The Effect of Pre-Operative Transversus Abdominis Plane (TAP) Block in the Post Operative Opioid Consumption in Morbid Obese Patients Undergoing Laparoscopic Gastric Bypass Surgery: A Prospective,Randomized, Blinded Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Pre-Operative Transversus Abdominis Plane (TAP) Block in the Post Operative Opioid Consumption in Morbid Obese Patients Undergoing Laparoscopic Gastric Bypass Surgery: A Prospective,Randomized, Blinded Study (NCT01075087), a randomized na study. The primary outcome is Quality of Recovery 40 Score.

2. Clinical Question

The clinical question is about a measured recovery score after surgery, not simply whether a block was administered or whether pain was present. A higher score is positioned toward the high end of the stated scale, so the score’s direction is interpretable from the registry description. The comparison is between randomized groups, with the primary outcome assessed at a specified postoperative time. The registry record does not describe how participants were selected, how the block was delivered beyond the intervention description, or how the score was collected. These details limit how completely the question can be reconstructed from the record alone.

3. Trial Design

The study is registered as completed and is described as prospective, randomized, blinded, and parallel-group. Participants were assigned to placebo or an active comparator. The active comparator was a bilateral TAP block using 20 cc of 0.5% ropivacaine on each side; the placebo group received sterile normal saline in the block. Enrollment is listed as 19. The posted outcome figures show 9 participants in the placebo group and 10 in the active-comparator group for the primary endpoint.

The primary endpoint was the Quality of Recovery 40 Score at 24 hours postoperatively. It is reported as a median with an inter-quartile range. The registry describes the scale as running from 40, low, to 200, high. A secondary outcome is listed as 24 Hour Total Opioid Consumption, but its result is not reported in the registry record. Although the record says there were 2 outcome measures, it gives numerical results for the primary score in the registry record for this analysis; the other outcome’s values are not reported in the registry record.

The record lists triple masking, but does not identify which participants, clinicians, or assessors were masked, or how masking was maintained. The allocation sequence method, allocation concealment, and details of the randomization procedure are not reported in the registry record. The study start is recorded as 2010-03, and primary completion as 2012-07. The record names Northwestern University as sponsor. It gives no protocol-level explanation of the sample-size rationale, intended recruitment, or planned statistical analysis. These omissions do not establish that the procedures were absent; they mean the relevant details are not reported in the registry record.

With randomized allocation, the intended comparison is between groups that differ by assigned block treatment. Randomization helps guard against systematic differences at assignment, while masking can reduce some risks of biased care or outcome assessment. Neither label, by itself, establishes that allocation was concealed or that masking was successful. In a small study, the observed group summaries can also be sensitive to the particular participants enrolled. The design therefore supplies a useful framework for interpreting the comparison, but the record does not contain enough detail to assess every implementation feature.

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: 26 were assessed for eligibility. 7 were excluded ( 4 did not meet inclusion criteria and 3 refused to participate).

Overall Study

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 Quality of Recovery 40 Score, measured over 24 hours post operatively.

The primary endpoint is the Quality of Recovery 40 Score measured 24 hours postoperatively. The registry describes this as a score on a scale from 40, the low end, to 200, the high end. The outcome is intended to represent recovery as captured by that score at a defined time after surgery. Using a specified time point makes the two randomized groups’ summaries comparable at the same stage of follow-up, as long as outcome collection and analysis are conducted consistently.

The measure is reported using medians and inter-quartile ranges rather than means and standard deviations. A median identifies the midpoint of the observed score distribution, while the inter-quartile range describes the central spread of observations. These summaries can be useful when data are skewed or when a small number of values could disproportionately influence a mean. The registry record does not report the individual scores, the distribution’s shape, or the scoring and data-collection procedures. It also does not explain what size of score difference would be considered important to patients or clinicians. Thus, the numerical result can describe the observed group summaries, but its clinical importance cannot be determined from the registry record alone.

The record lists 24-hour total opioid consumption as a secondary outcome. Its result is not reported in the registry record. It should therefore not be inferred from the primary recovery score or from the intervention description. The primary endpoint addresses recovery-score comparison; it does not substitute for a measured result on opioid consumption.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports a Wilcoxon (Mann-Whitney) comparison for the primary outcome. This is a rank-based method: rather than relying on the original scores alone, it orders the observations and compares their ranks between groups. Rank-based procedures can be useful when the outcome distribution may not be well represented by a normal model, or when the analysis is intended to avoid strong assumptions about distributional shape. The method does not automatically test a difference between medians in every setting. Its interpretation depends on how the distributions differ, and the registry’s specific reported estimand is described as a median difference (net).

What do the median and inter-quartile range describe?

A median is the middle of an ordered set of observations. It gives a measure of location that is less affected by unusually high or low values than the arithmetic mean. The inter-quartile range gives the lower and upper quartile boundaries, describing the central spread of the observed scores. Here, the placebo median is 170.0 with an inter-quartile range of 160.0 to 175.0, while the active-comparator median is 175.5 with an inter-quartile range of 170.0 to 189.0. The registry does not show the underlying participant-level scores, so these summaries cannot reveal the full distribution, overlap between groups, or possible outliers.

How should the reported contrast be read?

The analysis reports a net median difference of -5.5. The word “net” signals a contrast between groups, but the record does not specify the subtraction order in the result description. The point estimate should therefore be quoted as reported, without assigning its sign to a particular group by inference. It should also not be treated as a newly calculated difference between the two displayed medians: a rank-based comparison and a difference between group medians are not necessarily the same estimand.

The 90% confidence interval runs from -26 to 3. A confidence interval describes the uncertainty associated with an estimate under the statistical method and its assumptions. It is not a range containing a fixed proportion of individual participant outcomes, nor is it a probability statement about the true value after the data have been observed. Because this interval crosses 0, it includes a no-contrast value and values on either side of it. Its width indicates uncertainty about the magnitude and direction of the contrast. The record does not give a clinical threshold for an important score difference, so the interval cannot be translated into a threshold-based judgment about clinical relevance.

What does the p-value contribute?

The reported p-value is .05. In general, a p-value assesses how compatible the observed data are with a specified null model, conditional on the model and analysis assumptions. It is not the chance that a treatment has no effect, and it is not a direct measure of the probability that the observed result occurred “by chance.” It should not be used in isolation to decide whether an effect is meaningful. The estimate and interval provide complementary information: the estimate gives the reported contrast, while the interval conveys its uncertainty. The registry does not report a prespecified decision threshold, the sidedness of the test, or additional details of the test implementation.

Why can over-dispersion matter?

As a general statistical point, over-dispersion occurs when observations vary more than an assumed model allows. If a method assumes less variability than is present, its uncertainty estimates may be too small and its inferential results too confident. Rank-based methods avoid some distributional assumptions, but they do not make every issue of variability or study design disappear. The registry record does not report an over-dispersion assessment, and this result is a rank-based comparison of a score rather than a reported count model. Over-dispersion should therefore be understood as a general modeling concept, not as a documented problem in this trial.

What limits the precision of the comparison?

The primary results are based on 9 placebo participants and 10 active-comparator participants. Small groups generally provide less information about the underlying distributions than larger groups, and each observed score can carry substantial influence. Randomization does not guarantee that small groups will have similar baseline characteristics. The registry record does not provide baseline balance summaries or participant-level data, so the degree of any imbalance cannot be assessed from this result. The confidence interval is a direct indication that the estimated contrast remains uncertain.

The record lists one reported analysis. It does not report a full statistical analysis plan, treatment of missing endpoint values, a prespecified estimand beyond the stated outcome, or sensitivity analyses. No recalculated result is given in the registry record for this analysis. The posted estimate and inferential statistics should consequently be treated as the registry’s reported analysis rather than as a result independently verified from raw data. A recalculation from summary statistics would not reproduce participant-level ranks and would not replace the sponsor’s analysis.

10. Analyses Reported by the Sponsor

The registry reports the sponsor-side analysis as a Wilcoxon (Mann-Whitney) comparison, with a median difference (net) of -5.5, a 90% confidence interval from -26 to 3, and p = .05. The group medians and inter-quartile ranges are also posted. The record does not provide an independent recalculation of this rank-based result from participant-level data, and the participant-level scores are not reported in the registry record.

Accordingly, there is no competing recalculated estimate to set against the reported result in this account. A calculation based only on group summary statistics could not reconstruct the rank ordering used by the Wilcoxon analysis. The fact that the displayed group medians are 170.0 and 175.5 does not make their arithmetic contrast interchangeable with the reported net median difference. No discrepancy between a recalculation and the sponsor’s result is identified in the registry record. The sponsor’s reported analysis is therefore the result to interpret, while its precision and limitations are assessed through the reported confidence interval, p-value, and small group sizes.

The record does not report further detail about the analysis implementation, the contrast direction, or whether other analyses were conducted. The listed result should not be expanded into claims about unreported analyses or outcomes.

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary endpoint, Quality of Recovery 40 Score at 24 hours postoperatively, and identifies 24 Hour Total Opioid Consumption as a secondary outcome. It also lists 2 outcome measures and one reported analysis. The opioid-consumption result is not reported in the registry record. No further outcome-specific analysis details are reported for that secondary measure.

When a study tests multiple outcomes, time points, subgroups, or alternative analyses, the chance of finding an apparently unusual result can increase if each is treated as an independent opportunity for a positive finding. This is the general issue of multiplicity. Prespecified distinctions between primary and secondary outcomes can help readers understand which result is central, but the registry record does not report a multiplicity adjustment or a complete analysis plan. It is therefore not possible to determine whether the posted p-value was adjusted, whether other endpoints were examined, or how any additional tests were handled. The absence of those details should not be taken as proof that no plan or adjustment existed; they are not reported in the registry record.

Missing-data handling is also not reported in the registry record. The primary endpoint summaries list 9 participants in the placebo group and 10 in the active-comparator group, but the record does not explain whether these represent all randomized participants with available measurements, an analysis population defined by protocol, or another set. It does not describe imputation, exclusion rules, or sensitivity analyses for missing scores. Enrollment is listed as 19, but no participant-flow explanation is reported in the registry record. No additional total should be inferred from the arm-level figures.

The record does not state whether the primary analysis followed intention-to-treat principles, used a per-protocol population, or applied another approach. Analysis-population definitions matter because they specify which assigned participants contribute to the estimate and how departures from treatment assignment or follow-up are handled. Without these details, the reported group summaries remain interpretable as posted results, but the exact analysis population and the potential influence of missing data cannot be assessed.

12. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The posted safety figures show 0 serious adverse events among 9 placebo participants at risk and 0 among 10 active-comparator participants at risk. For other adverse events, the figures are 3 among 9 at risk in the placebo group and 1 among 10 at risk in the active-comparator group. These are counts as recorded; they are not adjusted comparisons and do not establish a treatment effect.

Serious adverse events and other adverse events are distinct reporting categories. The absence of recorded serious events in these groups does not establish that the interventions are free of risk, especially in a study with small group sizes. The record does not provide event descriptions for the other adverse events or further context about severity, timing, relatedness, or how events were collected. No serious-event terms are listed. Death counts are not reported in the registry record.

Safety counts should be interpreted alongside the population at risk, follow-up period, and completeness of reporting. The registry record does not provide enough detail to assess those aspects fully. These figures describe what was posted for this study; they should not be used alone to compare broader safety profiles or to make clinical decisions.

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

The posted result answers a narrow question: how the randomized groups’ Quality of Recovery 40 Scores compared at 24 hours postoperatively in this study. The active-comparator group had a higher observed median score than the placebo group, and the recorded rank-based estimate was a net median difference of -5.5. The reported 90% confidence interval, from -26 to 3, crosses 0 and spans contrasts in either direction. The result is therefore uncertain in both direction and magnitude.

This does not establish that the TAP block improves recovery. The observed group medians alone do not prove that a difference is reliable, and the reported estimate does not establish that the groups are equivalent. A confidence interval that includes 0 can reflect limited information as well as a value near no difference; it cannot by itself distinguish those explanations. The record does not report a threshold for a clinically important score difference, so statistical summaries cannot determine whether a contrast would matter to patients or clinicians.

The findings also do not answer the secondary question about 24-hour total opioid consumption, because that result is not reported in the registry record. Nor do the safety counts provide a complete assessment of harms: the study records no serious adverse events in either group, but other adverse-event descriptions and further safety context are not reported. The small group sizes make estimates vulnerable to the influence of individual observations and limit how confidently the result can be extended beyond the participants studied.

In general, randomized comparisons can support causal interpretation when allocation, follow-up, outcome measurement, and analysis are well implemented. The registry describes randomization and triple masking, but does not report enough detail to evaluate all these features. The result is best understood as a small-study, time-specific comparison with an imprecise posted estimate, rather than as a definitive conclusion about recovery or opioid use.

14. Why This Trial Matters Statistically

This trial is statistically instructive because it places a rank-based comparison, group medians, and an interval estimate side by side. The medians describe the observed central scores, but they are not a substitute for the reported Wilcoxon comparison. Keeping these quantities distinct prevents a common interpretive error: assuming that a test using ranks necessarily reports the simple difference between the two displayed medians.

The confidence interval is important because it makes uncertainty visible. The point estimate alone can seem more conclusive than the underlying data warrant. Here, the 90% interval extends from -26 to 3 and includes 0, so the result is compatible with a range of possible net contrasts. The p-value of .05 does not remove that uncertainty or establish clinical importance. Reading the estimate, interval, and group summaries together gives a more complete account than labeling the result by a threshold alone.

The small group sizes also highlight why randomization is not a guarantee of balance or precision. Random allocation is a design safeguard, but with small groups chance differences and influential observations remain possible. Reporting participant flow, baseline characteristics, missing-data handling, and analysis populations would help readers assess how the randomized design connects to the posted analysis; those details are not reported in the registry record.

Finally, the record illustrates the distinction between an outcome being listed and an outcome having interpretable results available. Total opioid consumption is named as a secondary outcome, yet its result is not reported in the registry record. A clear account of which outcomes have results, and which analyses were prespecified or adjusted for multiplicity, is important for interpreting a study without filling gaps by assumption.

15. Limitations

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

The registry record leaves important design and analysis details unreported. It does not describe the randomization sequence or allocation concealment, identify which roles were masked, or explain how masking was maintained. It also does not provide detailed eligibility criteria, baseline characteristics, participant flow, or reasons for any missing outcome data. These omissions prevent a full assessment of how the study was conducted and who contributed to the primary analysis.

The primary endpoint summaries are based on 9 placebo participants and 10 active-comparator participants. Such small groups limit precision and make the observed summaries potentially sensitive to individual scores. The reported 90% confidence interval from -26 to 3 is broad and includes 0. The record does not state what score difference would be clinically important, so the practical meaning of the estimated contrast cannot be judged from the registry result alone.

The reported net contrast does not specify the subtraction order in its description, and the record does not explain further analysis details, such as the sidedness of the test or the full prespecified analysis plan. The group medians should not be used to infer a contrast direction for the reported estimate. The registry lists the secondary opioid-consumption outcome but its result is not reported in the registry record. Multiplicity procedures and missing-data methods are also not reported.

Safety reporting is limited to counts of serious and other adverse events. Event descriptions, timing, relatedness, and death counts are not reported in the registry record. The trial is specific to the described surgical setting and population, and the available record does not establish how broadly its results apply. These limitations call for a cautious reading of the posted comparison, not an assumption that unreported procedures or information were absent.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Effect of Pre-Operative Transversus Abdominis Plane (TAP) Block in the Post Operative Opioid Consumption in Morbid Obese Patients Undergoing Laparoscopic Gastric Bypass Surgery: A Prospective,Randomized, Blinded Study — NCT01075087.
• Registry record last updated 2014-06-26; status last verified 2014-05.
• Results first posted 2014-06-26.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT01075087 is a completed, prospective, randomized, triple-masked, parallel-group study sponsored by Northwestern University. It enrolled 19 participants undergoing laparoscopic gastric bypass surgery. The placebo group received sterile normal saline in the block; the active-comparator group received a bilateral TAP block using 20 cc of 0.5% ropivacaine on each side.

The primary outcome was the Quality of Recovery 40 Score at 24 hours postoperatively, measured on a scale from 40, low, to 200, high. The placebo median was 170.0, with an inter-quartile range of 160.0 to 175.0; the active-comparator median was 175.5, with an inter-quartile range of 170.0 to 189.0. The reported Wilcoxon (Mann-Whitney) analysis gave a net median difference of -5.5, a 90% confidence interval from -26 to 3, and p = .05.

The registry also lists 24-hour total opioid consumption as a secondary outcome, but its result is not reported in the registry record. The primary estimate is imprecise, and further details about analysis populations, missing data, and multiplicity are not reported in the registry record.