Zero Heat Flux Thermometry System Comparison Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Zero Heat Flux Thermometry System Comparison Trial (NCT01670760), a na na study. The primary outcome is Body Temperature Difference in Degrees Celsius.

2. Clinical Question

The clinical question concerns agreement between two ways of measuring temperature, rather than whether one treatment changes a health outcome. The stated hypothesis is that deep tissue temperature measured by zero-heat-flux thermometry will agree with nasopharyngeal temperatures during surgery. Both readings are taken in the same participants, so the comparison relies on paired, simultaneous measurements rather than a comparison between separate groups.

The registry describes readings every 5 to 10 minutes, or as clinically indicated, from incision to closure. It gives an average surgery duration of 57 minutes. The recorded primary endpoint is a mean temperature difference analyzed using a repeated-measures Bland and Altman technique. The registry record does not report the numerical estimate of that difference or its uncertainty. Consequently, the stated objective is clear, but the recorded results do not establish how closely the methods agreed in this study.

3. Trial Design

This is a single-group device comparison trial. The registry lists an enrollment of 20 and identifies zero-heat-flux thermometry as the intervention. Its arm description says that all patients have deep tissue temperature monitored from the nasopharyngeal and lateral forehead sites simultaneously. The two measurement locations therefore provide paired readings within participants; the record does not describe a separate control arm.

The allocation field is listed as NA, and the masking field is NONE. The registry does not describe random assignment or masking. The record also identifies the study model as single group. It should therefore be read as a measurement-agreement investigation, not as a randomized comparison of treatments or a like-for-like trial of independent groups.

The start date is 2013-04, primary completion is 2013-06, and status is COMPLETED. The intervention is identified as a device, named zero-heat-flux thermometry. The official title refers to the 3M SpotOn Temperature Monitoring System. The phase is listed as NA. Additional details about the surgical procedures, participant eligibility, setting, or demographic composition are not reported in the registry record.

According to the registry, measurements were collected every 5 to 10 minutes, or as clinically indicated, for the duration of surgery, beginning at incision and ending at closure. The average duration of surgery was 57 minutes. The stated analysis approach is the Bland and Altman repeated-measures technique, with the primary measure defined as a least-squares mean and dispersion reported as a standard error. Numerical results for this endpoint are not reported in the registry record, so the design and intended analysis can be described, but the size and precision of the observed agreement cannot be evaluated from the record.

The registry does not report a sample-size justification or a detailed statistical analysis plan. A planning illustration based on the observed effect is distinct from the trial’s design and should not be interpreted as a design rationale or as observed power.

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 Body Temperature Difference in Degrees Celsius, measured over Every 5 to 10 minutes, or as clinically indicated, for the duration of the surgery from the time of incision to the time of closure. The average duration of surgery was 57 minutes..

The primary endpoint is body temperature difference in degrees Celsius. It is defined as the bias between simultaneous readings: zero-heat-flux thermometry at the forehead minus the nasopharyngeal temperature. A positive value would mean that the forehead reading is higher on average than the nasopharyngeal reading; a negative value would mean it is lower. This sign interpretation follows directly from the stated subtraction order and does not indicate the size of any observed difference.

The endpoint is intended to describe agreement between measurement methods. When two devices or measurement sites are compared, the average difference can reveal systematic offset: whether one method tends to read higher or lower than the other. The repeated-measures Bland and Altman approach is relevant because readings are collected repeatedly during the same surgery, rather than as a single independent pair for each participant.

The registry describes temperature collection every 5 to 10 minutes, or as clinically indicated, from incision to closure. It specifies a least-squares mean for the endpoint and a standard error as the dispersion measure. The numerical mean difference, standard error, and any limits of agreement are not reported in the registry record. Thus, the endpoint’s intended meaning is clear, but its recorded value and the degree of uncertainty around that value cannot be described.

Agreement is not the same as correlation. Two methods can move together over time yet differ systematically in their readings. The difference-based endpoint focuses on the size and direction of that offset, which is why it addresses the stated measurement question more directly than a simple association between readings.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The named analysis is a Bland and Altman repeated-measures technique. In general, Bland and Altman methods examine paired differences between measurement methods, rather than asking only whether the methods are correlated. For each paired reading, the difference has a direction and magnitude. Across paired readings, the average difference describes systematic bias, while the spread of differences describes how far individual pairs tend to vary around that bias.

Repeated measurements introduce an additional feature: readings collected from the same participant are related. General statistical methods for repeated measures account for this within-participant dependence when estimating uncertainty. If that dependence were ignored, the apparent amount of independent information could be overstated and standard errors could be inaccurate. The registry identifies a repeated-measures Bland and Altman technique but does not report its detailed implementation, assumptions, or model specification.

The primary endpoint is a least-squares mean of the temperature difference, and the stated dispersion measure is the standard error. In general, a least-squares mean is a model-based estimate of an average, potentially accounting for terms in a statistical model. The terms included in this trial’s model are not reported in the registry record. A standard error describes how precisely an estimated mean is determined under the analysis; it is not the same as the standard deviation of individual differences and does not, by itself, convey the likely range of differences for individual readings.

A confidence interval, if reported, would give a range of values compatible with the data and analysis under its assumptions. It would help readers assess the precision of the mean difference. The registry record does not report a confidence interval for the primary endpoint. Nor does it report numerical limits of agreement, which in general are used to describe the range within which individual method differences may fall. Without these quantities, the posted record cannot support a detailed assessment of either average bias or individual-level agreement.

Agreement and correlation answer different questions. Correlation describes how two measurements vary together; it may be high even when one method consistently reads higher than the other. A difference-based approach is suited to the stated question because it evaluates the offset between simultaneous readings. The result must still be interpreted in context: a small average bias alone would not necessarily imply that individual paired readings are close, since the spread around the average also matters.

The measurements are described as occurring every 5 to 10 minutes, or as clinically indicated, during surgery. This creates repeated paired observations within the same participant, and possibly differing numbers or timing of observations across participants. The record does not report how irregular timing, missing readings, or varying numbers of observations were handled. It also does not state whether any covariates or other adjustments were used.

The primary question is one of measurement performance, not a treatment effect. The registry’s single-group structure and simultaneous measurement description do not supply a randomized intervention contrast. Therefore, common concepts used for treatment trials, such as a treatment-versus-control effect, do not describe the main estimand. The relevant quantity is the difference between the two measurement methods.

Sample-size calculations can be used in general to illustrate how many participants might be needed to detect a specified effect under stated assumptions. The record’s planning illustration uses a two-sided significance level of 0.05, equal allocation between two hypothetical arms, and a normal approximation, with the target effect expressed as a stated fraction of the observed effect. These are planning assumptions, not a description of how the single-group trial was conducted. The registry does not report the trial’s own sample-size justification. Planning illustrations are not observed power, and hypothetical two-arm calculations should not be mistaken for this study’s paired measurement design.

The registry record does not provide the numerical primary outcome estimate or its standard error. Consequently, no effect size, confidence interval, statistical significance, or precision assessment can be stated from the recorded outcome information. General explanation of the methods clarifies what the analysis was intended to assess, but it cannot substitute for the absent results.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Zero-Heat-Flux")
n   <- c(20)
m   <- c(-0.28)
sp  <- c(0.027)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Zero-Heat-Flux  20  -0.280  0.121  -0.337  -0.223

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and one analysis. That description does not establish whether other analyses were conducted or whether multiple comparisons were considered in the full analysis plan. A multiplicity adjustment or an explanation of how multiple outcomes or analyses were handled is not reported in the registry record.

In general, multiplicity matters when many statistical tests are performed: the chance of finding an apparently notable result by chance can increase across a collection of tests. The appropriate response depends on which outcomes and comparisons were planned and on the purpose of the analyses. The record does not report a statistical plan detailed enough to assess those choices. The single listed endpoint should not be taken as proof that no additional analyses occurred.

The registry describes repeated temperature measurements during surgery but does not report the amount or pattern of missing data. It does not state how unavailable readings, interrupted monitoring, or participants without complete paired observations were handled. Missing-data procedures and sensitivity analyses are not reported in the registry record.

The analysis population is also not described in detail. The registry lists enrollment of 20, but does not specify whether all enrolled participants contributed to the primary analysis, how exclusions were handled, or whether the analysis required a minimum number of paired readings. The population definition for the primary endpoint is not reported in the registry record. These omissions limit assessment of whether the analyzed data represent all enrolled participants and how missing or incomplete measurements might affect the estimated agreement.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events for the Zero-Heat-Flux group, with 20 participants at risk and 0 affected. It also reports 20 participants at risk for other adverse events, with 11 affected. Deaths are reported as 0. No top serious adverse-event terms are listed.

These figures describe the counts recorded in the registry; they do not explain the types, timing, duration, severity grading, or relatedness of the other adverse events. Those details are not reported in the registry record. The count of participants affected is also not a measure of the number of separate event episodes, and the record does not clarify further event-level details.

Safety information should be read in light of the study’s size and design. This was a single-group study with enrollment of 20, not a randomized comparison against a separate control group. The recorded counts therefore do not provide a comparative estimate of safety between treatment groups. The record reports no serious adverse events and no deaths in the listed group, but these counts alone do not establish the presence or absence of risks beyond the participants and events recorded.

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

The study is designed to assess agreement between two simultaneous temperature measurements during surgery: zero-heat-flux thermometry at the forehead and nasopharyngeal monitoring. Its primary endpoint is the mean difference, defined as the forehead reading minus the nasopharyngeal reading. This setup is appropriate to a question about measurement agreement because both readings are taken in the same participants over the course of surgery.

The registry record does not report the numerical primary outcome estimate, its standard error, a confidence interval, or limits of agreement. As a result, the posted results do not show the average size or direction of the difference, nor how much individual paired readings varied. The stated hypothesis is not enough to determine whether the observed readings agreed closely. A conclusion about the magnitude or precision of agreement cannot be drawn from the recorded outcome information.

The record does not state an acceptable threshold for differences between the measurement methods. Without a prespecified or otherwise justified criterion, even a numerical mean difference would require contextual interpretation. Average bias and variation in individual differences answer different questions, and both would be relevant to judging agreement.

This is not a randomized treatment trial. It does not compare clinical outcomes between intervention and control groups, and the registry does not report evidence about whether use of one measurement method changes patient outcomes. It is a measurement comparison in a single group. Its findings, if fully reported, would concern the relationship between the two temperature methods in the participants and conditions studied.

The registry reports enrollment of 20 and an average surgery duration of 57 minutes, but does not provide enough detail to characterize the participants or the procedures further. Those omissions, together with the missing numerical endpoint result, limit the conclusions that can be drawn. The study’s stated aim is identifiable; the degree to which its observed data support that aim is not ascertainable from the registry record.

14. Why This Trial Matters Statistically

Measurement methods are often evaluated by comparing readings taken at the same time, because the central question is whether the methods produce sufficiently similar values. This trial’s design is statistically distinct from a comparison of independent groups: the forehead and nasopharyngeal readings are paired within participants and collected repeatedly during surgery. Correctly recognizing that structure is important when interpreting both the estimate and its uncertainty.

The registry names a repeated-measures Bland and Altman technique, which directs attention to differences between methods rather than correlation alone. In general, an average difference describes systematic bias, while the spread of differences informs how much individual readings may diverge. Considering only an average can obscure substantial variation across paired measurements. The registry record does not report the numerical results needed to assess either aspect.

The study also illustrates why a stated hypothesis and a statistical method do not substitute for reported outcome estimates. Without the mean difference and its uncertainty, readers cannot determine the direction, size, or precision of the observed agreement. Without limits of agreement or comparable information on individual differences, the performance of the methods for individual readings cannot be characterized from the registry record.

Finally, the single-group design helps define what the study can address. It is a comparison of measurement methods, not a randomized test of clinical benefit or a comparison against an independent control group. Keeping that distinction clear prevents measurement agreement from being interpreted as evidence about treatment effects or patient outcomes. The missing numerical endpoint results make this distinction especially important: the record describes the intended statistical question, but does not report the result needed to answer it.

15. 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 most consequential limitation in the registry record is the absence of a numerical result for the primary temperature-difference endpoint. No estimated bias, standard error, confidence interval, or limits of agreement are reported. The registry therefore does not allow readers to quantify average agreement, assess precision, or evaluate variation in individual paired readings.

The record gives little detail about the participants and surgical context beyond an enrollment of 20 and an average surgery duration of 57 minutes. Eligibility criteria, participant characteristics, and the types of surgery are not reported in the registry record. This limits assessment of how broadly the measurement findings might apply to other patient or procedural settings.

Measurements were scheduled every 5 to 10 minutes, or as clinically indicated, but the registry does not describe the number of readings contributed by each participant or how differences in measurement frequency were handled. Missing readings, exclusions, and the analysis population are not described. The detailed statistical model, assumptions, and handling of within-participant dependence are also not reported.

The registry does not state an acceptable agreement threshold, so it is not possible to determine what degree of difference would have been considered important for the intended purpose. Nor does the record report a sample-size justification or full statistical analysis plan. Although a planning illustration is described, it is not the trial’s own design justification and is not observed power.

The single-group design is suited to paired measurement comparison but does not provide a randomized control group. The record also reports no masking. These features should be considered when interpreting the study as a measurement investigation, without treating it as a controlled comparison of clinical interventions.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Zero Heat Flux Thermometry System Comparison Trial — NCT01670760.
• Registry record last updated 2020-09-22; status last verified 2020-09.
• Results first posted 2020-08-21.
• 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.

19. Record Summary

The registry describes a completed, single-group device study of zero-heat-flux thermometry during surgery. Enrollment was 20. The planned comparison was between simultaneous temperature readings from the lateral forehead and nasopharyngeal sites, collected every 5 to 10 minutes or as clinically indicated from incision to closure. Average surgery duration was 57 minutes.

The primary endpoint was the temperature difference in degrees Celsius, defined as zero-heat-flux temperature minus nasopharyngeal temperature. The listed method was a repeated-measures Bland and Altman analysis, with a least-squares mean and standard error. The record does not report the numerical primary outcome result or its uncertainty, so the degree of agreement cannot be evaluated from the registry results.

The safety record lists 0 serious adverse events among 20 participants at risk, 11 participants affected by other adverse events among 20 at risk, and 0 deaths. Further details about the other adverse events are not reported in the registry record.