Ketamine Effect After Laparoscopic Gastric Reduction: A Randomized, Double-Blinded, Placebo Controlled Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Ketamine Effect After Laparoscopic Gastric Reduction: A Randomized, Double-Blinded, Placebo Controlled Study (NCT01997515), a randomized phase 4 study. The primary outcome is Quality of Recovery 40.

2. Clinical Question

The clinical rationale in the registry record connects postoperative pain management with concern about respiratory depression and hypoxemia in this surgical population. It describes ketamine as an intraoperative multimodal agent and identifies recovery and respiratory outcomes as questions of interest. Those considerations explain the motivation for the trial, but they do not establish what the posted outcome data demonstrate.

The primary outcome results are reported as medians and interquartile ranges for each arm. The posted results show a median score of 170.0 in Group K and 179.0 in Group P. These are descriptive summaries; the registry record does not report a statistical test, confidence interval, or adjusted estimate comparing the groups. The displayed medians alone do not establish whether the groups differ beyond the observed summaries.

The record lists postoperative opioid consumption, postoperative pain scores, and length of hospital stay as secondary outcomes. Those outcomes are not presented in the results information. Their numerical results and analysis details are not reported in the registry record.

3. Trial Design

This was a randomized, parallel-group, placebo-controlled trial listed as phase 4. The study title identifies it as double-blinded, and the registry record classifies masking as triple. The record does not identify which groups of people were masked, so the specific masking arrangements are not reported in the registry record. The sponsor was Northwestern University.

The registry record lists enrollment as 80 and the study status as completed. The study start is recorded as 2013-11, and primary completion as 2019-07-26. For the primary outcome, results are posted for 36 participants in Group K and 35 participants in Group P. The safety summary lists 40 participants at risk in each group. The record does not explain how these outcome populations relate to enrollment or provide participant-flow details, so reasons for the different counts are not reported in the registry record.

Group K received ketamine as an intraoperative bolus and infusion, with dosing adjusted to body weight. Group P received the same amount of saline. The registry record does not report additional details about treatment administration, adherence, or how the random sequence was generated and implemented.

The primary endpoint was Quality of Recovery 40 at 24 hours. The registry record describes the measure as a score ranging from 40 to 200, with low scores representing very poor recovery and high scores representing outstanding recovery. The results are summarized by median and interquartile range. Secondary outcomes listed are postoperative opioid consumption, postoperative pain scores, and length of hospital stay.

The registry record does not report a protocol-level sample-size justification, a statistical analysis plan, allocation concealment procedures, interim analyses, or a detailed account of analysis populations. It also does not post a formal comparison of the primary outcome between arms. The sample-size section on this page is a planning illustration based on the observed effect, not evidence of the trial’s original design assumptions or its achieved power.

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

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, measured over 24 hours.

The primary endpoint is the Quality of Recovery 40 questionnaire score at 24 hours. The record describes this as a score on a scale from 40 to 200: lower scores correspond to very poor quality of recovery, while higher scores correspond to outstanding quality of recovery. The outcome is intended to summarize a participant’s overall postoperative recovery rather than report a single symptom or clinical event.

A recovery questionnaire can capture multiple aspects of how a person is doing after surgery in a single summary measure. That makes it useful for a trial whose stated objective concerns overall quality of recovery. The registry record describes this endpoint as the main objective, with the investigators hypothesizing a greater global score in the ketamine group.

The posted summaries use medians and interquartile ranges. A median gives the middle value of the observed scores when arranged in order. An interquartile range describes the middle portion of those scores, from its lower to upper bound. These summaries convey the central location and spread of the observed outcomes without requiring the scores to be summarized by a mean and standard deviation.

The reported median was 170.0 for Group K, with an interquartile range from 158.0 to 177.0. For Group P, the median was 179.0, with an interquartile range from 166.0 to 187.0. These descriptive values do not, on their own, quantify the uncertainty in a between-group effect. A confidence interval or formal comparison is not reported in the registry record.

The endpoint is specified at 24 hours. The record does not provide further measurement or scoring procedures, details about questionnaire completion, or information about the handling of missing responses. Those details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is summarized by a median and interquartile range rather than a mean and standard deviation. In general, the median is the central observation after scores are ordered. It is less affected by unusually high or low values than the mean. The interquartile range gives the lower and upper bounds around the middle portion of the observed scores, showing how dispersed that central portion is.

For Group K, the posted median is 170.0 and the interquartile range is 158.0 to 177.0. For Group P, the median is 179.0 and the interquartile range is 166.0 to 187.0. These are summaries within each arm. They do not directly provide a confidence interval for a difference between arms, and they do not indicate the result of a statistical test. The record does not report whether the original analysis used a rank-based test, a model, or another method.

In general, a comparative analysis is needed to distinguish the observed arm-level summaries from an estimate of how outcomes differ between groups. Such an analysis may report an effect estimate and its uncertainty, often using a confidence interval, and may also report a test result. A confidence interval describes a range of values compatible with the data and the assumptions of the method. Its width communicates precision. Neither a confidence interval nor a formal test of the primary outcome is reported in the registry record.

Random assignment is intended, in general, to make the comparison between treatment groups less vulnerable to systematic differences in baseline characteristics. The registry record identifies the study as randomized, but does not report the sequence-generation method, allocation concealment, or baseline characteristics. It is therefore not possible from this record to assess those implementation details or describe adjustment for any imbalances.

The study is described as double-blinded in its title and as triple-masked in the registry classification. Masking can, in general, reduce the influence of expectations on care, reporting, or outcome assessment. The record does not identify who was masked or describe how masking was maintained. The specific protections against unmasking are not reported in the registry record.

There are no formal analyses posted in the registry record. In particular, it does not report a primary-outcome p-value, confidence interval, model specification, covariate adjustment, or prespecified analysis method. The results should therefore be read as descriptive summaries rather than as the output of a documented comparative statistical analysis. No adjusted effect or inferential conclusion can be reconstructed from the posted medians and interquartile ranges alone.

The record describes the primary outcome as a score on a bounded scale from 40 to 200. In general, bounded outcomes have limits that can affect their distribution, especially if observations cluster near a boundary. The posted medians do not show the full distribution, and the registry record does not include enough information to assess its shape, skewness, or concentration near either limit. There is likewise no reported discussion of whether the analysis accounted for such features.

The registry record lists secondary outcomes involving opioid consumption, pain scores, and hospital stay. It does not report numerical results or analytic methods for them. When a trial evaluates multiple outcomes, multiplicity can matter: the chance of obtaining at least one apparently notable result can change as the number of comparisons increases. In general, an analysis plan may address this through a prespecified hierarchy or adjustment, but neither a multiplicity strategy nor enough outcome results to evaluate one is reported in the registry record.

The sample-size section on this page is a planning illustration based on the observed effect, with stated assumptions of a two-sided significance level of 0.05, equal allocation, and a normal approximation. It is not the trial’s original sample-size justification, and it is not observed power. The registry record does not report the original sample-size calculation or its assumptions. Planning calculations describe hypothetical requirements under chosen assumptions; they do not establish the precision or evidential strength of the completed trial’s posted results.

In general, over-dispersion means that observed variability is greater than a model expects. It can make standard errors too small if a model does not accommodate the extra variability. The registry record does not identify a count model or report event-count analyses for the secondary outcomes, so over-dispersion cannot be assessed for those outcomes from the posted primary summaries.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists Quality of Recovery 40 as the primary outcome and lists postoperative opioid consumption, postoperative pain scores, and length of hospital stay as secondary outcomes. It does not report a prespecified hierarchy among outcomes, an adjustment for multiple comparisons, or another multiplicity strategy. In general, multiplicity matters when several outcomes or comparisons are examined because the interpretation of isolated findings can depend on how many analyses were planned. Here, the available record does not allow an assessment of that issue.

The results information includes the primary outcome but no numerical results for the listed secondary outcomes. Those secondary results and their analysis methods are not reported in the registry record. The record also does not report interim analyses, whether the primary endpoint or analysis was changed, or a detailed statistical analysis plan.

Outcome summaries are posted for 36 participants in Group K and 35 participants in Group P. Enrollment is listed as 80, and the safety summary uses 40 participants at risk in each arm. The record does not provide a participant-flow account or explain these different counts. It does not state whether the primary analysis was based on all randomized participants, participants who received assigned treatment, or participants with available outcome data. The analysis populations and reasons for unavailable outcome data are not reported in the registry record.

The record does not describe missing questionnaire responses, how incomplete scores were handled, or whether any imputation was used. It also does not report sensitivity analyses examining the effect of missing data. In general, missing-data methods rely on assumptions about why outcomes are unavailable; without a description of missingness and the analysis approach, those assumptions cannot be evaluated.

These omissions limit interpretation of the posted summaries. They do not demonstrate that missing data or multiplicity affected the results; rather, the registry record does not report enough detail to assess whether or how those issues were handled.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

The safety summary reports 40 participants at risk in Group K and 40 in Group P. It records zero serious adverse events in each group, zero other adverse events in each group, and zero deaths in each group. The registry record lists no top serious adverse-event terms.

These figures mean that the posted safety summary records no events in the listed categories for the participants counted as at risk. They do not show that the risk of an event is zero. A study’s observed event counts are limited to the participants and observation period represented in the record, and the record does not specify the safety follow-up duration or provide detailed event definitions.

The safety counts should be read separately from the primary quality-of-recovery summaries. They do not provide a formal comparison of safety between groups, and the registry record does not report a statistical analysis of adverse events. The record also does not explain why the safety population is 40 participants per group when the primary outcome summaries include 36 and 35 participants. That relationship is not reported in the registry record.

Zero reported events are a descriptive finding, not proof that an intervention has no adverse effects or that the groups have identical safety. The figures should be interpreted within the scope of the posted counts and the information about ascertainment available in the registry record.

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

The posted results show descriptive Quality of Recovery 40 scores at 24 hours for the ketamine and placebo groups. The median was 170.0 in Group K and 179.0 in Group P. The corresponding interquartile ranges were 158.0 to 177.0 and 166.0 to 187.0. These summaries provide information about the observed central scores and their spread in the two reported outcome groups.

The registry record does not report a formal between-group analysis, confidence interval, or p-value for the primary outcome. As a result, the posted summaries do not establish the precision of a comparative effect or whether the observed difference in medians is consistent with a dependable group difference. They also do not establish a causal effect beyond what could be assessed through a documented analysis of the randomized trial.

The study’s stated hypothesis anticipated a greater global recovery score in the ketamine group. The posted median in that group is lower than the placebo-group median, but this descriptive direction should not be treated as a definitive test of the hypothesis. Without the planned comparison and its uncertainty, it is not possible to determine whether the observed pattern is compatible with chance variation or to characterize the size of an underlying effect.

The registry record lists secondary outcomes, but does not report their numerical results in the information. It therefore does not support conclusions about opioid consumption, pain scores, or hospital stay. Similarly, the safety summary reports zero serious adverse events, other adverse events, and deaths in each listed group, but those counts do not demonstrate that event risk is absent or equivalent between groups.

The record documents a completed randomized trial and posts outcome summaries, but important details for interpretation are not reported: the formal analysis method, participant flow, missing-data handling, analysis populations, and original sample-size justification. The results are consequently best treated as a limited descriptive account of the posted data, rather than a complete statistical assessment of the trial’s primary or secondary questions.

13. Why This Trial Matters Statistically

This trial is statistically notable because it posts arm-specific summaries for a patient-centered recovery outcome but does not report a formal comparison of those summaries. Medians and interquartile ranges are useful descriptions of observed scores, yet they do not quantify the uncertainty around a treatment contrast. Readers may see the two groups’ values in tables and plots, but those displays cannot replace an estimate and uncertainty measure from a comparative analysis.

The registry record states a clear direction for the investigators’ hypothesis: a greater global quality-of-recovery score was expected in the ketamine group. The observed median is lower in that group than in the placebo group. The absence of a reported test or confidence interval makes this a useful example of why the direction of a descriptive summary and the strength of statistical evidence are distinct questions.

The record also illustrates how reporting populations can shape interpretation. Enrollment is listed as 80, the primary outcome summaries include 36 and 35 participants, and safety counts use 40 participants per arm. Without participant flow or analysis-population details, it is difficult to know how these summaries relate to the randomized sample. This is not evidence that the counts are incorrect; it is a limit on what can be determined from the registry record.

Finally, the trial lists several secondary outcomes but does not report their results in the information. When multiple outcomes are of interest, transparent reporting of the analysis plan and multiplicity approach helps readers distinguish prespecified primary evidence from exploratory comparisons. Those details are not reported in the registry record. The case underscores the value of reporting methods and uncertainty alongside outcome summaries, without implying a clinical conclusion from the available data.

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 main limitation for statistical interpretation is that the registry record does not report a formal comparison of the primary outcome. The medians and interquartile ranges describe the two groups, but no confidence interval, p-value, adjusted estimate, or model result is posted. The comparative uncertainty therefore cannot be evaluated from the record.

Participant counts are not fully reconciled. Enrollment is listed as 80, while the primary outcome summaries include 36 participants in Group K and 35 in Group P, and the safety summary lists 40 participants at risk in each arm. Participant flow, analysis populations, and explanations for these different counts are not reported in the registry record. Missing questionnaire data and its handling are also not described.

The registry record does not report the original sample-size justification, the statistical analysis plan, allocation concealment, the random-sequence method, or the identities of those masked. It does not report whether the primary analysis was adjusted for baseline characteristics, how the score distribution was assessed, or whether sensitivity analyses were conducted. The sample-size material on the page is a planning illustration rather than the trial’s documented design calculation.

Although secondary outcomes are listed, their numerical results and analytic methods are not reported in the registry record. Nor is a multiplicity strategy reported. This leaves the secondary questions and the handling of multiple outcomes unresolved in the posted information.

The safety summary provides event counts but does not report the duration of safety follow-up, detailed event definitions, or methods for event ascertainment. Zero recorded events in the listed categories should therefore be interpreted as counts in the posted safety summary, not as evidence that risk is absent. These limitations concern the completeness of the available record and do not establish that the trial itself did or did not address the issues.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Ketamine Effect After Laparoscopic Gastric Reduction: A Randomized, Double-Blinded, Placebo Controlled Study — NCT01997515.
• Registry record last updated 2019-10-07; status last verified 2019-10.
• Results first posted 2019-10-07.
• 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

NCT01997515 is a completed, phase 4, randomized, parallel-group, placebo-controlled study of intraoperative ketamine during laparoscopic gastric reduction surgery. Its title describes the trial as double-blinded; the registry classification lists triple masking. Enrollment is recorded as 80, and the sponsor is Northwestern University.

The primary outcome is Quality of Recovery 40 at 24 hours. The posted median was 170.0 in Group K, with an interquartile range of 158.0 to 177.0, and 179.0 in Group P, with an interquartile range of 166.0 to 187.0. The primary outcome summaries include 36 and 35 participants, respectively. No formal comparison is reported in the registry record.

The record lists postoperative opioid consumption, postoperative pain scores, and length of hospital stay as secondary outcomes. Their numerical results are not reported in the registry record. The safety summary records zero serious adverse events, zero other adverse events, and zero deaths in each group, with 40 participants at risk per group. Analysis methods, participant flow, missing-data handling, and the original sample-size justification are not reported in the registry record.