Trimodal Prehabilitation for Aneurysm Surgery Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trimodal Prehabilitation for Aneurysm Surgery Study (NCT02292927), a non-randomized na study. The primary outcome is Change From Baseline in Metabolic Equivalents (METS) at Six Weeks.

2. Clinical Question

The study asked whether a trimodal prehabilitation programme before planned aortic aneurysm repair was acceptable and could be evaluated for its pre-operative impact on functional capacity. The registry describes a feasibility study intended to inform the design of a larger randomized controlled trial, rather than a randomized treatment comparison.

The study also set out to assess acceptability and compliance, functional fitness, quality of life, anxiety and depression, smoking changes, and hospital resource use. These aims describe what the feasibility study planned to evaluate; they should not be read as evidence that the outcomes were measured or that results were reported. The registry record does not provide outcome analyses from which to quantify a prehabilitation effect.

3. Trial Design

This was a completed, single-centre feasibility study with a parallel, non-randomized design and no masking. The registry lists 25 participants enrolled. It describes a pre-intervention group treated as standard before the intervention and a post-intervention group receiving the prehabilitation programme. The record explicitly cautions that these arms are not a like-for-like control comparison.

The listed study start was 2014-11, and primary completion was 2015-12. The brief summary describes a duration of 1 year from 1st June 2014; the relationship between that description and the listed registry dates is not explained in the registry record. The status is completed. The phase is listed as NA, which is consistent with the record describing a feasibility study rather than reporting a drug-development phase.

The intervention was behavioral and is named as trimodal prehabilitation. Its description says that a rehabilitation programme was introduced. Detailed information on the programme’s content, timing, intensity, adherence procedures, or delivery is not reported in the registry record. The study population was people undergoing elective open or endovascular aneurysm repair, with the stated capacity to consent and fitness to undertake pre-operative exercise.

The stated purpose was to assess acceptability and pre-operative impact on functional capacity, and to support the design of a larger randomized controlled trial. The brief summary lists potential measures including the physical function section of SF-36, peak flow, six-minute walk testing, quality of life, anxiety and depression, smoking changes, and length of hospital stay. The listed secondary outcomes include HDU/ITU resource use and length of stay. The registry does not report results for these measures.

Non-random allocation and the before-versus-after group descriptions limit causal interpretation. Differences between groups may reflect factors other than the intervention, including differences in participants or care over time; the record does not report adjustment methods that could address such differences. No masking was used. The registry record does not report a detailed protocol, a statistical analysis plan, or a sample-size justification for this feasibility study.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change From Baseline in Metabolic Equivalents (METS) at Six Weeks, measured over Collected at baseline and (expected) 6 weeks.

The primary endpoint was change from baseline in metabolic equivalents (METS) at six weeks. METS are a measure of exercise capacity or physical fitness. The record defines one MET as 3.5 mL 02 uptake/kg per minute, described as resting oxygen uptake in a sitting position. Higher achieved exercise capacity in METS is described in the registry as having been associated with improved survival in an older adult population; that contextual description does not establish an outcome of this study.

A change-from-baseline endpoint is intended to represent how a participant’s measurement differs from their own starting value by the follow-up assessment. In general, this can help distinguish a follow-up level from the level at study entry. To estimate a group change, however, the record must provide observed measurements or a summary of those changes. To compare groups, measurements must also be available in the relevant groups, and the analysis must account for the study design.

The registry states that METS were collected at baseline and at an expected six weeks. It also states that no patients in the pre-intervention group underwent pre-operative METS testing. No observed METS values, change estimates, measures of spread, confidence intervals, or statistical test results are reported in the registry record. Consequently, the record does not permit a quantitative assessment of change or a comparison of change between the pre-intervention and post-intervention groups.

The endpoint is relevant to the stated feasibility aim because it concerns physical capacity before surgery. Its presence in the registry does not, by itself, show that complete measurements were obtained or that a meaningful group effect can be estimated. The record does not report the precise timing of the six-week measurement relative to surgery for each participant.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods help distinguish the study’s question, the evidence actually recorded, and the conclusions that the evidence can support. In this record, the primary endpoint is identified, but its results and analysis are not posted. The explanations below describe general statistical principles and how they relate to the registry information.

What does non-randomized allocation imply?

In a randomized study, allocation is determined by a chance process, which tends to balance measured and unmeasured participant characteristics across groups in expectation. This study was non-randomized. The registry describes one group before the intervention and another after its introduction, and explicitly cautions that they are not a like-for-like control comparison. Group differences can therefore reflect the intervention, differences in participants, or changes in care and context over time. Without a reported analysis addressing these possibilities, a difference between groups cannot be attributed solely to prehabilitation.

The parallel design means the registry presents separate groups rather than describing each participant as receiving both conditions. A parallel label alone does not make the groups comparable. Lack of masking means the registry reports no masking of participants or study personnel. The record does not describe whether outcome assessors were masked, so that detail is not reported in the registry record.

What would a change-from-baseline estimate mean?

In general, a change score is a follow-up measurement compared with the same participant’s baseline measurement. A group-level summary of changes can describe average or typical movement in the measured outcome. Its interpretation depends on available paired measurements, the summary statistic used, and the analysis population. The registry identifies the primary outcome parameter as a mean and its dispersion as the full range, but it does not post the mean change, range, or participant-level data.

A confidence interval is a statistical range that conveys the precision of an estimated effect under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, while an interval that includes effects in different directions may leave the direction uncertain. No confidence interval for METS is reported in the registry record, so precision cannot be assessed. A p-value, when reported, measures how compatible the observed data are with a specified statistical model and null hypothesis; it does not quantify the size or importance of an effect. No p-value for the primary outcome is reported.

Why is the missing pre-intervention METS testing important?

The record says that no patients in the pre-intervention group underwent pre-operative METS testing. This is not simply a small or imprecise comparison: the stated primary outcome lacks the pre-intervention group’s pre-operative testing data needed to make a baseline-based comparison for that group. The record does not report which other participants had usable baseline or follow-up values, or whether a within-group estimate was calculated for the post-intervention group. A numerical change cannot be reconstructed from the endpoint title or from the adverse-event figures.

Missing outcome measurements can affect an estimate if the participants with recorded outcomes differ from those without them. Statistical approaches to missing data require information about the extent and pattern of missingness and assumptions about why values are missing. The registry record does not report missing-data methods or reasons for missing measurements. It would therefore be inappropriate to assume that missing outcome data were random, complete, or handled by a particular method.

How should the planning illustrations be read?

Sample-size illustrations are planning aids, not results from participants. The stated illustration uses a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; it varies the effect to detect as a stated fraction of the observed effect. For time-to-event tables, the stated quantity is a total number of events; other tables refer to participants per arm. These are design assumptions for the illustration, not a report of the study’s own planned enrollment calculation or its statistical plan. The record does not provide a sample-size justification for this feasibility study.

Planning calculations based on an observed effect can be especially sensitive to how that effect was estimated. A small study can produce an uncertain estimate, and an estimate used as a planning input should not be treated as a stable prediction. Sample-size illustrations do not show that a study had a particular probability of detecting an effect after the fact. The registry record does not report observed power, and sample-size planning figures should never be interpreted as observed power.

What can be inferred from the posted analysis information?

The registry lists zero analyses. That means no analyzed outcome results are represented in the record. It does not establish that no analysis was performed outside the registry, but any such analysis is not reported in the registry record and cannot be evaluated from this entry. The record also does not report the statistical model, covariates, handling of repeated measures, assumptions checks, or an analysis population definition. Without those details and without outcome estimates, a quantitative assessment of effect size, precision, or robustness is not possible.

Over-dispersion is a general concern when outcome variability is greater than a statistical model assumes; it can make standard errors too small if ignored. The registry does not identify a count model or report dispersion diagnostics for the listed resource-use outcomes, so it is not possible to say whether over-dispersion arose or how it was handled. This illustrates why the endpoint values and analysis details are necessary in addition to a study design label.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures and no analyses. It does not report a statistical analysis plan specifying which outcomes were confirmatory, how outcomes were ordered, or how multiple statistical tests would be handled. Multiplicity arises when several hypotheses are tested: with more tests, the chance of at least one apparently notable result can increase. Statistical approaches can control that risk, but the registry record does not state whether any such approach was planned or used. No conclusion about multiplicity adjustment can be drawn from an empty analysis listing.

Missing-data handling is also not reported in the registry record. The primary outcome description states that no patients in the pre-intervention group underwent pre-operative METS testing. This prevents the record from presenting a baseline-based METS comparison for that group, and no observed endpoint values or analysis are posted. The record does not give a complete account of the availability of follow-up METS measurements in the post-intervention group or reasons any measurements may be absent.

The analysis populations are not described. The registry does not report whether analyses were intended to include all enrolled participants, only participants with available endpoint measurements, or another defined population. It also does not report a flow of participants through assessment, intervention, surgery, and follow-up. Without those details, readers cannot determine the denominator behind any primary outcome estimate; no such estimate is posted in any case.

These omissions do not demonstrate that missing data or multiple testing caused bias. They mean the registry does not provide the information needed to assess either issue. The absence of reported methods should not be replaced with assumptions about the protocol or the analysis.

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 registry lists adverse-event figures separately for the post-intervention and pre-intervention groups. For the post-intervention group, 12 are listed at risk and 0 serious adverse events and 0 other adverse events are listed. For the pre-intervention group, 13 are listed at risk and 0 serious adverse events and 0 other adverse events are listed. No serious adverse-event terms are listed.

These are registry entries, not a complete account of how safety was monitored. The record does not report the definitions used for serious or other adverse events, the duration or completeness of follow-up, how events were solicited, or whether all participants were assessed in the same way. Death counts are not reported in the registry record. A listed zero should therefore be read as zero events recorded in that category in the registry entry, not as proof that no event occurred or that the intervention is safe.

The study was non-randomized and its arms are not described as a like-for-like control comparison. The figures do not establish whether safety differed between groups, and they do not support a causal comparison. They also do not speak to the primary METS endpoint or to the other feasibility outcomes. A cautious reading separates the recorded adverse-event counts from conclusions about event ascertainment, comparative safety, and clinical effect, none of which can be established from these entries alone.

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

The record establishes that a completed, single-centre feasibility study evaluated a prehabilitation programme in the setting of elective aortic aneurysm surgery. It identifies functional capacity, measured by change from baseline in METS at an expected six weeks, as the primary outcome. It also describes aims related to acceptability and potential design of a larger randomized controlled trial. These are useful descriptions of the study’s purpose and intended measurements.

The record does not establish the size or direction of a METS change. It provides no observed METS values, change estimate, confidence interval, or test result. In addition, it states that no patients in the pre-intervention group underwent pre-operative METS testing. The registry therefore cannot support a primary-endpoint comparison between the groups. A lack of posted results is not evidence that the endpoint did not change; it is a lack of reported outcome evidence in this registry record.

The non-randomized, before-and-after group structure also prevents interpreting the arms as equivalent groups differing only in access to prehabilitation. The registry explicitly cautions against a like-for-like comparison. Even if group results were available, differences could be associated with participant composition or the timing of the intervention, and the record does not report an adjustment strategy.

The safety entries list zero serious and zero other adverse events in each group, but information on event definitions and ascertainment is not reported in the registry record. Those entries are not enough to establish comparative safety. Likewise, the record lists other planned or secondary outcomes, including hospital resource use and length of stay, without posting analyzed findings for them.

The appropriate conclusion is narrow: this registry entry describes a feasibility study and its intended measures, but it does not provide the statistical results needed to quantify functional-capacity change or assess other outcomes. It neither demonstrates benefit nor demonstrates absence of benefit. A larger randomized trial was an intended next step in the stated rationale; the registry record does not report its design or results.

13. Why This Trial Matters Statistically

This study matters statistically because it illustrates the gap between defining a clinically relevant endpoint and having data that permit its analysis. METS at six weeks was specified as the primary measure of physical fitness, and the feasibility aims included assessing whether a larger randomized trial could be designed. Yet the registry says that the pre-intervention group had no pre-operative METS testing and posts no outcome analyses. The intended endpoint is therefore not accompanied by the information needed to estimate a comparative effect.

The case also shows why design labels should not be mistaken for causal evidence. A parallel structure describes how groups are organized, but non-random allocation does not make them comparable. Here the registry itself warns that the groups are not like-for-like controls. This matters when interpreting before-and-after programme evaluations, where changes over time and differences between participants can coincide with an intervention.

Feasibility studies can have a different role from efficacy trials. Their purpose may include determining whether recruitment, intervention delivery, adherence, and outcome measurement are workable. The brief summary identifies acceptability and compliance as intended considerations, but the registry does not post their results. It also describes the study as intended to inform design and power for a larger randomized trial. That rationale should not be confused with a reported sample-size justification or proof that a subsequent trial was conducted.

Finally, the record demonstrates the value of transparent reporting of outcome availability, analysis populations, missing-data methods, and uncertainty. Without these, readers cannot distinguish a precisely estimated small effect from an inconclusive or unavailable estimate. The absence of analysis in the registry is not itself a statistical finding about the intervention; it defines the limit of what this record can support.

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.

The limitations specific to this study begin with the absence of posted primary outcome results. The registry identifies change in METS at six weeks but provides no baseline or follow-up values, summary of change, measure of uncertainty, or statistical test. It also states that no patients in the pre-intervention group underwent pre-operative METS testing, so a direct group comparison for this endpoint is not supported by the reported data.

The non-randomized design and the registry’s explicit warning that the arms are not like-for-like controls limit causal interpretation. No reported adjustment methods address potential differences between participants or changes over time. The study was unmasked; any masking of assessors is not reported in the registry record. The programme is described only as introduction of a rehabilitation programme, and detailed content, delivery, adherence, and fidelity information is not reported.

The record does not report an analysis plan, sample-size justification, analysis populations, missing-data methods, or multiplicity approach. It lists six outcome measures but no analyses, so results for the primary or secondary outcomes cannot be assessed. The listed aims include several assessments, but the record does not establish which were completed or how many measurements were available.

Generalisability is also limited by the record describing a single-centre feasibility study among patients undergoing planned elective aortic surgery. It does not report enough detail about participant characteristics to judge how closely the enrolled group reflects other surgical populations. The safety entries lack reported definitions and follow-up details, and death counts are not reported in the registry record.

The record lists a duration of 1 year from 1st June 2014 in the brief summary, alongside a start of 2014-11 and primary completion of 2015-12. Their relationship is not explained. This reporting ambiguity does not establish an error, but readers cannot reconcile the timeline from the registry information alone.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Trimodal Prehabilitation for Aneurysm Surgery Study — NCT02292927.
• Registry record last updated 2019-07-17; status last verified 2019-05.
• Results first posted 2019-07-17.
• 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 describes NCT02292927, the Trimodal Prehabilitation for Aneurysm Surgery Study, as a completed, single-centre feasibility study sponsored by Imperial College London. It enrolled 25 participants and used a non-randomized, unmasked, parallel design. The intervention group received a prehabilitation programme; the other group was treated as standard before the intervention.

The primary endpoint was change from baseline in METS at an expected six weeks. The registry reports that no patients in the pre-intervention group underwent pre-operative METS testing and lists zero analyses. No primary or secondary outcome estimates are posted. The record cautions that the arms are not a like-for-like control comparison.

Adverse-event entries list zero serious and zero other events in each group; death counts are not reported in the registry record. The stated purpose was to assess acceptability and pre-operative functional capacity and inform planning of a larger randomized controlled trial. The entry does not establish a treatment effect or provide the outcome data needed to estimate one.