Comparison of Vital HEAT (vH2) Temperature Management System to Upper-body Forced-air Warming: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Vital HEAT (vH2) Temperature Management System to Upper-body Forced-air Warming (NCT00815191), a randomized na study. The primary outcome is Intraoperative Distal Esophageal (Core) Temperature.

2. Clinical Question

The study was randomized and used a parallel-group design. Its primary objective, as described in the registry summary, was to compare core temperature during surgery. The primary outcome was recorded at one hour, and the registry identifies it as a continuous measure reported as a mean in degrees Celsius.

The clinical question is about temperature under the two warming approaches at the specified measurement time. The registry does not report a non-inferiority margin, which is the prespecified maximum difference that would be considered acceptable for a non-inferiority conclusion. Without that margin, the decision rule for the primary question cannot be reconstructed from the posted record alone. The sponsor’s reported analysis is labeled as a non-inferiority or equivalence analysis, but the label does not supply the missing margin or explain which criterion was applied.

The posted figures describe the observed groups and their temperatures; they do not by themselves establish that either warming approach is clinically preferable. The meaning of the sponsor’s conclusion depends on its own analysis and on design details that are not reported in the registry record.

3. Trial Design

The registry record describes a completed randomized study with a parallel design and single masking. It lists enrollment as 73. The study began in 2008-01, and primary completion is recorded as 2008-12. The sponsor is The Cleveland Clinic. The phase is listed as not applicable.

The two arms are labeled Warm-water Sleeve and Forced Air in the outcome results. The record associates the former with the Vital HEAT (vH2) Temperature Management System and the latter with forced-air warming. The intervention descriptions refer to a forced-air warming cover and the Vital HEAT system. These differing labels appear in the registry record; the record does not provide further detail reconciling them.

The primary outcome is intraoperative distal esophageal (core) temperature at one hour. It is a continuous outcome expressed in degrees Celsius. The registry reports an outcome mean and standard error for each arm. It lists 37 participants in the Warm-water Sleeve group and 34 in the Forced Air group for this outcome.

Single masking is recorded, but the registry record does not state which people were masked. The record does not report the randomization procedure, allocation concealment, the original sample-size assumptions, or the planned analysis population. Details of adherence to the assigned warming approach and of any treatment switching are not reported in the registry record.

The outcome record includes one primary measure and one reported analysis. No secondary outcomes are posted. The trial status is completed, but a completed status does not supply missing design or analysis details. In particular, the registry record does not report an interim-analysis plan or a full statistical analysis plan. These omissions limit assessment of how closely the posted analysis follows the original protocol.

4. Participant Flow and Accounting

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

Overall Study

Reasons for not completing this period:

5. Baseline Characteristics

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

Population: 5 patients with missing data, including 3 in the warm-water sleeve group and 2 in the forced air group.

6. Primary Endpoint

The registry lists the primary outcome as Intraoperative Distal Esophageal (Core) Temperature, measured over at 1 hour.

The primary endpoint is intraoperative distal esophageal temperature, identified as core temperature, measured at one hour and expressed in degrees Celsius. The outcome is continuous, and the registry reports a mean for each study arm with a standard error. Temperature measured during surgery provides an observation of core thermal status at the specified time while patients are receiving the assigned warming approach.

In general, a continuous endpoint retains information across its measurement scale rather than reducing each observation to a category. Comparing group means can describe the average measured temperature in each arm at the selected time. The standard error describes the estimated uncertainty in a group mean; it is not the same quantity as the spread of individual patient temperatures.

The choice of a one-hour measurement defines the time point to which the result applies. It does not describe temperature across the entire operation or establish what happened at other times. The registry record does not report the endpoint’s measurement protocol, the handling of measurements that were unavailable, or whether additional temperature summaries were collected but not posted.

The study’s stated objective frames the endpoint as a non-inferiority question. For that interpretation, a difference in means must be judged against a prespecified non-inferiority margin. That margin is not reported in the registry record. Consequently, the endpoint and its observed group summaries can be described, but the criterion used to decide non-inferiority cannot be independently checked from the posted information.

7. Results Posted in the Registry

• Forced Air: mean 35.87 versus 35.96 on control; difference -0.09 (95% CI -0.32 to 0.14), standardized effect d = -0.18; z-test p = 0.443.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: intraoperative core temperature at one hour. The registry summarizes it with a mean and standard error in each arm. The reported sponsor analysis is an analysis of variance (ANOVA) with a mean difference for final values. A separate, simple unadjusted re-calculation uses the posted arm summaries. Because the registry marks a discrepancy between the re-calculation and the sponsor analysis, the sponsor’s own analysis takes precedence as the trial’s reported inferential result.

What does a mean difference describe?

A mean difference expresses the contrast between two group averages on the outcome’s original scale. Here that scale is degrees Celsius. The sign depends on which group is subtracted from which. A negative Forced Air minus Warm-water Sleeve estimate indicates a lower reported mean in Forced Air under that subtraction order; reversing the order reverses the sign. The sponsor-reported estimate is 0.091, while the simple re-calculation is -0.09 under its stated contrast. The differing estimates and directions underscore that the contrasts or analysis details are not aligned in the posted record. The registry does not explain why.

A group mean does not show the full distribution of individual observations. The standard error describes uncertainty in estimating the mean, whereas a standard deviation describes variability among individual measurements. The outcome record supplies standard errors, not standard deviations. A pooled standard deviation appears among the re-calculated comparison details, but it is an unadjusted derived summary and should not be mistaken for an outcome value reported by the sponsor.

What is ANOVA doing?

In general, ANOVA is a method for assessing differences in means across groups. For a two-group comparison, its basic mean-comparison question is closely related to other methods for comparing means, subject to the model assumptions and details of the fitted analysis. The registry reports ANOVA and a mean difference for final values, but does not provide the model specification, covariates, residual checks, or other details needed to reproduce the sponsor’s result. It also does not state whether the analysis adjusted for baseline temperature or other variables.

Model assumptions matter because the standard errors, confidence interval, and test result depend on how the observations are modeled. General considerations for a continuous outcome include whether observations are independent, whether the model adequately describes the data, and whether the uncertainty calculation is appropriate. The registry record does not report diagnostic checks or enough underlying data to assess those assumptions. These are general methodological considerations, not claims about what was or was not true in this trial.

How should the p-values be understood?

A p-value measures how compatible the observed data are with a specified null hypothesis under the assumptions of the test. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. The simple re-calculation reports an unadjusted p-value of 0.443 for a conventional comparison of the posted summaries. The sponsor reports a p-value below < 0.001 for its analysis, which is labeled non-inferiority or equivalence. These p-values concern different analyses and cannot be read as a direct contradiction about the same test unless the hypotheses and methods match; those details are not reported.

In general, a non-inferiority test asks whether the result rules out a difference worse than a prespecified margin in a specified direction. An equivalence test asks whether the difference is sufficiently contained within prespecified bounds. These are not the same question as whether a conventional test detects any difference. The registry’s combined label does not identify which hypothesis, margin, or decision rule was used. Since the margin is not reported in the registry record, the sponsor’s inferential claim cannot be independently evaluated against that threshold.

What does the confidence interval add?

A confidence interval gives a range of values compatible with the data and the method used, reflecting uncertainty in the estimated contrast. It adds information about precision and direction beyond a p-value. The simple re-calculation gives a 95% confidence interval from -0.320 to 0.140. The sponsor’s analysis gives a 95% confidence interval from -0.139 to 0.321. Because the point estimates and limits differ, the intervals should be attributed to their respective analyses rather than combined. A confidence interval is not a guarantee that the true effect lies in the reported range, and it does not resolve the unreported non-inferiority margin.

The registry record contains only summary results for this endpoint, not individual-level measurements. That limits alternative modeling, exploration of distributional features, and checks of how missing observations may have affected the estimate. The record does not report whether all randomized participants contributed outcome data, whether analyses followed intention-to-treat or per-protocol principles, or how any missing values were handled. In non-inferiority settings, analysis population and missing-data choices can be particularly important; this is a general methodological point, not a finding about the conduct of this trial.

10. Confidence Intervals and Precision

The simple unadjusted re-calculation estimates a Forced Air minus Warm-water Sleeve mean difference of -0.09°C. Its 95% confidence interval extends from -0.320 to 0.140. The interval includes zero, meaning that the re-calculated summary is compatible with effects on either side of no difference under that method. The width also indicates that the point estimate alone should not be treated as a precise description of the contrast.

The sponsor-reported analysis has a different estimate, 0.091, and a 95% confidence interval from -0.139 to 0.321. This interval also includes zero. The sponsor’s estimate and interval must be kept separate from the recalculation because the registry record identifies a discrepancy. The sponsor’s analysis takes precedence as the reported trial analysis, but the record does not explain why the values differ.

In general, a confidence interval expresses uncertainty in an estimated effect under the analysis assumptions. A narrower interval indicates greater precision than a wider interval on the same scale and under comparable methods. Neither interval supplies the non-inferiority margin, which is essential for judging whether the range excludes effects considered unacceptably worse. The registry record does not report that margin, so the precision information cannot independently verify a non-inferiority conclusion.

The intervals also pertain to the one-hour endpoint, not temperatures at other points during surgery. The posted record does not provide enough information to assess the stability of the result under alternative models, missing-data assumptions, or analysis populations. The observed group standard errors and confidence intervals quantify some uncertainty, but do not remove those interpretive limits.

11. Planning a Similar Trial: Sample Size

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

The planning figures are participants per arm, not total events. They are illustrations based on the observed effect, not the trial’s original design assumptions. The planning assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect. The registry record does not report the original sample-size assumptions used to design the trial.

The 80% power column gives an illustrative number of participants per arm for a future study to have an 80% chance of detecting the specified effect under those planning assumptions, if the assumptions and effect are appropriate. The 90% power column gives the corresponding illustration for a 90% chance. These are prospective planning quantities, not descriptions of the probability that the completed trial found a true effect. This is not observed power.

The listed effect scenarios are 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. For 100% of the observed effect, the illustration is 474 participants per arm for 80% power and 634 per arm for 90% power. For 75% of the observed effect, it is 842 participants per arm for 80% power and 1,127 per arm for 90% power. For 50% of the observed effect, it is 1,893 participants per arm for 80% power and 2,534 per arm for 90% power.

The pattern reflects a general statistical principle: smaller effects are harder to distinguish from random variation, so detecting them with a given power generally requires more participants. These calculations use the observed effect as their starting point; they are not a recommendation for a future trial and do not establish that the observed effect is the effect a future study should target. Their interpretation is also limited because the registry does not report the trial’s original design assumptions or the non-inferiority margin.

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 = -0.090; pooled standard deviation σ = 0.494.
2. n = 2 × (1.96 + 0.842)² × 0.494² / -0.090² = 473.1, rounded up to 474 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 <- -0.0900000000000034                      # observed difference in means
sigma <- 0.494105867902469                     # 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(815191)
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 = 474 (80% power), 634 (90% power)
 75% of observed effect: n per arm = 842 (80% power), 1,127 (90% power)
 50% of observed effect: n per arm = 1,893 (80% power), 2,534 (90% power)
power.t.test: 474.1 
Simulated power at n = 474 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 registry reports an ANOVA of mean difference in final values, labeled as a non-inferiority or equivalence analysis. The sponsor-reported estimate is 0.091, with a 95% confidence interval from -0.139 to 0.321, and the reported p-value is below < 0.001. This is the result to identify as the sponsor’s own analysis.

A simple unadjusted re-calculation from the posted arm summaries gives a different estimate and direction: -0.09 for Forced Air minus Warm-water Sleeve, with a 95% confidence interval from -0.320 to 0.140 and an unadjusted p-value of 0.443. The registry explicitly marks a discrepancy. The sponsor’s own analysis therefore takes precedence over this re-calculation when describing the trial’s reported analysis.

Precedence does not explain the discrepancy or make the sponsor’s result independently reproducible. The registry record does not provide enough information about the sponsor’s model, contrast direction, analysis population, missing-data handling, or non-inferiority margin to reconcile the two estimates. Nor does it clarify whether the reported test was a non-inferiority test, an equivalence test, or which decision rule was used. The sponsor result should be reported as posted, with those limitations stated, rather than combined with the re-calculation or treated as a fully verifiable conclusion.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure and one reported analysis, with no secondary outcomes posted. The record does not report whether the study protocol specified additional outcomes or analyses that were not included in the posted results. It also does not report a multiplicity adjustment or explain whether any adjustment was considered necessary.

In general, multiplicity arises when researchers conduct several statistical tests or assess several outcomes. Repeated testing can increase the chance of at least one apparently unusual result, so an analysis plan may specify how to account for multiple comparisons. The single posted analysis does not establish that only one analysis was planned or conducted. The registry record does not provide enough detail to assess the full testing family.

Missing-data handling is not reported. The record does not say whether every randomized participant had a one-hour temperature recorded, whether measurements were excluded, or whether any missing values were imputed. It also does not report the number analyzed in each group as a distinct analysis-population statement; outcome summaries list 37 and 34 participants. It is not possible to determine from these summaries alone whether those counts match the randomized groups or how missing observations were treated.

The analysis population is also not reported in terms such as intention-to-treat or per-protocol. In general, these populations can answer different questions, and their distinction can matter in a non-inferiority analysis. This is especially relevant because exclusions, nonadherence, or missing outcomes can influence the estimated group contrast. The registry record does not provide the participant flow, protocol deviations, or sensitivity analyses needed to assess those issues.

The non-inferiority margin and the detailed statistical analysis plan are not reported. Those omissions prevent independent evaluation of the sponsor’s labeled conclusion and of whether the reported analysis followed a prespecified rule. These are absences in the registry record, not evidence that the trial did or did not have such procedures in its full protocol.

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 adverse-event record lists 37 participants at risk for serious adverse events in the Warm-water Sleeve group and 34 in the Forced Air group. It records zero serious adverse events in each group. The record also lists zero other adverse events for the groups. Death counts are not reported in the posted results.

These figures should be read as the adverse-event counts recorded in the registry, not as proof that no adverse events of any kind occurred outside the reported categories or reporting period. The registry record does not provide further detail on event definitions, collection procedures, follow-up duration, or the method used to judge whether events were related to the warming approach.

Zero recorded events in the listed groups is a descriptive observation. It does not establish that the risk is zero, particularly when event counts are sparse. In general, when no events are observed, uncertainty about the underlying event rate remains; the count alone does not provide a precise upper bound. No safety comparison or uncertainty interval for adverse events is reported in the registry record.

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

The posted results describe a randomized comparison of two warming approaches and report one-hour intraoperative core-temperature summaries. The group means are 35.96°C for Warm-water Sleeve and 35.87°C for Forced Air, with standard errors of 0.081 and 0.085. The sponsor’s reported analysis is labeled non-inferiority or equivalence and gives an estimate of 0.091 with a 95% confidence interval from -0.139 to 0.321.

The registry also marks a discrepancy between that sponsor analysis and a simple unadjusted re-calculation. The latter gives a mean difference of -0.09 and a 95% confidence interval from -0.320 to 0.140. These results should not be presented as if they were one analysis. The sponsor’s analysis takes precedence as the trial’s reported analysis, while the discrepancy remains unexplained in the registry record.

The record does not report the non-inferiority margin. Thus, the sponsor’s analysis label and statistical result do not allow an independent check of whether a prespecified non-inferiority criterion was met. The registry also does not report enough detail to reproduce the analysis, including the full model, analysis population, and missing-data methods.

The result does not establish a difference in clinical outcomes, because no secondary outcomes are posted. It does not describe temperature throughout the operation, since the primary measure is specified at one hour. The adverse-event listing records zero serious adverse events and zero other adverse events in each group, but does not provide event definitions, follow-up detail, or death counts. These entries should not be taken as comprehensive evidence about all possible safety outcomes.

In general, statistical results are limited to the outcome, time point, population, and methods that were measured and reported. The registry supports a description of one-hour temperature summaries and of the sponsor’s reported analysis, but missing design and analysis details limit stronger conclusions about non-inferiority, equivalence, or broader clinical effects.

17. Why This Trial Matters Statistically

This trial raises a central issue in interpreting non-inferiority studies: the label of the analysis is not enough to evaluate the conclusion. A non-inferiority interpretation depends on a prespecified margin, the direction of the comparison, and an analysis that can be understood in relation to that margin. The registry labels the sponsor’s analysis as non-inferiority or equivalence but does not report the margin or clarify which criterion was applied.

The record also illustrates why the analysis source and contrast definition matter. The sponsor-reported estimate is 0.091, while the simple unadjusted re-calculation is -0.09 under the Forced Air minus Warm-water Sleeve contrast. The registry identifies a discrepancy, so the sponsor’s analysis takes precedence as the official reported analysis. At the same time, a reader cannot use that precedence to resolve the difference without the model and methods that produced the sponsor’s result.

Precision is another important part of the interpretation. Both reported confidence intervals include zero, but their estimates and limits are not identical. Confidence intervals describe uncertainty under their respective methods; they do not substitute for the missing non-inferiority margin. Statistical significance, interval width, and a non-inferiority decision address related but distinct questions.

The trial is also a reminder that registry summaries can leave important analysis details unavailable. The record identifies randomization, parallel groups, masking, the one-hour endpoint, and group summaries, but does not report the analysis population, missing-data approach, or original sample-size assumptions. Naming these omissions helps distinguish what the posted evidence establishes from what cannot be reconstructed.

Finally, the planning illustrations are based on the observed effect and should be read as prospective design scenarios, not as evidence about the completed trial’s power. Together, these issues make the study statistically informative as an example of how design labels, contrasts, uncertainty, and transparent reporting shape interpretation.

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 trial-specific details needed to evaluate the primary result are not reported in the registry record. Most importantly, the non-inferiority margin is absent. Without it, the sponsor’s labeled non-inferiority or equivalence analysis cannot be checked against its decision threshold. The registry also does not clarify which of those two types of conclusion was intended.

The sponsor’s reported mean difference and the simple unadjusted re-calculation differ in value and direction. Although the record marks the discrepancy and the sponsor’s analysis takes precedence, the reason for the difference is not reported. The model specification, contrast coding, covariate adjustment, and calculation details are not available to reconcile the estimates.

The registry record does not identify the analysis population or explain how missing one-hour temperature measurements were handled. It does not provide participant flow, adherence information, or sensitivity analyses. Those omissions limit assessment of whether the reported groups and methods represent the randomized comparison and how robust the conclusion is to analysis choices.

The primary endpoint is recorded at one hour only. The registry does not provide temperature measurements at other time points, a measurement protocol, or additional clinical outcomes. No secondary outcomes are posted. Consequently, the posted endpoint cannot describe performance across the entire operation or address outcomes beyond the specified temperature measure.

The record says masking was single but does not identify who was masked. It does not report allocation concealment, the randomization procedure, or diagnostic checks for the statistical model. It also does not report the original sample-size assumptions. Adverse-event entries are limited to the recorded categories and do not include death counts or detailed follow-up information. These limitations concern the information available in the registry record and do not establish what was or was not documented elsewhere.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Comparison of Vital HEAT (vH2) Temperature Management System to Upper-body Forced-air Warming — NCT00815191.
• Registry record last updated 2016-07-18; status last verified 2016-06.
• Results first posted 2016-07-18.
• 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, parallel-group study sponsored by The Cleveland Clinic. It lists enrollment as 73 and single masking. The study began in 2008-01, with primary completion in 2008-12. The stated objective was to compare intraoperative distal esophageal core temperature with Vital HEAT and upper-body forced-air warming during open abdominal surgery under general anesthesia; the summary specifies open colectomy.

The primary outcome is mean core temperature at one hour, reported in degrees Celsius with standard errors. The arm labels are Warm-water Sleeve and Forced Air. The sponsor reports an ANOVA mean difference labeled non-inferiority or equivalence; a simple unadjusted re-calculation differs, and the registry marks a discrepancy. The sponsor’s own analysis takes precedence as the reported trial analysis.

The registry record does not report the non-inferiority margin, analysis population, missing-data methods, or original sample-size assumptions. No secondary outcomes are posted. The adverse-event listing records zero serious and zero other adverse events in each group; deaths are not reported.