This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Perioperative Active Warming Techniques in Colorectal Surgeries (NCT00913978), a randomized na study. The primary outcome is The Primary Outcome Measure Will be the Percentage of Intraoperative Time the Participants Body Temperature is Above 36 Degrees Celcius..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00913978 |
| Phase | NA |
| Condition | Normothermia |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 50 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Northwestern University |
| Results posted | Yes |
2. Clinical Question
Population
Patients undergoing colorectal surgery. The registry record describes perioperative warming after patients enter the operating room. It does not report further eligibility criteria or a more detailed description of the population included in the outcome results.
Intervention
Group 1 received warming with the VitaHeat underbody resistive mattress, together with IV fluid warmers once in the operating room.
Comparator
Group 2 received the upper body Bair Hugger forced air warming blanket, together with IV fluid warmers once in the operating room. The registry identifies this as the warming approach currently used at the institution in its study summary.
Primary question
How did the arms compare on the mean percentage of intraoperative time that participants’ body temperature was above 36 degrees Celsius, measured with an esophageal temperature probe? The registry’s hypothesis proposed that the underbody mattress would be equally effective as forced air warming for maintaining normothermia. The posted results are descriptive arm summaries; a statistical test or estimate of the between-arm contrast is not reported in the registry record.
3. Trial Design
This was a randomized, parallel-group study of two active warming devices in colorectal surgery. The registry lists single masking, but does not identify who was masked or explain how masking was maintained. Allocation concealment, the random sequence method, and the procedures used to implement randomization are not reported in the registry record.
The study compared a VitaHeat underbody resistive warming mattress with an upper body Bair Hugger forced air warming blanket. Both groups also received IV fluid warmers after entering the operating room. The planned enrollment was 50. The primary outcome results list 25 participants in the VitaHeat arm and 21 in the Bair Hugger arm. The reason the reported arm counts differ from the planned enrollment is not reported in the registry record.
The primary outcome timeframe is 1 day. The registry describes the study as terminated, with a start date of 2017-04-13 and a primary completion date of 2018-12-21. The reason for termination, whether it occurred before planned completion, and any consequences for recruitment or follow-up are not reported in the registry record. The phase is listed as NA.
One secondary outcome is posted: post-operative temperature on admission to the post-operative care unit. The registry records 2 outcome measures and 0 analyses. Details of the secondary outcome results, the analysis population, and the statistical plan 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
| Stage | Group 1: VitaHeat | Group 2: Bair Hugger |
|---|---|---|
| STARTED | 26 | 24 |
| COMPLETED | 25 | 21 |
| NOT COMPLETED | 1 | 3 |
Reasons for not completing this period:
| Reason | Group 1: VitaHeat | Group 2: Bair Hugger |
|---|---|---|
| Surgeon choice | 1 | 3 |
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: 1 subjects in the Vitaheat group and 3 subjects in the Bair Hugger group were not included in the analysis.
| Characteristic | Unit | Group 1: VitaHeat | Group 2: Bair Hugger | Total |
|---|---|---|---|---|
| Participants analysed | 25 | 21 | 46 | |
| Age, Continuous | Years | 58.36 (24 to 78) | 60.76 (28 to 75) | 59.5 (24 to 78) |
| Sex: Female, Male: Female | Participants | 15 | 10 | 25 |
| Sex: Female, Male: Male | Participants | 10 | 11 | 21 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 1 | 0 | 1 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 24 | 21 | 45 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 1 | 0 | 1 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 1 | 1 | 2 |
| Race (NIH/OMB): White | Participants | 21 | 19 | 40 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 2 | 1 | 3 |
| Region of Enrollment: United States | participants | 25 | 21 | 46 |
| Weight in kilogram (kg) | kilograms | 78.55 (57.5 to 144.9) | 78.76 (48.1 to 106.4) | 78.65 (48.1 to 144.9) |
| Length of hospital stay in days | Days | 3.88 (1 to 10) | 3.1 (0 to 6) | 3.5 (0 to 10) |
6. Primary Endpoint
The registry lists the primary outcome as The Primary Outcome Measure Will be the Percentage of Intraoperative Time the Participants Body Temperature is Above 36 Degrees Celcius., measured over 1 day.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | percent time |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint measures the percentage of time spent in the operating room with body temperature above 36 degrees Celsius. The registry says temperature was measured using an esophageal temperature probe and summarizes the endpoint as a mean for each arm. The timeframe is 1 day.
This endpoint focuses on how consistently temperature remained above a stated threshold during the intraoperative period, rather than on a single temperature measurement. In general, a percentage-of-time measure can describe the duration of threshold attainment across the measured period. It does not, by itself, show the pattern of temperature changes, the exact times when readings crossed the threshold, or the distribution of individual participants’ measurements.
The posted mean is 47.1 for VitaHeat and 72.0 for Bair Hugger. The registry also reports a full range of 0.0 to 100.0 for each arm. A measure of variability around each mean, such as a standard deviation or confidence interval, is not reported in the registry record. Consequently, these summaries alone do not establish how precisely the arm means were estimated or whether an observed difference is compatible with chance variation.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome is the mean percentage of intraoperative time above 36 degrees Celsius. It is 47.1 in the VitaHeat arm and 72.0 in the Bair Hugger arm. Descriptively, the reported mean is higher for the Bair Hugger arm. This is an observation about the posted arm summaries, not a conclusion from a reported statistical comparison.
The registry does not report a between-arm estimate with a confidence interval, a p-value, or another inferential analysis for this endpoint. Without such information, the precision of the apparent contrast and the range of values compatible with the data cannot be assessed from the registry record. The listed full range is 0.0 to 100.0 in each arm; this broad range does not substitute for a measure of variation around the mean. The spread value is not reported in the registry record.
The registry’s study summary states an equivalence-oriented hypothesis: that the underbody mattress would be equally effective as forced air warming in maintaining normothermia. A pair of arm means does not establish equivalence. In general, equivalence requires a prespecified margin defining what difference would count as acceptably similar, together with an analysis designed to assess the contrast against that margin. Such a margin and an equivalence analysis are not reported in the registry record. The record also does not report a non-inferiority margin or analysis.
The result should therefore be read as a descriptive summary of the reported primary endpoint among the participants included in each arm’s outcome data. It does not establish that one device is better, worse, or equivalent. Randomization is a design feature intended, in general, to support fair comparisons, but it does not replace reporting the analysis, uncertainty, and handling of missing observations. Those details are not reported in the registry record.
The planned enrollment was 50, while the endpoint arm counts are 25 and 21. The record does not explain the relationship between planned enrollment and the arm counts included in this outcome summary. It also does not report whether every randomized participant contributed an endpoint measurement or which analysis population was used. Therefore the arm means should not be assumed to represent all participants enrolled or randomized.
The study is marked terminated. This status does not explain why the trial ended or whether termination affected the outcome findings; the reason is not reported in the registry record. The registry’s summary should be interpreted within these reporting limits rather than as a definitive test of the stated hypothesis.
9. Statistical Methods Explained
The primary outcome is a continuous summary expressed as percent time. The registry reports a mean for each arm, with a full range as the dispersion description. General statistical interpretation of a mean is that it locates the average across the observations contributing to that arm’s summary. It does not show whether individual observations cluster near the mean or vary widely around it.
What does a confidence interval add?
In general, a confidence interval communicates the uncertainty around an estimated quantity, such as an arm mean or a difference between arm means. Its width reflects both the amount of information in the data and the variability of the observations, under the assumptions of the method used. A confidence interval for the between-arm contrast would help readers assess which contrast values are compatible with the data and the analysis. No confidence interval for either arm mean or for the contrast is reported in the registry record.
What can be inferred from the arm means?
The means are 47.1 for VitaHeat and 72.0 for Bair Hugger. They permit a descriptive comparison of the reported summaries. They do not alone quantify uncertainty, establish a statistically supported difference, or test the study’s stated equivalence hypothesis. No p-value or inferential test for the primary outcome is reported in the registry record. A statistical test, even when reported, would not by itself establish clinical importance; interpretation also depends on the design, measurement, and prespecified question.
What does the reported range tell readers?
The registry’s dispersion description is “Full Range,” with endpoints of 0.0 and 100.0 for both arms. The endpoint is bounded as a percentage, so a range extending across those bounds gives little detail about how values are distributed within the arms. A range is particularly sensitive to the most extreme observations and does not convey the typical distance of values from the mean. The registry does not report a standard deviation, standard error, or other more informative measure of dispersion for this outcome.
How should the equivalence hypothesis be assessed?
As a general principle, equivalence is not demonstrated merely because two results appear similar or because a conventional test fails to find a difference. An equivalence assessment requires an acceptable difference to be defined in advance and an analysis that evaluates whether uncertainty around the observed contrast lies within that margin. The registry summary states an expectation of equal effectiveness, but an equivalence margin and the corresponding statistical procedure are not reported in the registry record. The available means therefore do not answer the equivalence question on their own.
What do the design and sample-size details establish?
Randomized allocation is intended, in general, to reduce systematic differences between treatment groups at assignment. The registry identifies the study as randomized and parallel, but does not describe the randomization procedure or allocation concealment. It lists single masking without specifying who was masked. The planned enrollment is 50; the primary outcome summaries list 25 and 21 participants by arm. No rationale for the planned enrollment or account of the difference between planned enrollment and reported arm counts is given.
The sample-size assumptions describe a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. These are planning assumptions, not observed power, and they do not establish that the study was designed around a prespecified clinically meaningful effect. The design rationale and its own statistical plan are not reported in the registry record. No sample-size illustration values are reported in the registry record.
In general, over-dispersion means that observed variability is greater than a statistical model assumes. When present, it can make standard errors too small and intervals or tests too optimistic if the analysis does not account for it. The registry does not report a variability estimate or modeling approach for this endpoint, so whether over-dispersion is relevant cannot be assessed from the posted results.
The record lists 0 analyses. This means no analysis record is posted in the registry, not that the outcome necessarily had no analysis in practice. The analysis method, treatment of missing outcome data, and whether the primary comparison was adjusted are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 2 outcome measures, including the primary endpoint and one secondary outcome: post-operative temperature on admission to the post-operative care unit. It records 0 analyses. The statistical plan for evaluating these outcomes, including any approach to multiple comparisons, is not reported in the registry record. Without that plan, it is not possible to determine whether the primary endpoint was the sole confirmatory comparison or how any additional analyses were intended to affect interpretation.
Missing-data handling is not reported in the registry record. The primary outcome arm summaries list 25 participants for VitaHeat and 21 for Bair Hugger, while planned enrollment is 50. The record does not explain why these figures differ, whether some randomized participants lacked an outcome measurement, or how any missing measurements were handled. No assumptions about missingness or imputation method are reported.
The analysis population is also not reported in the registry record. In general, results can differ depending on whether analyses include all randomized participants, only those who received assigned treatment, or a defined subset with usable outcome measurements. The registry does not identify which approach produced these arm summaries. The outcome data therefore cannot be assumed to represent an intention-to-treat analysis or any other specific analysis population.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Group 1: VitaHeat | 0 | 25 | 0.0% |
| Group 2: Bair Hugger | 0 | 21 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Group 1: VitaHeat | 0 of 25 |
| Group 2: Bair Hugger | 0 of 21 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Group 1: VitaHeat | 3 of 25 |
| Group 2: Bair Hugger | 2 of 21 |
Most frequent serious adverse event terms
| Event term | Organ system | Group 1: VitaHeat | Group 2: Bair Hugger |
|---|---|---|---|
| Myocardial infarction | Cardiac disorders | 0 of 25 | 0 of 21 |
| Cardiac Arrest | Cardiac disorders | 0 of 25 | 0 of 21 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Group 1: VitaHeat | Group 2: Bair Hugger |
|---|---|---|---|
| Urinary tract infection | Renal and urinary disorders | 3 of 25 | 0 of 21 |
| Bladder injury | Renal and urinary disorders | 0 of 25 | 1 of 21 |
| Deep vein thrombosis | Vascular disorders | 0 of 25 | 1 of 21 |
| Pneumonia | Respiratory, thoracic and mediastinal disorders | 0 of 25 | 0 of 21 |
| Device burn injury to skin | Respiratory, thoracic and mediastinal disorders | 0 of 25 | 0 of 21 |
Serious events with the highest arm-level rate: myocardial infarction (0.0%), cardiac arrest (0.0%).
The registry reports 0 serious adverse events among the 25 participants listed at risk in the VitaHeat arm and 0 among the 21 participants listed at risk in the Bair Hugger arm. Deaths are recorded as 0 in both arms. The serious adverse event terms listed include myocardial infarction and cardiac arrest, each reported as 0.0%.
Other adverse events are reported for 3 participants in the VitaHeat arm and 2 participants in the Bair Hugger arm, with 25 and 21 listed at risk, respectively. These are counts as posted; the registry does not provide details about the events, their severity, timing, or relationship to the warming devices. It also does not report a comparative safety analysis.
In general, observing no serious events in an arm does not prove that the underlying risk is absent. Rare outcomes may not occur in a study even when some risk exists, and a safety comparison depends on the event definitions, follow-up, and precision of the estimates. The record’s event counts should therefore be read as descriptive reports for this study, not as proof that either device is safer.
12. What the Result Does, and Does Not, Mean
The posted results show arm-level mean percentages of intraoperative time above 36 degrees Celsius: 47.1 for VitaHeat and 72.0 for Bair Hugger. These figures describe the endpoint as recorded in the registry. The higher reported mean is in the Bair Hugger arm, but the registry does not report an inferential comparison or uncertainty interval for the contrast.
The result does not establish that the devices are equivalent, despite the hypothesis described in the study summary. Equivalence requires a margin and an analysis that assesses the contrast relative to that margin; neither is reported in the registry record. Nor can the data be taken as evidence that either device should be selected in clinical practice. The registry findings are not medical advice.
The primary endpoint concerns time above a temperature threshold during the operation. It does not on its own describe other aspects of temperature control, later outcomes, or the secondary outcome of post-operative temperature on admission to the PACU. Although that secondary outcome is listed, its results are not reported in the registry record.
The record identifies the study as terminated and gives planned enrollment and arm-level endpoint counts, but does not explain the termination or how participants without endpoint data were handled. These reporting gaps limit assessment of precision, potential bias, and the scope of the findings. The appropriate reading is descriptive: the registry presents two means and adverse-event counts, but does not provide enough analysis detail to determine the strength of evidence for a difference or for equivalence.
13. Why This Trial Matters Statistically
This trial raises a useful statistical question about how to evaluate a claim of equal performance. The study summary frames its hypothesis around the possibility that the underbody mattress would be equally effective as forced air warming. That wording calls for more than comparing two arm means: the analysis needs to define how much difference would still count as acceptably similar and quantify uncertainty around the comparison.
The primary outcome is a percentage of intraoperative time above a threshold, rather than a single temperature measurement. That choice summarizes duration, but arm means alone conceal the distribution of participants’ measurements and the variation around each mean. The reported full range spans the stated bounds in each arm, and no additional measure of dispersion is reported. This makes clear why effect estimates and uncertainty measures matter alongside averages.
The record also illustrates how trial status, planned enrollment, and outcome counts need context. The study is marked terminated, and the arm-level outcome counts differ from the planned enrollment. The reason and analysis-population details are not reported in the registry record. Without them, readers cannot determine whether the posted means include all eligible outcome measurements or how missing data might affect interpretation.
Finally, the safety counts demonstrate the distinction between reporting no serious adverse events in these study arms and establishing comparative safety. A study’s observed counts do not alone quantify uncertainty or rule out uncommon events. Transparent definitions, follow-up details, and comparative estimates are necessary for a stronger assessment.
14. 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 reporting gaps limit interpretation. The record does not report the reason for termination, the randomization procedure, allocation concealment, or who was masked. These omissions prevent readers from assessing how assignment was implemented and what the single-masking designation means in practice.
The primary outcome is summarized by a mean and full range, but no standard deviation, confidence interval, or inferential comparison is reported. The registry lists no analysis records. The planned enrollment is 50, while arm-level endpoint counts are 25 and 21; the reason for this difference, the number of randomized participants with usable outcomes, and the analysis population are not reported in the registry record.
The study summary describes an equivalence hypothesis, but the registry does not report an equivalence margin or an analysis designed to test equivalence. The protocol rationale, statistical plan, sample-size justification, and any interim analyses are not reported in the registry record. The sample-size assumptions describe a planning illustration rather than the trial’s own design.
The registry lists a secondary outcome but does not report its results. It also does not give detailed adverse-event definitions, event timing, follow-up duration for safety, or a comparative safety analysis. These limitations do not show that the study was conducted incorrectly; they identify information not reported in the registry record that is needed for fuller evaluation.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Perioperative Active Warming Techniques in Colorectal Surgeries — NCT00913978.
- Registry record last updated 2020-01-13; status last verified 2020-01.
- Results first posted 2020-01-13.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
NCT00913978 is a randomized, parallel-group study of perioperative active warming in colorectal surgery. It compares the VitaHeat underbody resistive warming mattress with the Bair Hugger upper body forced air warming blanket; both arms also used IV fluid warmers. The registry lists single masking and a planned enrollment of 50.
The primary outcome is mean percentage of intraoperative time above 36 degrees Celsius, measured with an esophageal temperature probe over 1 day. The posted means are 47.1 for VitaHeat and 72.0 for Bair Hugger. No primary-outcome inferential analysis is reported in the registry record. The study is marked terminated, and the reason is not reported. The record lists one secondary outcome, post-operative temperature on PACU admission, without posted results.
Serious adverse events and deaths are recorded as 0 in both arms. Other adverse events are listed as 3 and 2. The record does not report the analysis population, missing-data handling, or the statistical plan.