This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for A Test of Neural Inertia in Humans With Xenon (NCT02768727), a na phase 2 study. The primary outcome is Xenon Concentrations at Which Consciousness is Lost and Regained.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02768727 |
| Phase | Phase 2 |
| Condition | Neurocognitive Dysfunction |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 29 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Pennsylvania |
| Results posted | Yes |
2. Clinical Question
The study asks whether the brain concentration of xenon at loss of consciousness is the same as the concentration at return of consciousness. Thalamic xenon was to be assessed using CT imaging during xenon exposure. The registry description frames a significant difference between the two concentrations as evidence of hysteresis in circuits regulating arousal. This is a question about whether the two transition points coincide, rather than a comparison of xenon with a separate control treatment.
Population
The brief summary describes healthy volunteers ages 20-40 years. The primary outcome population is participants who completed a full induction and emergence xenon exposure with full-length concentration steps. The registry enrollment is 29; the number meeting the primary outcome population definition is not reported in the registry record.
Intervention
Participants received inhaled xenon gas, with concentrations ranging from 0% to 60%, according to the brief summary. The arm description identifies xenon anesthesia and CT imaging as part of the study approach.
Comparator
There is no separate control arm in the single-group design. The endpoint contrasts the thalamic xenon concentration at loss of consciousness with the concentration at return of consciousness within the study question.
Primary question
Are the thalamic xenon concentrations at loss and return of consciousness identical? The registry description says a significant difference would be interpreted as evidence of hysteresis. The numerical endpoint results and the analysis used to judge significance are not reported in the registry record.
The registry also names neurocognitive recovery, wristwatch actigraphy, and EEG delta power as secondary outcomes. Those measures broaden the study's stated interest beyond the primary concentration comparison, but their numerical results are not reported in the registry record. The primary question remains focused on the concentration associated with two transitions in consciousness under xenon exposure.
3. Trial Design
NCT02768727, titled “A Test of Neural Inertia in Humans With Xenon,” is listed as a phase 2 study sponsored by the University of Pennsylvania. Its status is completed. The recorded start is 2016-04, and the recorded primary completion is 2019-12-01. The condition listed is neurocognitive dysfunction, while the brief summary describes healthy volunteers ages 20-40 years. These registry descriptions should be read as separate record fields; the record does not explain the relationship between them.
The design is single-group, with allocation listed as NA and masking listed as none. Xenon is the sole intervention and the sole arm described. Accordingly, the primary question is not a randomized comparison between xenon and another assigned treatment. It instead concerns the measured concentration at loss and return of consciousness during xenon exposure. The registry does not report a separate control group or a between-group treatment contrast.
The brief summary says the study would enroll 24 healthy volunteers, while the registry enrollment is 29. The record does not explain this difference, and enrollment should not be taken as the number included in the primary analysis. The primary outcome description restricts its population to participants completing a full induction and emergence exposure with full-length concentration steps. The count meeting that criterion is not reported in the registry record.
The primary outcome is listed as a mean continuous measure, with thalamic xenon in mg/mL as its unit and standard error as its dispersion measure. Its timeframe is 4 hours. Three secondary outcomes address neurocognitive recovery, gross rest or activity measured by wristwatch actigraphy, and brain electrical activity measured by EEG delta power. The registry lists four outcome measures and one analysis, but does not identify the statistical procedure used for the primary comparison.
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
| Stage | Xenon |
|---|---|
| STARTED | 29 |
| COMPLETED | 13 |
| NOT COMPLETED | 16 |
Reasons for not completing this period:
| Reason | Xenon |
|---|---|
| Failure to meet inclusion criteria despite phone screen | 5 |
| Dose-finding timecourse | 1 |
| Oral secretions leading to supervising study physician termination of study | 6 |
| Equipment failure | 2 |
| Withdrawal by Subject | 1 |
| Subject dislodged xenon mask during exposure | 1 |
Analysis population for the primary outcome, as defined in the registry: All participants who completed a full induction and emergence xenon exposure with full-length concentration steps.
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.
| Characteristic | Unit | Xenon |
|---|---|---|
| Participants analysed | 29 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 29 |
| Age, Categorical: >=65 years | Participants | 0 |
| Age, Continuous | years | 24.0 (20 to 35) |
| Sex: Female, Male: Enrolled – Female | Participants | 12 |
| Sex: Female, Male: Enrolled – Male | Participants | 17 |
| Sex: Female, Male: Completing study – Female | Participants | 8 |
| Sex: Female, Male: Completing study – Male | Participants | 5 |
| Race/Ethnicity, Customized: White | Participants | 15 |
| Race/Ethnicity, Customized: Black or African American | Participants | 4 |
| Race/Ethnicity, Customized: Asian | Participants | 2 |
| Race/Ethnicity, Customized: Hispanic | Participants | 5 |
| Race/Ethnicity, Customized: Other/No Response | Participants | 3 |
| Region of Enrollment: United States | participants | 29 |
6. Primary Endpoint
The registry lists the primary outcome as Xenon Concentrations at Which Consciousness is Lost and Regained, measured over 4 hours.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Error |
| Unit | Thalamic Xenon (mg/mL) |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is titled “Xenon Concentrations at Which Consciousness is Lost and Regained.” It concerns thalamic xenon concentration, measured in mg/mL, at the loss and return of consciousness. CT imaging is identified as the means of determining brain xenon concentration. The recorded timeframe is 4 hours, and the population is limited to participants completing a full induction and emergence xenon exposure with full-length concentration steps.
The endpoint is used to address whether the two transition concentrations are identical. The registry description states that a significant difference would be taken as evidence of hysteresis in circuits regulating arousal. In general, comparing concentrations at both transitions can describe whether the measured state change follows the same concentration point in each direction. The endpoint therefore operationalizes the study's stated neural inertia question through a continuous measurement.
The measure is characterized as a mean with standard error. In general, a mean describes the central value of a continuous measurement, while a standard error describes the precision of an estimated mean. It is not the same quantity as the spread of individual participant values. The record does not report the mean concentration at either transition, the standard errors, the estimated difference, a confidence interval, or a significance result. Therefore, the endpoint's observed direction, size, and precision are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record states the scientific question and the intended endpoint, but it does not report numerical primary results. In particular, no mean thalamic xenon concentration at loss or return of consciousness is reported, and no standard error or estimated difference is reported. There is also no confidence interval, p-value, or other stated statistical test result. The record therefore does not establish from its posted results whether the two measured concentrations were identical, different, or estimated with enough precision to distinguish between those possibilities.
The endpoint description proposes an interpretation: if the concentrations are significantly different, the study would regard that as evidence of hysteresis in circuits regulating arousal. That statement describes the intended interpretation of a possible result; it is not itself a report that such a difference was observed. Without the actual estimates and inferential result, the proposed interpretation cannot be applied to the trial's outcome.
Because this is a single-group study, the primary question is not answered by comparing assigned treatment groups. The scientific contrast is between the two points of consciousness transition under xenon exposure. The registry does not report how observations at those points were statistically compared, whether the analysis accounted for repeated measurements, or what criterion was used to determine statistical significance. Those details are not reported in the registry record.
The stated primary population is also narrower than the overall enrollment field: it includes participants completing a full induction and emergence exposure with full-length concentration steps. The number of participants meeting that definition and the number contributing to the endpoint are not reported in the registry record. As a result, the enrollment value cannot establish the analysis population size or the precision of the endpoint estimate.
Three secondary outcomes are named, covering neurocognitive recovery, rest or activity, and EEG delta power. Their names indicate the domains measured, but do not convey observed effects. Numerical results for these outcomes are not reported in the registry record. The record lists four outcome measures and one analysis, but does not clarify how that analysis relates to the outcomes or whether multiplicity was addressed.
In general, a confidence interval would communicate the uncertainty around an estimated concentration or contrast, while a p-value would address compatibility with a specified null hypothesis under an analysis model. Neither can replace the effect estimate itself, and neither is reported for the primary endpoint in the registry record. Without these results, the most defensible interpretation is limited to the study question, outcome definition, and design, not an empirical conclusion about neural inertia.
9. Statistical Methods Explained
The registry identifies the primary outcome as a continuous measure summarized by a mean and standard error. This describes the intended form of the endpoint summary, but does not identify the statistical test or model used to compare loss and return of consciousness. The method, adjustment strategy, and assumptions behind the analysis are not reported in the registry record.
What does a mean describe?
In general, a mean is a way to summarize the central level of a continuous measurement. Here the measured quantity is thalamic xenon concentration in mg/mL. For the clinical question, the relevant summaries would concern concentration at loss of consciousness and at return of consciousness. Reporting both estimates would let readers see their levels, while a directly estimated contrast would communicate the size and direction of the difference. The registry record does not report those values.
What does the standard error describe?
In general, the standard error describes how precisely a sample-based estimate, such as a mean, is estimated. It is not a description of the range of values among individual participants. A small standard error can accompany measurements that vary considerably among people if the estimate is based on enough informative observations; conversely, participant variability and estimation precision are distinct concepts. The primary outcome lists standard error as the dispersion measure, but no actual standard error is reported in the registry record. Thus the stated summary type does not by itself show how precise the endpoint estimate was.
Why does the comparison structure matter?
In general, an analysis should reflect how observations arise. If two measurements come from the same participant, their within-person relationship can matter to the uncertainty of the estimated contrast. If measurements are independent, the analysis has a different structure. The registry describes loss and return of consciousness in the same xenon exposure question, but does not state the statistical procedure, whether the data were analyzed as paired observations, or how any incomplete measurement sequences were handled. It would be inappropriate to assume a particular model from the endpoint title alone.
What would an interval add?
In general, a confidence interval presents a range of values compatible with the data and analysis under its assumptions. For this endpoint, an interval around the concentration contrast could show both the estimated difference and the precision of that estimate. An interval containing values near no difference would not, by itself, prove equality; interpretation depends on the interval's width and the scientific context. The registry record does not report a confidence interval or a prespecified equivalence margin. It therefore does not support a conclusion that the concentrations are equivalent.
What is the role of a significance test?
In general, a significance test evaluates data relative to a null hypothesis and an analysis model. A result below a chosen threshold is not a measure of the size or importance of an effect. The registry's endpoint description uses a significant difference as the proposed evidence for hysteresis, but the record does not report the test, its threshold, or a p-value. The description should not be mistaken for evidence that the threshold was met.
How should the listed analysis count be read?
The registry lists one analysis and four outcome measures, but does not describe the analysis method or map it to a particular outcome. A count of analyses is not enough to establish whether the primary and secondary outcomes were analyzed separately, whether a single model covered multiple outcomes, or whether adjustments were made. No analysis-specific estimates are reported in the registry record.
Why can over-dispersion matter?
In general, over-dispersion occurs when observed variability is greater than a model assumes. If present, standard errors calculated under an overly restrictive variance assumption may be too small, making results appear more precise than warranted. The relevance of over-dispersion depends on the outcome and model. The primary endpoint is continuous, and the registry does not report a model or evidence about over-dispersion; there is no basis in the record to say that this issue was assessed or affected the analysis.
The record also includes planning assumptions for sample-size illustrations: two-sided significance level 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of an observed effect. It specifies that non-time-to-event illustrations would be participants per arm. Those assumptions describe planning illustrations, not the trial's single-group design, and no resulting sample-size values are reported in the registry record. They are not observed power and do not substitute for the trial's reported endpoint estimates. A sample-size justification for this study is not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry names the primary endpoint and three secondary outcomes: neurocognitive recovery upon emergence, gross rest or activity measured using wristwatch actigraphy, and brain electrical activity measured by EEG delta power. It lists four outcome measures and one analysis. These entries identify the areas of measurement but do not specify how many hypotheses were tested, which outcomes were included in the listed analysis, or whether any multiplicity adjustment was used. A multiplicity plan is not reported in the registry record.
In general, when several outcomes or comparisons are examined, the chance of at least one apparently unusual result can depend on the number and structure of the analyses. Methods for addressing multiplicity vary according to the scientific aims and analysis plan. The record does not say whether outcomes were treated as confirmatory or exploratory, whether there was an ordered testing strategy, or whether the significance threshold was adjusted. No inference about adjustment should be drawn from the listed analysis count alone.
The primary outcome population is defined as participants completing a full induction and emergence xenon exposure with full-length concentration steps. The record does not report how many participants met that definition, whether any participants were excluded from the analysis, or how missing or incomplete observations were handled. It also does not describe an intention-to-treat, per-protocol, or other analysis population. Those details are not reported in the registry record.
In general, missing-data methods can affect estimates when not all planned measurements are available. Transparent reporting would identify the amount and pattern of missingness and explain the assumptions used to analyze incomplete observations. The registry does not provide those details, so the potential effect of missing measurements on the primary or secondary outcomes cannot be assessed. Interim analyses and stopping rules are not reported in the registry record.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Xenon | 0 | 29 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Xenon | 0 of 29 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Xenon | 0 of 29 |
The adverse-event entry for the Xenon group lists 29 at risk for serious adverse events and 0 affected. It also lists 29 at risk for other adverse events and 0 affected, with 0 deaths. No top serious adverse-event terms are listed. These are the registry's posted counts for the categories shown.
In general, an at-risk count identifies the group represented in an adverse-event summary, while an affected count reports the recorded events or participants according to that registry field's convention. The record does not define the counting convention in the information, so the figures should be quoted as listed rather than reinterpreted. The adverse-event entries do not report event timing, severity details beyond the serious-event category, duration, or individual-level information.
Zero affected in the posted categories means no events are recorded in those categories in this entry; it should not be extended into a claim that every possible harm was absent. The adverse-event figures are separate from the primary concentration endpoint and do not supply evidence about whether the loss and return concentrations differed. The registry does not provide additional safety analysis details, and the reported counts do not establish the completeness of safety surveillance.
12. What the Result Does, and Does Not, Mean
The registry record documents a completed phase 2, single-group study of xenon with a primary question about thalamic xenon concentration at loss and return of consciousness. It defines the endpoint as a mean continuous measure in mg/mL, with standard error as the dispersion measure, and identifies CT imaging as the means of determining brain concentration. The record also defines the primary population by completion of a full induction and emergence exposure with full-length concentration steps.
What the record does not provide is the primary endpoint's observed means, standard errors, contrast, confidence interval, or significance result. It therefore does not permit a reader to judge the direction, magnitude, or precision of any difference between the two transition concentrations. The endpoint description explains how the investigators proposed to interpret a significant difference, but it does not report that such a difference was found. Nor does the record report evidence establishing that the values were equivalent.
The single-group design also limits what can be inferred about comparisons with other anesthetic agents. The brief summary states an objective concerning whether the order of neurocognitive function is invariant among anesthetic agents, but the intervention and arm descriptions identify xenon, with no separate comparator arm described. A finding from this design alone cannot be treated as a randomized comparison among anesthetic agents. The record does not explain how that broader objective was addressed.
The intended enrollment of 24 volunteers in the brief summary and the registry enrollment of 29 are both recorded, but the reason for the difference is not stated. Neither value establishes how many participants contributed to the primary endpoint. The registry's primary population definition makes completion of specific exposure steps relevant, but its analysis count is not reported.
Overall, the registry supports a description of the research question, design, endpoint, and posted adverse-event counts. It does not support a conclusion about whether neural inertia was observed, how large any concentration difference was, or how precisely it was estimated. Those conclusions require numerical outcome results and analysis details that are not reported in the registry record.
13. Why This Trial Matters Statistically
This trial is statistically interesting because it expresses a question about neural inertia as a comparison of a continuous brain concentration at two transitions: loss and return of consciousness. That framing makes clear that the scientific issue is not only whether consciousness changes during xenon exposure, but whether the measured concentration associated with the transition differs by direction. The endpoint description links a difference to hysteresis, while leaving the actual statistical evidence unavailable in the registry record.
The single-group design makes the distinction between a within-study transition comparison and a controlled treatment comparison important. A concentration measured at two stages of an exposure is not the same estimand as a difference between independently assigned treatment groups. The stated primary population, restricted to participants with full induction and emergence and full-length concentration steps, also matters for defining which observations can inform the endpoint. The number meeting that definition is not reported.
The record illustrates why a measure's summary label is not a result. Calling the outcome a mean with standard error tells readers the planned summary format, but does not reveal the estimated mean, participant variability, or precision. A direct contrast and its uncertainty would be needed to evaluate the central question. Without them, the scientific rationale can be described, but the empirical finding cannot be reconstructed.
It also shows the value of distinguishing planning illustrations from the design actually registered. The listed sample-size assumptions refer to equal allocation between two arms, whereas this study is registered as single-group with allocation NA. No illustration values or study-specific sample-size justification are reported. Those planning assumptions should therefore not be treated as evidence about the trial's observed precision or power.
Finally, the presence of several secondary outcomes raises questions about analysis planning and multiplicity that the record does not resolve. The registry names the outcomes and lists one analysis, but gives no analysis plan or numerical results. This makes the trial a useful example of how registry design fields can identify a question without supplying enough information to evaluate its statistical answer.
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 most important limitation for interpreting the registry record is the absence of numerical primary outcome results. The outcome is defined, but its means, standard errors, estimated contrast, interval estimate, and significance result are not reported. No empirical conclusion about the primary question can be drawn from the endpoint description alone.
The primary analysis population is specified by completion of a full induction and emergence xenon exposure with full-length concentration steps, but the number meeting that criterion is not reported. The registry enrollment is 29, while the brief summary describes an intended enrollment of 24 healthy volunteers; the record does not explain the difference. Neither entry identifies the number contributing to the primary endpoint or the reasons any records might not contribute.
The study is listed as single-group, with allocation NA and no masking. The record does not describe a comparator arm, and the primary question therefore does not represent a randomized between-treatment comparison. While the brief summary includes an objective about whether neurocognitive function order is invariant among anesthetic agents, the registry descriptions do not identify a comparative design addressing that objective. The relationship between the broad objective and the listed single-group intervention is not reported.
Methods needed to assess the statistical result are also absent: the test or model, handling of repeated measurements, missing-data approach, multiplicity procedure, and any prespecified threshold for significance are not reported in the registry record. The listed mean and standard error do not resolve these omissions. The record also does not report a sample-size justification or interim-analysis plan.
These limitations concern what can be concluded from the registry entry. They do not establish that the study lacked further methods or results outside the record; those details are simply not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Test of Neural Inertia in Humans With Xenon — NCT02768727.
- Registry record last updated 2026-08-31; status last verified 2026-08.
- Results first posted 2026-08-31.
- 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.
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18. Record Summary
NCT02768727 is a completed phase 2, single-group study sponsored by the University of Pennsylvania. It evaluates xenon exposure and asks whether thalamic xenon concentrations at loss and return of consciousness are identical. The primary endpoint is a mean concentration in mg/mL, with standard error listed as the dispersion measure and a 4 hours timeframe. The primary population is participants completing a full induction and emergence exposure with full-length concentration steps.
The registry enrollment is 29, while the brief summary describes an intended enrollment of 24 healthy volunteers ages 20-40 years. The record does not explain the difference or report the number contributing to the primary analysis. Three secondary outcomes cover neurocognitive recovery, actigraphy, and EEG delta power. Numerical primary and secondary results, analysis methods, missing-data handling, and multiplicity procedures are not reported in the registry record. The adverse-event entry lists 0 serious events, 0 other events, and 0 deaths.