Comparison of Ambu Auragain and I-Gel Supraglottic Airways in Adult Patients at an Ambulatory Surgery Center: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Ambu Auragain and I-Gel Supraglottic Airways in Adult Patients at an Ambulatory Surgery Center (NCT04286581), a randomized na study. The primary outcome is Oropharyngeal Leak Pressure (OLP).

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked, parallel-group study comparing two supraglottic airway devices in adult patients at an ambulatory surgery center. One group was assigned to receive an I-Gel laryngeal mask airway and the other an Ambu Auragain laryngeal mask airway for airway maintenance during general anesthesia. The registry lists the phase as not applicable and the study status as completed. The sponsor is the University of Minnesota.

The recorded enrollment is 148. For the posted primary outcome, each group has 70 participants with a reported mean and standard deviation. The registry does not explain the relationship between the enrollment figure and the outcome-group counts, or report whether all enrolled participants contributed to this outcome. It would therefore be inappropriate to infer why the counts differ or to assume a particular analysis population.

The study start date is 2021-03-22, and the primary completion date is 2021-10-31. The masking designation is single, but the registry record does not identify which people were masked or describe how masking was implemented. It identifies random allocation and a parallel model, but does not report the allocation procedure, concealment method, or the trial’s original sample-size assumptions.

The primary outcome was oropharyngeal leak pressure measured immediately after placement. Time to placement and sore throat are listed among secondary outcomes; sore throat appears twice in the registry list. The record lists four outcome measures, but reports no statistical analyses. The randomized design makes a between-group comparison relevant to the study question, but details needed to assess the conduct of that comparison are not reported in the registry record.

4. Participant Flow and Accounting

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

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Oropharyngeal Leak Pressure (OLP), measured over immediately after placement.

The primary endpoint is oropharyngeal leak pressure, reported as a mean with standard deviation in cm H20. The registry says it was measured immediately after airway insertion. Its stated procedure was to close the expiratory valve while maintaining fresh gas flow at 3 liters/minute until equilibrium was reached, then report the pressure in cmH2O.

In general, leak pressure is a measure of the pressure at which gas begins to escape around an airway device. It is used as a way to characterize the seal formed by a placed airway. The registry’s research question uses this measure to compare the two devices, specifically asking whether the I-Gel produces a higher pressure than the Ambu Auragain. This is a measure of device performance under the registered measurement procedure; it is not, by itself, a report of patient symptoms or overall clinical benefit.

The posted results give an average for each group and a standard deviation describing variation among participants. They do not give individual measurements, a median, the range of observed values, or details about measurement reliability. The registry record also does not report a threshold that would define a meaningful difference in leak pressure. Consequently, the group averages can be described and compared statistically, but the record alone does not establish what size of difference would matter clinically.

7. Results Posted in the Registry

• Ambu Auragain Laryngeal Mask Airway: mean 22.60 versus 20.90 on control; difference 1.70 (95% CI -0.21 to 3.61), standardized effect d = 0.30; z-test p = 0.081.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a pressure measurement rather than a count or category. The registry reports the mean and standard deviation for each group, then gives a mean difference for the comparison. A mean summarizes the center of a set of measurements, while a standard deviation describes how spread out participant values are around that group’s mean. These summaries describe the observed groups; they do not show every participant’s measurement or the shape of the measurement distribution.

What does the mean difference represent?

The reported comparison subtracts the I-Gel group mean from the Ambu Auragain group mean. The resulting estimate is 1.7 cm H20. A positive estimate therefore corresponds to a higher observed average in the Ambu Auragain group. This direction is the reverse of the registry’s directional wording, which asks whether the I-Gel is higher. The sign of a difference depends on the order of subtraction; the direction should always be interpreted using the stated comparison order rather than the sign alone.

A mean difference retains the original measurement unit, so the estimate is expressed in cm H20. It describes the gap between group averages, not the difference for every participant. The group standard deviations indicate variation within each group, whereas the interval around the mean difference reflects uncertainty in the estimated group contrast. These are distinct kinds of information: variation among participants is not the same as uncertainty about the average difference.

What does the interval tell the reader?

In general, a confidence interval gives a range of estimates reasonably compatible with the data and the procedure used to calculate the interval. It communicates precision as well as direction. A narrow interval indicates more precision than a wide interval, all else being equal. The reported limits for this comparison are -0.207 and 3.607 cm H20. Since the range crosses zero, the posted results do not exclude a zero mean difference under the interval procedure. The registry does not report the confidence level or the method used to calculate the interval, so those details cannot be assessed from the record.

How should the p-value be read?

The unadjusted p-value is 0.081. In general, a p-value describes how compatible the observed data are with a specified null model, subject to the analysis assumptions. It is not an effect size, does not measure the importance of a result, and is not the probability that the null model is true. Here, the registry does not identify the statistical test or give enough analytic detail to verify its assumptions. The p-value is therefore best treated as a reported inferential summary, not as a complete account of the analysis.

The term “unadjusted” indicates that this p-value is reported without an adjustment for multiple comparisons. The registry lists secondary outcomes, but does not state how many hypotheses were included in the inferential analysis, whether the primary comparison was part of a prespecified testing hierarchy, or whether any multiplicity procedure was planned. No adjusted result is posted. The implications of those omissions cannot be reconstructed from the available record.

What can be said about the analysis population?

The outcome summaries give 70 participants in each arm, while the recorded enrollment is 148. The registry does not identify whether the posted comparison follows an intention-to-treat, per-protocol, or other analysis population. It also does not report missing primary outcomes, exclusions after randomization, or the reasons any enrolled participants may not appear in the outcome groups. These details matter because an analysis based on a subset can differ from one that includes all randomized participants, particularly if missingness or exclusions are related to group assignment or outcome values. No such pattern can be inferred from the counts alone.

The registry identifies the trial as randomized, but does not describe the sequence generation or allocation concealment. It labels masking as single without specifying who was masked. Randomization and masking can reduce particular sources of bias when appropriately implemented, but the record does not contain enough detail to evaluate their implementation in this study. This is a limitation of the documentation, not evidence that the methods were or were not carried out as intended.

What assumptions underlie the planning illustrations?

In general, a sample-size calculation uses a target effect, variability assumptions, significance level, power, and a design structure to estimate how many participants would be needed. The registry record’s planning illustration uses the observed effect as its reference and considers planning for 100%, 75%, and 50% of that observed effect. It assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The figures are participants per arm because this is a comparison of continuous outcomes, not a time-to-event calculation.

The record does not report the trial’s original sample-size justification or the assumptions used when the study was designed. The posted planning illustration therefore cannot be treated as proof that the completed trial had a particular planned power. In general, smaller target effects require larger samples to distinguish them from random variation, given otherwise similar assumptions. That principle helps explain the direction of the planning figures but does not establish that any particular effect is clinically meaningful.

All of these statistical explanations are general unless explicitly tied to the posted values. The underlying analysis plan, choice of test, interval procedure, handling of missing values, and analysis population are not reported in the registry record. A complete evaluation of the statistical methods would require those details; they should not be inferred from the mean, standard deviation, interval, and p-value alone.

10. Confidence Intervals and Precision

The estimated mean difference is 1.7 cm H20, with the comparison defined as Ambu Auragain minus I-Gel. The reported interval runs from -0.207 to 3.607 cm H20. Its width indicates that the estimate is not tightly determined by the posted outcome data. The lower end is below zero and the upper end is above zero, so the interval includes no mean difference as well as positive and negative possibilities.

In general, a confidence interval is useful because it shows a range of effect values compatible with the data and the interval method, rather than relying on a single estimate. It does not mean that each value in the interval is equally likely, nor that there is a specified probability that the true value lies in this particular interval. The registry does not report the confidence level or the procedure used to derive these limits. Those omissions prevent a fuller evaluation of how the interval was constructed.

The group standard deviations are 6.0 for the I-Gel and 5.5 for the Ambu Auragain, based on 70 participants in each posted outcome group. They describe participant-to-participant spread, not the precision of the group contrast by themselves. The interval is the direct summary of uncertainty for the reported comparison. Although the estimate is positive, the interval does not establish a positive underlying difference, and its range does not support a precise conclusion about the direction or size of the contrast.

Precision also depends on whether the analyzed participants represent the randomized groups and whether outcomes are missing. The registry does not report missingness or the analysis population, and the outcome counts do not account for the recorded enrollment figure. Those gaps leave uncertainty about the scope of the estimate in addition to the statistical uncertainty expressed by the interval.

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 apply to a continuous outcome comparison and use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The registry record does not report the original sample-size assumptions used to design the trial, so these figures should be read only as a separate planning illustration based on the observed effect.

The 80% power column represents the number of participants per arm that the planning calculation associates with an 80% chance of detecting the target effect under its assumptions, if that target effect were the true effect. The 90% power column gives the corresponding planning number for a 90% chance. These are design concepts, not guarantees about a future study’s result. The entries are shown for planning at 100%, 75%, and 50% of the observed effect. At each power target, planning for a smaller fraction of the observed effect requires more participants per arm. The posted entries progress from 180 to 320 to 720 participants per arm for 80% power, and from 241 to 429 to 964 participants per arm for 90% power.

In general, higher target power requires a larger planned sample when other assumptions are held fixed, and smaller effects are harder to distinguish from random variation. The calculation does not show how likely the observed trial result was to be correct, and it does not retrospectively measure the trial’s power. This is not observed power. The registry does not state whether the trial’s original design used the same effect, significance level, allocation, or approximation assumptions as this illustration.

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 = 1.700; pooled standard deviation σ = 5.755.
2. n = 2 × (1.96 + 0.842)² × 5.755² / 1.700² = 179.9, rounded up to 180 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 <- 1.7                      # observed difference in means
sigma <- 5.75543221661067                     # 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(4286581)
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 = 180 (80% power), 241 (90% power)
 75% of observed effect: n per arm = 320 (80% power), 429 (90% power)
 50% of observed effect: n per arm = 720 (80% power), 964 (90% power)
power.t.test: 180.9 
Simulated power at n = 180 per arm: 0.797 (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 time to placement and sore throat as secondary outcomes, with sore throat appearing twice in the list. It reports four outcome measures overall but lists no statistical analyses. The record does not explain whether the repeated sore throat entry reflects separate measures, duplicate listing, or some other distinction. Results for these secondary outcomes are not included in the registry entries considered for this account.

When several outcomes or comparisons are tested, the chance of observing at least one apparently notable result by chance can increase. In general, a multiplicity plan may define a primary hypothesis, allocate significance across tests, or otherwise control interpretation across a family of comparisons. The registry record does not report a multiplicity adjustment, testing hierarchy, or which secondary outcomes were included in statistical testing. The posted p-value is described as unadjusted. No adjusted p-value or multiplicity strategy is reported, so the effect of multiple testing cannot be evaluated.

Missing-data handling is also not reported. The record does not state how many participants had missing primary outcome measurements, whether any participants were excluded from analysis, or what methods were used if measurements were unavailable. The posted outcome groups each contain 70 participants, while the registry enrollment is 148, but the record does not explain the difference. Counts alone do not identify whether the discrepancy reflects missing data, exclusions, or another reporting detail.

The analysis population is not described as intention-to-treat, per-protocol, or another defined set. The registry does not state whether all randomized participants were analyzed in their assigned groups. These omissions matter because the population and missing-data approach shape the interpretation of a randomized comparison. They should be treated as unreported information, not evidence that a particular approach was used or that particular data were missing.

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

The posted results show that the observed mean oropharyngeal leak pressure was 20.9 cm H20 in the I-Gel group and 22.6 cm H20 in the Ambu Auragain group. The reported mean difference, defined as Ambu Auragain minus I-Gel, is 1.7 cm H20. This describes the direction and size of the observed average contrast in the outcome groups reported by the registry.

The interval from -0.207 to 3.607 cm H20 includes zero. Thus, the posted comparison does not rule out no difference in the group means, and it also leaves uncertainty about the size and direction of the underlying contrast. The unadjusted p-value of 0.081 is another summary of uncertainty under the analysis model, but the statistical test and its assumptions are not reported. Neither the p-value nor the observed ordering should be interpreted as a probability that one device is superior.

The result does not establish that either device produces a meaningfully higher pressure in the population of interest. The registry does not report a threshold for clinical importance, and the outcome is a pressure measure taken immediately after placement. The result also does not address all aspects of airway management, patient experience, or outcomes beyond the registered measure. It should not be generalized from the primary endpoint to outcomes that were not reported.

In general, a randomized comparison can help assess differences between assigned groups, but the strength of interpretation depends on how allocation, masking, follow-up, and analysis were implemented. The registry identifies randomization and single masking but leaves implementation details and the analysis population unreported. The posted data therefore support a description of the measured outcome and its statistical uncertainty, not a broad conclusion about clinical effectiveness or safety.

The adverse-event record lists zero participants at risk and zero affected in each group, along with zero deaths, and no serious-event terms. These entries do not provide event-level detail or explain the zero at-risk counts. They should be read as the registry’s recorded fields, rather than as a complete demonstration that no adverse events occurred. No medical advice or treatment recommendation follows from these statistical summaries.

15. Why This Trial Matters Statistically

This trial is statistically interesting because it asks a direct comparison question using a continuous outcome and reports both group-level variability and an estimated mean difference. The direction of the reported estimate is easy to misread unless the subtraction order is made explicit: the estimate is Ambu Auragain minus I-Gel, while the registered question asks whether the I-Gel value is higher. Clear direction-setting is essential whenever an analysis presents a difference between two groups.

The interval adds important information that a point estimate alone cannot convey. Although the observed group averages differ, the interval includes zero and spans values on both sides of it. This illustrates why a result should not be reduced to a single mean difference or a threshold-based reading of a p-value. The estimate and its uncertainty address different parts of the statistical question and need to be considered together.

The record also illustrates the distinction between a trial’s design and a later planning illustration. The study is identified as randomized and parallel, but its original sample-size justification is not reported. The separate planning figures use the observed effect and stated assumptions; they are not evidence about the trial’s original design or a retrospective measure of its power. Keeping those concepts separate helps prevent planning quantities from being mistaken for observed results.

Finally, the record’s gaps are relevant to interpretation, not just documentation. The analysis population, missing-data approach, multiplicity plan, and specific inferential method are not reported. The enrollment and posted outcome-group counts also are not reconciled. These details would help readers evaluate how the reported comparison relates to all enrolled or randomized participants and how the primary finding fits alongside other outcomes. Statistical transparency includes both the numerical estimate and the methods needed to understand it.

16. 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 posted primary outcome summaries include 70 participants in each group, while the recorded enrollment is 148. The registry does not reconcile those counts or state how many participants were randomized, had outcome measurements, or were included in the analysis. This limits assessment of the analysis population and completeness of primary outcome data. It is not possible to determine from the record whether the counts reflect missing measurements, exclusions, or another explanation.

The registry identifies single masking but does not say who was masked or how masking was maintained. It identifies random allocation but does not describe sequence generation or allocation concealment. These details are relevant to evaluating potential sources of bias, but their absence from the record does not establish that the procedures were inadequate.

The statistical test, interval construction method, confidence level, and original sample-size justification are not reported. The record does not define the analysis population, describe any adjustment for covariates, or explain handling of missing outcomes. It also does not report a multiplicity plan despite listing secondary outcomes. These omissions limit independent assessment of the inferential result and its place among the trial’s outcomes.

The endpoint is measured immediately after placement, and the record does not report a clinically meaningful threshold for interpreting pressure differences. The secondary outcome list repeats sore throat, and secondary outcome results are not reported in the registry record. Adverse-event fields list zero at-risk counts without explanatory detail. These limitations constrain conclusions to the posted primary outcome summaries and registry descriptions; they do not justify assumptions about unreported results or procedures.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Comparison of Ambu Auragain and I-Gel Supraglottic Airways in Adult Patients at an Ambulatory Surgery Center — NCT04286581.
• Registry record last updated 2022-12-19; status last verified 2022-11.
• Results first posted 2022-12-19.
• 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.

20. Record Summary

The registry record describes a completed, randomized, single-masked, parallel-group comparison of I-Gel and Ambu Auragain laryngeal mask airways in adult patients at an ambulatory surgery center. The sponsor is the University of Minnesota. The recorded enrollment is 148; the posted primary outcome groups each contain 70 participants. The study start date is 2021-03-22, and primary completion is dated 2021-10-31.

The primary outcome is mean oropharyngeal leak pressure measured immediately after placement. The group means are 20.9 cm H20 for I-Gel and 22.6 cm H20 for Ambu Auragain. The reported mean difference, Ambu Auragain minus I-Gel, is 1.7 cm H20, with an interval from -0.207 to 3.607 and an unadjusted p-value of 0.081. The interval includes zero.

Time to placement and sore throat are listed as secondary outcomes, with sore throat repeated. The statistical test, analysis population, missing-data approach, multiplicity plan, and original sample-size assumptions are not reported in the registry record.