Glottic View Using Supraglottic Devices in Pediatric Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Glottic View Using Supraglottic Devices in Pediatric Patients (NCT02532465), a randomized na study. The primary outcome is Acceptable View of the Glottic Aperature (Grade I-II).

2. Clinical Question

The registry’s stated aim is to compare the fiberoptic view through the internal aspect of Air-Q and i-gel. The clinical motivation is that supraglottic devices may be used as rescue airway devices when managing difficult airways, and a clearer passage to the glottic opening may be useful when a device is used as a conduit to aid endotracheal intubation.

The primary outcome is a count of participants with an acceptable view, not a direct measure of successful intubation, rescue success, or a patient’s longer-term outcome. Grade I means the glottic aperture is seen completely without obstruction. Grade II means it is seen partially, with visual obstruction of less than 50%. The registry also lists airway insertion time and time to achieve the best fiberoptic view as secondary outcomes. Their numerical results are not reported in the registry record.

3. Trial Design

The registry describes a randomized, parallel-group trial with no masking. The study compares two devices: Air-Q and i-gel. The registered enrollment is 50. The primary outcome results list 24 participants in each arm; the registry record does not explain the difference between the enrollment figure and the outcome denominators.

The record identifies the study population as pediatric patients and lists operative surgical procedures as the condition. It does not report further eligibility criteria or participant characteristics in the results, so details such as age distribution, airway difficulty, or procedure types cannot be characterized from this record.

The primary endpoint is the number of participants with an acceptable Grade I or Grade II fiberoptic view at 15 seconds after insertion of Air-Q or i-gel. The record lists airway insertion time and time to achieve the best fiberoptic view as secondary outcomes, but does not give their result values. The study is marked completed. Its start is recorded as 2015-08 and its primary completion date as 2018-07-26.

Random allocation can help make baseline characteristics comparable on average, while a parallel design assigns participants to one device group rather than having each participant receive both devices for the primary comparison. The registry does not report the sequence-generation method, allocation concealment, or any masking procedures beyond stating that masking was none. The original sample-size justification and detailed analysis plan are not reported in the registry record. Those omissions limit how fully the design and the analysis can be reconstructed.

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

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.

6. Primary Endpoint

The registry lists the primary outcome as Acceptable View of the Glottic Aperature (Grade I-II), measured over 15 seconds after insertion of Air-Q or i-gel.

The primary endpoint counts participants whose fiberoptic examination showed an acceptable view of the glottic aperture 15 seconds after insertion of the assigned device. The acceptable categories are Grade I and Grade II. Grade I is a complete view without obstruction; Grade II is a partial view with less than 50% visual obstruction. The outcome is therefore binary at the participant level: a participant either meets this registered definition of an acceptable view or does not.

This endpoint addresses the study’s stated comparison of the view through the internal aspect of the two supraglottic devices. A standardized assessment time gives the comparison a defined point after insertion, rather than allowing the primary measurement to be taken at an unspecified time. Categorizing the view also produces an outcome that can be summarized as counts and compared between randomized arms.

The endpoint is a measure of fiberoptic visibility, not a direct measure of whether endotracheal intubation was completed, whether a rescue airway was successful, or whether complications occurred. The registry does not establish that an acceptable view guarantees any of those outcomes. Its secondary outcomes include airway insertion time and time to achieve the best fiberoptic view, but their numerical results are not reported in the registry record.

7. Results Posted in the Registry

• I-gel: 87.5% (21/24) versus 83.3% (20/24) on control; risk difference 4.2 percentage points (95% CI -15.8 to 24.1), risk ratio 1.05 (0.83–1.33); unadjusted two-proportion z-test p = 0.683.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is reported as participant counts: the number meeting the acceptable-view definition and the number of participants in each arm. For Air-Q, the record reports 20 participants with an acceptable view among 24; for i-gel, it reports 21 among 24. Because the endpoint is binary, a natural comparison is the difference between the two arms’ event proportions. A risk difference expresses the absolute contrast in the chance of the recorded outcome, with its sign indicating which arm has the higher observed proportion.

The posted comparison is an unadjusted risk difference for i-gel relative to Air-Q. “Unadjusted” means that the comparison is not described as controlling for other participant characteristics or prognostic variables. The registry record does not report a covariate-adjusted analysis. The point estimate is positive, corresponding to a numerically higher observed proportion for i-gel, but statistical interpretation depends on uncertainty as well as direction. The confidence interval crosses zero, so values consistent with either direction of difference remain plausible.

A confidence interval gives a range of values compatible with the data under the method used to calculate it. It is not a guarantee that the true effect lies in the interval, nor does it describe the range of individual participant outcomes. When an interval for a risk difference includes zero, the data do not rule out no difference at the conventional level associated with that interval procedure. The width of the interval is also important: a wide interval signals that the estimate is imprecise, even if its point estimate has a clear direction.

The record also reports a risk ratio and an odds ratio. A risk ratio compares the proportions with an event between the arms, while an odds ratio compares event odds. Both measures describe relative rather than absolute contrasts, and their values are interpreted against a null value of one. Their confidence intervals include that null value. Neither relative measure removes the uncertainty arising from the limited number of participants. For a common event such as this outcome, odds ratios and risk ratios are different measures and should not be treated as interchangeable.

The unadjusted p-value is 0.683. A p-value measures how unusual data at least as discrepant as those observed would be under a statistical model in which the null hypothesis of no difference holds. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. A large p-value such as the one reported is not evidence of equivalence; an equivalence conclusion would require an appropriate design and prespecified equivalence margins, which are not reported in the registry record.

These are general interpretations of the statistical methods. The registry record does not identify the exact procedure used to calculate the confidence intervals, nor does it provide a detailed statistical analysis plan. The posted p-value is labelled unadjusted; no multiplicity adjustment is reported. The primary endpoint is a count outcome rather than a continuous measurement, so a mean and standard deviation are not the relevant summary for this result.

Why can a small event-count comparison be uncertain?

In a binary outcome, each participant contributes either an event or a non-event. With a limited number of participants, changing the classification of a small number of observations can materially affect the estimated proportion and the difference between arms. This is one reason uncertainty intervals matter alongside the observed counts. The record’s equal outcome denominators make the arm counts straightforward to compare, but they do not make the estimate precise.

Randomization supports a comparison of assigned groups, but it does not guarantee that the groups are identical in every characteristic, especially in a small study. The registry record does not list baseline characteristics or report an adjusted analysis. It is therefore not possible to assess balance or determine whether any adjustment was planned. Randomization also does not resolve missing-outcome concerns; the record does not describe missing data or the handling of participants without a recorded primary endpoint.

What can be learned from the secondary outcomes?

The registry names airway insertion time and time to achieve the best fiberoptic view as secondary outcomes. They may address different practical aspects of device use from the primary acceptable-view classification. However, numerical results for these outcomes are not reported in the registry record. No conclusions about their values, between-arm differences, or statistical uncertainty can be drawn from the listed outcome names alone.

10. Confidence Intervals and Precision

Precision concerns how narrowly the data estimate the comparison, not whether the observed direction is favorable to one device. The primary comparison’s confidence interval includes zero and extends to values on either side. Thus, the registry results are compatible with a possible higher acceptable-view proportion in either arm, as well as little or no difference. The interval is broad, so the point estimate should not be read as a precise measure of the underlying contrast.

The arm counts—20 of 24 for Air-Q and 21 of 24 for i-gel—are the observed results for the participants represented in the primary outcome record. They are not exact estimates of what would occur in all pediatric patients or in every airway-management setting. The posted confidence intervals express sampling uncertainty under the calculation method used; they do not account automatically for possible selection, measurement, or missing-data biases.

The record reports a risk ratio and an odds ratio as well as the risk difference. The confidence intervals for the relative measures include their null value of one. These intervals reinforce that the data do not establish a clear separation between the arms, but they do not prove equivalence. The statistical plan and interval calculation details are not reported in the registry record, which limits independent assessment of the methods.

Greater precision would generally require more information, often from a larger study with a suitable design and complete outcome reporting. The posted sample-size calculations are planning illustrations based on the observed effect; they are not evidence that the original study was designed to achieve a particular precision. The trial’s own original design assumptions are not reported in the registry record.

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 planning figures are participants per arm, not total events. They are illustrations based on the observed effect and on detecting stated fractions of that effect. The figures assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The original trial’s own sample-size assumptions or justification are not reported in the registry record.

The 80% power column describes the planned number of participants per arm under which the specified effect would be detected in 80% of repeated studies, if the planning assumptions and effect were correct. The 90% power column uses a higher probability of detecting that effect under those assumptions, and therefore requires a larger planned sample. These are design calculations, 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 listed participant requirements increase as the effect to be detected becomes smaller: a smaller contrast is harder to distinguish from random variation, so a larger study is needed under the stated assumptions. For example, the registry’s planning figures for 100% of the observed effect are 1,126 participants per arm for 80% power and 1,506 per arm for 90% power. For 75% of the observed effect, they are 2,061 and 2,758 participants per arm, respectively. For 50% of the observed effect, they are 4,768 and 6,382 participants per arm.

This is not observed power. It is a planning illustration calculated from the observed effect, and it does not establish that the trial had a particular probability of detecting its true effect. The calculations also do not replace the unreported original design rationale or an assessment of whether the observed effect is a suitable target for future planning.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.833; treatment proportion p₁ = 0.875; average p̄ = 0.854.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.4991 = 0.9783.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.4983 = 0.4193.
4. n = (0.9783 + 0.4193)² / (0.0417)² = 1,125.1, rounded up to 1,126 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
p0 <- 0.833333333333333                          # control proportion
p1 <- 0.875                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2532465)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 1,126 (80% power), 1,506 (90% power)
 75% of observed effect: n per arm = 2,061 (80% power), 2,758 (90% power)
 50% of observed effect: n per arm = 4,768 (80% power), 6,382 (90% power)
power.prop.test: 1125.1 
Simulated power at n = 1,126 per arm: 0.803 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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 one primary endpoint and two secondary outcomes: airway insertion time and time to achieve the best fiberoptic view. It does not report a multiplicity adjustment or explain how inference across these outcomes was handled. When multiple outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase; methods to address that issue depend on the analysis plan. Because that plan is not reported in the registry record, it is not possible to determine whether or how multiplicity was considered.

The record does not report a missing-data plan, the number of participants lacking a primary endpoint, or the reasons for any absent outcome measurements. The registry reports 24 participants in each primary outcome arm and an enrollment of 50, but it does not explain the difference. The recorded counts alone cannot establish whether all randomized participants were analyzed, whether the outcome was unavailable for some participants, or how any missing results were treated.

An analysis population is the set of participants whose data are included in a particular analysis. The registry record does not state whether the primary analysis used all randomized participants, only participants who received the assigned device, or another defined population. It does not report an intention-to-treat analysis or a per-protocol analysis. These details matter because exclusions after randomization can affect comparability between groups.

Randomization is a feature of the trial design, but the record does not give enough detail to evaluate allocation implementation or the effect of missing outcomes. It also does not report sensitivity analyses for alternative missing-data assumptions. Without these details, the results can be interpreted as the recorded comparison among the stated outcome denominators, but the robustness of that comparison to missingness and analysis-population choices cannot be assessed.

The registry names two secondary outcomes, but their numerical results are not reported in the registry record. Their absence means they cannot be used to corroborate or qualify the primary result. The record reports no analyses in the results metadata, and it does not provide a full statistical analysis plan. Conclusions about prespecification, selective reporting, or analytic choices would therefore go beyond the available record.

14. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The adverse-event record lists 25 participants at risk in each arm. It reports zero serious adverse events, zero other adverse events, and zero deaths for Air-Q and for i-gel. No serious adverse-event terms are listed.

These figures describe the safety counts recorded in the registry; they do not establish that no adverse events occurred outside the definitions, observation period, or reporting process used for the record. The registry entry does not give further detail about safety-event definitions, collection methods, follow-up duration, or the relationship of events to the devices. It also does not explain why the safety denominators are 25 per arm while the primary outcome denominators are 24 per arm.

Zero reported events should therefore be read as zero events recorded in these categories, not as proof that the devices carry no risk. The safety figures are descriptive and come from a limited trial population. They do not support broad conclusions about uncommon events or safety in other settings.

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

The posted primary results show that an acceptable Grade I–II fiberoptic view was recorded for 20 of 24 participants in the Air-Q arm and 21 of 24 in the i-gel arm. The observed comparison is numerically in the direction of a higher acceptable-view proportion with i-gel, but the confidence interval includes no difference and values in either direction. The unadjusted p-value is 0.683. The evidence is therefore inconclusive about a difference in this specific endpoint.

That interpretation is different from saying the devices are equivalent. A non-significant test does not demonstrate that two devices have the same effect, and the broad interval leaves meaningful uncertainty about the possible contrast. The study’s outcome denominators are small, and the registry record does not report an equivalence design or margin. The result should not be converted into a claim of sameness.

The endpoint concerns fiberoptic visibility 15 seconds after insertion. It does not directly measure successful endotracheal intubation, airway rescue, or patient outcomes. Although the registry’s rationale connects clearer views with use as a conduit to aid intubation in difficult airways, the primary outcome is still a visual classification. No direct conclusion about intubation success follows from the counts reported.

The registry lists airway insertion time and time to achieve the best fiberoptic view as secondary outcomes, but their numerical results are not reported in the registry record. The safety record reports no serious or other adverse events and no deaths in either group, but limited event reporting and sample size cannot rule out risks not captured in the entry.

Overall, the record contributes a randomized comparison of two devices on a narrowly defined visual endpoint. It does not settle which device is preferable across clinical circumstances, nor does it establish a result for populations or settings not described in the record. The missing details about participant characteristics, outcome completeness, analysis populations, and statistical methods further constrain interpretation.

16. Why This Trial Matters Statistically

This trial illustrates an important distinction in biostatistics: an observed difference is not the same as convincing evidence of a difference. The arm counts are close, the estimated contrast favors i-gel numerically, and the unadjusted p-value is 0.683. Yet the confidence interval includes effects on both sides of no difference. A careful reading considers the estimate and its uncertainty together rather than treating the p-value as a verdict.

It also demonstrates why the endpoint must remain connected to the question it measures. A fiberoptic view is relevant to the study’s stated device comparison, but it is not the same outcome as intubation success or patient benefit. Statistical results can be precise about a defined measurement while remaining limited in what they say about broader clinical questions.

The gap between the registered enrollment of 50 and the primary outcome denominators of 24 per arm highlights the importance of reporting participant flow and missing outcomes. Without an explanation, readers cannot tell why the denominators differ or assess the implications for the analysis. Transparent reporting of analysis populations and missing-data handling is central to judging whether a randomized comparison remains interpretable.

Finally, the planning calculations show how the required study size depends on the effect a future study aims to detect and the desired power. They are based on the observed effect, however, and do not reveal the original trial’s design rationale. Separating an illustrative calculation from a trial’s original sample-size plan prevents retrospective calculations from being mistaken for evidence about how the study was designed.

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 provides limited detail about the participants beyond identifying them as pediatric patients and listing operative surgical procedures. Eligibility criteria, participant characteristics, airway-difficulty details, and the clinical setting are not reported in the registry record. This restricts assessment of how well the results apply to other pediatric populations or airway-management circumstances.

The primary outcome reports 24 participants in each arm, whereas registered enrollment is 50. The reason for the difference is not reported in the registry record. Participant flow, outcome availability, exclusions, and the analysis population are also not described. This prevents assessment of whether missing outcomes or post-randomization exclusions could have affected the comparison.

The record identifies the trial as randomized, parallel, and unmasked, but does not report how the allocation sequence was generated or concealed. It does not provide a detailed statistical analysis plan, the method used for the confidence intervals, or a sample-size justification for the original design. It also does not report baseline characteristics or an adjusted analysis.

The endpoint is a fiberoptic view classification at 15 seconds, rather than a direct measure of intubation or patient outcome. Numerical results for the two listed secondary outcomes are not reported in the registry record. Safety counts are reported, but further details about event definitions and follow-up are not given. Together, these limits mean that the posted results address a narrow endpoint and do not answer broader questions about device performance, safety, or clinical outcomes.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Glottic View Using Supraglottic Devices in Pediatric Patients — NCT02532465.
• Registry record last updated 2019-08-22; status last verified 2019-07.
• Results first posted 2019-08-22.
• 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.

21. Record Summary

NCT02532465 is a completed randomized, unmasked, parallel-group comparison of Air-Q and i-gel in pediatric patients. The registered enrollment is 50. The primary outcome is the number of participants with an acceptable Grade I–II fiberoptic view 15 seconds after device insertion.

The primary outcome counts are 20 of 24 for Air-Q and 21 of 24 for i-gel. The unadjusted p-value is 0.683, and the confidence interval for the risk difference includes no difference. The registry also lists airway insertion time and time to achieve the best fiberoptic view as secondary outcomes, but their numerical results are not reported in the registry record.

The safety entry reports zero serious adverse events, zero other adverse events, and zero deaths in both groups. Details about missing outcomes, analysis populations, original sample-size assumptions, and the statistical analysis plan are not reported in the registry record.