Comparison of I-gel to the Laryngeal Mask Airway: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of I-gel to the Laryngeal Mask Airway (NCT00706823), a randomized na study. The primary outcome is Time Required for Intubation.

2. Clinical Question

The primary comparison concerns the full interval from device insertion to confirmation of endotracheal intubation, not insertion time alone. The registry also lists secondary outcomes concerning intubation difficulty, oropharyngeal discomfort, successful gastric drainage tube placement assessed by fiberoptic scope visualization, and number of attempts. These outcomes address other aspects of device use, but the primary result is the continuous time measure.

The clinical question is framed around a specific population and setting. It does not, by itself, answer how the devices compare in populations or procedures not described in the record. Details such as the intended analysis population, additional eligibility criteria, and the definition of any clinically important difference in time are not reported in the registry record.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group trial comparing the i-gel with the Laryngeal Mask Airway-Unique. Enrollment was 50. The record marks the study completed and lists its phase as NA. The start is recorded as 2008-02 and primary completion as 2008-08.

The two arm descriptions correspond to patients receiving i-gel or LMA-Unique for intubation. Each arm has 25 participants in the posted primary outcome results. The record does not identify who was masked, how randomization was generated or concealed, or whether masking could be maintained during device use. Those design details are not reported in the registry record.

The study summary says the devices were evaluated in anesthetized patients undergoing elective general surgery, including assessment during mechanical ventilation. It describes a broader interest in insertion, device position, drain-tube patency, and sealing properties. The posted primary outcome, however, is time required for intubation. The registry lists four secondary outcomes: level of difficulty for intubation, participants with oropharyngeal discomfort, participants with successful gastric drainage tube placement assessed by fiberoptic scope visualization, and number of attempts.

The registry does not report the trial's original sample-size justification, its prespecified analysis plan, or details of recruitment and follow-up. The planning figures associated with the observed result are separate illustrations and should not be treated as the assumptions used to design this completed trial.

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 Time Required for Intubation, measured over duration of intubation.

The primary endpoint is time required for intubation, measured in seconds. The registry defines the interval as beginning with insertion of the supraglottic airway device and ending at successful endotracheal tube intubation, verified by detection of CO2 on the anesthesia machine capnogram. The posted summaries report a mean and standard deviation for each arm.

This endpoint is used to compare the duration of a defined procedural sequence between the randomized groups. It captures more than the placement of the supraglottic device: the clock continues until endotracheal intubation is confirmed. Accordingly, the reported mean should be understood as the time for that complete interval, rather than a measure of device insertion alone.

As a general statistical point, a continuous time measure can retain information about the magnitude of observations, rather than reducing the outcome to whether a threshold was crossed. Its interpretation still depends on the measurement definition and on how representative the recorded values are. The registry does not report a clinically important threshold for this endpoint, nor does it provide individual observations or details of the time distribution. The result therefore describes the posted group summaries and their estimated between-group contrast; it does not establish how important a given time difference is in practice.

7. Results Posted in the Registry

• LMA-Unique: mean 30.04 versus 21.04 on control; difference 9.00 (95% CI 1.59 to 16.41), standardized effect d = 0.67; z-test p = 0.017.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each observation is a duration measured in seconds. The registry presents the arithmetic mean and standard deviation for each group. A mean gives the group's average time, while a standard deviation describes how spread out times are around that average. Neither summary reveals the shape of the underlying distribution or the presence of unusually long or short observations.

What does the mean difference express?

The reported comparison is a difference in group means. The recalculation uses the LMA-Unique mean relative to the i-gel mean, so a positive estimate corresponds to a longer average time in the LMA-Unique group. The estimate is 9.0 seconds. This is an unadjusted contrast reconstructed from the posted group summaries; it is not an adjusted estimate from a model controlling for other participant characteristics.

As a general statistical point, the mean difference retains the original measurement unit, which makes it possible to interpret the contrast in seconds. The estimate describes group averages and does not mean that every participant in one arm had a longer time than every participant in the other. Individual-level data are not reported in the registry record.

How does the t-test work?

The registry identifies a two-sided t-test for the primary comparison. A t-test evaluates whether the observed difference in means is compatible with a null model in which the population means are equal, taking account of sampling variability. A two-sided test considers departures in either direction. The registry reports p=0.02, while the recalculation from the group summaries gives p=0.017.

As a general statistical point, the t-test relies on assumptions about the sampling process and the behavior of the outcome or the estimated mean. The registry record does not provide diagnostic checks, individual observations, or enough detail to assess those assumptions directly. The posted standard deviations, 12.6 seconds and 14.1 seconds, describe the observed within-arm spread, but they do not by themselves demonstrate that every model assumption is satisfied.

What does the confidence interval add?

The recalculated 95% confidence interval for the mean difference is 1.588 to 16.41 seconds. A confidence interval combines an estimate with its sampling uncertainty. As a general explanation, the interval is generated by a procedure that, under its assumptions, would cover the target population quantity at the stated rate across repeated studies. It is not a probability statement about this particular fixed interval, and it does not show the range of individual participant times.

The registry's analysis listing gives the confidence level as 95 but does not include its own interval limits or its own mean-difference estimate. The interval and estimate are therefore the unadjusted recalculation from the posted summaries, rather than values quoted from the registry's reported test.

What is a standardized effect?

The recalculation also reports a pooled standard deviation of 13.37 seconds and a standardized effect of 0.673. Standardizing expresses the mean contrast relative to pooled variability, rather than in seconds. As a general statistical point, this can aid comparisons across outcomes that use different measurement scales, but it is less directly interpretable than the mean difference in the original unit. It does not define a clinically important effect, and the registry does not report such a threshold.

The recalculated standard errors for the group means are 2.52 seconds for i-gel and 2.82 seconds for LMA-Unique. A standard error describes the estimated sampling variability of a statistic, not the spread of participant observations. The standard deviations and standard errors answer different questions: the former describe variation among observed times, while the latter concern the precision of estimated means.

What is recalculated and what is reported?

The recalculated estimate, confidence interval, standardized effect, standard errors, and p-value are unadjusted calculations from the posted summary statistics. The registry's own analysis is identified as a two-sided t-test and reports p=0.02. The discrepancy indicator is false. The registry does not report an adjusted model for this endpoint. These distinct sources should not be conflated: the sponsor's test is the trial's reported analysis, while the recalculation is a check derived from the arm-level summaries.

As a general statistical point, any recalculation from group summaries is limited by the information those summaries retain. It cannot inspect data quality, identify influential observations, reconstruct missing values, verify protocol adherence, or assess subgroup patterns. Those matters are not reported in the registry record.

10. Confidence Intervals and Precision

The recalculated mean difference is 9.0 seconds, with a 95% confidence interval from 1.588 to 16.41 seconds. This interval communicates uncertainty in the estimated difference more fully than the point estimate alone. The lower and upper limits are both on the positive side for the contrast defined as LMA-Unique minus i-gel, but the interval still spans a range of possible population mean differences under the calculation's assumptions.

Precision is affected by both variability and the amount of information available. The reported standard deviations are 12.6 seconds in the i-gel arm and 14.1 seconds in the LMA-Unique arm, with 25 participants in each arm. Those summaries show that observed times varied within both groups. The confidence interval reflects uncertainty in the comparison; it should not be read as a prediction interval for an individual patient's time.

As a general statistical point, a narrower interval indicates greater precision for the quantity being estimated, whereas a wider interval leaves more uncertainty about its magnitude. Precision and clinical importance are separate: the interval does not specify what size of difference would matter in practice. The registry does not report a clinically important threshold, so the clinical meaning of the interval's values cannot be determined from the record alone.

The registry's own analysis reports p=0.02 but does not list confidence limits for the mean difference. The interval is the unadjusted recalculation from the posted summary statistics. It quantifies uncertainty for that recalculated contrast and should not be mistaken for a separately reported sponsor 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 sample-size table and curve are planning illustrations based on the observed effect, not the original trial design. The figures are participants per arm, not total participants or total events. They use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. The trial's own original design assumptions are not reported in the registry record.

For planning for 100% of the observed effect, the illustration gives 35 participants per arm for 80% power and 47 participants per arm for 90% power. For planning for 75% of the observed effect, it gives 62 participants per arm for 80% power and 83 participants per arm for 90% power. For planning for 50% of the observed effect, it gives 139 participants per arm for 80% power and 186 participants per arm for 90% power.

In plain language, the 80% power column describes the planned number per arm under which the assumed design would have an 80% chance of detecting the chosen effect at the stated significance level, if the assumptions hold. The 90% column uses a higher chance of detection for that same chosen effect and therefore calls for more participants. Smaller target effects are harder to distinguish from random variation, so they require more participants per arm in these illustrations.

These are planning calculations, not observed power. They do not describe the probability that the completed trial's conclusion is correct, and they are not evidence that the original trial was designed using these figures.

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 = 9.000; pooled standard deviation σ = 13.371.
2. n = 2 × (1.96 + 0.842)² × 13.371² / 9.000² = 34.6, rounded up to 35 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 <- 9                      # observed difference in means
sigma <- 13.3710508188399                     # 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(706823)
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 = 35 (80% power), 47 (90% power)
 75% of observed effect: n per arm = 62 (80% power), 83 (90% power)
 50% of observed effect: n per arm = 139 (80% power), 186 (90% power)
power.t.test: 35.6 
Simulated power at n = 35 per arm: 0.796 (20000 replicates)

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

13. Analyses Reported by the Sponsor

The registry's own primary analysis is listed as a two-sided t-test, with p=0.02. The unadjusted recalculation from the posted arm summaries reports a mean difference of 9.0 seconds, a 95% confidence interval from 1.588 to 16.41 seconds, and p=0.017. The registry does not provide its own estimate or confidence limits in the analysis listing, so the recalculated estimate and interval should not be presented as sponsor-reported values.

The discrepancy indicator is false. The registry result and the recalculated p-value are numerically close, with the registry value reported at a different precision. The sponsor's own analysis takes precedence if a discrepancy is flagged; no discrepancy is flagged in this record. The recalculation remains a simple, unadjusted reconstruction from group-level means, standard deviations, and sample sizes, not a replacement for the trial's analysis.

The record does not give further detail about the sponsor's test implementation, analysis population, handling of missing data, or any covariate adjustment. Those details cannot be inferred from the reported p-value alone.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures and identifies four secondary outcomes: level of difficulty for intubation, participants with oropharyngeal discomfort, successful gastric drainage tube placement assessed by fiberoptic scope visualization, and number of attempts. The primary outcome is time required for intubation. The record does not explain whether outcomes were ranked in a prespecified hierarchy or how the testing of multiple outcomes was handled.

As a general statistical point, when several outcomes or comparisons are tested, the chance of obtaining at least one apparently unusual result can increase if each is interpreted without considering the family of tests. Methods such as adjustment or a prespecified hierarchy can address that issue, but the registry does not report whether any such approach was used. The primary p-value should therefore be interpreted as the reported test for this endpoint, not as evidence that multiplicity was addressed.

The registry record does not report missing-data counts, reasons for missingness, imputation methods, or sensitivity analyses. It also does not specify whether the primary analysis included every randomized participant, only participants with measured outcomes, or another analysis population. Although the arm summaries report 25 participants in each group, those figures alone do not establish how all randomized participants were handled in every analysis.

Randomized allocation is recorded, but the analysis strategy for preserving that allocation is not reported. The record also does not describe protocol deviations or exclusions. Without these details, the effect of missing outcome data or exclusions on the estimate cannot be assessed from the posted information. This is a reporting limitation, not evidence that missing observations or exclusions occurred.

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 serious adverse event figures list zero affected participants among 25 at risk in the i-gel arm and zero among 25 at risk in the LMA-Unique arm. The registry therefore records no serious adverse events in either arm for the reported safety information. Death counts are not reported in the registry record.

For other adverse events, the record lists 6 affected participants among 25 at risk in the i-gel arm and 10 among 25 at risk in the LMA-Unique arm. These counts describe participants recorded as affected; they do not establish that an event was caused by the assigned device. The record does not provide event descriptions for these other adverse events, their severity, timing, or attribution.

As a general statistical point, counts from a study of this size provide limited information about uncommon events. The listed figures should be read as the registry's reported counts, not as proof that serious events cannot occur or as a complete assessment of comparative safety. Further safety details are not reported in the registry record.

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

The primary result describes a difference in average time for the defined interval from supraglottic airway insertion to confirmed endotracheal intubation. The observed means were 21.04 seconds with i-gel and 30.04 seconds with LMA-Unique. The unadjusted recalculated mean difference, expressed as LMA-Unique minus i-gel, is 9.0 seconds, with a 95% confidence interval from 1.588 to 16.41 seconds. The registry's reported two-sided test gives p=0.02.

These results do not establish whether a difference of this size is important to patients, clinicians, or procedural decisions. The registry does not report a clinically important threshold for time. Statistical evidence about a group difference is not the same as evidence about practical value, and a p-value does not quantify the probability that one device is superior.

The result also does not answer every question raised by the study description. The registry identifies other areas of interest, including insertion, position, drainage, and sealing, and lists secondary outcomes concerning discomfort, intubation difficulty, gastric tube placement, and attempts. The primary time result cannot stand in for numerical findings on those outcomes. Their results are not reported in the record.

The findings apply to the recorded study population and setting: non-obese adult patients undergoing elective general surgery while anesthetized. The record does not support extending the result to other populations or settings. It also does not provide sufficient detail to assess missing data, analysis-population choices, or the clinical importance of the observed contrast.

In short, the posted results show a longer average measured interval in the LMA-Unique arm than in the i-gel arm, with an estimated difference and uncertainty interval. They do not, by themselves, determine the clinical value of that difference or support medical advice.

17. Why This Trial Matters Statistically

This trial illustrates why an endpoint's operational definition matters. “Time required for intubation” might sound like a measure of placing the supraglottic device, but the registry defines it as the interval from device insertion through successful endotracheal tube intubation confirmed by capnography. That definition determines what the group means and the estimated difference actually represent.

It also shows the value of distinguishing a difference in original units from a test result. The mean difference is expressed in seconds, while the p-value summarizes compatibility with a null model under the test's assumptions. The confidence interval adds information about precision. Neither a p-value nor a confidence interval supplies a clinical importance threshold, which is not reported in the registry.

The comparison also provides a setting for separating sponsor-reported analysis from unadjusted recalculation. The registry reports its own two-sided t-test, while the reconstructed contrast and interval use posted summary statistics. Keeping those sources distinct helps avoid presenting a derived result as if it were the sponsor's reported estimate.

Finally, planning figures based on an observed effect are not the same as the original design rationale or the realized evidential strength of a completed study. The trial's original sample-size assumptions are not reported. The distinction matters when readers use a planning illustration to think about future studies: its assumptions are explicit, but it cannot retrospectively explain how the trial was designed.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary result is based on 25 participants per arm, and the study population is described as non-obese adults undergoing elective general surgery. The result should not automatically be generalized beyond that population or setting. The registry does not report more detailed eligibility criteria, participant characteristics, or the number screened.

The endpoint combines device insertion with subsequent successful endotracheal intubation and confirmation. It is therefore not an isolated measure of insertion time. The registry does not report individual times, distributional plots, or diagnostic checks for the t-test assumptions. The available summaries cannot show whether a small number of observations strongly influenced the mean.

The registry does not report the original sample-size justification, a clinically important difference, or the full prespecified statistical plan. It does not identify who was masked, explain the randomization procedure, or describe allocation concealment. Missing-data handling, analysis populations, exclusions, and protocol deviations are also not reported in the registry record.

Although secondary outcomes are listed, their numerical results are not available in the record. The handling of multiple outcomes is not reported. Safety information is limited to the listed participant counts; event descriptions, attribution, timing, and death counts are not reported. These gaps limit how fully the primary result and the broader comparison can be evaluated.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Comparison of I-gel to the Laryngeal Mask Airway — NCT00706823.
• Registry record last updated 2017-02-20; status last verified 2017-01.
• Results first posted 2011-04-05.
• 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

The registry record describes a completed, randomized, single-masked, parallel-group comparison of i-gel and Laryngeal Mask Airway-Unique in non-obese adults undergoing elective general surgery. Enrollment was 50; the posted primary outcome summaries include 25 participants in each arm.

The primary endpoint was time from supraglottic airway insertion to confirmed endotracheal intubation. Mean times were 21.04 seconds for i-gel and 30.04 seconds for LMA-Unique. The registry reports a two-sided t-test with p=0.02; an unadjusted recalculation gives a mean difference of 9.0 seconds, with a 95% confidence interval from 1.588 to 16.41 seconds.

The record lists four secondary outcomes and reports zero serious adverse events in each arm. Important design and analysis details, including missing-data handling and the original sample-size rationale, are not reported in the registry record.