Transversus Abdominis Plane (TAP) Block for Postoperative Analgesia After Laparoscopic Colonic Resection: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Transversus Abdominis Plane (TAP) Block for Postoperative Analgesia After Laparoscopic Colonic Resection (NCT01339273), a randomized na study. The primary outcome is Morphine Consumption in the First 48hours After the Operation.

2. Clinical Question

3. Trial Design

The registry describes a randomized, double-masked, parallel-group controlled trial. It lists an enrollment of 72 and identifies Oxford University Hospitals NHS Trust as sponsor. The record lists the phase as not applicable. The study start is recorded as 2011-09, the primary completion as 2013-12, and the status as completed.

Participants were assigned to ultrasound-guided TAP block or local anaesthetic infiltration of laparoscopic port sites. The primary outcome results report 28 participants in each arm. The registry does not explain how those outcome counts relate to the enrollment of 72, including whether the difference reflects exclusions, missing measurements or another reason. The analysis population and the handling of participants after randomization are not reported in the registry record.

The double-masked label indicates that masking was part of the registered design, but the record does not specify which groups of people were masked or how masking was maintained and assessed. The comparator description notes that plasters were placed where a TAP-block puncture would be made, consistent with an attempt to make the procedures less distinguishable; further details are not reported. The registry does not describe the method used to generate or conceal the random allocation sequence.

The research question focused on postoperative analgesia after laparoscopic large bowel resection. The registry's background describes concerns about pain, opioid-related effects and recovery, but the primary registered measure was morphine consumption rather than a direct pain rating. Secondary outcomes include pain and nausea scores at 48 hours and several measures of postoperative recovery. Further procedural and clinical eligibility criteria are not 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.

Population: 8 cases converted to open and therefore excluded from analysis. 7 cases had incomplete and missing follow up data from the ward and were excluded from analysis.

6. Primary Endpoint

The registry lists the primary outcome as Morphine Consumption in the First 48hours After the Operation, measured over 48 hours after the operation.

The primary endpoint is total morphine consumption during the first 48 hours after the operation, measured in mg. The registry says that consumption was to be calculated from the drug chart and the patient-controlled analgesia pump. It reports the endpoint as a mean with a 95% confidence interval.

Morphine consumption is an analgesia-related outcome: it records how much rescue opioid was used during a defined postoperative period. It is not a direct measure of pain intensity. A lower amount could reflect less need for rescue analgesia, but interpretation also depends on pain, rescue-medication availability and use, and other aspects of care. The registry's central question compares TAP block with local anaesthetic infiltration; the primary endpoint therefore offers one way to assess analgesic requirements, not a complete account of pain relief or recovery.

The reported mean is 47.3 mg for TAP block, with a 95% confidence interval from 36.2 to 58.5, and 46.7 mg for infiltration, with a 95% confidence interval from 36.2 to 57.3. Each arm's reported outcome count is 28. The registry does not report a formal between-arm estimate or inferential test for this endpoint. It also does not report the distribution of individual morphine-consumption values or additional details about the calculation beyond the drug chart and pump records.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the reported mean describe?

A mean summarizes the values in a group by representing their average. Here, the measured quantity is total morphine consumption during the first 48 hours after surgery, in mg. The reported means describe the outcome groups listed in the registry: 28 participants for TAP block and 28 for local anaesthetic infiltration. A mean can be informative about a group's overall level, but it does not show how values vary between individuals or whether a small number of unusually high or low values influence the summary.

The registry identifies the endpoint as continuous and says that it is summarized by a mean and 95% confidence interval. It does not report standard deviations, medians, ranges or distribution plots for this outcome. Those additional summaries could help readers understand variability and skewness, but their absence does not justify inferring what the individual observations looked like.

How should a confidence interval be read?

A confidence interval expresses uncertainty around an estimate using a stated method. In repeated use of the same method under its assumptions, intervals would capture the target quantity at the stated confidence level at the corresponding long-run rate. For an individual trial, the interval gives a range of values compatible with the observed data and calculation approach; it is not a probability statement that the fixed true value has a particular chance of lying inside this specific interval.

The intervals reported for the two means are 36.2 to 58.5 mg for TAP block and 36.2 to 57.3 mg for infiltration. Their breadth signals that the means are not estimated with pinpoint precision. These are separate arm-specific intervals. They are not a confidence interval for the difference between treatments. A direct treatment comparison would require an estimated contrast and its uncertainty, neither of which is reported in the registry record.

Why is the direct comparison important?

The question is comparative: whether TAP block provides better pain relief than local anaesthetic infiltration. Comparing two arm means informally does not supply the uncertainty around their difference. The appropriate comparative estimate depends on a prespecified analysis and its assumptions, and may also depend on whether adjustments or other design features were used. The registry does not report a formal two-arm analysis for the primary endpoint, so the posted summaries cannot be used to recover a sponsor's intended inferential result.

General statistical practice also distinguishes statistical uncertainty from clinical importance. A comparison can be estimated precisely yet be of limited practical importance, or be uncertain despite a potentially meaningful difference. Assessing practical importance would require a clinically relevant threshold and contextual information; these are not reported in the registry record. No threshold should be inferred from the arm means alone.

What assumptions matter for a mean?

General: a mean is most straightforward to interpret when the measurement and analysis population are well defined and the observations are not dominated by extreme values. Morphine use can vary between people, and a distribution with a long tail can make a mean sensitive to high values. The registry does not report distributional diagnostics or details of any transformation or alternative analysis. It is therefore not possible to assess from the record whether the mean was accompanied by checks addressing skewness or influential observations.

General: uncertainty calculations also rely on assumptions about the observations and the method used to estimate variability. The registry provides the confidence intervals but does not describe the calculation method, model, or assumptions in enough detail to reproduce them. The label “95% Confidence Interval” identifies the reported uncertainty measure, not every analytic choice behind it.

How do planning illustrations differ from trial results?

General: sample-size planning asks how many participants would be needed to target a specified degree of precision or chance of detecting an effect under stated assumptions. The planning assumptions recorded for this trial use a two-sided significance level of 0.05, equal allocation, a normal approximation and an effect defined as a stated fraction of the observed effect. Such an illustration is conditional on those assumptions and on the effect used for planning. It is not a result observed in the trial and is not evidence that the trial had a particular probability of detecting an effect. No planning counts or fraction values are reported in the registry record described by these results.

In particular, planning illustrations should not be interpreted as observed power. Observed power is not a substitute for examining the estimate and its confidence interval. Here, the registry does not report a comparative confidence interval or test for the primary outcome, so the arm-level intervals are the principal posted information about precision. They do not establish the probability that either intervention is better.

What can and cannot be reproduced?

The arm means and their intervals can be quoted as posted: 47.3 mg (36.2 to 58.5) for TAP block, and 46.7 mg (36.2 to 57.3) for infiltration. No recalculated comparison is reported, and the record does not provide the inputs needed to produce a defensible unadjusted comparison from summary statistics, such as an arm-specific measure of variability. The skip note indicates that values were missing or not estimable for a two-arm comparison of this continuous endpoint. The sponsor's own analysis does not take precedence over a recalculation in this case because no discrepancy is reported; however, no sponsor comparison is posted to interpret.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies 14 outcome measures and reports 13 secondary outcomes posted. The listed secondary outcomes include pain and nausea scores at 48 hours, time to first request for rescue analgesia, time to mobilisation, time to successful fluid intake, time to resumption of normal diet, time to first bowel motion and time to first flatus. The record does not describe a multiplicity strategy, such as whether a particular secondary outcome was designated as most important or whether the chance of false-positive findings across multiple tests was addressed. Without that information and the corresponding comparisons, the secondary outcomes should not be treated as a single confirmatory set.

The registry does not report missingness for the primary outcome, reasons for missing measurements, or a method for handling missing data. It also does not state whether all randomized participants were included in the primary analysis, whether participants were analyzed according to allocated group, or whether a per-protocol or other population was used. The outcome count of 28 in each arm and the overall enrollment of 72 are both reported, but the record does not reconcile them. They should not be interpreted as evidence of a particular kind of exclusion or missingness.

The record does not describe interim analyses, stopping rules, a statistical analysis plan or covariate adjustment. These matters are not reported in the registry record. Their absence from the record limits assessment of how outcomes and analyses were selected and how the results relate to the original analysis plan; it does not establish that a particular procedure was or was not used outside the registry record.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event summary reports zero serious adverse events among 36 participants at risk in the TAP-block group and zero among 35 participants at risk in the local-anaesthetic-infiltration group. It also reports zero other adverse events among 36 and 35 participants at risk, respectively. These are counts recorded in the registry's adverse-event results; they should not be read as proof that no adverse events could occur or that the interventions have no risks.

The serious-adverse-event denominators differ from the primary-outcome counts, which are 28 per arm. The registry does not explain these different group sizes, so the adverse-event figures should be interpreted using their own at-risk counts rather than assumed to describe the same analysis population as the primary outcome. The deaths fields are not populated with counts; death information is not reported in the registry record.

The registry lists no serious adverse-event terms. The summary does not provide event descriptions, timing, severity criteria, attribution to intervention or comparator, or details of how adverse events were collected. Zero reported events in these fields therefore describes the posted record, not a complete assessment of safety across all possible outcomes or over longer follow-up.

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

The primary results describe mean morphine consumption in the first 48 hours after surgery for the two reported groups. The mean is 47.3 mg after TAP block and 46.7 mg after local anaesthetic infiltration, with reported 95% confidence intervals of 36.2 to 58.5 mg and 36.2 to 57.3 mg, respectively. These summaries provide an account of the observed outcome groups and show uncertainty around each arm's mean.

They do not establish whether one approach provides better pain relief. Morphine consumption is not the same as pain intensity, and the registry does not report a formal between-arm estimate or test for this endpoint. Nor does it report an interpretable comparative result for the secondary outcomes in the registry record. The primary outcome therefore cannot stand in for the entire range of pain, nausea, recovery and safety questions.

The data also do not establish that the interventions are equivalent. Similar arm means alone are not an equivalence analysis. Such an interpretation would require a prespecified margin and a comparative estimate with suitable uncertainty; these are not reported in the registry record. Conversely, the lack of a reported comparison does not mean that no difference exists. It means the record does not quantify the treatment contrast for the primary endpoint.

The registered status is completed, but the posted summaries remain limited by the unreconciled difference between total enrollment and primary outcome group counts, the absence of a described analysis population, and missing details about the statistical methods. The adverse-event counts record zero events in the listed categories, but the available information does not provide a comprehensive safety assessment. The fairest reading is descriptive: the registry gives arm-level averages and confidence intervals, while leaving the comparative inference and several aspects of outcome completeness and analysis unspecified.

13. Why This Trial Matters Statistically

This trial poses a statistically important design question because it compares two active approaches to local anaesthesia in a surgical setting, rather than comparing an intervention with no analgesic procedure. The control group received local anaesthetic infiltration at the port and extraction sites, while the other group received an ultrasound-guided TAP block. The contrast therefore concerns the relative performance of two specified approaches within the registered care context.

The primary measure, morphine consumption during the first 48 hours, is a continuous outcome that can summarize rescue opioid use. Reporting means and confidence intervals offers more information than reporting a mean alone, because it conveys uncertainty around each arm estimate. But the scientific question is about the difference between groups, and arm-level summaries are not a substitute for a direct contrast and its uncertainty. This distinction is central to interpreting randomized trials: the design creates a basis for a causal comparison, while the reported analysis is needed to quantify that comparison.

The registry also illustrates why denominators and analysis populations matter. Enrollment is 72, whereas the primary-outcome summaries list 28 participants per arm and adverse-event summaries list 36 and 35 at risk. Those counts may refer to different outcome sets, but the record does not explain their relationship. Readers therefore cannot assume that every result describes the same participants or that a particular missing-data process accounts for the differences.

Finally, the trial's analgesia question is broader than its primary endpoint. Pain ratings, nausea, rescue-medication timing and recovery milestones are listed as secondary outcomes. A statistical interpretation should distinguish a primary endpoint from a collection of secondary measures and account for the possibility of multiple comparisons. The registry does not report how that issue was handled. These features make the record useful for understanding what was planned and what arm-level results were posted, while also showing why complete comparative analyses and transparent denominators are important.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

A central limitation of the posted results is that they give arm-level means and confidence intervals but no formal comparison for the primary endpoint. Without a between-arm estimate and its uncertainty, the direction and precision of the treatment contrast cannot be established from the registry record. The close means should not be used as proof of equivalence or absence of a difference.

The record lists enrollment of 72, but the primary outcome summaries include 28 participants in each arm. The adverse-event summaries use at-risk counts of 36 and 35. The record does not explain these denominators or report reasons for missing outcome measurements. This prevents a clear account of how complete the primary outcome was and which participants contributed to each result.

Additional methods details are not reported: the allocation-sequence method, allocation concealment, who was masked, the analysis population, the statistical model and the calculation method for the confidence intervals. The record also does not describe distributional checks, variability measures beyond the intervals, covariate adjustment, a multiplicity approach, interim analyses or the statistical analysis plan. These are limits on what can be evaluated from the registry record; they are not evidence that a specific method was absent from all study materials.

The listed primary outcome measures morphine use rather than pain directly. Although pain scores and several recovery outcomes are listed as secondary measures, the registry entries do not provide their numerical results. The adverse-event summary gives zero counts in its listed categories but does not describe ascertainment, event definitions, attribution or follow-up duration. Finally, the registry includes several conditions and does not give detailed eligibility criteria, so the enrolled population's clinical composition cannot be characterized beyond those listed conditions.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Transversus Abdominis Plane (TAP) Block for Postoperative Analgesia After Laparoscopic Colonic Resection — NCT01339273.
• Registry record last updated 2020-02-05; status last verified 2020-01.
• Results first posted 2020-02-05.
• 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.

18. Record Summary

The registry record describes a completed, randomized, double-masked, parallel-group trial sponsored by Oxford University Hospitals NHS Trust. It lists enrollment of 72 and compares ultrasound-guided TAP block with local anaesthetic infiltration of laparoscopic port sites in laparoscopic colonic resection. The primary endpoint is total morphine consumption in the first 48 hours after surgery.

For the primary outcome, the reported mean is 47.3 mg (95% confidence interval 36.2 to 58.5) for TAP block and 46.7 mg (95% confidence interval 36.2 to 57.3) for infiltration, with 28 participants reported per arm. A formal comparative estimate is not posted. The adverse-event summary reports zero serious and zero other adverse events among 36 and 35 participants at risk, respectively; deaths are not reported. The record does not explain the differing denominators or describe the primary analysis population, missing-data handling or multiplicity strategy.