Angiotensin II Pathway and Postoperative Hypoxemia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Angiotensin II Pathway and Postoperative Hypoxemia (NCT05055570), a registered phase not stated study. The primary outcome is The Difference Concentrations of ANG II in Serum Between Patients With and Without Postoperative Hypoxemia..

2. Clinical Question

The clinical motivation is that postoperative hypoxemia can occur after acute type A aortic dissection, while its cause is not fully understood. The registry describes angiotensin II as a component of the renin-angiotensin system and frames the study as an investigation of its possible role and mechanism. That rationale does not establish that ANG II causes hypoxemia, or that a measured difference would establish a mechanism.

Hypoxemia is defined using the oxygenation index, the ratio of arterial partial pressure of oxygen to fraction inspired oxygen. The primary outcome description specifies an index of less than or equal to 200 for two consecutive times within the first 24 hours after operation. The group descriptions distinguish an index of less than or equal to 200 from an index greater than 200.

The central statistical question is therefore a comparison of a continuous laboratory measure across groups defined by a postoperative clinical measurement. The registry specifies that the ANG II measure is to be described using a median and inter-quartile range, but the actual group medians, inter-quartile ranges, and any estimate of the difference are not reported in the registry record. The record consequently states the question and measurement approach, but not the numerical answer.

3. Trial Design

The registry identifies this as a completed study sponsored by Beijing Anzhen Hospital. The recorded start date is 2021-08-12, and the primary completion date is 2022-06-01. Enrollment is listed as 88. The registry does not describe an intervention: its intervention entry is “No intervention.” The groups are defined by postoperative oxygenation index rather than by assignment to a treatment.

The hypoxemia group is defined by an oxygenation index of less than or equal to 200. The non-hypoxemia group is defined by an oxygenation index greater than 200. The primary outcome description adds that postoperative hypoxemia requires the index to be less than or equal to 200 for two consecutive times within the first 24 hours after operation. The registry does not explain how the group description and the two-consecutive-measurement criterion were operationalized together.

This is not a randomized comparison. The registry states that allocation is not stated and that the arms are not a like-for-like control comparison. Because group membership reflects postoperative oxygenation status, the comparison does not isolate the effect of an assigned exposure or treatment. Differences between groups, if reported, would be associations in this clinical setting and could also reflect other differences between patients.

The primary outcome is the difference in serum ANG II concentrations between patients with and without postoperative hypoxemia. Blood was collected within 24 hours after surgery, and the concentration unit is pg / mL. Secondary outcomes listed in the registry concern risk factors for postoperative hypoxemia and duration of stay in the intensive care unit. The record lists three outcome measures, but does not provide results for them. It lists zero analyses, and the analysis methods, eligibility details, and recruitment approach 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

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 The Difference Concentrations of ANG II in Serum Between Patients With and Without Postoperative Hypoxemia., measured over Within 24 hours after surgery.

The primary endpoint concerns serum ANG II concentration, measured in pg / mL, in patients with and without postoperative hypoxemia. Blood samples were taken within 24 hours after surgery. The registry describes the endpoint as a difference in concentrations between the two groups and specifies the median and inter-quartile range as the summary approach.

ANG II is relevant to the question because the registry’s rationale links it to the renin-angiotensin system and to proposed processes involving aortic dissection and pulmonary inflammation. Measuring its serum concentration can describe whether the observed distribution differs across the postoperative oxygenation groups. Such a comparison may help characterize a possible association, but it cannot by itself show that ANG II caused hypoxemia or explain a biological mechanism.

The oxygenation index is the ratio of arterial partial pressure of oxygen to fraction inspired oxygen. The primary outcome description defines postoperative hypoxemia as an index less than or equal to 200 for two consecutive times within the first 24 hours after operation. This classification supplies the basis for comparing the serum measure across the groups.

The registry does not report the group medians, inter-quartile ranges, a contrast between groups, or uncertainty around that contrast. Thus, the measurement and intended summary are specified, but the numerical endpoint result is not reported in the registry record. Without those results, the direction, magnitude, and precision of any difference cannot be evaluated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a comparison of serum ANG II concentrations between groups classified by postoperative oxygenation. The concentration is a continuous measurement, and the registry specifies the median and inter-quartile range as its summary. No inferential analysis is recorded, so the statistical methods below explain how such summaries and comparisons are generally interpreted; they do not describe analyses demonstrated in the registry record.

What does a median describe?

In general, the median is the midpoint of an ordered set of measurements: observations on either side are distributed around it. It is less affected by unusually high or low values than the arithmetic mean. The inter-quartile range describes the spread across the middle portion of the ordered observations. Reporting both can give a reader a sense of a group’s typical concentration and variability without assuming a symmetric distribution.

These summaries do not show every feature of the data. Two groups can have similar medians but different spreads or distribution shapes. They can also have different medians while their individual measurements overlap substantially. A comparison based only on medians and inter-quartile ranges does not, by itself, establish whether a difference is statistically distinguishable from sampling variability. The registry does not report the actual summaries or a test of the group contrast.

What would an effect estimate add?

In general, an effect estimate gives a numerical description of the contrast between groups. Its interpretation depends on how the contrast is defined and on the scale used. An interval around the estimate conveys its precision: a narrower interval indicates greater precision under the analysis assumptions, while a wider interval indicates greater uncertainty. No contrast or interval for the ANG II endpoint is reported in the registry record, and the precise contrast intended by the wording “difference concentrations” is not further described.

A hypothesis test, if used, would address how compatible the observed data are with a specified null hypothesis under the test’s assumptions. A p-value alone would not describe the size or clinical importance of a difference. Nor would it establish a causal relationship. The registry lists zero analyses, so no test choice, test result, or assumptions can be attributed to this study from the record.

Why does the group definition matter?

The groups are based on postoperative oxygenation, with hypoxemia defined by an oxygenation index less than or equal to 200 for two consecutive times within the first 24 hours after operation. The non-hypoxemia group is described using an index greater than 200. This is an outcome-based classification, not randomized allocation. A statistical comparison therefore describes how the measured ANG II concentrations vary across these categories; it does not estimate what would happen if patients were assigned to a different treatment.

In general, a nonrandomized group comparison may be affected by confounding. A confounder is a factor associated with both the group classification and the measurement under study, which can make a crude contrast differ from the association that would remain after appropriate adjustment. Adjustment requires relevant variables to be measured and an analysis plan to be specified. The registry does not report an adjustment method or candidate covariates. It is therefore not possible to tell whether the primary comparison was adjusted or how potential confounding was handled.

How should planning illustrations be read?

The registry’s sample-size assumptions describe planning illustrations based on the observed effect, not the trial’s own design. They specify a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. These are assumptions for illustrations, not evidence that the study was designed to achieve a particular power. They should not be interpreted as observed power, which is not a useful substitute for reporting the estimated effect and its uncertainty.

The registry further distinguishes illustrations for time-to-event outcomes, which use total events, from other illustrations, which use participants per arm. These conventions concern planning calculations rather than observed clinical results. No numerical sample-size illustration is stated in the registry record, and no sample-size justification from the investigators is reported. The sample-size rationale for the completed study is not reported in the registry record.

What can be concluded from the methods record?

The record allows the reader to identify the endpoint, measurement unit, timing, group definitions, and descriptive summary. It does not identify a model, test, covariate set, missing-data method, or analysis population. Those omissions mean that the intended question is clear at a broad level, but the reproducibility and inferential interpretation of a numerical result cannot be evaluated from the registry record. General statistical principles can explain what different methods would mean, but they should not be mistaken for methods actually reported for this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome concerning serum ANG II concentrations and secondary outcomes concerning risk factors for postoperative hypoxemia and duration of stay in the intensive care unit. It also lists three outcome measures, but does not report outcome results or analyses. A multiplicity strategy—such as a hierarchy of hypotheses, an adjustment to account for multiple comparisons, or an explanation that the secondary analyses are exploratory—is not reported in the registry record.

In general, testing multiple outcomes or contrasts can increase the chance of finding at least one apparently notable result by chance. How that issue should be handled depends on the prespecified questions and analysis plan. Since neither an analysis plan nor test results are reported, it is not possible to assess whether multiplicity was addressed or how it would affect interpretation.

Missing-data handling is also not reported in the registry record. The record does not describe whether any serum measurements or oxygenation measurements were unavailable, how such observations would be treated, or whether the primary analysis used all eligible patients or a subset. No assumptions about missingness or sensitivity analyses are stated. This does not establish that data were missing; it means the registry record does not describe their status or handling.

The analysis population is not defined in the registry record. Enrollment is listed as 88, while the adverse-event records list group-specific numbers at risk of 25 and 63. Those adverse-event entries do not establish the analysis population for the primary endpoint. The registry does not explain whether all enrolled patients contributed serum measurements or how patients were assigned to the endpoint analysis. These uncertainties limit assessment of selection, completeness, and the relationship between enrollment and the analyzed groups.

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 5% reporting threshold.

The adverse-event entries report zero serious adverse events in the hypoxemia group and zero in the non-hypoxemia group. They also report zero other adverse events in each group. The record lists one death in the hypoxemia group and zero in the non-hypoxemia group. The numbers at risk in these entries are 25 for the hypoxemia group and 63 for the non-hypoxemia group.

These entries should be read as registry-reported counts, not as a complete safety comparison. The study lists no intervention, and the groups are defined by postoperative oxygenation status rather than randomized treatment assignment. The counts therefore do not compare the safety of assigned treatments. The record does not provide event definitions, timing, causes of death, follow-up duration, or an explanation of how adverse events were collected. It also does not report whether all events were captured or whether any were judged related to an intervention.

Zero reported events do not establish that an event could not occur or that the groups had equivalent safety. The death count is reported separately from the serious and other adverse-event counts, and the registry does not explain how those categories relate. Interpretation should remain limited to the counts and group-specific numbers at risk recorded in the registry.

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

The registry establishes that investigators asked whether serum ANG II concentrations differed between patients classified with and without postoperative hypoxemia after acute type A aortic dissection. It describes serum sampling within 24 hours after surgery, specifies pg / mL as the unit, and defines the hypoxemia category using the oxygenation index. It also indicates that concentrations were to be summarized using medians and inter-quartile ranges.

What the record does not establish is the answer to that question. It does not report the group concentrations, their contrast, or uncertainty around the contrast. No direction or magnitude of an ANG II difference can therefore be stated. The completed status of the study and its enrollment entry do not provide the missing endpoint results.

Even if a numerical difference were reported, this design would not show that ANG II caused postoperative hypoxemia. The groups are classified by oxygenation after surgery and are not randomized treatment groups. A difference could reflect other characteristics related to both serum concentration and oxygenation. Without a reported adjustment approach, the role of such factors cannot be assessed.

The study also cannot be interpreted as testing whether an ANG II-targeted treatment prevents hypoxemia: no intervention is listed. Its stated purpose is to investigate a pathway and provide reference for clinical application, but the registry does not report a mechanistic analysis or a treatment effect. The secondary outcomes are listed without results, so they cannot add evidence about risk factors or intensive care unit stay.

The appropriate reading is narrow: the record describes a completed, nonrandomized comparison and its measurement plan, but does not report the statistical results needed to judge association, precision, or robustness. It neither demonstrates a beneficial effect nor supports a conclusion that ANG II is unrelated to postoperative hypoxemia.

13. Why This Trial Matters Statistically

This study is statistically notable for the distinction between measuring a biological marker and making a causal claim. Serum ANG II is compared across groups defined by postoperative oxygenation. Such a comparison can characterize an association, but the group structure does not provide the protection against confounding that random assignment is intended to offer. Clear interpretation depends on presenting the group data, the contrast, and any adjustment strategy.

The outcome’s timing and definition also matter. Blood sampling is specified within 24 hours after surgery, and hypoxemia is defined using repeated oxygenation-index criteria within the first 24 hours after operation. These details set the intended temporal and clinical frame for the comparison. The record does not explain how timing of each sample related to the oxygenation measurements, so the sequence and alignment of measurements cannot be evaluated further.

Descriptive summaries are useful, particularly when a distribution may not be well represented by a mean and standard deviation. Medians and inter-quartile ranges can convey typical values and spread. But descriptive summaries need to be accompanied by the actual values and an appropriate contrast to support interpretation. In this record, the summary method is named while the numerical results and analysis are absent.

Finally, a registry record can make planned questions and definitions transparent without supplying a complete report of findings. Here, enrollment, group criteria, outcomes, and adverse-event counts are recorded, but the primary endpoint analysis is not. This makes the record useful for understanding the study’s stated question while leaving its empirical answer unresolved. That distinction is important whenever a study’s rationale is biologically plausible but its numerical evidence is not available in the registry.

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.

The central limitation for interpretation is that the registry does not report the primary endpoint results. Without group medians, inter-quartile ranges, or an estimated contrast, the observed association and its precision cannot be assessed. The registry also lists zero analyses, so no inferential method or result can be reviewed.

The comparison is not randomized, and allocation is not stated. Groups are defined by postoperative hypoxemia, so they are not like-for-like control groups. The registry does not report adjustment for other factors, leaving the possibility of confounding unresolved. It does not provide enough information to determine whether the group definition was applied consistently with the repeated-measurement criterion in the primary outcome description.

Several analysis details are not reported in the registry record: eligibility criteria, the analysis population, the number of available serum samples, missing-data handling, the statistical model or test, and any multiplicity approach. The registry does not describe sample-size justification for the study itself. Planning assumptions are not a substitute for a documented design rationale or an analysis of observed data.

The registry lists secondary outcomes but does not report their findings. Its adverse-event entries provide counts, but not event definitions, collection procedures, timing, follow-up duration, or the relationship between the separate death and adverse-event categories. These omissions limit safety interpretation as well as assessment of the clinical outcomes.

Finally, a serum concentration comparison alone would not establish a biological mechanism or a causal role for ANG II. Even a reported association would require cautious interpretation in light of group classification and possible confounding. The registry’s stated rationale is not itself evidence of a mechanism, and its completed status does not resolve the absence of results.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Angiotensin II Pathway and Postoperative Hypoxemia — NCT05055570.
• Registry record last updated 2024-01-26; status last verified 2023-04.
• Results first posted 2024-01-26.
• 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

NCT05055570 is a completed study sponsored by Beijing Anzhen Hospital, with enrollment listed as 88. It concerns acute type A aortic dissection and postoperative hypoxemia. No intervention is listed, and the registry states that the comparison is not randomized and that allocation is not stated.

The primary question concerns serum ANG II concentrations in hypoxemia and non-hypoxemia groups. Blood sampling is specified within 24 hours after surgery; the endpoint is summarized using medians and inter-quartile ranges. Hypoxemia is defined using the oxygenation index, including a criterion of less than or equal to 200 for two consecutive times within the first 24 hours after operation.

The registry lists secondary outcomes on risk factors and intensive care unit stay, but does not report outcome results or analyses. Primary endpoint concentrations and their statistical comparison are not reported in the registry record. Adverse-event entries report zero serious and zero other adverse events in both groups, with one death in the hypoxemia group and zero in the non-hypoxemia group.