Effect of Single Dose Ketamine and Magnesium on Postoperative Pain in Patients Undergoing Bariatric Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effect of Single Dose Ketamine and Magnesium on Postoperative Pain in Patients Undergoing Bariatric Surgery (NCT02334059), a randomized na study. The primary outcome is Total Hydromorphone Use.

2. Clinical Question

The clinical question concerns whether hydromorphone use differs among the listed treatment groups in the setting of bariatric surgery. The registry’s stated rationale is the importance of opioid-sparing analgesia in the post-operative obese population and the limited literature on ketamine and magnesium in bariatric surgical patients. That rationale explains the topic of the trial; it is not evidence of a treatment effect.

Three groups allow the trial to study ketamine, the combination of ketamine and magnesium, and placebo. However, the record does not specify which pairwise or overall comparison was designated as the principal test, whether each active group was to be compared with placebo, or whether the combination was to be compared directly with ketamine alone. The posted primary outcome information therefore does not establish the intended contrast or report the findings for any contrast.

3. Trial Design

The registry describes a randomized, triple-masked, parallel-group trial with an enrollment of 108. The listed interventions are ketamine, ketamine plus magnesium, and placebo. The record gives a ketamine dose of 0.5 mg/kg IV, a combination regimen of ketamine 0.5 mg/kg IV plus magnesium 2 grams IV, and placebo described as normal saline. The registry does not report the randomization method, allocation concealment procedures, or the identities of the groups included in the masking term.

The parallel model means participants were assigned to a treatment group rather than being described as receiving each treatment in sequence. The record does not report further design details, such as the allocation ratio or the timing of treatment relative to surgery. Although the study is identified as randomized and triple-masked, the specific procedures used to implement those features are not reported in the registry record.

The trial is listed with phase NA and status COMPLETED. The listed start is 2015-11, and primary completion is dated 2019-03-13. The sponsor is Milton S. Hershey Medical Center. The registry identifies three outcome measures and lists pain scores using a verbal analogue scale and intraoperative minimum alveolar concentration of desflurane as secondary outcomes. It does not provide numerical results for those outcomes in the information available for this analysis.

The primary outcome is total hydromorphone use, expressed as a mean with a 95% confidence interval. Its timeframe is described as during surgery and 24 hours post-op, while its outcome description says total use in the first 24 hours post-operatively. The registry does not clarify the difference between these descriptions. It also does not report a primary comparison or provide a single result suitable for interpreting the outcome across the three groups.

The record lists 108 enrolled participants. Its adverse-event entries list group denominators of 37 for ketamine, 34 for ketamine plus magnesium, and 37 for placebo. The registry does not explain in this information how those denominators relate to enrollment, randomization, treatment receipt, or inclusion in each efficacy analysis. Those distinctions matter: enrollment does not by itself establish how many participants contributed data to a particular endpoint.

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 Total Hydromorphone Use, measured over During surgery and 24 hours post-op.

The primary endpoint is total hydromorphone use, reported as a mean in mcg/Kg. Hydromorphone is an opioid analgesic, and the trial’s stated rationale focuses on opioid-sparing analgesia after bariatric surgery. Measuring total use can describe the amount of this medication used over the specified period, making it relevant to the trial’s stated research question. This description concerns the endpoint’s role; it does not establish that any treatment reduced medication use.

The registry specifies a mean and a 95% confidence interval as the outcome parameter and dispersion measure. A mean represents the average measured amount in a group. A confidence interval describes uncertainty around an estimate under the statistical method used to construct it. Its width is relevant to precision: a narrower interval indicates greater precision than a wider interval, given the same estimation framework. The registry information does not include the arm-level means or confidence intervals, so the size and precision of the observed results cannot be assessed.

The time window needs careful reading. The timeframe says “During surgery and 24 hours post-op,” whereas the outcome description says “Total hydromorphone use in 1st 24 hours post-operatively.” These wordings do not define precisely the same measurement window. The registry does not resolve whether intraoperative use is included in the primary endpoint or clarify the exact start and end points of measurement.

The record also does not state the primary comparison, analysis population, or how missing measurements were handled. Without those details and the numerical results, the endpoint definition alone cannot answer whether groups differed or how precisely any difference was estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a randomized, triple-masked, parallel-group trial and a continuous primary measure summarized as a mean with a 95% confidence interval. Those terms describe aspects of design and reporting, but the record does not give the statistical analysis plan or a numerical result for the primary outcome. The explanations below are general statistical context, not claims about methods that this trial used beyond the details explicitly recorded.

What does randomization contribute?

In general, randomization assigns participants to groups by chance. Its purpose is to reduce systematic differences between groups at assignment, including differences that may not have been measured. It does not guarantee that groups will be identical, especially in a finite trial, and it does not remove the need to report how assignment was implemented. The registry says that allocation was randomized but does not report the sequence-generation method, allocation concealment, or allocation ratio.

The parallel design means treatment groups are followed alongside one another rather than describing a crossover sequence. The registry lists three arms. It does not give details on treatment timing or on how participants were handled if they did not receive their assigned regimen. Those details can affect interpretation of an analysis and cannot be inferred from the word “parallel.”

What does triple masking mean?

Masking is intended to limit the influence of treatment knowledge on conduct, assessment, or interpretation. The registry labels the study triple-masked, but does not identify which roles were masked or describe how masking was maintained. Therefore, the label can be reported, but the specific practical safeguards cannot be evaluated from this record.

How should a mean be understood?

For a continuous outcome, the mean is the arithmetic average of measured values in the group being summarized. The primary outcome is total hydromorphone use in mcg/Kg. An average can provide a concise description, but it does not show the full distribution of individual observations. Information about spread, skew, outliers, or the distribution of values is not reported in the registry information available for this analysis. In general, those features may matter when choosing or evaluating a statistical model.

What does a confidence interval communicate?

In general, a confidence interval expresses uncertainty about an estimated quantity under the assumptions of the calculation method. It is not a guarantee that a particular interval contains the true value, and it is not a direct measure of clinical importance. The interval’s width gives information about precision, while its location describes the values compatible with the estimate and method. The registry specifies 95% confidence intervals for the primary outcome but does not provide their numerical values. It is therefore not possible to assess precision for this trial’s primary outcome.

When comparing groups, an interval around a contrast is often more directly informative than separate intervals around each group mean. The registry record does not identify a contrast or state whether comparisons were adjusted. No comparison-specific estimate or interval can be interpreted from the listed endpoint definition alone.

Why do comparison choices matter?

With three groups, more than one contrast can be considered: an active regimen against placebo, the combination against ketamine, or other comparisons. These answer different questions. General statistical practice distinguishes a prespecified primary contrast from additional analyses because examining multiple contrasts can increase the chance of at least one apparently notable result. The registry does not state the intended primary contrast or report a multiplicity procedure. No correction or testing strategy should be attributed to the trial without such information.

The record notes that the primary outcome has several categories or time points and is not reduced to one comparison. This makes the absence of a clearly reported primary contrast especially consequential. A result for one time point or category would not automatically describe all other time points or categories. The exact structure of those categories or time points is not reported in the registry information used for this analysis.

What is over-dispersion, and is it relevant?

In general, over-dispersion occurs when observed variability is greater than a statistical model assumes. It can make uncertainty estimates too small if the model fails to account for that extra variation. It is not possible to determine from the registry record whether over-dispersion applies to this endpoint or whether a model accommodating it was considered. The primary outcome is described as a mean of a continuous measure, but no distributional diagnostics or model details are reported.

What does a planning illustration mean?

In general, a sample-size calculation translates assumptions about an effect, variability, allocation, significance level, and desired power into a planning target. Such a calculation is not an observed result and does not show the probability that the completed trial found a real effect. A planning illustration based on an observed effect is also conditional on that estimate, which may be uncertain. The record describes an illustration using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects defined as fractions of an observed effect. Those are illustration assumptions, not evidence of the trial’s own design rationale. The registry does not report the trial’s sample-size justification or any interim-analysis plan.

In general, power is a design quantity tied to a specified alternative and assumptions; it should not be presented as “observed power” after results are known. The illustration’s stated convention distinguishes participants per arm for ordinary outcomes from total events for time-to-event outcomes. The primary measure in this record is continuous, not identified as a time-to-event endpoint. No numerical planning target is reported in the registry information available for this analysis, and no target should be mistaken for the number analyzed.

What can be evaluated from this record?

The design labels, intervention descriptions, primary outcome definition, and adverse-event counts can be described. The statistical analysis plan, analysis populations, handling of missing values, primary contrast, and numerical efficacy findings are not reported in the registry record. As a result, readers cannot check whether the chosen analysis matched the design, whether uncertainty was estimated appropriately, or whether conclusions were robust to alternative assumptions.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures and identifies pain scores using a verbal analogue scale and intraoperative minimum alveolar concentration of desflurane as secondary outcomes. The primary measure is total hydromorphone use. The record also indicates that the primary outcome involves several categories or time points and is not reduced to one comparison. However, it does not identify a primary contrast among the three treatment groups, specify which time point or category was the principal one, or describe a plan for controlling multiplicity.

In general, multiplicity arises when several hypotheses, outcomes, time points, or group contrasts are tested. Considering more tests can increase the chance of obtaining at least one apparently unusual result by chance. Statistical plans may address this through prespecification, adjustment, or a hierarchy of tests. The record does not report whether any such approach was used, so none should be assumed. Numerical results for the secondary outcomes are not reported in the registry information available for this analysis.

Missing-data handling is also not reported in the registry record. There is no description of how missing outcome measurements were identified, whether any imputation was used, or how incomplete follow-up was handled. The analysis populations are not described: the record does not state whether the primary analysis included all randomized participants, only participants who received treatment, or another defined group.

These omissions limit assessment of possible bias. The enrollment figure does not by itself establish the denominator for an efficacy analysis, and the group counts in the adverse-event entries do not establish how many participants contributed primary outcome data. Without analysis denominators, missingness details, and a stated analysis population, the completeness and comparability of outcome data cannot be evaluated.

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 0% reporting threshold.

The registry’s serious-adverse-event entries list zero serious events for ketamine, zero for ketamine plus magnesium, and zero for placebo. They also list zero other events and zero deaths in each group. The denominators recorded for those entries are 37, 34, and 37, respectively, in the same group order. These figures describe the registry entries; they do not establish that every possible event was captured or that the groups had equivalent safety.

In general, an event count is interpreted in relation to the number of people observed, the event definitions, the length of follow-up, and the completeness of ascertainment. The registry information does not give definitions for serious and other events, describe how events were collected, or specify the observation window for these safety entries. It also does not provide a comparative statistical analysis of safety.

Zero recorded events should not be read as proof that the underlying event risk is zero. It means that no events in the listed categories were entered for the stated group denominators in these registry entries. The counts do not describe unrecorded events, events outside the registry’s categories, or outcomes beyond the reported observation period. They also cannot be used to infer a difference between treatments without a prespecified comparison and suitable uncertainty estimates.

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

The registry record documents a completed randomized, triple-masked, parallel-group trial of ketamine, ketamine plus magnesium, and placebo in patients undergoing bariatric surgery. It identifies total hydromorphone use as the primary outcome and gives a mean and 95% confidence interval as its intended summary. It also lists secondary outcomes concerning pain scores and desflurane MAC.

What the record does not provide is the numerical primary outcome result or a single primary comparison. The group means, confidence intervals, and statistical tests are not reported in the information available for this analysis. Consequently, the magnitude and direction of any difference cannot be described, and the precision of an estimated effect cannot be judged. No claim about the comparative effect of the interventions follows from the trial’s rationale, design, or completion status alone.

The endpoint timeframe is described in two ways: “During surgery and 24 hours post-op” and “Total hydromorphone use in 1st 24 hours post-operatively.” The record does not clarify whether intraoperative use is included in the primary measure. That ambiguity makes it important not to imply a more precise measurement window than the registry states.

The listed zero adverse-event counts are descriptive entries, not proof of absence of all harms or evidence that the regimens have the same safety profile. The event definitions, collection methods, and safety follow-up window are not reported. Likewise, no numerical findings are available for the listed secondary outcomes in this analysis.

In general, a trial result is interpreted by considering the estimate, its uncertainty, the prespecified comparison, outcome measurement, and analysis population. Several of these elements are not reported in the registry record. The appropriate reading is therefore limited: the record establishes the trial’s stated design and measures, but does not allow an assessment of treatment differences or their statistical precision.

13. Why This Trial Matters Statistically

This trial raises a useful statistical question about how a three-arm study should define and communicate its main comparison. Ketamine, ketamine plus magnesium, and placebo represent distinct groups, but those groups can support different scientific contrasts. Comparing each active regimen with placebo asks a different question from comparing the combination directly with ketamine alone. Without a stated primary contrast, readers cannot tell which comparison was intended to carry the main inferential weight.

The endpoint also highlights the importance of precise outcome definitions. Total hydromorphone use is described as the primary measure, but its timeframe is worded as both during surgery and 24 hours post-op and as the first 24 hours post-operatively. Clear measurement boundaries are necessary for reproducibility and for interpreting what a group mean represents. The registry does not resolve that wording difference.

For statistical interpretation, a mean without its numerical estimate and confidence interval cannot convey either the observed amount or its precision. Similarly, a completed status and a stated sample size do not substitute for analysis denominators or outcome results. The distinction between enrollment and the participants included in an endpoint analysis is central to assessing how much information supports an estimate.

The registry’s stated rationale concerns opioid-sparing analgesia and sparse literature involving ketamine and magnesium in bariatric surgical patients. That context explains why the question was studied. Statistically, however, a clear comparison, transparent analysis plan, outcome reporting, and uncertainty estimates are needed to determine what the results support. The information does not report those efficacy results, so it cannot establish whether the groups differed or how precisely a difference was estimated.

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 interpreting this trial from the registry record is the absence of numerical efficacy results for the primary outcome. The record names total hydromorphone use and its intended summary, but does not provide group means, confidence intervals, or a reported test. It also does not identify one primary comparison among the three groups. Without those elements, neither the direction nor the size of an effect can be assessed.

The endpoint’s time window is not fully clear. The timeframe refers to surgery and 24 hours post-op, while the description refers to the first 24 hours post-operatively. The registry does not explain whether these phrases refer to the same measurement period or whether intraoperative use is included.

The record does not report the trial’s eligibility criteria, randomization method, allocation concealment, allocation ratio, or the specific roles covered by triple masking. It also does not describe the primary analysis population, missing-data procedures, protocol deviations, or a statistical analysis plan. These gaps prevent assessment of whether all randomized participants were analyzed as intended and whether incomplete outcome data could affect the results.

Although secondary outcomes are listed, their numerical findings are not reported in the registry information available for this analysis. The record does not state how multiple comparisons, outcome categories, or time points were handled. The adverse-event entries list no events, but the definitions, surveillance methods, and observation window are not given. These limitations mean the entries cannot support a comprehensive comparison of safety.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Effect of Single Dose Ketamine and Magnesium on Postoperative Pain in Patients Undergoing Bariatric Surgery — NCT02334059.
• Registry record last updated 2020-06-01; status last verified 2020-05.
• Results first posted 2019-11-19.
• 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 NCT02334059, a completed randomized, triple-masked, parallel-group trial sponsored by Milton S. Hershey Medical Center. It lists an enrollment of 108 and three groups: ketamine at 0.5 mg/kg IV, ketamine at 0.5 mg/kg IV plus magnesium 2 grams IV, and placebo described as normal saline.

The primary outcome is total hydromorphone use in mcg/Kg, summarized as a mean with a 95% confidence interval. Its timeframe wording differs between surgery plus 24 hours post-op and the first 24 hours post-operatively. Pain scores using a verbal analogue scale and intraoperative minimum alveolar concentration of desflurane are listed as secondary outcomes.

The registry does not report a single primary comparison or numerical efficacy results for the primary outcome in the information available for this analysis. Its adverse-event entries list zero serious events, zero other events, and zero deaths for each group. The record does not describe the statistical analysis plan, missing-data handling, or analysis populations.