Trial Comparing Transversus Abdominis Plane Block Versus Epidural Anesthesia for Pain Management in Colorectal Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trial Comparing Transversus Abdominis Plane Block Versus Epidural Anesthesia for Pain Management in Colorectal Surgery (NCT02591407), a randomized na study. The primary outcome is Post-operative Mean Numeric Pain Scale..

2. Clinical Question

The endpoint is a patient-reported pain score on a scale where zero means “no pain” and 10 means “the worst pain imaginable.” The reported comparison is between group means, rather than a comparison of each postoperative day as a separate primary result. The observed arm means were 2.32 for TAP Block- Exparel and 2.12 for Continuous Epidural Analgesia. The posted mean difference, defined as TAP block minus epidural, was 0.2 units on the scale.

The registry record describes the study as a prospective randomized clinical trial in elective colorectal surgery, with perioperative pain management in an enhanced recovery pathway as its context. It does not report a threshold for a clinically important difference in this score. The comparison therefore addresses the observed average scores and their statistical uncertainty; by itself, it does not establish whether a difference of a particular size would matter to patients or clinicians.

3. Trial Design

The registry record identifies this as a completed, randomized, parallel-group trial with no masking. The listed interventions are TAP Block and Continuous Epidural Analgesia. The TAP arm is described as a transversus abdominis plane block utilizing Exparel, while the other arm is described as continuous epidural analgesia. The record lists an enrollment of 200 and identifies Trinity Health Michigan as the sponsor.

The listed conditions are colon cancer, rectal cancer, and colonic diverticulosis. The stated setting is elective colorectal surgery, and the trial’s stated purpose is to compare pain management approaches in the context of an enhanced recovery pathway. The registry record gives a start date of 2016-01-12, a primary completion date of 2017-12-31, and a status of COMPLETED. These record details describe the registered study; they do not provide additional information about how participants moved through the trial.

The primary outcome is the mean Numeric Pain Scale score, with measurements on postoperative days 0, 1, 2, and 3 averaged into one value. The posted primary outcome includes 87 participants in the Continuous Epidural Analgesia arm and 92 in the TAP Block- Exparel arm. The registry record does not report why these outcome counts differ from the enrollment figure, how many participants were randomized to each arm, or how missing outcome observations were handled.

The record lists five secondary outcome descriptions concerning patient use of narcotic analgesia on postoperative days 0 through 3; postoperative day 0 appears twice in the listed descriptions. It also lists seven outcome measures overall. The registry record does not report the trial’s original sample-size justification, the intended allocation ratio, or further operational details such as the timing and conduct of randomization. No masking was used, so the study is identified as open-label in its design information.

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.

Randomization

Reasons for not completing this period:

Follow-up

Reasons for not completing this period:

Analysis

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 Mean Numeric Pain Scale., measured over Post-operative day 0,1,2,3.

The primary endpoint is the postoperative mean Numeric Pain Scale score. Patients completed the Numeric Pain Scale on postoperative days 0, 1, 2, and 3, and those specified time-point data were averaged into a single value. Thus, the posted primary result describes an average across the listed postoperative period rather than separate primary comparisons for each day.

The scale runs from zero, meaning “no pain,” to 10, meaning “the worst pain imaginable.” It is a patient-completed pain screening tool intended to assess pain severity at that moment in time. Averaging observations across the specified days gives a single continuous outcome for each participant, which can then be summarized by a group mean and standard deviation. The posted arm means are 2.12 for Continuous Epidural Analgesia and 2.32 for TAP Block- Exparel; each arm has a reported standard deviation of 1.44.

As a general statistical point, a continuous score preserves gradations in reported pain rather than reducing responses to categories. Its mean gives a measure of the group’s average score, while the standard deviation describes how spread out participant scores are around that average. These summaries do not show the full distribution of individual scores or whether the average difference is important to patients. The registry record does not report a clinically important difference threshold for this outcome, nor does it describe how the four measurements were combined if a participant missed one or more days.

7. Results Posted in the Registry

• TAP Block- Exparel: mean 2.32 versus 2.12 on control; difference 0.20 (95% CI -0.22 to 0.62), standardized effect d = 0.14; z-test p = 0.353.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous: each participant contributes a Numeric Pain Scale value averaged across postoperative days 0, 1, 2, and 3. The posted summary reports a mean and standard deviation for each randomized arm. A mean difference is a natural summary for comparing group averages on the same scale. The reported contrast is TAP Block- Exparel minus Continuous Epidural Analgesia, so a positive value means the posted mean was higher in the TAP arm.

As a general statistical explanation, the standard deviation describes variability among participant scores, while the standard error describes uncertainty in an estimated quantity such as a group mean. A mean difference’s standard error reflects uncertainty from both arms. The registry record gives arm standard deviations of 1.44 and reports a confidence interval and an unadjusted p-value for the mean difference. It does not describe the precise inferential procedure used to calculate those results.

A confidence interval is a range of values compatible with the observed data under the assumptions of the analysis. It communicates the precision of an estimate more directly than a p-value alone. The interval for the posted mean difference crosses zero, so the data do not rule out a zero difference at the interval’s corresponding confidence level. The registry record does not state the confidence level in the outcome record, so no particular confidence level should be inferred from the interval alone.

The reported p-value is unadjusted. In general, a p-value describes how unusual data at least as inconsistent with a null hypothesis would be under that hypothesis and the model assumptions. It is not the probability that the null hypothesis is true, nor does it quantify the clinical importance of an effect. Because the result is identified as unadjusted, it should not be described as accounting for multiple comparisons. The registry record does not report a multiplicity procedure or a hierarchy of confirmatory tests.

Why can repeated measurements matter?

General statistical context: measurements from the same participant over time are usually related rather than independent. Averaging the listed daily scores into one participant-level outcome is one way to create a single summary for a group comparison. That summary does not reveal the day-specific pattern or estimate whether the treatment contrast changes across days. The registry record states that the four time points were averaged, but does not provide details about incomplete daily records, weighting of time points, or any alternative longitudinal analysis.

What does over-dispersion mean?

General statistical context: over-dispersion occurs when the observed variation is greater than a statistical model expects. It can make standard errors too small if the model does not allow enough variability. The posted primary endpoint is a continuous score and the registry record does not report an over-dispersion assessment or model-based adjustment. The arm standard deviations provide descriptive information about variability, but do not by themselves establish whether any fitted model was well calibrated.

What can be said about the analysis population?

The posted primary outcome has 87 participants in the epidural arm and 92 in the TAP arm. The registry record gives overall enrollment as 200 but does not explain the relationship between enrollment and the outcome counts. It does not report whether the primary analysis followed intention-to-treat principles, whether participants were analyzed as randomized, or whether any participants were excluded after randomization. Those details are important for evaluating how the randomized comparison was preserved in the analysis.

The registry record lists seven outcome measures and five secondary outcome descriptions. It does not report analysis details for those secondary outcomes in the registry record, and it lists zero analyses. The primary summary statistics and comparison are nevertheless posted. No detailed statistical analysis plan, covariate adjustment, interim analysis, or handling of protocol deviations is reported in the registry record. These absences mean that the posted summaries cannot establish whether the analysis was prespecified or whether all planned analyses are represented.

What does the sample-size illustration assume?

The planning illustration uses the observed effect as its reference and considers the stated fractions of that effect. Its stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. These are assumptions for the planning illustration, not evidence about the trial’s original design. The registry record does not report the original sample-size justification or its design assumptions.

In general, a power calculation estimates how many participants would be needed under specified assumptions to have a stated chance of detecting a chosen effect, if that effect and model assumptions were correct. The displayed sample sizes are planning illustrations, not a retrospective measure of how likely this completed trial was to find a result. Smaller effects require more participants under the same planning framework. The assumptions and target effects must be considered together when interpreting any such calculation.

10. Confidence Intervals and Precision

The estimated mean difference is 0.2 units on the Numeric Pain Scale, with TAP Block- Exparel minus Continuous Epidural Analgesia as the direction of subtraction. The confidence interval extends from a negative value to a positive value and therefore includes zero. Its span reflects uncertainty in the estimated difference: the posted data are compatible with values on either side of no mean difference under the interval’s assumptions.

The interval should be considered alongside the arm means, 2.32 for TAP Block- Exparel and 2.12 for Continuous Epidural Analgesia, and the standard deviation of 1.44 in each arm. The standard deviations describe variation among participant scores; the confidence interval describes precision in the estimated between-arm mean difference. These answer different questions and should not be treated as interchangeable measures.

The registry record does not report a clinically important difference threshold for the Numeric Pain Scale. It is therefore not possible to use the posted interval to classify the entire range as clinically unimportant or important. An interval that includes zero also does not demonstrate equivalence: equivalence requires a prespecified margin and an analysis designed to assess whether the interval lies within it, neither of which is reported in the registry record.

The unadjusted p-value is 0.353. A p-value gives a test result under a null hypothesis and model assumptions, while the confidence interval shows a range of estimates consistent with the data under its procedure. The registry record does not specify the confidence level or the method used to construct the interval. Interpretation should therefore remain with the reported direction, magnitude, and fact that the interval crosses zero, without assigning unreported methodological details.

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’s 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 set in turn to 100%, 75%, or 50% of the observed effect. These are planning assumptions for an illustration computed from the observed effect; the trial’s own original design assumptions and sample-size justification are not reported in the registry record.

For 100% of the observed effect, the illustration lists 814 participants per arm for 80% power and 1,090 participants per arm for 90% power. For 75% of the observed effect, it lists 1,447 participants per arm for 80% power and 1,937 participants per arm for 90% power. For 50% of the observed effect, it lists 3,256 participants per arm for 80% power and 4,358 participants per arm for 90% power.

In plain terms, the 80% power column gives the modeled number of participants per arm for an 80% chance of detecting the specified effect under the stated assumptions. The 90% power column gives the corresponding modeled number per arm for a 90% chance. These are not counts of participants observed in the trial. They are not observed power.

The pattern reflects a general planning principle: a smaller effect is harder to distinguish from random variation, so more participants are needed under otherwise unchanged assumptions. The illustration uses the observed effect as its reference, so the figures depend on that estimate as well as on the planning assumptions. They do not establish what sample size the investigators intended or whether the completed trial met its original design target. A curve associated with these calculations should be read as a display of the same dependence on assumed effect and sample size, not as a separate trial result.

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 = 0.200; pooled standard deviation σ = 1.440.
2. n = 2 × (1.96 + 0.842)² × 1.440² / 0.200² = 813.8, rounded up to 814 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 <- 0.2                      # observed difference in means
sigma <- 1.44                     # 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(2591407)
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 = 814 (80% power), 1,090 (90% power)
 75% of observed effect: n per arm = 1,447 (80% power), 1,937 (90% power)
 50% of observed effect: n per arm = 3,256 (80% power), 4,358 (90% power)
power.t.test: 814.7 
Simulated power at n = 814 per arm: 0.797 (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 the primary Numeric Pain Scale outcome and five secondary outcome descriptions relating to patient use of narcotic analgesia on postoperative days 0, 1, 2, and 3. Postoperative day 0 appears twice among the descriptions. The record lists seven outcome measures overall, but does not report a detailed outcome hierarchy or identify which secondary comparisons were intended to be confirmatory.

The posted p-value for the primary comparison is unadjusted. The registry record does not report whether a multiplicity adjustment was planned or used for the primary and secondary outcomes, or whether any testing sequence controlled the chance of false-positive findings across analyses. This matters because examining multiple outcomes can affect the interpretation of individual p-values. The available record does not provide enough detail to determine how that issue was addressed.

The registry record lists zero analyses, although primary arm summaries and a primary comparison are posted. It does not provide a statistical analysis plan, specify any covariate adjustment, or describe whether interim analyses were conducted. Interim analyses and their procedures are not reported in the registry record.

Missing data handling is also not reported in the registry record. In particular, the record does not explain how the four daily pain measurements were averaged when any day’s observation was unavailable, whether imputation was used, or what rules determined inclusion in the primary analysis. The posted primary outcome counts are 87 for Continuous Epidural Analgesia and 92 for TAP Block- Exparel; the registry record does not explain how those counts relate to the enrollment of 200.

The analysis population is not defined. The registry record does not state whether all randomized participants were analyzed in their assigned arms, whether a per-protocol population was used, or whether participants were excluded from analysis. These limitations prevent a full assessment of missingness, participant exclusions, and the analysis’s relationship to randomization. They do not change the values posted for the primary comparison, but they constrain what can be concluded about the analysis process.

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 registry record reports serious adverse event counts of zero in both arms. The number at risk is 87 for Continuous Epidural Analgesia and 92 for TAP Block- Exparel. It also reports zero other adverse events in both groups, with the same numbers at risk, and zero deaths in each arm.

These figures describe what is recorded for the listed groups and outcomes. They should not be read as proof that no adverse events of any kind occurred, or as evidence that the two approaches have identical safety profiles. The registry record does not report confidence intervals for these counts, detailed event descriptions, the duration of safety follow-up, or the criteria used to classify events. The top serious event terms list is empty.

As a general statistical point, zero recorded events in a group is a count, not a guarantee that the underlying risk is zero. Safety estimates depend on the number of participants observed, the duration and completeness of follow-up, and how events are identified and recorded. The registry record provides the group counts at risk but does not report those additional details, so interpretation should stay close to the posted counts.

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

The posted primary result describes a small positive mean difference of 0.2 Numeric Pain Scale units for TAP Block- Exparel compared with Continuous Epidural Analgesia. The arm means were 2.32 and 2.12, respectively, and the confidence interval crosses zero. The unadjusted p-value was 0.353. Together, these results indicate that the posted estimate is uncertain and that the registry record does not show a statistically significant difference under the reported unadjusted test.

This does not establish that the two approaches are equivalent, that their effects are identical, or that the observed difference is clinically unimportant. The record does not give a clinically important difference threshold or an equivalence margin. A nonsignificant result is not a demonstration that no difference exists; it can also reflect uncertainty around the estimate. The confidence interval is relevant because it indicates that values on either side of zero remain compatible with the analysis.

The result also does not describe the day-by-day pain pattern. Scores from postoperative days 0, 1, 2, and 3 were averaged into one value. The record does not report separate primary comparisons by day or a model of change over time. Nor does it say how incomplete daily measurements were handled. Thus, the posted average cannot answer whether pain scores differed at a particular postoperative time point or followed different trajectories.

The registered trial is randomized, but the posted registry information is not a full account of conduct and analysis. Details of the randomized population, missing data, analysis population, multiplicity procedures, and original sample-size justification are not reported in the registry record. Those gaps limit assessment of the strength and scope of the findings.

The results should be understood as a comparison of the posted group averages and their statistical precision for the registered endpoint. They do not support medical advice or a general recommendation about pain management. They also do not establish findings for outcomes beyond those reported, or for settings and populations not described in the registry record.

16. Why This Trial Matters Statistically

This trial illustrates why an estimated effect, its precision, and its clinical meaning should be considered separately. The posted mean difference is 0.2 scale units, while the confidence interval spans values on both sides of zero. The p-value alone does not communicate the range of effects compatible with the data, and the point estimate alone does not show how uncertain the comparison is.

The endpoint also highlights a design choice with consequences for interpretation. The pain measurements from postoperative days 0, 1, 2, and 3 were averaged into a single value. That produces a summary for comparing group means, but it does not show whether the contrast is consistent across days. A reader should distinguish an average-over-time result from estimates at individual time points or from an analysis of change over time.

The planning illustration shows how sample-size requirements depend on the effect size investigators seek to detect. Under its stated assumptions, the number of participants per arm rises as the target effect becomes a smaller fraction of the observed effect. This is a general feature of statistical planning, not evidence that the original trial was designed using those assumptions. The original sample-size justification is not reported in the registry record.

Finally, the record includes useful information about randomization, masking, arms, outcomes, and posted results, but it does not report several details needed to fully assess analysis choices. Missing data, analysis populations, multiplicity, and the trial’s statistical plan are not described. Reading the estimates alongside these limitations keeps the interpretation focused on what the posted results can support, without treating an incomplete statistical record as a complete account of trial conduct.

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 primary outcome is an average of scores from postoperative days 0, 1, 2, and 3. The registry record does not report separate day-specific primary results, so the posted average cannot show the time course of pain scores. It also does not describe how the average was calculated when one or more daily measurements were missing.

The outcome counts are 87 in the Continuous Epidural Analgesia arm and 92 in the TAP Block- Exparel arm, while the registered enrollment is 200. The record does not explain the relationship between these figures, including whether the difference reflects missing measurements, exclusions, or another reason. The analysis population and handling of missing data are not reported in the registry record.

The trial is listed as randomized and unmasked, but the record does not provide further details about allocation procedures or the analysis plan. It does not report a clinically important difference threshold for the pain scale, an equivalence margin, or the original sample-size justification. The planning illustration based on the observed effect should not be mistaken for the trial’s original design calculation.

The registry lists five secondary outcome descriptions, with postoperative day 0 appearing twice, and seven outcome measures overall. The registry record does not report detailed results or analysis procedures for those secondary outcomes. It also does not report multiplicity handling, interim analyses, or whether adjustment for other variables was used. These omissions limit evaluation of the full set of analyses and the context for the unadjusted primary p-value.

Safety figures are reported as counts, but the record does not give detailed event descriptions, follow-up duration, or confidence intervals. More broadly, registry summaries do not supply all details required to evaluate trial conduct and analytic decisions. The posted primary result should therefore be interpreted as a summary comparison with identifiable gaps in the available methodological record.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Trial Comparing Transversus Abdominis Plane Block Versus Epidural Anesthesia for Pain Management in Colorectal Surgery — NCT02591407.
• Registry record last updated 2026-01-28; status last verified 2026-01.
• Results first posted 2026-01-28.
• 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

The registry record describes NCT02591407, a completed, prospective randomized parallel-group trial comparing TAP Block- Exparel with Continuous Epidural Analgesia for perioperative pain management in elective colorectal surgery. The study is listed as unmasked, with enrollment of 200 and Trinity Health Michigan as sponsor. The registered conditions are colon cancer, rectal cancer, and colonic diverticulosis.

The primary endpoint is the Numeric Pain Scale mean averaged across postoperative days 0, 1, 2, and 3. The posted arm means are 2.32 for TAP Block- Exparel and 2.12 for Continuous Epidural Analgesia; the reported mean difference is 0.2, with a confidence interval that crosses zero and an unadjusted p-value of 0.353. The record also lists secondary narcotic-use outcomes and reports zero serious adverse events in each arm.

Important details—including missing-data handling, analysis population, multiplicity procedures, and the original sample-size justification—are not reported in the registry record. The posted estimates describe the registered comparison but do not establish equivalence or clinical importance.