability that the null hypothesis is true, and it does not quantify the clinical importance of the result. The primary comparison and both posted secondary comparisons have unadjusted p-values of <0.001. The registry does not report the testing procedure or any adjustment for multiple comparisons, so these values should be read as unadjusted results.

Why do confidence intervals matter?

A confidence interval gives a range of effect values compatible with the data under the method used to calculate it. It conveys uncertainty around the estimated difference and is usually more informative than a p-value alone. The primary interval is entirely above zero, consistent with the positive posted mean difference. The secondary intervals are also reported as excluding zero. The registry record does not state the confidence level or provide a detailed description of the interval method.

What is standardized effect size?

A standardized effect size expresses a mean difference relative to a pooled measure of variation, rather than in the original units. This can help compare effects measured on different scales, but it depends on the variability in the study population and does not replace the original-unit result. The posted primary standardized effect is 1.227. Its interpretation should be cautious because the registry does not report a prespecified target effect or a clinical threshold for the VAS.

What assumptions underlie these summaries?

General statistical interpretation of means and mean differences relies on considering the outcome distribution and the analysis assumptions. For example, a mean can be sensitive to unusually high or low observations, and a standard deviation may not describe a skewed distribution well. The registry does not report diagnostic checks, transformations, covariate adjustment, or an alternative analysis. Those methods should not be inferred from the presence of means, standard deviations, p-values, or intervals.

The randomized parallel design supports comparison between assigned groups, but the registry record does not specify the analysis population or explain how deviations from assigned treatment were handled. It also does not report the treatment of missing measurements. These details can affect the meaning of a group comparison, particularly when the enrollment and outcome counts differ.

11. Confidence Intervals and Precision

The primary mean difference is 0.8 VAS points, with the PECS II group having the higher reported mean. Its confidence interval lies entirely above zero. This indicates that the posted interval does not include no mean difference, while still allowing a range of plausible positive differences. The registry reports an unadjusted p-value of <0.001. The lower endpoint is recorded to more than three decimal places, so the exact endpoint is not reproduced.

A confidence interval describes statistical uncertainty under the method used to construct it; it does not capture every source of uncertainty. It cannot account for unreported missing-data decisions, measurement issues, or limitations in the study's design and reporting. The registry record does not state the confidence level or the precise interval method, so interpretation is limited to the posted endpoints and their relation to zero.

The posted secondary intervals also exclude zero: the difference in time to first rescue analgesia is -4.9 hours, with interval endpoints -5.336 and -4.464; the difference in cumulative nalbuphine consumption is 5.0 milligrams, with endpoints 3.657 and 6.343. The direction of each difference depends on the comparison order, PECS II relative to MTP. These intervals express statistical precision for each separate outcome, not certainty that the observed contrast will recur in another population or setting.

Precision is distinct from clinical importance. The registry does not identify a minimum clinically important difference for the VAS, a threshold for rescue timing, or a clinically meaningful difference in nalbuphine consumption. The interval can therefore describe uncertainty in the statistical estimate, but the record does not establish what range of values would matter clinically.

12. 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 illustrations use the observed effect as a reference and show participant counts for assumed fractions of that effect. For these continuous outcomes, the displayed figures are participants per arm, not total participants or total events. The registry's general planning 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 the stated fraction of the observed effect. The original trial's own design assumptions and sample-size justification are not reported in the registry record.

The 80% power column describes the number of participants per arm that the planning calculation estimates would be needed for an 80% chance of detecting the assumed effect under those assumptions. The 90% power column gives the corresponding planning count for a 90% chance. Higher target power generally requires more participants for the same assumed effect. The rows use 100%, 75%, and 50% of the observed effect; as the assumed effect gets smaller, the planning counts increase.

These are prospective planning illustrations based on the observed study effect, not observed power. They do not tell whether the completed trial had a particular probability of detecting an effect, and they should not be interpreted as evidence that the original design was adequate or inadequate. The registry record does not report the assumptions used when the trial was designed, nor whether any sample-size target was revised.

The registry's general note distinguishes continuous outcomes from time-to-event planning: time-to-event figures are total event counts, while other figures are participants per arm. The posted outcomes are continuous measures, so their planning figures are per arm. Planning counts depend on the assumed effect and stated assumptions; they are not observations from the trial.

13. 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 = 0.800; pooled standard deviation σ = 0.652.
2. n = 2 × (1.96 + 0.842)² × 0.652² / 0.800² = 10.4, rounded up to 11 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 <- 0.8                      # observed difference in means
sigma <- 0.651920240520265                     # 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(6187909)
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 = 11 (80% power), 14 (90% power)
 75% of observed effect: n per arm = 19 (80% power), 25 (90% power)
 50% of observed effect: n per arm = 42 (80% power), 56 (90% power)
power.t.test: 11.5 
Simulated power at n = 11 per arm: 0.781 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists several outcomes: the primary hour-4 VAS score, pain assessments at other postoperative times, time to first rescue analgesia, cumulative nalbuphine consumption, and side effects and complications. Considering multiple outcomes creates a multiplicity issue: even when no underlying group differences exist, testing many outcomes can increase the chance of at least one small p-value. The record does not report a multiplicity adjustment, a prespecified testing hierarchy, or a plan identifying which secondary comparisons were confirmatory.

The posted p-values for the primary and two secondary continuous outcomes are unadjusted. The registry record does not say whether these outcomes were selected for reporting before results were known, how the other listed outcomes were analyzed, or why numeric results are not posted for all listed measures. The absence of reported details means the unadjusted p-values cannot be treated as though they were corrected for the number of comparisons.

Missing-data methods are also not reported in the registry record. The study lists enrollment of 88 and arm descriptions of 44 participants per group, whereas the primary outcome summaries show 42 per group. The record does not explain whether the difference reflects unavailable measurements, exclusions, or another reason. It does not identify an intention-to-treat, per-protocol, or other analysis population, and it does not describe imputation or sensitivity analyses.

These omissions do not change the posted numerical summaries, but they limit assessment of how complete and robust the comparisons are. Randomization is a design feature; it does not by itself clarify how missing observations or deviations after randomization were handled. A reader cannot determine from the registry record whether the outcome analyses retained the balance created by assignment or whether alternative handling of missing data would change the estimates.

15. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: pneumothorax (2.4%).

The registry reports serious adverse events in 1 of 42 participants in the MTP group and 0 of 42 in the PECS II group. It reports no deaths in either group. The record also lists pneumothorax at 2.4% among the top serious-event terms, but the posted summary does not identify the group associated with that term. These counts are descriptive and do not establish that a block caused or prevented an event.

Other adverse events are reported for 12 of 42 participants in the MTP group and 23 of 42 in the PECS II group. The registry does not provide further event definitions, severity categories for these other events, or an explanation of how they were collected. The counts should therefore be read as the registry's reported group totals, not as a complete characterization of risk.

With these group sizes, rare events may be represented by very few observations. The figures do not establish that an unreported event did not occur, nor do they provide a precise estimate of comparative safety. The registry record does not report a detailed safety analysis or causal assessment.

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

The posted primary result describes a higher mean VAS score at hour-4 in the PECS II group than in the MTP group. The mean difference is 0.8 points, and the interval lies above zero. This is a statistical description of the analyzed groups at a specified assessment time. It is not, by itself, proof that the observed difference was caused by the block assignment or that it applies beyond the participants and procedures represented in the record.

The result does not establish the clinical importance of the difference. The registry explains the scale's direction but does not provide a threshold for a meaningful change in VAS score. Nor does the primary endpoint represent pain across the entire postoperative period. The registry lists additional pain time points, but numeric results for those assessments are not reported in the registry record.

The secondary summaries offer related information about rescue analgesia and nalbuphine use, but they do not eliminate uncertainty about the primary comparison. They are unadjusted, the record does not describe a multiplicity plan, and details about rescue criteria are not reported. The registry also does not explain the difference between total enrollment, arm descriptions, and the outcome-summary counts.

Statistical significance should not be confused with certainty, clinical value, or a recommendation for care. The confidence interval characterizes uncertainty in the estimated mean difference under its calculation method, while other uncertainties remain because key analysis and reporting details are absent. The available record supports a cautious account of what was measured and reported, not a broader claim about all patients undergoing mastectomy or about other settings.

The results describe two specific ultrasound-guided procedures with the stated bupivacaine regimens in female patients scheduled for modified radical mastectomy. They do not establish how different doses, techniques, patient groups, or postoperative protocols would compare. Those questions are not answered by the registry results.

17. Why This Trial Matters Statistically

This trial is statistically useful because it reports a randomized, parallel-group comparison with a continuous primary endpoint and group summaries in the original VAS units. Readers can see the observed means, standard deviations, mean difference, interval, and unadjusted p-value. Reporting the effect in the scale's own units helps keep the comparison connected to what was measured rather than relying only on a significance test.

The record also illustrates why several pieces of information are needed to interpret a trial result. A p-value alone does not convey the size or precision of a difference; the mean difference and interval add that context. Secondary outcomes provide additional perspectives, while multiple comparisons make unadjusted inferences more tentative. Safety counts likewise require careful interpretation because small event counts and limited detail constrain what they can establish.

At the same time, the registry record leaves important questions unanswered. It does not describe the analysis plan, missing-data methods, analysis populations, multiplicity handling, or the original sample-size rationale. The outcome summaries also contain fewer participants per group than the arm descriptions, with no explanation. These details are relevant to judging completeness and robustness, not merely administrative background.

For statistical education, the record shows the distinction between observed estimates and planning illustrations. The planning calculations use fractions of the observed effect under stated assumptions; they are not the original design justification or a measure of the completed trial's power. Keeping those interpretations separate prevents a common misreading of post-study planning calculations.

18. 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.

A key reporting limitation is the difference between the registry's total enrollment of 88 and the 42 participants per group in the posted primary outcome summaries. The arm descriptions specify 44 patients in each group. The record does not explain how these counts relate, whether any participants lacked outcome measurements, or how the analyzed groups were defined. Attrition or exclusions should not be inferred from these counts alone.

The registry does not report the statistical analysis plan, the method used to calculate intervals, the confidence level, or whether any covariates were included. It does not specify the analysis population, missing-data handling, or sensitivity analyses. The primary result is therefore interpretable as a posted unadjusted group comparison, but its robustness to alternative analytic decisions cannot be assessed from the record.

Multiplicity is another limitation. Several outcomes and assessment times are listed, but adjustment methods or a hierarchy of testing are not reported. Numeric results are posted for the primary endpoint and two secondary measures, while results for other listed outcomes are not reported in the registry record. This leaves uncertainty about the completeness of outcome reporting and the role of each comparison.

The trial is described as single-masked, but the record does not state who was masked or how masking was maintained. It also does not detail the rescue-analgesia criteria, which may be relevant to interpreting time to first rescue and medication consumption. Finally, the record does not provide a clinical threshold for an important VAS difference or details that would establish how representative the results are of settings beyond the stated population and procedures.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: PECS II vs. MTP for Analgesia After MRM — NCT06187909.
• Registry record last updated 2026-01-21; status last verified 2026-01.
• Results first posted 2025-08-13.
• 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.

22. Record Summary

The registry record describes a completed randomized, single-masked, parallel-group study sponsored by Ain Shams University. It compares ultrasound-guided PECS II and MTP blocks for postoperative analgesia in female patients undergoing modified radical mastectomy. The study start is recorded as 2024-01-01, primary completion as 2024-07-01, and total enrollment as 88.

The primary outcome is VAS pain severity at hour-4. The posted mean was 1.4 in the MTP group and 2.2 in the PECS II group, with a mean difference of 0.8 and an unadjusted p-value of <0.001. The outcome summaries include 42 participants per group. Numeric secondary results are posted for time to first rescue analgesia and cumulative nalbuphine consumption; results for other listed outcomes are not reported in the registry record.

The record does not report the original sample-size justification, detailed statistical plan, missing-data approach, analysis population, or multiplicity handling. The difference between enrollment, arm descriptions, and outcome counts is not explained.