The Effect of Prolonged Inspiratory Time on Pulmonary Mechanics in Obese Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Prolonged Inspiratory Time on Pulmonary Mechanics in Obese Patients (NCT02961920), a randomized na study. The primary outcome is PaO2(Partial Pressure of Oxygen in Arterial Blood).

2. Clinical Question

The rationale in the registry record is that prone positioning and abdominal compression may affect respiratory mechanics and oxygenation in obese patients. It describes a Wilson frame as allowing the abdomen to hang only partially, with possible effects on peak airway pressure and dynamic compliance. These statements explain the investigators’ motivation; they do not establish what happened in the randomized comparison.

The clinically relevant statistical question is whether the recorded PaO2 values differ between the assigned ventilator settings, and how precisely any difference is estimated. The registry record does not report a numerical estimate, its uncertainty, or a statistical test for a single comparison. It therefore does not establish the direction or size of an observed difference.

3. Trial Design

The registry record describes a randomized, parallel-group trial with no masking. The planned enrollment is 50. The two groups were assigned different ventilator I:E settings: 1:1 or 1:2. Both interventions are described as ventilator settings used during spine surgery in the prone position in obese patients. The allocation ratio, the method used to generate the random sequence, and whether allocation was concealed are not reported in the registry record.

The record lists the trial as completed, with a start date of 2016-11 and a primary completion date of 2019-04. The phase is listed as NA. Gachon University Gil Medical Center is identified as the sponsor. These design and administrative details do not supply the results of the comparison.

Random assignment is intended, in general, to make groups comparable on average at the start of a study, including with respect to factors that were not measured. Whether it achieved similar groups in this trial cannot be assessed from the registry record because baseline characteristics are not reported. With no masking, those involved in the study may have known the assigned ventilator setting; the record does not describe additional steps to limit the influence of that knowledge on measurement or care.

The primary endpoint is PaO2, a continuous measurement reported in mmHg. Its stated timeframe extends from ten minutes after tracheal intubation to 90 min after prone positioning. The registry record does not specify a single selected measurement time, the timing of all measurements, or the method used to summarize the measurements for analysis. Actual enrollment by group and the number included in the primary analysis 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:

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: did not achieve stydy portocol schedule 2

6. Primary Endpoint

The registry lists the primary outcome as PaO2(Partial Pressure of Oxygen in Arterial Blood), measured over ten minutes after tracheal intubation to 90 min after prone position.

The primary endpoint is PaO2, or the partial pressure of oxygen in arterial blood, measured in mmHg. It is a continuous measure: its values can vary across a range rather than being limited to event categories. The registry record describes the outcome using a mean and standard deviation and gives the timeframe as ten minutes after tracheal intubation to 90 min after prone positioning.

In general, an arterial oxygen measurement is used to describe oxygenation in the blood. Comparing its distribution between randomized groups can help quantify how the recorded measurements differed under the assigned conditions. The mean describes the central value of a group’s measurements, while the standard deviation describes their spread. Neither alone gives the precision of a between-group estimate; that also depends on the analysis and the amount of usable data.

The record does not report the group means, standard deviations, a between-group contrast, or an uncertainty interval for PaO2. It also does not identify a single time point for a standalone comparison. The outcome entry is described as having several categories or time points and is not reduced to one comparison. Thus the endpoint’s name, unit, summary type, and broad timeframe are available, but a numerical estimate of the treatment contrast is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The record identifies the endpoint as a continuous measure summarized using a mean and standard deviation. It also identifies the trial as randomized, parallel, and unmasked. These descriptions give a basic framework for understanding the intended comparison, but they do not specify the statistical procedures used to analyze the outcome. The analysis method, model, covariate adjustment, and handling of measurements at multiple times are not reported in the registry record.

What does a mean describe?

In general, the mean is the arithmetic center of a set of measurements. For an endpoint such as PaO2, a group mean can describe the average recorded value for participants included in the analysis. Comparing the means is one way to express a difference between groups, but the mean alone does not show the spread of individual measurements or the uncertainty around the estimated contrast.

The standard deviation describes how spread out observations are around a group mean. It is not the same as a confidence interval for the difference between groups. A standard deviation describes variability among measurements; a confidence interval describes uncertainty in an estimate, given the data and an analysis model. The registry record names the mean and standard deviation as the summary type but does not report their values.

How would a randomized comparison be interpreted?

In general, random allocation supports a comparison of outcomes according to assigned group. The group contrast is interpreted in light of the outcome definition, the analysis population, missing measurements, and the statistical model. Randomization does not ensure that every measured characteristic is exactly balanced in the observed participants, and it does not remove the need to report how participants were analyzed. Baseline characteristics, allocation procedures, and the analysis population are not reported in the registry record.

Because the endpoint timeframe covers multiple points or categories, the analysis could in principle compare groups at a specified time, model repeated measurements, or use another prespecified summary. These approaches answer different questions and can make different assumptions about the relationship among measurements from the same participant. The registry record does not report which approach was used, how many measurements were planned or collected, or how the outcome was condensed for analysis. The posted primary outcome is not reduced to one comparison.

What do uncertainty measures contribute?

In general, a confidence interval communicates the precision of an estimated group contrast. A narrower interval indicates greater precision under the model used, while a wider interval indicates more uncertainty. An interval also makes it possible to assess which effect sizes remain compatible with the data; it should be interpreted alongside the estimate and the outcome scale. No confidence interval for the primary PaO2 comparison is reported in the registry record.

A p-value is calculated under a statistical model and a specified null hypothesis. In general, it indicates how unusual the data would be if the null hypothesis and model assumptions held; it does not state the probability that a treatment effect is real. It also does not communicate the size of an effect. No primary-outcome p-value is reported in the registry record, and the analysis used to generate one is not reported.

Why can over-dispersion matter?

In general, over-dispersion means that observed variability is greater than a model expects. It matters when the analysis assumes a particular variance structure, because underestimated variability can make uncertainty appear too small. This concept is most relevant to outcomes analyzed with distributional models that impose a mean–variance relationship. PaO2 is identified as a continuous outcome summarized by a mean and standard deviation; the registry record does not report a model or any assessment of over-dispersion. It would therefore be inappropriate to assert that over-dispersion was present or that a particular correction was used.

What do the planning assumptions mean?

The registry record describes a planning illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation, and a normal approximation. It states that the effect to detect is a specified fraction of the observed effect. Such calculations are planning illustrations, not observed trial results and not evidence that the trial had a particular probability of detecting an effect. The registry record does not report the numerical planning outputs or the particular effect fractions in the information available for this analysis. The trial’s own sample-size justification and the assumptions used for its original design are not reported in the registry record.

More generally, sample-size calculations depend on the target effect, outcome variability, significance level, allocation, and analysis assumptions. A calculation based on an observed effect can be sensitive to the observed estimate, especially when that estimate is uncertain. It should not be described as observed power. In this case, the primary outcome estimate and its variability are not reported in the registry record, so the planning illustration cannot be independently interpreted as a numerical result.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is described as having several categories or time points, but the registry record does not reduce it to a single comparison. When multiple time points, outcome measures, or statistical tests are examined, multiplicity can increase the chance of obtaining a nominally unusual result by chance. In general, a study may address this through a prespecified primary time point, a statistical adjustment, a hierarchical testing strategy, or another plan. The registry record does not report whether any such approach was specified or used.

The number of analyses reported is zero in the available registry information. A detailed statistical analysis plan, the primary analysis model, any adjustment for baseline values, and the exact contrasts tested are not reported in the registry record. It is therefore not possible to determine whether the reported outcome categories or time points were analyzed separately, jointly, or by a selected summary.

Missing-data methods are also not reported in the registry record. The record does not state whether any PaO2 measurements were missing, why they might have been missing, or how missing values were handled. It does not identify an analysis population, such as all randomized participants or only those with available measurements. Actual participant counts contributing to the primary outcome analysis are not reported in the registry record.

These omissions limit both the assessment of bias and the interpretation of precision. In general, missingness can affect a result if the availability of measurements is related to participant characteristics or outcomes. The extent and direction of any such effect cannot be assessed without information about missing observations and the analysis approach. No conclusion about multiplicity control or missing-data handling can be drawn from the registry record.

11. 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 0% reporting threshold.

The registry safety entries list the I:E 1:2 group with 24 participants at risk and zero serious adverse events, zero other adverse events, and zero deaths. The I:E 1:1 group is also listed with 24 participants at risk and zero serious adverse events, zero other adverse events, and zero deaths. These are the figures recorded for the listed groups.

In general, an event count of zero means that no events of that type were recorded among the participants included in that safety entry. It does not prove that the underlying risk is absent. The number of participants at risk gives context for the count, but the registry record does not report the safety observation period, event definitions, collection procedures, or whether every participant was assessed for the same duration.

These safety entries should be read separately from the primary PaO2 endpoint. They do not indicate the measured oxygenation values, the hemodynamic results, or the precision of a comparison between groups. The record’s hypothesis about oxygenation without hemodynamic instability cannot be evaluated from these event counts alone. Further details on the safety analysis and the relationship between the listed at-risk participants and the full trial population are not reported in the registry record.

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

The registry record establishes that the study was designed to compare two ventilator I:E settings in obese patients undergoing prone spine surgery, and that PaO2 was designated as the primary endpoint. It also records a randomized, parallel-group design without masking and a planned enrollment of 50. These registry entries describe the question and design; they do not establish the outcome of the comparison.

The registry record does not report a single numerical comparison of PaO2, the group-level outcome summaries, or an uncertainty interval. As a result, the posted information cannot show whether PaO2 differed between groups, the size or direction of any difference, or how precisely it was estimated. No conclusion about the stated oxygenation hypothesis or hemodynamic stability follows from the available primary-outcome information.

In general, evidence about a treatment contrast depends on more than the existence of randomization. Readers need an interpretable outcome estimate, its uncertainty, and enough information about the analysis to understand what was compared. Here, the endpoint timeframe spans multiple points or categories, and the registry record does not state a single analysis comparison. The analysis population, missing-data handling, and statistical methods are also not reported in the registry record.

The safety entries record zero serious adverse events, zero other adverse events, and zero deaths in each listed group, with 24 participants at risk in each. Those observations describe the recorded safety entries but do not establish the absence of risk or replace an analysis of the primary endpoint. The registry information supports a description of the trial’s design and outcome question, but not a conclusion about the comparative effect of the assigned settings.

13. Why This Trial Matters Statistically

This trial raises a useful statistical question because the intervention is a ventilator setting and the primary endpoint is a continuous physiological measurement. A continuous endpoint can be described with group means and variability, and a between-group contrast can be expressed on the original measurement scale. The record identifies PaO2 in mmHg and a mean with standard deviation as the outcome summary, giving readers the broad form of the intended measurement.

The design also highlights the importance of specifying when an outcome is measured. The timeframe runs from ten minutes after tracheal intubation to 90 min after prone positioning, and the outcome entry is described as involving several categories or time points. A single-time comparison and a summary across repeated measurements need not answer the same question. Clear reporting of the chosen time point, analysis method, and uncertainty would be needed to interpret the result.

Randomization provides a framework for comparing assigned groups, while lack of masking and incomplete reporting of allocation and analysis procedures leave questions about how the comparison was conducted. The registry record does not report a single primary outcome estimate or the methods needed to assess its precision. This is a reminder that a trial design and a stated hypothesis are not substitutes for reported outcome data.

The planning assumptions also illustrate a general distinction: sample-size calculations are prospective planning tools, whereas the trial result is an estimate from observed data. A planning illustration based on an observed effect does not establish observed power or demonstrate an effect. Without the numerical outcome results and analysis details, the main statistical contribution of the record is to define the comparison and identify what information is missing for an effect estimate.

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.

A central limitation of the registry information is the absence of a reported numerical primary-outcome comparison. Group means, standard deviations, an effect estimate, and an uncertainty interval are not reported in the registry record. The direction, magnitude, and precision of any difference in PaO2 therefore cannot be assessed.

The endpoint timeframe covers multiple points or categories, but no single comparison is reported. The registry record does not specify which measurement time was primary for analysis or how measurements across the stated period were summarized. It also does not report whether repeated measurements were modeled together, analyzed separately, or reduced using another method.

Other details needed to judge the comparison are not reported in the registry record. These include actual enrollment by group, baseline characteristics, the primary analysis population, the number of participants with usable PaO2 measurements, and the handling of missing data. The allocation sequence method, allocation concealment, and any procedures to address the lack of masking are also not reported. The original sample-size justification and the trial’s statistical analysis plan are not reported in the registry record.

The safety entries report counts for participants at risk and recorded events, but do not describe the observation period, event definitions, or safety collection methods. These limitations do not imply that a particular bias or problem occurred; they mean that the registry information does not permit those issues to be evaluated. The conclusions must be limited to the design and reported entries rather than an estimate of comparative outcome effects.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Effect of Prolonged Inspiratory Time on Pulmonary Mechanics in Obese Patients — NCT02961920.
• Registry record last updated 2019-11-05; status last verified 2019-10.
• Results first posted 2019-10-07.
• 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.

18. Record Summary

The registry record describes a completed randomized, parallel-group, unmasked trial comparing mechanical ventilation at I:E ratios of 1:1 and 1:2 during prone spine surgery in obese patients. Planned enrollment was 50. The primary endpoint was PaO2 in mmHg, summarized as a mean and standard deviation, with a stated timeframe from ten minutes after tracheal intubation to 90 min after prone positioning.

The primary outcome is not reduced to a single comparison, and a numerical comparison is not reported in the registry record. Analysis methods, analysis populations, and missing-data handling are also not reported. Safety entries list 24 participants at risk in each group and zero serious adverse events, zero other adverse events, and zero deaths in both groups.