Anesthesia and Motor Evoked Potential (MEP) Recruitment: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Anesthesia and Motor Evoked Potential (MEP) Recruitment (NCT02199314), a na na study. The primary outcome is Effect of Pulse Train Length on Transcranial Motor Evoked Potentials (TcMEP) Area Under Total Intravenous Anesthesia (TIVA) and TIVA Plus 3% Desflurane.

2. Clinical Question

The study aims to test the hypothesis that larger motor responses can be recruited by transcranial stimulation. Its specific focus is whether the area response across pulse-train lengths differs between the anesthetic conditions. The record describes measurements at two time points and says that data from different pulse-train lengths were used to calculate regression coefficients for each participant under each condition.

The within-participant structure means that each person contributes measurements under both conditions. In general, this can account for stable differences between participants when comparing their measurements. It does not, by itself, establish that any difference is caused by desflurane: other changes over time or during the procedure could also be relevant. The registry record does not report an endpoint result, so it cannot establish the direction or size of any observed change.

3. Trial Design

This is a completed, single-group study with enrollment of 30 participants. It is listed as a study of idiopathic scoliosis, sponsored by Children's Hospital Medical Center, Cincinnati. The registry lists phase as NA, allocation as NA, and masking as NONE. The record gives a start date of 2013-03 and primary completion of 2016-04.

The design uses participants as their own controls. TcMEPs are recorded under TIVA and again after desflurane is added. The arm description specifies desflurane at 3% and says measurements are obtained after at least 5 minutes. The primary outcome description gives the post-addition interval as 5 minutes and describes measurements at two time points during a surgical procedure. It does not describe a separate control group receiving a different anesthetic regimen.

The outcome procedure describes a series of 15 transcranial motor evoked potentials under TIVA and again after desflurane is added. It says there were 3 runs of pulse trains with lengths of 5, 6, 7, 8, and 9, with each train separated by 30 seconds. The runs were averaged to obtain TcMEP amplitude and area values for the pulse-train lengths. Regression coefficients for area versus pulse length were then calculated for each participant under TIVA and under TIVA plus desflurane.

The record does not report random allocation, and the listed allocation is NA. It also does not report masking procedures, beyond listing masking as NONE. The described within-participant measurements should therefore not be interpreted as a blinded, randomized, parallel-group comparison. The sequence described is measurement under TIVA followed by measurement after desflurane is added; details about counterbalancing or other order procedures are not reported in the registry record.

The registry marks the study COMPLETED, but completion status does not state how many participants completed the outcome measurements or contributed to the final endpoint. That number, along with details about withdrawals and exclusions, is not reported in the registry record.

4. Participant Flow and Accounting

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

Before assignment: There was no group assignment - each participant was to be his/her own control.

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.

Population: 30 participants initially enrolled. 12 were withrdrawn prior to any analysis. Data from 18 participants analyzed as 18 participants had part 1 of study procedures completed. 14 participants completed the study, that is had both part 1 and part 2 procedures.

6. Primary Endpoint

The registry lists the primary outcome as Effect of Pulse Train Length on Transcranial Motor Evoked Potentials (TcMEP) Area Under Total Intravenous Anesthesia (TIVA) and TIVA Plus 3% Desflurane, measured over 15 minutes.

The primary endpoint is a count of participants, rather than a mean response or an average difference between anesthetic conditions. The registry defines the count as participants with MEP area ratios significantly different from 1 at all times and conditions: TIVA alone and TIVA plus 3% desflurane, at both time points. The endpoint title focuses on the effect of pulse-train length on TcMEP area under those conditions.

To construct the measurements, the record describes averaging the runs for the pulse-train lengths of 5, 6, 7, 8, and 9. The resulting TcMEP amplitude and area values were used to calculate regression coefficients for area versus pulse length for each participant under each anesthetic condition. The final endpoint then concerns the number of participants meeting the stated significance criterion for MEP area ratios.

In general, a count endpoint can convey how many participants meet a prespecified criterion, but it does not show the magnitude of the underlying response or how close other participants were to that criterion. A finding that a ratio differs significantly from 1 is also dependent on the statistical test and uncertainty calculation used. Those details are not reported in the registry record. Neither the count nor its denominator among participants completing the study is reported, so the endpoint cannot be interpreted quantitatively from the registry record.

The endpoint is relevant to the stated question because it connects pulse-train length, MEP area, and the two anesthetic conditions. However, the record does not provide the participant-level measurements, regression estimates, ratios, or endpoint result. It therefore does not show whether the criterion was met, or how consistently measurements changed across participants.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information in the registry record is limited to the outcome definition and measurement procedure. It describes regression coefficients derived from TcMEP area across pulse-train lengths for each participant, followed by a count of participants meeting a significance criterion for MEP area ratios. It does not report the analysis results or a detailed statistical analysis plan. The concepts below explain what the stated methods would mean in general; they are not claims about unreported procedures.

What does the regression describe?

Regression is a way to describe how an outcome changes in relation to a predictor. In this study description, pulse-train length is the predictor and TcMEP area is the outcome. A regression coefficient can represent a feature of that relationship, such as its direction or rate of change, depending on the model used. The registry says coefficients were calculated for each participant under TIVA and under TIVA plus desflurane, but it does not specify the regression form, the exact coefficient used, or how participant-level coefficients were compared.

Calculating a coefficient separately for each participant can preserve the within-participant structure: each participant has a response pattern under each condition. A later comparison could examine those patterns or derive ratios from them. The record, however, does not define the ratio formula or state how uncertainty in the coefficients was carried into the ratio. Without those details and the results, the endpoint cannot be reconstructed from the description alone.

What does a ratio different from 1 mean?

In general, a ratio equal to 1 indicates equality of the quantities in its numerator and denominator, while a ratio different from 1 indicates a relative difference. The registry defines its endpoint using MEP area ratios significantly different from 1, but it does not give the ratio's numerator and denominator. It also does not report whether the test was one-sided or two-sided, what significance threshold was applied, or how the test was calculated. The stated criterion therefore cannot be independently interpreted as a particular size or direction of change.

Statistical significance and magnitude are different ideas. A test addresses whether data are sufficiently inconsistent with a specified null value under a statistical model; it does not itself describe how large a difference is or how precisely it is estimated. A confidence interval, when reported, helps convey precision by showing a range of values compatible with the data and model. No confidence interval for this endpoint is reported in the registry record.

Why does the repeated-measures structure matter?

Measurements from the same participant are generally related. In a paired analysis, that dependence is used rather than ignored. Treating paired observations as if they came from unrelated participants can misstate uncertainty because within-participant similarities are not accounted for. The study description makes clear that each participant is their own control, but it does not identify the statistical method used for comparing conditions or time points.

There are measurements across several pulse-train lengths, anesthetic conditions, and time points. General statistical practice requires attention to how correlated observations are handled and which comparisons are central. A model might represent participant-level variation and repeated measurements, but no such model is specified in the registry record. It would be inappropriate to assume a particular paired test, mixed model, or other method.

How should multiplicity be considered?

When multiple hypotheses or contrasts are tested, the chance of at least one apparently significant result can increase if each test is judged separately without adjustment. This is a general issue, not evidence that a particular error occurred in this study. The endpoint refers to significance at all times and conditions, but the record does not explain how the tests were combined, whether adjustment was planned, or whether one contrast was designated as primary within that endpoint. The handling of multiple comparisons is not reported in the registry record.

The outcome description also says that averages from 3 runs were used. Averaging repeated runs can reduce the influence of run-to-run variability in the resulting measurement, in general. It does not replace a description of the uncertainty in participant-level estimates or the analysis of differences between conditions. The record does not provide run-level data or estimates of measurement variability.

What do the planning assumptions tell readers?

The stated sample-size planning assumptions specify a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a fraction of the observed effect. These are planning assumptions rather than results from the trial. The record describes a single-group study in which each participant is their own control, so equal allocation between two arms does not describe the actual study design. Planning illustrations based on those assumptions should not be read as a design justification, as an analysis of observed data, or as observed power.

Observed power is not a substitute for an effect estimate and its uncertainty. In general, post-study interpretation is more informative when it reports the estimated effect, a confidence interval, and the analysis population. The registry record does not report those elements for the primary endpoint. The number of listed analyses is 0, and no sponsor analysis or recalculated result is reported.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("MEPs Pre and Post Desflurane at 2 Time Points")
n      <- c(14)
events <- c(2)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  MEPs Pre and Post Desflurane at 2 Time Points  14  2  14.3  1.8  42.8  4.0  39.9  4.3  40.5

11. Multiplicity, Missing Data and Analysis Populations

The endpoint involves more than one measurement context: pulse-train lengths of 5, 6, 7, 8, and 9, TIVA and TIVA plus desflurane, and two time points. Its definition refers to ratios being significantly different from 1 at all times and conditions. The registry record does not explain whether these comparisons were handled as a family, whether any adjustment for multiple testing was planned, or exactly how the criterion across conditions and time points was applied.

In general, multiplicity matters when several tests can contribute to a conclusion. If each test is considered separately, the chance of at least one false-positive finding may be higher than for a single test. Methods for addressing this issue depend on the scientific question and analysis plan. No such method is reported in the registry record, so no adjustment should be assumed.

The record does not report how missing measurements were handled, whether participants were excluded from the endpoint analysis, or which analysis population was used. Although the endpoint description refers to participants who completed the study, the number completing it and the number with usable measurements are not reported in the registry record. The relationship between the enrolled group and the endpoint denominator is therefore unclear.

The study is marked COMPLETED, but that status does not establish complete outcome data for every enrolled participant. Reasons for missingness, withdrawals, deviations from the measurement procedure, and any imputation or other missing-data approach are not reported in the registry record. The listed number of analyses is 0, and no endpoint results are reported. These omissions limit assessment of both the analysis and the potential for bias from incomplete data.

12. 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.

Most frequent non-serious adverse event terms

The registry safety summary lists 18 participants at risk for the serious adverse-event summary and reports 0 serious adverse events and 0 deaths. It lists 18 participants at risk for the other adverse-event summary and reports 1 other adverse event. No serious adverse-event terms are listed.

These are the counts recorded in the safety summary. They should not be treated as rates or percentages: no rate calculation is reported, and no additional denominator or exposure-time information is given. The 18 participants listed at risk are not the same as the enrollment figure of 30, and the reason for that difference is not reported in the registry record. The record does not explain how the safety group was defined or whether the safety and primary endpoint populations were the same.

A count of 0 reported serious events does not establish that no risks exist; it describes the events recorded in this summary. Likewise, the single other event cannot be attributed to a particular cause from the information reported. The registry summary does not provide event descriptions, timing, severity details for the other event, or an assessment of relatedness to desflurane.

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

The registry record establishes that the study was designed to measure TcMEPs under TIVA and again after desflurane was added, using pulse-train lengths from 5 to 9 and measurements at two time points. It also defines a primary endpoint based on the number of participants whose MEP area ratios were significantly different from 1 at all times and conditions. These details describe the question and measurement approach, not the answer.

The primary endpoint result is not reported in the registry record. Without the count, its denominator, participant-level estimates, and uncertainty, it is not possible to determine what the posted outcome data show about the relationship between pulse-train length and MEP area in the two anesthetic conditions. The record therefore does not establish the direction, size, consistency, or precision of a difference.

The within-participant design allows each person to contribute observations under both conditions. In general, this can reduce the influence of stable differences between people. It does not remove every alternative explanation for a difference: measurements made at different times may also reflect time-related or procedural changes. The record does not describe analyses addressing such influences, and allocation is listed as NA rather than as randomized.

The absence of a reported endpoint result is not evidence that the endpoint was null or that the conditions were equivalent. Equivalence requires a suitable design and a prespecified margin, neither of which is reported in the registry record. Nor does the record permit a claim that desflurane increases or decreases motor responses. It documents the intended comparison but not a quantitative result supporting either direction.

The safety counts are also limited in scope. The registry lists 0 serious adverse events and 0 deaths, alongside 1 other adverse event in the safety summary. Those counts do not provide a full account of event types, relatedness, or risks beyond the recorded summary. The most accurate interpretation is that the registry describes the measurement protocol and a limited safety summary, while the primary statistical findings are not reported.

14. Why This Trial Matters Statistically

This study is statistically interesting because it uses repeated measurements within participants to examine a physiological response under two anesthetic conditions. The design makes the participant their own control, which can be useful when stable differences between people are large relative to changes within a person. That structure also calls for analysis methods that respect the dependence among repeated observations.

The response is measured across pulse-train lengths, and the outcome description uses regression coefficients for area versus pulse length. That approach focuses on a pattern across stimulation settings rather than a single measurement alone. The registry then defines a count endpoint using significance of MEP area ratios relative to 1. This distinction raises useful questions about how a continuous response pattern is reduced to a binary criterion and how much information that count retains about the size of individual responses.

The endpoint also spans anesthetic conditions and time points. Such repeated dimensions make clear why a statistical plan should specify the target contrast, how correlated observations are handled, and how multiple tests are interpreted. The registry record does not report those details or the endpoint results. The design can therefore be understood, but its inferential conclusions cannot be evaluated from the posted record.

Finally, the planning assumptions described for sample-size illustrations use equal allocation between two arms, while the study is described as a single-group within-participant comparison. This difference is a reminder that planning calculations depend on design assumptions and cannot be treated as evidence about the precision or power actually achieved. A reported estimate, interval, denominator, and analysis description would be needed to assess the statistical evidence for the study's primary question.

15. Limitations

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

The main limitation for interpretation is that the registry record does not report the primary endpoint result. It provides no endpoint count, denominator, effect estimate, confidence interval, or p-value. The described outcome cannot therefore be evaluated for magnitude, direction, or precision.

The endpoint description does not define the MEP area ratio's numerator and denominator, the exact significance test, or the threshold used. It also does not specify how the regression coefficients were calculated or how uncertainty in those coefficients informed the final count. These details are necessary to understand or reproduce the endpoint analysis.

The record describes within-participant measurements under TIVA and after addition of desflurane, at two time points, but does not report how repeated measurements or time effects were handled statistically. The measurement sequence is described as TIVA followed by TIVA plus desflurane; counterbalancing or other procedures to address order effects are not reported. Allocation is NA, so this is not a randomized comparison between separate groups.

The number completing the study and the endpoint analysis population are not reported in the registry record. Missing-data handling, exclusions, withdrawals, protocol deviations, and reasons for unavailable measurements are also not reported. The safety summary covers 18 participants at risk, but the relationship of that group to enrollment and outcome completion is not explained.

Multiplicity procedures are not reported despite measurements across pulse-train lengths, conditions, and time points. The statistical analysis plan, sample-size justification for the actual within-participant design, and interim-analysis details are not reported in the registry record. The listed planning assumptions are for equal allocation between two arms and should not be mistaken for the study's actual design or an observed-power calculation.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Anesthesia and Motor Evoked Potential (MEP) Recruitment — NCT02199314.
• Registry record last updated 2020-09-22; status last verified 2017-11.
• Results first posted 2020-09-22.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT02199314 is a completed, single-group study titled “Anesthesia and Motor Evoked Potential (MEP) Recruitment.” It enrolled 30 participants with idiopathic scoliosis and was sponsored by Children's Hospital Medical Center, Cincinnati. The registry lists phase and allocation as NA and masking as NONE.

Participants had TcMEPs measured under TIVA and again after addition of 3% desflurane. The primary outcome concerns the count of participants whose MEP area ratios were significantly different from 1 at all times and conditions. The record describes measurements across pulse-train lengths of 5, 6, 7, 8, and 9.

The primary endpoint result and statistical analyses are not reported in the registry record. The safety summary lists 0 serious adverse events, 1 other adverse event, and 0 deaths among the reported at-risk groups.