Air-Q® SP Versus Air-Q® and I-gel: A Randomized Clinical Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Air-Q® SP Versus Air-Q® and I-gel: A Randomized Clinical Trial (NCT01592760), a randomized na study. The primary outcome is Airway Seal Pressure After Device Placement.

2. Clinical Question

The endpoint is a measure of how much pressure the airway device can maintain before an audible leak or gastric insufflation is detected, up to a maximum of 40 cmH2O. The trial examined whether the self-pressurizing design maintained the airway differently from the other devices during general anesthesia. It was a device comparison, not a comparison of different anesthetic strategies or patient treatments.

The primary results are group averages: Air-Q had a mean seal pressure of 28.0 cmH2O, Air-Q SP 27.0 cmH2O, and i-gel 24.0 cmH2O. The unadjusted recalculated comparison of Air-Q SP with Air-Q estimated a mean difference of -1.0 cmH2O, while the comparison with i-gel estimated -4.0 cmH2O. Those estimates and their confidence intervals describe the observed results; they do not by themselves establish equivalence or determine clinical importance.

3. Trial Design

The registry record describes a randomized, double-masked, parallel-group device trial sponsored by the University of Wisconsin, Madison. It is marked completed. The recorded start is 2012-05, and primary completion is recorded as 2014-08. Enrollment was 225. The trial is listed as not applicable for phase, which is consistent with the registry’s classification of the interventions as devices rather than drug treatments.

The three groups received Air-Q, Air-Q SP or i-gel. The primary outcome results include 90 participants in the Air-Q group, 90 in the Air-Q SP group and 45 in the i-gel group. Air-Q was the reference group for the posted pairwise comparisons. The registry record does not report why the group sizes differed, how randomization was generated or concealed, who was masked, or whether the planned allocation ratio was the same as the final group sizes.

The primary outcome was airway seal pressure, measured within 5 minutes after device placement or study initiation. The record defines the measure using a manometer attached to the anesthesia circuit and notes that measurement was made with the head and neck neutral, the expiratory valve closed and fresh gas flow set to five liters per minute. The measure was capped at 40 cmH2O. Additional outcomes included placement, use time, positioning, gastric insufflation or aspiration, and oropharyngeal injury.

Although the trial is described as randomized and double-masked, the record does not report the full protocol, the details of the masking procedure, adherence to assigned device, or participant flow through the study. The original sample-size justification and planned statistical analysis are not reported in the registry record. No sponsor-reported comparison analyses are listed in the record; the pairwise comparisons discussed with the posted summary results are unadjusted recalculations from those summaries.

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.

Perioperative to Discharge

24-hour Follow-Up

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 Airway Seal Pressure After Device Placement, measured over Measured within 5 minutes after device placement/study initiation.

Airway seal pressure is the pressure at which the manometer needle equilibrates while an audible air leak from the oropharynx or gastric insufflation is associated with the reading. The registry defines a maximum measurement of 40 cmH2O. Measurements were made with the subject’s head and neck in a neutral position, the anesthesia machine’s expiratory valve closed, and fresh gas flow set to five liters per minute. The measurement was taken within 5 minutes after device placement or study initiation.

This endpoint provides a continuous measure of the seal achieved by a device under the specified measurement conditions. A higher value indicates that a higher circuit pressure was reached before the defined leak or insufflation endpoint. That makes it relevant to comparing airway sealing performance, but it is not a direct measure of every aspect of airway management, such as successful placement, injury or aspiration. Those topics were listed as separate outcomes.

Because the reported outcome is a mean with a standard deviation, the group average describes central tendency and the standard deviation describes the spread of individual measurements around that average. The primary results were 28.0 cmH2O for Air-Q, 27.0 cmH2O for Air-Q SP and 24.0 cmH2O for i-gel. The registry record does not report whether the primary endpoint was selected as a surrogate for a particular clinical outcome or provide a threshold for a clinically important difference.

7. Results Posted in the Registry

• Air-Q SP: mean 27.00 versus 28.00 on control; difference -1.00 (95% CI -3.07 to 1.07), standardized effect d = -0.14; z-test p = 0.343.
• I-gel: mean 24.00 versus 28.00 on control; difference -4.00 (95% CI -6.65 to -1.35), standardized effect d = -0.59; z-test p = 0.003.

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.

Device Placement Time

• 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:
  • Air-Q SP: mean 19.00 versus 25.00 on control; difference -6.00 (95% CI -8.94 to -3.06), standardized effect d = -0.60; z-test p = <0.001.
  • I-gel: mean 21.00 versus 25.00 on control; difference -4.00 (95% CI -8.43 to 0.43), standardized effect d = -0.34; z-test p = 0.077.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Air-Q SP than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between I-gel and the control. The interval gives the range of effects that remain compatible with the data.

Device Use Time (Min)

• 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:
  • Air-Q: mean 65.00 versus 60.00 on control; difference 5.00 (95% CI -5.85 to 15.85), standardized effect d = 0.13; z-test p = 0.366.
  • I-gel: mean 70.00 versus 60.00 on control; difference 10.00 (95% CI -3.89 to 23.89), standardized effect d = 0.27; z-test p = 0.158.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Air-Q and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between I-gel and the control. The interval gives the range of effects that remain compatible with the data.

Incidence of Oropharyngeal Injury

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Air-Q SP: 0.0% (0/90) versus 2.2% (2/90) on control; risk difference -2.2 percentage points (95% CI -5.3 to 0.8); unadjusted two-proportion z-test p = 0.155.
  • I-gel: 2.2% (1/45) versus 2.2% (2/90) on control; risk difference 0.0 percentage points (95% CI -5.3 to 5.3), risk ratio 1.00 (0.09–10.74); unadjusted two-proportion z-test p = 1.000.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Air-Q SP and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between I-gel and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes extend the primary airway-seal comparison to device placement, duration of use and possible complications. The posted results do not form a single consistent confirmation of the primary pattern: secondary measures address distinct aspects of use, have different scales and event frequencies, and are not interchangeable with seal pressure. A device can differ on one measure without the same pattern appearing on another.

Placement time is a continuous measure of the time needed to place a device. Device use time covers the period between successful placement and removal, with the registry describing it as approximately 2 hours. Oropharyngeal injury is a binary outcome reported as a participant count. The registry also lists outcomes such as placement success, ease of insertion, device position, gastric insufflation and aspiration, but their detailed results are not all present in the posted outcome summaries. Unreported outcome results are not evidence of no events or no differences.

Secondary results can help describe whether the primary result sits alongside other aspects of device performance, but they generally carry less weight for a confirmatory conclusion when many outcomes are examined and no multiplicity adjustment or testing hierarchy is reported. An unadjusted finding among several secondary comparisons may be due to chance, and a nonsignificant result may be too imprecise to rule out a meaningful difference. This is why effect estimates and intervals matter alongside p-values.

The primary outcome is a measure of airway seal pressure under specified conditions; the secondary endpoints add context rather than replacing it. The registry record does not report a prespecified framework for combining these outcomes into an overall judgment. Each secondary result should therefore be interpreted according to its own definition, measurement time and uncertainty, rather than treated as a vote for or against a device.

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

• Device Placement Time
• Device Placement Success Rate
• Device Ease of Insertion
• Device Position in Relation to the Vocal Cords
• Device Use Time (Min)
• Incidence of Gastric Insufflation
• Incidence of Gastric Aspiration
• Incidence of Oropharyngeal Injury

9. Statistical Interpretation

10. Statistical Methods Explained

What does a mean difference represent?

A mean difference subtracts one group’s average from another’s. In the recalculated comparisons, Air-Q is the reference: the Air-Q SP estimate compares its mean with Air-Q, and the i-gel estimate compares its mean with Air-Q. A negative estimate means that the comparison group’s average is lower than the Air-Q average. For the primary measure, Air-Q SP’s estimated mean difference is -1.0 cmH2O and i-gel’s is -4.0 cmH2O. These are differences between group averages, not measurements of how much every individual’s result changed.

The registry reports each group’s mean and standard deviation. The mean gives the average outcome, while the standard deviation describes dispersion among individual values. Standard deviation is not the same as a confidence interval: it characterizes participant-to-participant spread, whereas a confidence interval characterizes uncertainty about an estimated quantity such as a group difference.

How should a confidence interval be read?

A confidence interval gives a range of values compatible with the estimate under the statistical method used. Its width reflects precision: narrower intervals indicate more precise estimates, while wider intervals leave greater uncertainty. The primary Air-Q SP comparison has an interval from -3.066 to 1.066 cmH2O. The interval includes zero, so the result does not provide clear evidence of a nonzero difference under the unadjusted comparison. This is not proof of equality. The interval also does not encode whether a difference would matter clinically; the registry record does not report a threshold for clinical importance.

The i-gel comparison interval is from -6.646 to -1.354 cmH2O. It lies below zero, in the direction of a lower mean for i-gel relative to Air-Q. The corresponding p-value is 0.003. A p-value describes how incompatible the observed data are with a specified null hypothesis under a statistical model; it is not the probability that the null hypothesis is true or a measure of clinical importance. The recalculated p-values are unadjusted, and the registry does not list sponsor-reported analysis methods for these comparisons.

What do unadjusted comparisons leave out?

An unadjusted comparison is considered without a multiplicity correction or other adjustments. That is useful for describing the pairwise summary statistics but does not account for the fact that several devices and outcomes are examined. When multiple tests are conducted, the chance of at least one apparently notable result can increase. The registry record does not report a multiple-comparison procedure or a hierarchy that distinguishes confirmatory from exploratory outcomes. Consequently, the nominal p-values should not be treated as if they were adjusted confirmatory evidence.

The registry’s original analysis plan, model specification, missing-data approach and analysis population are not reported in the registry record. The recalculated comparisons are simple, unadjusted calculations from the posted means, standard deviations and group sizes. They do not account for covariates, clustering, repeated measures, protocol deviations or any unreported participant-level information. They cannot reproduce an analysis that may have used the original participant-level data.

Why does outcome type matter?

Airway seal pressure and placement time are continuous outcomes summarized by means and standard deviations. A mean-difference method compares their averages. Oropharyngeal injury is reported as a count of participants, so a risk difference compares the observed event proportions. These outcome types have different distributions and interpretations. A continuous measure’s variability is expressed in the endpoint’s units; a risk difference is expressed as a difference in event risk. Estimates across these outcome types should not be compared as if they shared a scale.

The posted group sizes differ, with fewer participants in the i-gel group than in either Air-Q group. Unequal group sizes can affect the precision of comparisons, especially when the smaller group also has substantial variability. The confidence intervals reflect uncertainty in each pairwise estimate, while the group summaries show why precision can differ across comparisons. The record does not report whether the unequal sizes were planned or arose during enrollment.

What are the planning illustrations?

The sample-size illustrations use the observed effect as a starting point and show hypothetical participant requirements under stated assumptions. They are not the original trial’s design justification. For each comparison, the illustrations consider the full observed effect and smaller fractions of that effect, with separate targets for 80% and 90% power. These are planning quantities, not results about the trial’s achieved power. Their assumptions and limitations are described in the sample-size discussion.

More generally, power is the probability that a planned statistical test will reject a specified null hypothesis if a particular effect is present, under the assumptions used for planning. It depends on the effect size, variability, sample allocation, significance level and analysis method. The registry record does not report the assumptions used to plan the original trial, so the planning illustrations should not be interpreted as evidence that the completed study was designed to detect a particular effect.

Confidence intervals and p-values offer related but different information. The interval emphasizes the range and precision of plausible effects; the p-value summarizes compatibility with a null hypothesis under a model. Neither removes uncertainty about study conduct, measurement, analysis choices or clinical relevance. For this trial, the registered endpoint definition and posted summaries support a comparison of average seal pressure, while several details needed for a full audit of the statistical analysis are not reported.

11. Confidence Intervals and Precision

The primary Air-Q SP versus Air-Q mean difference is -1.0 cmH2O, with a 95% confidence interval from -3.066 to 1.066. This interval crosses zero and spans values consistent with Air-Q SP having a lower or higher mean than Air-Q. The point estimate is close to zero, but the uncertainty is broad enough that the comparison does not demonstrate equality. The registry record gives no equivalence margin against which to judge whether the interval excludes differences considered important.

For i-gel versus Air-Q, the estimated difference is -4.0 cmH2O, with a 95% confidence interval from -6.646 to -1.354. The interval is entirely negative, supporting a lower average for i-gel relative to Air-Q in this unadjusted recalculation. Its width still matters: the data are compatible with a range of possible differences, rather than identifying a single exact value. The p-value for this comparison is 0.003, but statistical evidence against a zero difference is not itself evidence about clinical importance.

The groups’ standard deviations were 6.0 cmH2O for Air-Q and 8.0 cmH2O for Air-Q SP and i-gel. The spread of individual values is distinct from uncertainty in the estimated mean difference. The smaller i-gel group, with 45 participants compared with 90 in each Air-Q group, contributes to the precision of its comparison. These intervals come from unadjusted recalculations based on posted summary statistics; sponsor-reported analysis details are not reported in the registry record.

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 illustrations report participants per arm for the continuous-outcome comparisons. They are not totals across all groups and do not report total events. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set to the stated fraction of the observed effect. The original trial’s own sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the number of participants per arm in a hypothetical study planned to have an 80% chance of detecting the specified effect, if the assumptions hold. The 90% power column gives the corresponding per-arm number for a higher target chance of detection. For both columns, the illustrations consider planning for the full observed effect, 75% of the observed effect and 50% of the observed effect. Smaller effects require more participants to detect under the same assumptions, which is why the estimates grow as the target effect is reduced.

These figures are planning illustrations based on the effects observed in this trial. They do not describe the power achieved by the completed trial, and they are not observed power. In particular, they should not be used to infer that a result with a larger p-value was caused by inadequate enrollment. A planning exercise depends on assumptions about effect size, variability and analysis; changes to those assumptions can change the resulting participant requirement. The registry record does not report whether its original design used these same assumptions.

The illustrations are specific to the pairwise comparisons and their observed effects. Large differences in the displayed planning requirements across comparisons reflect the different estimated effects and variability used in the calculations, as well as group information. They are not recommended enrollment targets without a separately justified effect of interest and a prespecified design.

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 = -1.000; pooled standard deviation σ = 7.071.
2. n = 2 × (1.96 + 0.842)² × 7.071² / -1.000² = 784.9, rounded up to 785 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 <- -1                      # observed difference in means
sigma <- 7.07106781186548                     # 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(1592760)
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 = 785 (80% power), 1,051 (90% power)
 75% of observed effect: n per arm = 1,396 (80% power), 1,868 (90% power)
 50% of observed effect: n per arm = 3,140 (80% power), 4,203 (90% power)
power.t.test: 785.8 
Simulated power at n = 785 per arm: 0.802 (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 identifies a primary endpoint and several secondary outcomes, but it does not report a complete statistical analysis plan. The number of outcome measures recorded is 12, and the record contains no sponsor-reported comparison analyses. It does not describe whether particular secondary endpoints were intended to be confirmatory, how comparisons were prioritized, or whether tests were to be adjusted for multiple comparisons. Without such information, the posted unadjusted p-values should be read as individual comparisons rather than as a controlled family of confirmatory tests.

Multiplicity matters because examining multiple outcomes or pairwise device comparisons creates more opportunities for apparently notable results by chance. A prespecified hierarchy or adjustment can address that issue, but neither is reported in the registry record. The recalculated primary comparisons are also unadjusted. Their numerical results remain informative descriptions of the posted summaries, but they do not by themselves show that the trial-wide probability of a false-positive conclusion was controlled.

Missing-data methods and analysis populations are not reported in the registry record. The record does not specify whether the primary analysis included all randomized participants, only those with successful device placement, or another defined group. It also does not state how missing outcome measurements, device failures, protocol deviations or withdrawals were handled. The outcome group sizes show the numbers represented in the posted summaries, but do not establish how those numbers relate to the randomized population or explain any exclusions.

Interim analyses, stopping rules, covariate adjustment, model diagnostics and the handling of deviations from assigned device are not reported in the registry record. These details affect how results can be interpreted and reproduced. Their absence should not be filled in by assuming standard practice. A fuller protocol or statistical analysis plan would be needed to assess the original inferential strategy, including whether the equality hypothesis was tested using an equivalence design or a conventional difference test.

Because these analysis details are missing, conclusions should stay close to the endpoint definitions and posted summaries. The interval estimates describe uncertainty under the recalculation, not uncertainty about all possible sources of bias or unreported analysis decisions. The registry record does not establish that the results were adjusted for multiplicity or that every randomized participant contributed to each outcome.

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.

Most frequent non-serious adverse event terms

The registry reports no serious adverse events in the Air-Q group (0 of 90), Air-Q SP group (0 of 90) or i-gel group (0 of 45). These figures mean that no serious events are recorded for the groups in the posted safety results. They do not establish that the risk of a serious event is absent, particularly because the groups are limited in size and the registry record does not describe safety follow-up beyond the posted information.

For other, non-serious adverse events, the record lists 1 participant in each group: Air-Q (1 of 90), Air-Q SP (1 of 90) and i-gel (1 of 45). The registry does not provide serious adverse event terms, and the death counts are not reported in the registry record. A missing death count should not be interpreted as zero deaths.

These safety figures are descriptive counts, not evidence that the groups have equal safety profiles. The record does not report a comparative safety analysis, event definitions beyond the serious versus other categories, or details of relatedness and follow-up. Sparse event counts also limit the precision of any comparison. The figures should be read as what the registry recorded, not as a complete account of safety under all circumstances.

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

The primary endpoint captures airway seal pressure under a defined measurement procedure shortly after device placement. The registry results show group means of 28.0 cmH2O for Air-Q, 27.0 cmH2O for Air-Q SP and 24.0 cmH2O for i-gel. In an unadjusted recalculation, Air-Q SP was estimated to be -1.0 cmH2O relative to Air-Q, with a confidence interval that includes zero. That does not show that the devices are equal; it indicates that the estimated difference is uncertain and that the registry does not report an equivalence margin.

The i-gel comparison with Air-Q has an estimated mean difference of -4.0 cmH2O and a confidence interval below zero. This describes a lower average seal pressure for i-gel relative to Air-Q in the posted summary comparison. It is not a direct comparison of i-gel with Air-Q SP, and the registry record does not list a sponsor-reported analysis for these comparisons. Statistical evidence about a difference on this measurement does not alone establish a difference in overall device performance or patient outcomes.

Seal pressure is only one aspect of airway management. Placement success, ease, positioning, use time, injury, gastric insufflation and aspiration are distinct outcomes. The registry results and missing analysis details do not support combining them into a single measure of benefit or harm. Nor do the reported means establish how an individual patient’s airway would respond.

The record also does not report a clinically important threshold for seal pressure, a full analysis plan, missing-data methods, or a multiplicity strategy. These limitations affect how strongly the numerical comparisons can be interpreted. The results describe averages and uncertainty in this trial’s posted summaries; they do not provide medical advice, establish superiority overall, or settle whether any difference is important in practice.

17. Why This Trial Matters Statistically

This trial is statistically instructive because its clinical question includes both a claim of equality between Air-Q SP and Air-Q and a directional expectation about Air-Q SP relative to i-gel. Those questions require care in interpretation. A conventional difference comparison that does not detect a difference cannot establish equivalence. Demonstrating equivalence requires a prespecified acceptable range and an analysis designed around that range; the registry record does not report either.

The results also illustrate the importance of distinguishing an estimated effect from its precision. The Air-Q SP and Air-Q means are close, but the confidence interval still includes differences in either direction. For i-gel versus Air-Q, the interval lies below zero, but that pairwise result remains an unadjusted recalculation and does not answer every comparison implied by the trial’s hypothesis. Pairwise direction, uncertainty and the exact reference group all matter.

A further statistical lesson is that endpoint choice shapes the claim. Seal pressure is a continuous physiological measurement; it is not synonymous with device placement success, injury, aspiration or overall safety. The secondary outcomes complement the primary endpoint but have distinct definitions and inferential limitations. The registry does not report a hierarchy or multiplicity adjustment to show how the many outcomes should be weighed together.

Finally, a sample-size calculation based on an observed effect is a planning illustration, not evidence of the completed trial’s power. The original sample-size rationale is not reported. Keeping these distinctions clear prevents a descriptive device comparison from being interpreted more broadly than its endpoint, design and available statistical reporting allow.

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.

Several limitations are specific to interpreting this registry record. First, the Air-Q SP versus Air-Q primary comparison is a conventional unadjusted difference estimate, while the stated hypothesis refers to equal seal pressures. The record does not report an equivalence margin or an equivalence analysis, so the near-zero estimate cannot establish equivalence.

Second, the posted pairwise calculations compare each device with Air-Q. They do not include a direct Air-Q SP versus i-gel estimate, although the registry’s hypothesis describes that contrast. The group sizes also differ, with 45 participants reported for i-gel and 90 for each Air-Q group. The record does not explain the allocation pattern or whether these were the planned sizes.

Third, the seal-pressure measurement has a cap of 40 cmH2O. The group means are below that cap, but the registry record does not report the number of readings at the limit or how capped observations were handled analytically. It also does not report the distribution of individual measurements, so means and standard deviations provide limited information about possible skew, outliers or ceiling effects.

Fourth, the record lacks details on randomization procedures, masking implementation, analysis populations, missing data, protocol deviations and participant flow. The original statistical plan, sample-size justification and multiplicity handling are also not reported. These omissions limit assessment of bias, reproducibility and the confirmatory status of unadjusted results.

Finally, the primary endpoint is a physiological measurement rather than a direct summary of all clinically relevant outcomes. The registry record does not provide a clinical-importance threshold, and several listed secondary outcomes do not have detailed results in the posted summaries. These limitations constrain conclusions to the outcomes and information recorded.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Air-Q® SP Versus Air-Q® and I-gel: A Randomized Clinical Trial — NCT01592760.
• Registry record last updated 2017-03-17; status last verified 2017-02.
• Results first posted 2017-02-08.
• 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

NCT01592760 is a completed randomized, double-masked, parallel-group device trial sponsored by the University of Wisconsin, Madison. It enrolled 225 adults for comparison of Air-Q SP, Air-Q and i-gel airway devices under general anesthesia. The primary endpoint was airway seal pressure measured within 5 minutes after device placement or study initiation.

Posted primary group means were 28.0 cmH2O for Air-Q, 27.0 cmH2O for Air-Q SP and 24.0 cmH2O for i-gel. Unadjusted recalculations give a mean difference of -1.0 cmH2O for Air-Q SP versus Air-Q and -4.0 cmH2O for i-gel versus Air-Q. The registry record does not report the original sample-size justification, full statistical analysis plan, multiplicity handling or analysis population.