Evaluation and Control of WAG in PACU Within Patient and Caregiver Breathing Zone: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation and Control of WAG in PACU Within Patient and Caregiver Breathing Zone (NCT02428413), a randomized na study. The primary outcome is Waste Anesthetic Gas Measured by Parts Per Million Within PACU Caregiver's Breathing Zone With Caring for Patients.

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group study with no masking. Participants were assigned to either a standard oxygen mask or an ISO-Gard Mask. Because the study was unmasked, the record does not describe the comparison as blinded. It does not report further details about how randomization was generated, whether allocation was concealed, or how assignment was implemented.

The recorded enrollment is 125. The primary outcome results list 56 participants for the standard oxygen mask group and 52 for the ISO-Gard Mask group. These are the group counts attached to the reported outcome summaries; the registry record does not explain the relationship between the enrollment figure and the counts in those summaries, such as whether any participants lacked an outcome measurement or were excluded from an analysis.

The study status is completed. The recorded start is 2015-04 and the primary completion is 2015-11. The phase is listed as not applicable. The sponsor is Teleflex. The condition is described as waste anesthetic gas emanating from patients during post-operative recovery.

The registry lists four outcome measures and two analyses. The primary outcome concerns the mean waste anesthetic gas concentration in the caregiver’s breathing zone during the one-hour post-operative recovery period. The posted comparison is between the two mask groups. Other details of the trial design, including eligibility criteria, procedures for measuring gas, and the handling of protocol deviations, 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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: A study size of 100 randomized subjects will be used. Aforementioned sample size was determined to be able to detect an effect size of 0.57 that would provide 80% power and 5% type I error (95% confidence interval and p-0.05 level of significance). Two sample student t-test will be used to do data analysis.

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 Waste Anesthetic Gas Measured by Parts Per Million Within PACU Caregiver's Breathing Zone With Caring for Patients, measured over 1 hour post-operative recovery period.

The primary endpoint is the mean concentration of waste anesthetic gas measured in parts per million in the caregiver’s breathing zone while caring for patients. The timeframe is the one-hour post-operative recovery period. The registry describes the measure as gas emanating from the patient into the caregiver’s breathing zone. The posted summaries give a mean and standard deviation for each mask group.

This endpoint is used to quantify the gas concentration in the location relevant to the stated measurement question: the caregiver’s breathing zone during patient recovery. A continuous measurement retains information about the level of gas rather than reducing the result to a simple event count. Comparing group means provides one way to describe whether the average measured concentration differed between the mask groups in the recorded period.

The endpoint is a measurement of gas concentration, not a direct measure of health effects or clinical outcomes. The registry record does not report a threshold for interpreting a particular concentration, explain how individual measurements were collected or summarized over the recovery period, or describe whether other aspects of exposure were assessed. Those omissions limit how specifically the endpoint can be interpreted beyond the recorded concentration comparison.

7. Results Posted in the Registry

• ISO-Gard Mask: mean 56.90 versus 60.60 on control; difference -3.70 (95% CI -9.71 to 2.31), standardized effect d = -0.23; z-test p = 0.227.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a measured concentration reported as a mean in parts per million. For a continuous outcome, a group mean describes the average recorded measurement, while a standard deviation describes how spread out individual observations are around that mean. Neither summary alone describes the full distribution, and the registry record does not provide individual measurements or distribution plots in its text.

What does a mean difference represent?

A mean difference compares the average outcome between two groups. The recalculation expresses the ISO-Gard Mask mean relative to the standard oxygen mask mean. The estimate is -3.7 parts per million. The negative direction indicates that the recorded mean in the ISO-Gard group was lower than the recorded mean in the standard oxygen mask group. This is a description of the estimated contrast, not a conclusion about clinical importance or cause.

The reported group means are 56.9 for ISO-Gard and 60.6 for the standard oxygen mask. The corresponding standard deviations are 9.7 and 20.6. The estimate depends on the group summaries and the comparison definition; it does not account for any covariates. The registry record does not report a covariate-adjusted estimate.

How does the t-test fit?

A two-sample t-test is a method for comparing means in two groups. The registry’s reported analysis is a two-sided t-test. A two-sided test considers departures in either direction rather than testing only whether one named group has a higher mean. The sponsor reports p = 0.24. The unadjusted recalculation from the posted summaries gives p = 0.227.

In general, a p-value describes the compatibility of the observed data with a null model under the assumptions of the test. It is not the probability that the null hypothesis is true, nor does it measure the size or practical importance of a difference. A p-value also does not measure the probability that a future study will reproduce the estimate.

The t-test depends on assumptions about the data and the comparison. In general, observations should be independent within the analysis, and the test’s handling of variability between groups depends on its variance formulation. The registry lists a t-test but does not report whether it used a pooled-variance version, a variance-robust version, or diagnostic checks. The recalculation uses the posted summary statistics and is described as unadjusted; it is not a substitute for details about the sponsor’s full analysis.

What does the standard deviation tell the reader?

Standard deviation measures variability among observations in a group, in the same units as the outcome. Here, the two posted standard deviations differ. In general, unequal variability can matter for a mean comparison because the estimated uncertainty depends in part on how variable the observations are and how many are included. The registry does not report a separate analysis of variance or a sensitivity analysis, so the impact of the spread difference on the sponsor’s result cannot be assessed from the record alone.

The standard deviation is not the same as the standard error. A standard error describes the uncertainty in an estimated quantity, such as a group mean, rather than the spread of individual observations. The posted summaries also give standard errors for the group means in the recalculation: 2.753 for the standard oxygen mask and 1.345 for ISO-Gard. These quantities are distinct from the group standard deviations.

What is the role of the confidence interval?

A confidence interval gives a range of estimates compatible with the data and the interval’s statistical procedure. The recalculated 95% confidence interval for the mean difference extends from -9.705 to 2.305 parts per million. It spans zero, so the result is compatible with no mean difference as well as with differences in either direction. The interval’s endpoints express uncertainty under the calculation’s assumptions; they are not a range containing a specified proportion of individual measurements.

In general, a narrower interval indicates greater precision for the estimated contrast, while a wider interval indicates more uncertainty. Precision depends on factors including the observed variability and the amount of information available. The registry does not report enough detail to establish whether all randomized participants contributed outcome data or whether missing observations were handled in a particular way. That uncertainty affects how confidently the posted summaries can be connected to the original randomized groups.

The record includes a planned study-size narrative in the primary outcome description, but its text is incomplete. The planning illustration based on the observed effect is a separate calculation and should not be confused with the sponsor’s original design planning. Planning calculations ask how much information might be needed under specified assumptions; they do not establish what the original protocol intended unless those assumptions are documented.

10. Confidence Intervals and Precision

The recalculated mean difference is -3.7 parts per million, with a 95% confidence interval from -9.705 to 2.305. The interval shows that the estimate is uncertain: it includes zero and extends to negative and positive values. Under the calculation’s assumptions, the posted data are compatible with a range of possible mean differences rather than identifying one precise contrast.

A confidence interval describes uncertainty in an estimated group contrast. It does not show the spread of individual measurements, which is described separately by the group standard deviations. Nor does it give the probability that the true effect lies inside the particular interval. In general, the method used to construct the interval has a long-run coverage interpretation across repeated samples when its assumptions hold.

The means and standard deviations are reported for groups of 56 in the standard oxygen mask arm and 52 in the ISO-Gard arm. The registry does not explain whether these outcome counts reflect all randomized participants, nor does it report the amount or pattern of missing outcome data. That makes it difficult to assess whether the uncertainty calculation represents every randomized participant or only those with measurements available for the outcome summary.

The sponsor’s reported p-value is 0.24, while the recalculated unadjusted p-value is 0.227. Both describe the comparison as tested in the record, but neither p-value conveys the range of plausible differences as directly as the confidence interval. The interval is especially important for judging precision: it indicates that the data do not pin down the direction or magnitude of the mean contrast tightly. The record does not report a clinically meaningful difference threshold, so the practical importance of the interval’s values cannot be determined from the registry information.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations based on the observed effect, not the trial’s observed power. The listed figures are participants per arm, not total event counts. The assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each row considers an effect to detect equal to the stated fraction of the observed effect.

The column for 80% power gives the number of participants per arm that the illustration estimates would be needed to have an 80% chance of detecting the specified effect under those assumptions. The 90% power column gives the corresponding number per arm for a 90% chance. These are prospective planning quantities: they describe what a hypothetical study might require under the calculation’s assumptions, not the probability that this completed trial detected its effect.

The illustration includes planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. As the target effect gets smaller, more participants are needed to distinguish it from random variation at the stated significance level and power. The figures should be read as sensitivity scenarios, not as a recommendation or as a reconstruction of the trial’s original plan. The registry’s original design rationale is not established by these recalculated illustrations.

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 = -3.700; pooled standard deviation σ = 16.293.
2. n = 2 × (1.96 + 0.842)² × 16.293² / -3.700² = 304.4, rounded up to 305 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 <- -3.7                      # observed difference in means
sigma <- 16.2928361384371                     # 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(2428413)
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 = 305 (80% power), 408 (90% power)
 75% of observed effect: n per arm = 542 (80% power), 725 (90% power)
 50% of observed effect: n per arm = 1,218 (80% power), 1,630 (90% power)
power.t.test: 305.4 
Simulated power at n = 305 per arm: 0.803 (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 sponsor’s own reported comparison is a two-sided t-test with p = 0.24 for the standard oxygen mask and ISO-Gard groups. The unadjusted recalculation from the posted means, standard deviations, and group sizes gives a mean difference of -3.7 parts per million, a 95% confidence interval from -9.705 to 2.305, and p = 0.227.

The values are close, and the record does not identify a discrepancy. The sponsor’s analysis takes precedence as the trial’s own reported analysis. The recalculation is a straightforward, unadjusted check based on the posted summary statistics; it does not incorporate information that is not present in those summaries. The registry does not report enough detail about the sponsor’s analytic implementation to reproduce it fully or determine whether it included adjustments beyond the stated t-test.

The p-values should not be read as estimates of the size of the difference. The mean difference and its confidence interval describe the estimated contrast and its uncertainty, while the p-value summarizes the test result under its null model. The registry record does not report a prespecified interpretation threshold for the measured gas concentration.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures and two analyses. The primary outcome is identified as waste anesthetic gas in the caregiver’s breathing zone during the one-hour post-operative recovery period. No secondary outcome results are posted. The record does not explain the relationship between the listed outcome measures and analyses, or indicate which other outcomes were measured but not reported.

Multiplicity arises when several outcomes, comparisons, timepoints, or analyses are tested. In general, conducting multiple tests can increase the chance of finding an apparently unusual result by chance if each test is interpreted separately. Statistical plans may address this through prespecified hierarchies or adjustments, but the registry record does not report whether multiplicity was considered or how it was handled. No adjustment should be inferred from the reported p-value alone.

The record reports group summaries for the primary endpoint but does not describe missing-data rates, reasons for missingness, or any method used to handle missing values. It also does not state whether the reported comparison followed an intention-to-treat population, a per-protocol population, or another analysis population. The group counts attached to the outcome summaries do not establish how participants were handled outside those summaries.

Other details relevant to analysis are not reported in the registry record, including the exact randomization procedure, handling of protocol deviations, assumptions about the distribution of measurements, and any planned sensitivity analyses. These omissions do not invalidate the posted summaries, but they limit assessment of the full analysis process and how robust the result is to alternative reasonable choices.

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.

The registry lists zero serious adverse events in the standard oxygen mask group, among 56 participants at risk, and zero serious adverse events in the ISO-Gard Mask group, among 52 participants at risk. These figures describe the serious adverse event counts recorded for the listed groups. They do not establish that no adverse events of any kind occurred.

The record also lists zero other adverse events in each group, with the same at-risk counts. The deaths field is not reported for either group. No serious adverse event terms are listed. The registry does not provide event definitions, ascertainment procedures, follow-up duration for safety reporting, or detail about how adverse events were attributed or classified.

Zero recorded events in these group summaries should be interpreted within the limits of the reported safety information. The registry record does not report whether all participants had the same duration or completeness of safety follow-up, and it does not provide a separate assessment of risks beyond these adverse-event counts. These figures are descriptive registry entries and should not be treated as proof that an intervention has no safety concerns.

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

The posted results show that the mean measured waste anesthetic gas concentration was 60.6 parts per million in the standard oxygen mask group and 56.9 parts per million in the ISO-Gard Mask group during the stated one-hour post-operative recovery period. The unadjusted estimated mean difference for ISO-Gard relative to standard oxygen mask is -3.7 parts per million. The 95% confidence interval ranges from -9.705 to 2.305, and the sponsor’s two-sided test reports p = 0.24.

The interval includes zero, and its endpoints extend in both directions around zero. The data therefore do not identify a precise direction or magnitude for the mean contrast. This is not the same as demonstrating that the groups are equivalent. The registry does not report an equivalence margin or a threshold defining a difference that would be important for the measured endpoint.

The result concerns a gas concentration measured in the caregiver’s breathing zone, not a clinical health outcome. The record does not report outcomes that would show whether the measured concentration was associated with effects on patients or caregivers. It also does not provide a clinical interpretation threshold for the concentration values. Conclusions about health effects or safety beyond the recorded adverse-event entries are not supported by this endpoint comparison alone.

The record is informative about the measured outcome and the reported test, but interpretation is constrained by the absence of details about missing data, analysis populations, measurement procedures, and multiplicity handling. Secondary outcome results are not posted. The most defensible reading is limited to the group means, the estimated difference, and the uncertainty reported for this comparison.

17. Why This Trial Matters Statistically

This trial presents a useful statistical distinction between a difference in observed group means and the uncertainty around that difference. The ISO-Gard group’s posted mean is lower than the standard oxygen mask group’s mean, but the estimated contrast has a confidence interval that includes zero. The point estimate alone therefore does not convey how uncertain the comparison is.

The outcome is continuous and measured in parts per million, so both the scale of the mean difference and the variability of the observations matter. The posted standard deviations are different between groups. That makes it particularly important for readers to distinguish the observed spread of measurements from the uncertainty in the estimated mean difference. The registry reports a t-test, but does not provide enough methodological detail to evaluate all assumptions or any alternative analysis.

The planning illustration also demonstrates a general principle: smaller effects require more participants to detect under otherwise fixed planning assumptions. Those illustrations are based on the observed effect and should not be mistaken for the trial’s design justification or for observed power. They help readers understand the relationship between effect size, sample size, and desired power without changing what the completed trial observed.

Finally, registry transparency shapes interpretation. The record identifies a primary measure and reports group summaries, but does not give details on missing observations, analysis populations, or multiplicity. Recognizing those limits is part of interpreting the result responsibly: a statistical comparison can answer a defined measurement question while leaving broader scientific and clinical questions unresolved.

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 registry record provides limited detail about how the gas concentration was measured. It states that the endpoint concerns waste anesthetic gas in the caregiver’s breathing zone during a one-hour recovery period, but does not report the measurement device, sampling schedule, procedures for summarizing repeated readings, or quality-control methods. These details could affect how the recorded means are understood and compared.

The reported group counts for the primary outcome are 56 for the standard oxygen mask and 52 for ISO-Gard, while the recorded enrollment is 125. The record does not explain the relationship between these figures. It does not report missing outcome counts, reasons for missingness, participant flow, or which analysis population was used. As a result, it is not possible to determine from the registry record whether the outcome summaries include all randomized participants or how missing measurements may have affected the comparison.

The study was unmasked, and the registry does not report masking of measurement or analysis personnel. It also does not provide details about random sequence generation or allocation concealment. The record lists a t-test but does not describe its variance assumptions, diagnostics, or sensitivity analyses. These omissions limit assessment of potential sources of bias and the robustness of the statistical result.

Although four outcome measures and two analyses are listed, secondary results are not posted. The record does not report a multiplicity strategy or clarify whether all planned outcomes and analyses are represented. It also provides no clinical threshold for interpreting the measured concentrations, and no health outcome is reported that links the gas measurements to clinical consequences. These limitations narrow the interpretation to the posted concentration summaries and test.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Evaluation and Control of WAG in PACU Within Patient and Caregiver Breathing Zone — NCT02428413.
• Registry record last updated 2016-11-25; status last verified 2016-08.
• Results first posted 2016-09-29.
• 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 completed study was a randomized, unmasked, parallel-group comparison of the ISO-Gard Mask and a standard oxygen mask in post-anesthesia care. The registry records enrollment of 125 and identifies waste anesthetic gas in the caregiver’s breathing zone during a one-hour post-operative recovery period as the primary outcome.

The primary summaries report means of 56.9 parts per million for ISO-Gard and 60.6 parts per million for the standard oxygen mask. The unadjusted recalculated mean difference is -3.7, with a 95% confidence interval from -9.705 to 2.305; the sponsor reports a two-sided t-test with p = 0.24. The interval includes zero, so the estimate remains uncertain.

The registry does not report secondary outcome results, missing-data handling, analysis populations, or detailed measurement procedures. Safety entries list zero serious adverse events in each group, while deaths are not reported. Interpretation is therefore limited to the posted endpoint summaries and the registry’s stated analyses.