Intubation of Patients With an Unstable Cervical Spine Using the CMAC Device: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Intubation of Patients With an Unstable Cervical Spine Using the CMAC Device (NCT01113723), a randomized phase 4 study. The primary outcome is Intubation Time (Seconds).

2. Clinical Question

The trial’s stated purpose was to evaluate whether use of the CMAC device decreases the time required for intubation compared with fiberoptic bronchoscopy. The registry identifies both devices as commonly used in standard-of-care intubation practices for patients with cervical spine injury; it does not establish that either approach is preferable for an individual patient.

The primary result is a comparison of group mean times. Such a comparison describes the average duration in each assigned group, rather than the experience of every participant. It also addresses procedure time specifically: the posted primary outcome does not by itself establish differences in other aspects of the procedure, patient outcomes, or safety. Those questions require their own outcomes and analyses.

3. Trial Design

The registry describes a completed, randomized, prospective, single-masked, parallel-group study. Enrollment is listed as 140. The posted primary outcome results include 70 participants in the CMAC Device group and 70 in the Fiberoptic Bronchoscope group. Random allocation is intended, in general, to make treatment groups comparable on average with respect to factors that could affect the outcome; the registry record does not give details of how the allocation sequence was generated or concealed.

The trial is registered as phase 4 and lists Cedars-Sinai Medical Center as sponsor. The recorded start is 2009-12 and the primary completion is 2012-02. Its status is completed. The condition listed is laminectomy, while the study description focuses on patients with an unstable cervical spine. More detailed eligibility criteria, setting, participant characteristics, and the meaning of the single-masking designation are not reported in the registry record.

The parallel design assigns participants to one of the device groups rather than comparing both devices within each participant. The registry outcome summaries therefore present group-level means and standard deviations. The arm descriptions characterize the intervention as time to achieve successful tracheal intubation, while the primary outcome description specifies the interval from initial insertion of the laryngoscope blade to placement of the tracheal tube.

The registry does not report the trial’s original sample-size justification, its intended statistical analysis plan, or details about interim analyses. It also does not report which participants were included in each analysis population or how deviations from assigned treatment were handled. These omissions limit what can be concluded about the planned analysis, even though outcome summaries and comparison statistics are posted.

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 Intubation Time (Seconds), measured over 3 minutes.

The primary endpoint is intubation time in seconds, reported as a mean with a standard deviation. The outcome description defines the interval as the time following initial insertion of the laryngoscope blade until placement of the tracheal tube. The registry gives a timeframe of 3 minutes and describes the arm outcome as time to achieve successful tracheal intubation.

Procedure time is relevant to the trial’s stated question because the study was designed to compare how long intubation takes with the two devices. A continuous time measure retains information about the magnitude of duration rather than reducing the result to a simple event count. Comparing group means gives a concise summary of average procedure time, while the standard deviation describes how dispersed individual times are around each group mean.

In general, an average does not show the full distribution of participant results. Similar averages can accompany different degrees of variability, and some individual times may be substantially above or below their group mean. The posted summaries do not give the individual observations or additional distributional summaries, so they cannot show the shape of the time distribution or identify unusual observations.

The endpoint measures elapsed time, not every dimension of intubation quality or clinical outcome. The time result should therefore be read as evidence about the measured procedure-duration outcome, not as a complete assessment of the devices or of patient care.

7. Results Posted in the Registry

• Fiberoptic Bronchoscope: mean 59.00 versus 35.00 on control; difference 24.00 (95% CI 14.12 to 33.88), standardized effect d = 0.80; z-test p = <0.001.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Time to Obtain Glottis Visualization (Seconds)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Flexible Fiberoptic Scope (FFS): mean 16.00 versus 32.00 on control; difference -16.00 (95% CI -24.18 to -7.82), standardized effect d = -0.65; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Flexible Fiberoptic Scope (FFS) than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The posted secondary outcome concerns time to glottis visualization, a procedural milestone distinct from the primary endpoint of time to tracheal tube placement. Across the posted outcomes, the group pattern for this milestone does not align with the primary time comparison: the fiberoptic group has the lower mean for visualization time, whereas the CMAC group has the lower mean for total intubation time. This contrast illustrates why a component of a procedure should not be treated as a substitute for its overall duration.

The secondary endpoint can add context to the primary result by describing a separate part of the intubation process. It cannot, on its own, explain why the overall times differ, since the record does not report detailed procedural data or a mediation analysis. Nor does a difference in visualization time establish a difference in successful placement, safety, or patient outcomes beyond the outcomes explicitly posted.

The secondary comparison has an unadjusted p-value of <0.001. Secondary findings generally carry less confirmatory weight when the analysis plan and multiplicity strategy are not reported. If several outcomes are examined without adjustment, chance findings become more likely; the registry record does not state how the investigators addressed that issue. The secondary result is therefore best read as a distinct, supportive description rather than as an independent confirmation of the primary endpoint.

The registry identifies one secondary outcome by name and posts its group summaries and comparison. It does not report a hierarchy specifying which outcomes were intended to be confirmatory or how secondary outcomes would affect interpretation of the primary question. The separate procedural measure is useful context, but the primary comparison remains the direct result for the stated question about intubation time.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Time to Obtain Glottis Visualization (Seconds)

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports continuous outcomes as means and standard deviations. For the primary endpoint, the mean is the arithmetic average of the observed intubation times within an arm. The standard deviation describes the spread of observations around that average. It is not the uncertainty of the mean itself: uncertainty in a group mean depends both on the spread of observations and on the amount of information contributing to the estimate.

The primary comparison is a mean difference. Its direction is defined by subtracting the CMAC mean from the fiberoptic bronchoscopy mean. Consequently, a positive estimate indicates a larger mean in the fiberoptic group, and a negative estimate would indicate a larger mean in the CMAC group. The posted primary estimate is 24.0 seconds, with an interval from 14.12 to 33.88 seconds. Keeping the subtraction direction in view is essential when interpreting the sign of an estimate.

In general, a confidence interval summarizes the range of values compatible with the observed data under a particular statistical procedure and its assumptions. It conveys precision as well as direction: a narrower interval indicates more precision about the estimated difference, while a wider interval leaves more uncertainty about its magnitude. An interval is not a range containing every participant’s result, and it does not mean that individual outcomes lie within its endpoints.

The posted p-value for the primary comparison is unadjusted. In general, a p-value is calculated under a null hypothesis, commonly that the group means are equal, and reflects how unusual the data or a more extreme result would be if that model held. It does not quantify the probability that the null is true. A small p-value does not by itself establish that an effect is important in practice, and a larger p-value would not by itself establish equivalence.

Randomization is a design feature, not a statistical adjustment. In general, random assignment can reduce systematic differences between groups at the start of a study, but chance imbalances may remain. How allocation was implemented, whether the posted analysis followed assignment, and whether any covariates were included are not reported in the registry record. The design label alone cannot answer those questions.

The comparison also includes a pooled standard deviation of 29.83 and a standardized effect size of 0.804. In general, a standardized effect expresses a mean difference in units of a standard deviation, which can make results measured on different scales easier to compare. It does not replace the original-unit estimate: seconds remain more directly interpretable for this procedure. The registry record does not describe a clinical threshold for judging whether a particular difference in seconds is important.

Why can variability matter?

In general, the standard deviation affects how precisely a group mean and the difference between group means can be estimated. Greater variability makes it harder to distinguish a mean difference from random fluctuation when the amount of data is unchanged. The posted primary group standard deviations are 22.0 seconds and 36.0 seconds, so individual times were not all concentrated at the group means.

In general, over-dispersion means that observed variation is greater than a model assumes. If a statistical method underestimates variation, its standard errors can be too small and intervals too narrow. The registry does not report an over-dispersion assessment for these continuous time outcomes, and the posted summaries alone do not establish that such a problem occurred.

What does the secondary comparison represent?

The secondary outcome is also continuous and is summarized with a mean and standard deviation. Its comparison is a mean difference, with the posted estimate defined from the CMAC mean relative to the fiberoptic scope mean. In general, the sign of a mean difference depends on the subtraction order, so an estimate’s direction must be interpreted using the corresponding group definitions. This secondary measure describes time to a procedural milestone and is not the same endpoint as completion of intubation.

The registry lists unadjusted p-values for the posted primary and secondary comparisons. No multiplicity adjustment or confirmatory testing hierarchy is reported. In general, when several outcomes are tested, the chance of at least one apparently strong result can increase if each is assessed without accounting for the number of tests. This is one reason secondary findings are often interpreted as supportive or exploratory unless a prespecified analysis strategy establishes otherwise.

What is not documented?

The registry record lists no analysis records, although outcome summaries and comparison statistics are posted. The original trial’s statistical analysis plan, missing-data methods, analysis populations, and handling of protocol deviations are not reported in the registry record. The method used to construct the posted intervals and tests is not described there in enough detail to assess every assumption. These limits do not alter the arithmetic direction of the posted summary, but they constrain independent evaluation of the analysis process.

11. Confidence Intervals and Precision

The primary mean difference is 24.0 seconds, with an interval from 14.12 to 33.88 seconds. Every value in this interval is positive under the stated subtraction direction, so the posted interval is consistent with a greater mean in the fiberoptic group than in the CMAC group. The interval gives a range of plausible values for the mean difference under the method used; it is not a guarantee that the true value lies within those endpoints.

The interval is informative about precision because it shows that the estimate is not known exactly. Its width reflects both the observed variability and the amount of information in the groups, together with the interval method. The registry does not state the confidence level or give details of the interval procedure, so those features should not be inferred from the posted endpoints alone.

In general, a confidence interval and a p-value answer related but different questions. The p-value assesses compatibility with a null model, whereas an interval presents a range of estimates compatible with the data and method. The reported p-value is <0.001, but that does not eliminate uncertainty about the magnitude of the difference. The interval is therefore important for judging how precisely the size of the observed group contrast is estimated.

The secondary comparison also has an interval, from -24.18 to -7.818 seconds, around the posted mean difference of -16.0 seconds. Its negative direction follows the secondary outcome’s comparison definition. This interval describes uncertainty for the secondary group contrast, not for the primary intubation-time estimate. Each endpoint has its own variability and precision.

Precision is not the same as clinical importance or generalizability. A statistically precise estimate can still have uncertain relevance to decisions if the importance of a difference is not established; conversely, an imprecise estimate may leave a broad range of possible effects. The registry does not report a threshold for a clinically important difference, so the intervals cannot be classified against such a threshold from the record alone.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. The posted planning calculation uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each row considers an effect defined as a stated fraction of the observed effect. The columns describe the number of participants per arm for 80% power and for 90% power under those assumptions.

In plain terms, 80% power means that a study designed under the stated assumptions would have an 80% chance of detecting an effect of the specified size using the stated testing framework, if that effect were the true one. The 90% column describes the corresponding planning target with a higher probability of detection. These are planning illustrations based on the observed effect, not observed power.

Read the rows as alternative planning scenarios: one uses the full observed effect, another plans for 75% of the observed effect, and another plans for 50% of the observed effect. Smaller effects are harder to distinguish from random variation, so they require more participants under otherwise unchanged assumptions. The displayed participant counts are per arm; they should not be read as total trial enrollment.

These calculations are not the original design justification for the completed trial. The registry record does not report the trial’s original sample-size assumptions or target effect. The planning figures also depend on assumptions about allocation, significance level, and the statistical approximation; they are not guarantees that a future study will achieve the stated power or reproduce the observed effect.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 24.000; pooled standard deviation σ = 29.833.
2. n = 2 × (1.96 + 0.842)² × 29.833² / 24.000² = 24.3, rounded up to 25 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 24                      # observed difference in means
sigma <- 29.8328677803526                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1113723)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 25 (80% power), 33 (90% power)
 75% of observed effect: n per arm = 44 (80% power), 58 (90% power)
 50% of observed effect: n per arm = 98 (80% power), 130 (90% power)
power.t.test: 25.3 
Simulated power at n = 25 per arm: 0.796 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry record does not report a multiplicity adjustment, a hierarchy of outcomes, or a plan for interpreting multiple statistical tests. It posts an unadjusted p-value for the primary outcome and an unadjusted p-value for the secondary outcome. In general, when multiple hypotheses are tested, each unadjusted test can contribute to an increased chance of at least one apparently noteworthy result. The record does not provide enough information to determine whether other planned outcomes or analyses were also tested.

The registry lists 3 outcome measures, while it posts 1 secondary outcome by name. The relationship between all registered measures and the posted results is not explained in the available record. It is therefore not possible to establish whether the posted outcomes represent every planned analysis or whether any outcomes were omitted, changed, or not collected.

Missing-data methods are not reported in the registry record. The outcome summaries include 70 participants in each arm, but the record does not explain whether those figures represent all randomized participants, participants with available outcome data, or another analysis population. No imputation procedure, missingness description, or sensitivity analysis is reported. The posted sample counts alone cannot establish that no outcome data were missing.

The analysis populations are also not reported. The record does not specify whether analyses followed randomized assignment, included only participants who received the assigned device, or used another population definition. Handling of crossovers, protocol deviations, and excluded observations is not described.

The registry lists no analysis records, and it does not report the original statistical analysis plan or interim analyses. These absences should be treated as limits on what can be assessed, not as evidence that a particular method was or was not used. The group summaries remain interpretable as posted descriptive results, but the record does not fully document the inferential framework behind them.

15. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event record lists 70 participants at risk for serious adverse events in each device group, with 0 serious adverse events reported as affecting participants in either group. It also lists 70 at risk for other adverse events in each group, again with 0 affected participants reported. The fiberoptic group is labeled Flexible Fiberoptic Scope (FFS) in the adverse-event record.

These are posted event counts, not proof that no adverse event occurred outside the collection or reporting captured in the registry. The record does not give details about adverse-event definitions, surveillance duration, attribution to a device, or whether events were collected and adjudicated in the same way across groups. Counts of zero should therefore be read as zero events reported in these fields, rather than as a comprehensive guarantee of safety.

Death counts are not reported in the registry record. The posted adverse-event figures do not establish that the devices have equivalent safety, particularly without fuller definitions, follow-up details, and analysis methods. They describe what the registry reports and should not be used alone to make a clinical decision.

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

The primary result describes a lower average intubation time in the CMAC group than in the fiberoptic bronchoscopy group in the posted trial summaries. The estimated mean difference is 24.0 seconds in the direction of a longer mean in the fiberoptic group, and its interval is entirely positive. The unadjusted p-value is <0.001. Together, these statistics indicate a clear difference in the measured group means under the posted comparison, while leaving uncertainty about the exact size of that difference.

The result does not show that every CMAC intubation was faster than every fiberoptic intubation. It does not establish that the same difference would occur in other settings, among other patient groups, or with different operators. The registry record does not report participant characteristics, operator experience, detailed eligibility criteria, or contextual factors needed to assess how closely the trial population and procedures match other circumstances.

The result also does not answer every question about the devices. The primary endpoint measures elapsed time to tracheal tube placement. It does not by itself determine the quality of the procedure, patient outcomes, or comparative safety. The secondary visualization-time result concerns another procedural milestone and moves in a different direction, reinforcing that different outcomes can describe different aspects of the same procedure.

Statistical evidence and clinical importance are not interchangeable. The registry does not report a threshold for a meaningful time difference, so the posted estimates cannot establish how important the observed difference is in practice. The p-value is not a measure of benefit, and the confidence interval is not a clinical decision boundary.

The appropriate interpretation is limited to the randomized trial’s posted group summaries and unadjusted comparisons. The registry does not document the original analysis plan, missing-data handling, or analysis populations. Those limitations do not erase the observed data, but they leave aspects of the trial’s inferential process and applicability unresolved.

17. Why This Trial Matters Statistically

This trial illustrates why a clinical comparison should be read through the endpoint it actually measures. The primary outcome is a continuous procedure-time measure, so the group means, variability, mean difference, and interval each contribute distinct information. The mean difference conveys direction and magnitude in seconds; the standard deviations show that observations vary; and the interval communicates uncertainty about the group contrast.

It also demonstrates the value of attending to endpoint definitions. Time to glottis visualization and time to tracheal tube placement are related procedural measures, but they are not interchangeable. The posted group pattern differs between them, showing why an interpretation based on one milestone should not be extended automatically to the entire procedure or to other outcomes.

The record offers another statistical lesson: a small unadjusted p-value does not remove the need to consider precision, study design, and analysis transparency. The interval gives context for the estimated difference, while the unreported original analysis plan, multiplicity approach, and missing-data methods limit the degree to which the analysis can be independently assessed.

Finally, planning calculations based on an observed effect are not evidence about the completed trial’s original design assumptions. They illustrate how required sample size changes when the target effect changes and when the desired power changes. Keeping that distinction clear prevents retrospective planning figures from being mistaken for observed power or for the rationale that guided enrollment.

18. 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 registry record does not provide detailed eligibility criteria, participant characteristics, clinical setting, or operator experience. Those details would help readers judge how broadly the observed group comparison may apply. The condition field lists laminectomy, while the study description concerns intubation in patients with an unstable cervical spine; the relationship between that condition entry and the enrolled population is not further explained.

The primary outcome description gives the timing interval and a timeframe of 3 minutes, but the record does not explain further operational details such as how timing was recorded, who recorded it, or how unsuccessful or repeated attempts were handled. The arm descriptions refer to successful tracheal intubation, but no fuller procedural definitions are posted.

Although the design is labeled randomized and single-masked, details about sequence generation, allocation concealment, and who was masked are not reported in the registry record. The record also does not report the original sample-size justification, an analysis plan, interim analyses, or the methods used to handle missing data, crossovers, and protocol deviations. Analysis populations are not specified.

The posted adverse-event fields report zero affected participants but do not describe ascertainment, definitions, duration of safety follow-up, or attribution. Death counts are not reported in the registry record. The outcome summaries are informative about the posted results, but these reporting gaps constrain interpretation of safety and of the completeness of outcome capture.

The statistical comparisons are unadjusted, and no multiplicity approach is reported. The record does not provide individual participant data or a clinical threshold for a meaningful time difference. These limitations restrict assessment of model assumptions, robustness, clinical importance, and generalizability; they do not change the descriptive values reported for the trial.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Intubation of Patients With an Unstable Cervical Spine Using the CMAC Device — NCT01113723.
• Registry record last updated 2016-03-09; status last verified 2016-02.
• Results first posted 2016-03-09.
• 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.

22. Record Summary

NCT01113723 is a completed, randomized, prospective, single-masked, parallel-group phase 4 study sponsored by Cedars-Sinai Medical Center. It compared CMAC with fiberoptic bronchoscopy for tracheal intubation in patients with an unstable cervical spine. The registry lists enrollment as 140 and reports the primary outcome as mean intubation time in seconds.

The posted primary group summaries show a lower mean time in the CMAC group, with an unadjusted mean difference of 24.0 seconds for fiberoptic minus CMAC and an interval from 14.12 to 33.88 seconds. The record also posts a secondary measure of time to glottis visualization, adverse-event counts, and planning illustrations based on the observed effect.

The registry does not report the original sample-size justification, detailed analysis plan, missing-data methods, or analysis populations. The posted summaries describe the registered outcomes but do not establish clinical importance, comparative safety, or applicability beyond the trial population and procedures documented in the record.