Airway Scope and Macintosh Laryngoscope for Tracheal Intubation in Patients Lying on the Ground: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Airway Scope and Macintosh Laryngoscope for Tracheal Intubation in Patients Lying on the Ground (NCT00980590), a randomized na study. The primary outcome is Intubation Time.

2. Clinical Question

The clinical setting described in the registry is pre-hospital intubation under sub-optimal conditions, specifically patients lying on the ground. The comparison focuses on the duration of the intubation process, rather than a broad assessment of every aspect of airway management. The registry also lists overall intubation success, number of attempts, and incidence of complications as secondary outcomes, but their results are not reported in the registry record.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group trial comparing the Airway Scope with the Macintosh laryngoscope. The enrollment is listed as 100. The registry records the trial status as completed, with a start date of 2008-09 and primary completion in 2009-02. The sponsor is The Cleveland Clinic. The phase is listed as NA.

The arms are described as intubation with the Airway Scope and intubation with the Macintosh laryngoscope. Primary-outcome summaries report n 49 for the Airway Scope and n 50 for the Macintosh laryngoscope. The reason the endpoint counts do not match the listed enrollment is not reported in the registry record. The primary endpoint's eligible population is restricted to cases with no more than 3 intubation attempts, and cases exceeding that limit were excluded from the intubation-time calculation as failures. The record does not explain whether that rule accounts for the difference between enrollment and endpoint counts.

Random allocation means the trial was designed to assign participants to one of the two device groups by chance. In general, randomization can help limit systematic differences between groups at the start of a study, although it does not guarantee that all characteristics will be balanced. The registry does not report the method used to generate or conceal the allocation sequence. It identifies the trial as single-masked but does not report which people were masked or how masking was maintained.

The listed comparison is parallel: the groups receive different assigned devices rather than crossing over between them. The registry does not report details about the setting, operator training, eligibility criteria beyond the primary-outcome attempt limit, or the reasons for any withdrawals. Those details should not be inferred from the trial title or the summary description.

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

Analysis population for the primary outcome, as defined in the registry: Patients with number of intubation attempt no more than 3

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, measured over The time from picking up the Airway Scope or Macintosh laryngoscope to confirmation of tracheal intubation by capnography..

The primary endpoint is intubation time, a continuous measure reported as a mean with a standard deviation and measured in seconds. Its timeframe begins when the operator picks up the Airway Scope or Macintosh laryngoscope and ends when tracheal intubation is confirmed by capnography. It therefore captures the elapsed time across the defined intubation process, rather than time measured from a broader clinical starting point.

The registry defines the calculation in relation to the number of attempts. For cases with no more than 3 attempts, intubation time is the total time of the individual attempts. Cases exceeding that limit are defined as failures and excluded from the intubation-time calculation. The reported mean therefore applies to the registry's stated primary-outcome population, not necessarily to every enrolled participant. The counts represented in the endpoint summaries are n 49 for the Airway Scope and n 50 for the Macintosh laryngoscope.

As a general statistical point, time is useful when a study asks how long a defined task takes: it preserves information about duration rather than reducing the result to success or failure alone. But a mean time does not by itself describe the full distribution of times or the frequency of success. The registry lists overall intubation success, number of attempts, and complications as secondary outcomes, but does not report their results. Reading the time endpoint alongside those outcomes would be needed to understand other dimensions of the procedure; their absence from the posted results leaves those questions open.

7. Results Posted in the Registry

• Macintosh Laryngoscope: mean 35.00 versus 18.00 on control; difference 17.00 (95% CI 12.43 to 21.57), standardized effect d = 1.45; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is a continuous measurement: time in seconds. The registry reports a mean for each arm and a standard deviation to describe the spread of observations around that mean. For the Airway Scope, the reported mean is 18.0 seconds and the standard deviation is 4.0 seconds. For the Macintosh laryngoscope, the reported mean is 35.0 seconds and the standard deviation is 16.0 seconds. The arm summaries give n 49 and n 50, respectively.

What does a mean difference express?

A mean difference compares the average measurement in one group with the average in another, retaining the unit of the original measure. Here, the reported comparison is Macintosh laryngoscope relative to Airway Scope, and the estimate is 17.0 seconds. The positive direction corresponds to the higher reported mean in the Macintosh group. Because the endpoint is measured in seconds, the difference is also expressed in seconds. This makes the estimate interpretable in the same terms as the time recorded during intubation.

A mean describes the center of a set of values, but it does not describe every observation. Standard deviation gives information about variability within each group. It is not the uncertainty around the group mean: that uncertainty is reflected in the confidence interval for the comparison. The Macintosh group's standard deviation of 16.0 seconds is larger than the Airway Scope group's standard deviation of 4.0 seconds. That summary points to greater observed spread in the former group's times, but does not show whether the distribution is symmetric, whether it contains unusually long times, or how values are distributed across participants.

How should the confidence interval be read?

A confidence interval is a statistical range around an estimate. In general, it indicates the range of effect values reasonably compatible with the observed data and the method's assumptions. The interval for the mean difference extends from 12.43 to 21.57 seconds. It is presented for the Macintosh-versus-Airway comparison. The registry does not state the confidence level or provide enough detail to identify the full interval construction, so those details should not be presumed. The interval can still be read as showing uncertainty around the point estimate: the estimate is not exact, and the endpoints mark a range rather than a guarantee about the true value.

The interval's limits are both on the positive side of zero. For a difference, zero represents no difference in group means. As a general statistical explanation, an interval that excludes zero is consistent with evidence of a difference under the interval procedure used. This does not communicate the probability that a particular effect is true, and it does not establish that the estimate is free from bias or other study limitations.

What does the p-value add?

The posted unadjusted p-value is p < 0.001. In general, a p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the model assumptions were correct. It is not the probability that the null hypothesis is true, nor a measure of the clinical importance of the observed difference. The term unadjusted matters because the registry does not report adjustments for other variables or for multiple outcomes. No alternative adjusted p-value is posted.

Interpreting a p-value also depends on knowing the planned analysis and how many analyses were considered. The registry record does not report the statistical plan, a multiplicity strategy, or interim analyses. It lists zero posted analyses. Accordingly, the posted p-value can be described as the reported unadjusted value, but the record does not support claims about whether it was prespecified or how it relates to other analyses.

Why does the attempt-based rule matter?

The time endpoint is not defined for every case in the same way. For cases with no more than 3 attempts, the recorded endpoint is the total time of the individual attempts. Cases exceeding that limit are defined as failures and excluded from the calculation of intubation time. The mean comparison therefore concerns the eligible time observations rather than a combined measure of time and failure. Excluding failures from a time summary can make the interpretation dependent on who remains in the time analysis. The registry does not report the number of cases excluded under this rule or give group-specific failure counts, so the effect of the restriction on the comparison cannot be quantified from the record.

As a general methodological point, a continuous time outcome and a success outcome answer different questions. A mean time describes duration among the cases included in the time calculation. A success measure would describe whether intubation met a specified success definition. One cannot substitute for the other. The registry names overall success, number of attempts, and complications as secondary outcomes, but their results are not reported.

The design is randomized and parallel-group, which frames the intended comparison between assigned devices. Randomization can reduce systematic allocation differences in expectation, but the record does not include enough detail to assess allocation concealment, baseline balance, adherence, or deviations from assigned treatment. Single masking is recorded, but the identity of those masked is not reported. These omissions limit how fully the statistical result can be reconstructed from the registry record.

10. Confidence Intervals and Precision

The reported mean difference is 17.0 seconds, with a confidence interval from 12.43 to 21.57 seconds. The interval quantifies uncertainty around the estimated comparison: values within that range are compatible with the data under the method used. It should not be interpreted as a range containing every participant's difference in time, nor as a guarantee about the result in a future study. The registry does not report the confidence level or the method used to construct the interval.

The limits are above zero, the value corresponding to no difference in group means. The reported unadjusted p-value is p < 0.001. Together, these summaries indicate that the posted comparison is not centered near no difference, while the interval also shows that the estimate is not exact. The interval describes uncertainty in the mean difference, whereas the group standard deviations describe variation among the recorded times. Those are distinct aspects of the data.

Precision should also be understood in light of the endpoint definition. The primary time calculation excludes cases exceeding 3 attempts, which the registry classifies as failures. The arm counts in the primary summaries are n 49 for the Airway Scope and n 50 for the Macintosh laryngoscope, while the registry enrollment is 100. The record does not report the reason for the difference in counts, the number of failures excluded from the time calculation, or the confidence level for the interval. These missing details restrict a fuller assessment of precision and the population represented by the estimate.

11. 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 sample-size figures are planning illustrations based on the observed effect, not the original trial's design assumptions. The registry record does not report the trial's own sample-size justification or planning assumptions. The figures are participants per arm, not total events. Their stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect.

The 80% power column gives the planned number of participants per arm for a hypothetical study to have an 80% chance of detecting the effect used in that row, if the planning assumptions hold. The 90% power column gives the corresponding per-arm planning number for a higher chance of detection under the same assumptions. These are prospective planning quantities, not descriptions of what happened in this trial.

The rows consider planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The figures rise as the assumed effect becomes smaller: smaller effects need more participants to detect with the same target power and other assumptions. The display is therefore useful for illustrating how sample-size requirements depend on the effect researchers aim to detect, rather than as a report of the trial's actual design. This is not observed power.

The original design assumptions, including the target effect used by the investigators and any allowance for exclusions or failures, are not reported in the registry record. These illustrations should not be taken as evidence that the trial was planned around the observed difference or that the original sample size was adequate for every listed outcome.

12. 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 = 17.000; pooled standard deviation σ = 11.715.
2. n = 2 × (1.96 + 0.842)² × 11.715² / 17.000² = 7.5, rounded up to 8 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 <- 17                      # observed difference in means
sigma <- 11.714824514352                     # 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(980590)
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 = 8 (80% power), 10 (90% power)
 75% of observed effect: n per arm = 14 (80% power), 18 (90% power)
 50% of observed effect: n per arm = 30 (80% power), 40 (90% power)
power.t.test: 8.5 
Simulated power at n = 8 per arm: 0.775 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists intubation time as the primary outcome and identifies overall intubation success rate, number of intubation attempts, and incidence of intubation complications as secondary outcomes. It also lists 4 outcome measures and reports zero posted analyses. Although the secondary outcomes are named, their numerical results and analysis methods are not reported in the registry record.

Multiplicity arises when researchers make several statistical comparisons or assess several outcomes. As a general statistical point, examining multiple outcomes can increase the chance that at least one result appears unusual by chance. A planned approach may address that concern, but the registry does not report a multiplicity adjustment or a hierarchy for interpreting the secondary outcomes. The p-value reported for intubation time is explicitly unadjusted. It should not be treated as adjusted for other outcomes or analyses.

The registry does not report whether interim analyses were conducted, whether analyses were prespecified, or the statistical plan. It also does not report how missing outcome data were handled. The primary time definition excludes cases with more than 3 attempts as failures, but the number of such cases and their distribution by arm are not reported. The record does not specify whether any other endpoint observations were missing or excluded.

The analysis population is not fully described. The primary outcome is defined for patients with no more than 3 attempts, but the registry does not state whether the reported summaries follow an intention-to-treat population, a per-protocol population, or another analysis set. Nor does it state how adherence to assigned device use was assessed. These details matter because analysis populations can differ in who is included and what comparison they represent.

Random allocation is reported, but the registry does not describe allocation concealment, baseline characteristics, or any adjustments to the primary comparison. It also records single masking without identifying who was masked. These omissions do not negate the posted estimate, but they limit evaluation of the analysis choices and of how completely the reported comparison reflects the randomized design.

14. 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.

For the Airway Scope group, the registry lists 0 serious adverse events among 50 participants at risk and 0 other adverse events among 50 at risk. For the Macintosh laryngoscope group, it likewise lists 0 serious adverse events among 50 at risk and 0 other adverse events among 50 at risk. Death counts are not reported in the registry record.

These entries describe the adverse-event counts recorded in the registry. They do not establish that no adverse events occurred outside the outcomes captured or reported, and the record does not give event definitions, surveillance procedures, or the period over which events were assessed. A zero count is not proof that an event is impossible. It is a report of no events in the listed category and group, using the registry's recorded at-risk counts.

The safety entries should be read separately from the primary intubation-time result. They do not provide results for the listed secondary outcomes of success, number of attempts, or complications. Those outcome results are not reported in the registry record, so the posted adverse-event counts do not answer those questions.

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

The registry's primary-outcome summaries show a mean time of 18.0 seconds for the Airway Scope and 35.0 seconds for the Macintosh laryngoscope. The reported mean difference is 17.0 seconds in the Macintosh-versus-Airway comparison, with a confidence interval from 12.43 to 21.57 seconds and an unadjusted p-value of p < 0.001. These statistics describe a difference in average intubation time for the endpoint as defined in the record.

The estimate applies to cases with no more than 3 intubation attempts, because cases exceeding that limit are treated as failures and excluded from the time calculation. It is not a result for all enrolled participants regardless of attempts. The registry enrollment is listed as 100, while the primary summaries report n 49 for the Airway Scope and n 50 for the Macintosh laryngoscope; the record does not explain the difference. This further limits certainty about exactly which participants are represented by the summaries.

The time result does not establish a difference in overall intubation success, the number of attempts, complications, or other clinical outcomes. Those outcomes are listed as secondary measures, but their results are not reported in the registry record. The adverse-event entries list zero serious and zero other events in each arm, but details about event definitions and follow-up are not reported. Those entries should not be treated as a complete account of all possible safety outcomes.

More generally, a randomized comparison can inform the contrast between assigned groups within the trial, but the registry record does not provide enough information to assess every feature of implementation or analysis. It does not report which people were masked, the allocation method, the statistical plan, or the handling of missing observations. Nor does it report the confidence level for the interval. The result should therefore be interpreted as the posted summary for this trial, rather than as a universal estimate for other settings or circumstances.

The statistical result is a difference in measured time, not a recommendation about device choice. It does not establish that one device is preferable for a particular patient or setting. Such conclusions would require broader evidence about the outcomes and contexts relevant to that decision, which are not fully described in this registry record.

16. Why This Trial Matters Statistically

This trial raises a useful statistical question: how should a time comparison be interpreted when the endpoint is calculated only for cases meeting an attempt-based rule? The primary outcome is not simply a duration recorded for every enrolled participant. Cases with no more than 3 attempts contribute a total time across attempts, while cases exceeding the limit are defined as failures and excluded from the time calculation. This distinction makes the endpoint's population definition central to interpreting the mean difference.

The registry also illustrates why a mean difference, its uncertainty, and within-group variability answer different questions. The reported mean difference of 17.0 seconds describes the contrast between group averages. The confidence interval from 12.43 to 21.57 seconds describes uncertainty around that contrast under the method used. The standard deviations of 4.0 seconds and 16.0 seconds describe spread within the groups. These statistics are related but not interchangeable.

The randomized parallel-group design supplies a framework for comparing the assigned devices, but important implementation and analysis details are not reported. The masked group is not identified, and the registry does not state the allocation method, analysis population, or missing-data handling. The posted p-value is unadjusted, while the record does not report a multiplicity strategy for the primary and secondary outcomes. These are practical examples of why statistical interpretation depends on both numerical summaries and study documentation.

Finally, the registry lists secondary outcomes and adverse-event counts, but does not provide results for the secondary measures. This highlights the difference between outcomes named in a record and outcomes that can actually be interpreted from posted results. The time comparison is informative about its defined endpoint; it cannot stand in for outcomes that are not reported.

17. 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 leaves several trial-specific questions unresolved. Although it identifies the study as randomized and single-masked, it does not describe how allocation was generated or concealed, or who was masked. It does not provide details about the clinical setting, operator experience, training, participant eligibility beyond the attempt-based primary-outcome definition, or adherence to the assigned device. These omissions limit assessment of how the trial was conducted.

The primary time summaries apply only to cases with no more than 3 attempts. Cases beyond that limit are classified as failures and excluded from the time calculation, but the number of such cases and their distribution between groups are not reported. The registry lists enrollment as 100 and the primary summaries as n 49 and n 50; it does not explain the difference. The specific analysis population and handling of any other missing observations are also not reported.

The registry does not report results for overall intubation success, number of attempts, or incidence of complications, despite listing these as secondary outcomes. The serious and other adverse-event entries show zero events in the listed at-risk groups, but event definitions, ascertainment procedures, and follow-up details are not reported. Death counts are not reported in the registry record.

The statistical plan, confidence level for the interval, multiplicity strategy, and use of interim analyses are not reported. The record also does not state whether the primary comparison was adjusted for covariates. Accordingly, interpretation is limited to the posted unadjusted summary and its stated endpoint definition.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Airway Scope and Macintosh Laryngoscope for Tracheal Intubation in Patients Lying on the Ground — NCT00980590.
• Registry record last updated 2023-06-29; status last verified 2016-12.
• Results first posted 2017-02-06.
• 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.

21. Record Summary

The registry describes a completed randomized, single-masked, parallel-group comparison of the Airway Scope and Macintosh laryngoscope for tracheal intubation in patients lying on the ground. Enrollment is listed as 100. The sponsor is The Cleveland Clinic; the recorded start date is 2008-09 and primary completion is 2009-02.

The primary outcome is intubation time in seconds, defined from picking up the device to confirmation of tracheal intubation by capnography. The reported means are 18.0 seconds for the Airway Scope and 35.0 seconds for the Macintosh laryngoscope; the mean difference is 17.0 seconds, with a confidence interval from 12.43 to 21.57 seconds and an unadjusted p-value of p < 0.001. The endpoint excludes cases exceeding 3 attempts.

Secondary outcome results and several analysis details are not reported in the registry record. Adverse-event summaries list zero serious and zero other events in both groups, with death counts not reported.