Optiflow THRIVE for Delivery of Oxygen to Patients During Total Intravenous Anesthesia While Undergoing Radiology Procedures: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Optiflow THRIVE for Delivery of Oxygen to Patients During Total Intravenous Anesthesia While Undergoing Radiology Procedures (NCT04171037), a randomized na study. The primary outcome is Total Length of Desaturation Episodes (ToLDE) Per Patient/Surgical Procedure.

2. Clinical Question

The comparison is between two approaches to oxygen delivery during anesthesia, not between anesthesia and no anesthesia. The registry describes the study as a pilot and lists obstructive sleep apnea as the condition. The posted primary outcome is a continuous measure: minutes spent in all qualifying desaturation episodes combined for each patient and procedure. The randomized parallel-group design supports a comparison of the assigned groups, but the registry record does not report enough detail to establish how all enrolled participants were handled in the final analysis.

3. Trial Design

The study is listed as randomized, open-label, and parallel-group. Participants were assigned to Optiflow THRIVE or a non-rebreather facemask during total intravenous anesthesia for interventional radiology procedures. Masking is listed as none, so the registry does not describe a blinded comparison. The study is identified as a pilot; its phase is listed as not applicable.

The registry record reports an enrollment of 108. For the primary outcome, the posted group sizes are 50 in the Optiflow THRIVE arm and 51 in the control arm. These endpoint group sizes do not account for the full enrollment figure, and the reason for the difference is not reported in the registry record. The record does not describe whether participants were excluded from the analysis, had incomplete outcome data, or were analyzed according to their randomized assignment.

Both groups received 100% oxygen. The intervention group received it through Optiflow THRIVE at a high flow rate for 3 minutes before induction and at a higher rate through the end of the procedure. The control group received it through a non-rebreather mask at a lower rate for 3 minutes before induction and kept that rate through the procedure. This makes oxygen-delivery method and flow part of the contrast; the registry does not isolate their separate contributions.

The study is marked completed. Its recorded start date is 2019-10-04, and its primary completion date is 2024-06-21. No detailed protocol description, original sample-size justification, or trial-specific statistical analysis plan is 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.

Before assignment: A total of 114 patients were accrued, and 108 patients were randomized. Of the total number randomized, six patients were screen failures prior to the procedure and 1 patient had no follow-up measurements, leaving 101 patients deemed evaluable for the primary endpoint. This provided 50 patients on Optiflow THRIVE and 51 patients on Standard of Care.

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.

6. Primary Endpoint

The registry lists the primary outcome as Total Length of Desaturation Episodes (ToLDE) Per Patient/Surgical Procedure, measured over 60-minute observation window starting from the initiation of the propofol infusion and continuing for 60 minutes.

The primary endpoint is the total length of desaturation episodes per patient and surgical procedure, measured in minutes. It adds together the duration of all qualifying episodes during a 60-minute observation window that begins when the propofol infusion starts. A desaturation episode is defined as a fall in oxygen saturation to 92% or lower.

This measure captures duration, rather than only whether an episode occurred. A participant with several short episodes and a participant with a longer episode can therefore contribute different totals even if both experienced at least one event. The endpoint is reported as a mean and standard deviation for each group, with a mean difference comparing Optiflow THRIVE with the non-rebreather group.

Duration is relevant to the stated study question because it describes how much of the fixed observation period participants spent at or below the specified oxygen-saturation threshold. It does not, by itself, describe the severity of each episode, the cause of an episode, or outcomes outside the observation window. The registry also lists the number of desaturation episode events per patient or procedure as a secondary outcome, which addresses occurrence rather than total duration. The clinical importance of a given difference in minutes is not defined in the registry record.

7. Results Posted in the Registry

• Optiflow™ THRIVE: mean 34.00 versus 97.00 on control; difference -63.00 (95% CI -63.95 to -62.05), standardized effect d = -25.72; z-test p = <0.001.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Number of Desaturation Episode Events Per Patient/Surgical Procedure

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Optiflow™ THRIVE: 14.0% (7/50) versus 25.5% (13/51) on control; risk difference -11.5 percentage points (95% CI -26.8 to 3.9), risk ratio 0.55 (0.24–1.26); unadjusted two-proportion z-test p = 0.147.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Optiflow™ THRIVE and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes broaden the question beyond total desaturation duration. The number of desaturation episode events concerns whether participants experienced events; BIS episodes and PACU observation time concern other aspects of the procedural and recovery context. These measures are related to the primary question but are not interchangeable with the cumulative duration endpoint.

The one secondary result with posted data points in the same broad direction as the primary result, but its confidence interval includes no difference and its unadjusted p-value is 0.147. It is therefore less conclusive than the primary result in the registry's reported analysis. This does not establish that the outcomes conflict: an event-occurrence measure can differ in sensitivity and meaning from a duration measure, and the secondary result has its own uncertainty.

The registry lists three secondary outcomes, but results for BIS episodes and PACU observation time are not reported in the registry record. The record reports no secondary analyses. This limits assessment of how consistently the pattern extends across the planned outcome set and whether all intended analyses were completed or posted.

Unadjusted secondary results carry less weight when several outcomes are examined because each additional comparison creates more opportunity for a seemingly notable result to arise by chance. In general, multiplicity procedures can control that issue by adjusting interpretation or testing across a family of outcomes. The registry does not report whether a multiplicity plan was prespecified or used. Secondary findings are best treated as supportive or exploratory evidence, with attention to their uncertainty and to the absence of results for some listed outcomes, rather than as independent confirmation of the primary comparison.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Desaturation Episode Events Per Patient/Surgical Procedure
• Number of BIS Episodes
• PACU Observation Time

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous because it measures duration in minutes. The registry reports a mean and standard deviation for each randomized group. A mean describes the group average; a standard deviation describes how dispersed participant-level values are around that average. The reported mean difference is the Optiflow THRIVE mean minus the control mean, so a negative value corresponds to a lower average duration in the Optiflow THRIVE group.

What does the confidence interval convey?

In general, a confidence interval gives a range of effect estimates compatible with the observed data under the statistical procedure and its assumptions. Its width conveys precision: a narrower interval indicates less sampling uncertainty under that procedure, while a wider interval indicates more. It is not a range that contains every participant's outcome, and it is not a probability statement that the true effect has a particular chance of falling inside the interval. The registry reports a 95% interval for the primary mean difference; the analysis method and assumptions behind it are not reported in the registry record.

How should the p-value be read?

In general, a p-value measures how unusual results at least as discrepant as those observed would be under a specified null hypothesis and statistical model. It is not the probability that the null hypothesis is true, nor does it measure the size or clinical importance of a difference. The registry gives an unadjusted p-value of <0.001 for the primary comparison. The exact test or model used to produce it is not reported in the registry record, so the p-value should be interpreted as the posted result rather than as a fully documented analysis.

Why can dispersion matter?

In general, variability affects the uncertainty of a group mean and the precision of a between-group comparison. Standard deviations describe participant-level spread, whereas a standard error describes uncertainty in an estimated quantity. These are not interchangeable. When outcome variability differs across groups, an analysis may need to account for that difference rather than rely on a common-variance assumption. The posted standard deviations differ between the groups, but the registry does not state whether the trial analysis used a variance assumption, a robust method, an adjustment, or another approach.

The record also lists a pooled standard deviation of 2.45 and a recalculated standardized difference of -25.72. Standardized effects express a difference relative to a measure of variability and can be sensitive to unusually small dispersion estimates. They are not the clinical endpoint itself, and they do not replace the difference in minutes. The registry does not provide participant-level values or analysis diagnostics that would allow the distribution, outliers, or assumptions to be assessed.

What does randomization contribute?

In general, random assignment aims to make groups comparable at the start of a trial, on average, with respect to measured and unmeasured characteristics. It does not guarantee perfect balance in a particular study, prevent missing outcomes, or remove bias introduced after assignment. The registry identifies allocation as randomized but does not report the sequence-generation method, concealment procedures, or a participant flow account. Masking is listed as none, which means the registry does not describe a blinded trial.

The registry's planning illustration uses a normal approximation, equal allocation between two arms, a two-sided significance level of 0.05, and effects set as stated fractions of the observed effect. These are assumptions for that planning exercise, not evidence about the statistical test used for the primary trial analysis. The original trial design assumptions are not reported in the registry record. A planning calculation based on an observed effect also depends strongly on that effect and on its variability; it should not be read as a design justification or as a measure of the trial's observed evidential strength.

The registry reports no posted analyses for the secondary outcomes, even though results for one secondary measure are included. It also does not report a prespecified hierarchy, multiplicity adjustment, missing-data method, or analysis population definition. Those omissions restrict the ability to determine whether the posted comparisons follow a prespecified analysis plan.

11. Confidence Intervals and Precision

The primary mean difference is -63.0 minutes, and its reported 95% confidence interval runs from -63.95 to -62.05 minutes. Because the full interval lies on the negative side of zero, it indicates a precise negative estimate under the method used to calculate it. The unadjusted p-value is <0.001. The interval's narrowness should not be confused with certainty about every aspect of the result: it reflects sampling uncertainty as represented by the reported analysis, not uncertainty from unreported design, measurement, or analysis choices.

The registry record does not describe the calculation used for the confidence interval. It also does not explain the small standard deviations accompanying the group means or provide participant-level observations. Without those details, readers cannot independently assess whether the interval's assumptions fit the data or whether the analysis accounted appropriately for the structure of the outcome. A confidence interval can be numerically narrow while important uncertainties about measurement, missingness, or analysis remain.

For the secondary event-count outcome, the posted risk-difference interval crosses zero, and its unadjusted p-value is 0.147. That interval therefore does not resolve the direction of the underlying difference as clearly as the primary interval does. The registry does not post results for all the listed secondary measures, so the precision of the full outcome set cannot be assessed from the registry record.

12. Planning a Similar Trial: Sample Size

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

The planning figures are participants per arm, not total participants across both arms. They use the observed effect as a reference and show planning illustrations for detecting 100%, 75%, or 50% of that observed effect. For the primary continuous outcome, the displayed participant counts are 1 per arm for both 80% and 90% power at each of those effect fractions. The unusually small figures reflect the observed effect and the assumptions used in the illustration; they are not a statement about how the trial was originally designed.

The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The target effect is the stated fraction of the observed effect. The registry record does not report the trial's original sample-size justification or its original design assumptions. The planning exercise is not observed power: it is a prospective-style calculation using an observed effect as an input, not a measurement of the probability that this completed trial detected an effect.

In general, the 80% power column represents the number of participants per arm for a design intended to have an 80% chance of detecting the assumed effect, if the planning assumptions hold. The 90% column uses a higher target chance and generally requires more participants for the same effect. Smaller effects are harder to detect, so planning for a smaller fraction of the observed effect requires more participants. For the secondary binary outcome, the displayed counts rise as the assumed effect fraction decreases: for example, planning for 50% of the observed effect gives 832 participants per arm for 80% power and 1,113 per arm for 90% power.

These calculations are illustrations, not recommended sample sizes for a future study. Their relevance depends on whether the assumed effect and analysis model are credible for the future setting. The figures should not be interpreted as evidence that the completed trial was adequately or inadequately sized under its own protocol, which is not reported in the registry record.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -63.000; pooled standard deviation σ = 2.450.
2. n = 2 × (1.96 + 0.842)² × 2.450² / -63.000² = 0.0, rounded up to 1 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -63                      # observed difference in means
sigma <- 2.44961221420861                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(4171037)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 1 (80% power), 1 (90% power)
 75% of observed effect: n per arm = 1 (80% power), 1 (90% power)
 50% of observed effect: n per arm = 1 (80% power), 1 (90% power)
power.t.test: 1.4 
Simulated power at n = 1 per arm: NA (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome and three secondary outcomes. It reports an unadjusted primary p-value and an unadjusted p-value for the secondary desaturation-event outcome. A testing strategy for the outcome family, such as a prespecified hierarchy or multiplicity adjustment, is not reported in the registry record. Without that information, the strength of nominal p-values across several comparisons cannot be evaluated as if they arose from a single isolated test.

Multiplicity matters because examining several outcomes can increase the chance that at least one comparison appears notable even when there is no underlying effect. In general, a prespecified strategy can identify which outcomes are confirmatory and how later comparisons should be interpreted. The record does not state whether the secondary outcomes were exploratory, whether any formal control of multiplicity was planned, or whether analyses were selected after results were known.

Missing-data methods and analysis populations are also not described in the registry record. The enrollment figure is 108, while the posted primary-outcome group sizes are 50 and 51. The record does not explain this difference, report participant flow by group, or state whether any outcome values were missing. It does not specify whether analysis followed intention-to-treat, per-protocol, or another population definition. As a result, the influence of exclusions or incomplete observations cannot be assessed from the posted record.

The statistical analysis plan, details of the primary model or test, and handling of protocol deviations are not reported in the registry record. These gaps do not change the numerical results that are posted, but they limit independent assessment of whether the analysis followed a prespecified approach and how robust the findings are to alternative reasonable methods.

15. 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 adverse-event figures report no serious adverse events, other adverse events, or deaths among participants at risk in either group. The recorded at-risk counts are 50 for Optiflow THRIVE and 51 for the non-rebreather control group. The registry lists no serious adverse-event terms.

These figures describe what was recorded in the registry for the stated groups; they do not establish that no adverse events could occur or that the two approaches have identical safety profiles. The record does not provide event definitions, collection procedures, follow-up duration for adverse events, or a detailed safety analysis. With no recorded events, comparative estimates of event risk cannot be inferred from the posted figures. The registry's safety counts should therefore be read as a report of recorded events in this trial, not as a guarantee about safety in other settings or patients.

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

The posted primary result is a lower group mean for total desaturation-episode duration with Optiflow THRIVE than with the non-rebreather mask during the defined 60-minute observation window. The estimated mean difference is -63.0 minutes, with a 95% confidence interval from -63.95 to -62.05 minutes. This describes the recorded comparison in the trial; it does not establish that every participant had a shorter duration or that the same result would occur in another clinical setting.

The endpoint combines the duration of all qualifying episodes and is bounded by the observation window's definition, but the registry does not explain the outcome construction beyond that definition. The unusually narrow reported interval and the standard deviations deserve scrutiny alongside missing analysis details. The record does not provide participant-level data or enough information to assess the outcome distribution, verify the analysis, or understand the difference between enrollment and the primary outcome group sizes.

The primary finding does not settle every related question. The secondary event measure is less decisive, results for BIS episodes and PACU observation time are not reported in the registry record, and no multiplicity strategy is described. The posted comparison also does not establish how oxygen delivery affected outcomes outside the observation window, nor does it identify the separate contribution of device type and oxygen flow rate.

The registry calls this a pilot study, and its stated setting is patients with obstructive sleep apnea or potential high risk of airway obstruction undergoing interventional radiology procedures with total intravenous anesthesia. Generalization beyond that context requires evidence not provided by this record. These statistics describe the trial's posted results and their precision; they are not medical advice or a recommendation about oxygen-delivery choices.

17. Why This Trial Matters Statistically

This trial is statistically instructive because its primary outcome is a duration-based measure, while a related secondary outcome concerns whether participants had desaturation events. The distinction illustrates why endpoint choice matters: an average duration summarizes accumulated time, whereas event occurrence reduces experience to whether an event was observed. Different endpoint definitions can produce different levels of precision and answer different questions even within the same study.

The posted primary comparison is large relative to its reported variability and has a narrow confidence interval. That combination makes it especially important to understand the measurement scale, distribution, analysis method, and handling of participants whose results may not be included. The registry record does not provide enough detail to resolve those issues. Statistical precision should therefore be considered alongside the transparency and verifiability of the analysis, rather than treated as a substitute for them.

The study also highlights the distinction between trial design and retrospective planning illustrations. Calculations based on the observed effect can generate very small participant counts when the estimated effect is large relative to the estimated variability. Such calculations do not establish what assumptions informed the completed study, and they do not measure the completed trial's observed power. The original sample-size justification is not reported in the registry record.

Finally, the record demonstrates why a list of outcomes is not the same as a complete account of results. Several secondary outcomes are named, but results for some are not reported, and no multiplicity approach is described. Assessing a trial requires attention to outcome definitions, uncertainty, analysis choices, and completeness of reporting—not only whether a primary p-value crosses a conventional threshold.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several trial-specific uncertainties remain in the registry record. The primary endpoint group sizes total fewer participants than the recorded enrollment, but the reason is not reported. There is no participant flow account, explanation of exclusions, missing-data description, or statement of the analysis population. These omissions make it difficult to determine how the posted estimates relate to all randomized participants.

The primary mean difference has a very narrow confidence interval relative to the reported scale and group standard deviations. The record does not explain the statistical method, distributional assumptions, or calculation used for the interval. Participant-level data and diagnostics are not reported, so the outcome distribution and sensitivity to influential observations cannot be assessed. The posted estimate can be described, but it cannot be independently checked using the registry record alone.

The trial is open-label, and masking is listed as none. The record does not describe outcome ascertainment procedures that might reduce the influence of knowledge of assignment. The contrast also combines the device and oxygen-flow regimen; the registry does not separate these components. Details about sequence generation and allocation concealment are not reported in the registry record.

Results for two listed secondary outcomes are not reported, while the registry does not describe a multiplicity strategy. Adverse-event details beyond the recorded counts are also limited. Finally, the study context is specific to interventional radiology procedures under total intravenous anesthesia among patients described as having obstructive sleep apnea or potential high risk of airway obstruction. The extent to which the results apply outside that setting is not established by the posted record.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Optiflow THRIVE for Delivery of Oxygen to Patients During Total Intravenous Anesthesia While Undergoing Radiology Procedures — NCT04171037.
• Registry record last updated 2025-07-24; status last verified 2025-07.
• Results first posted 2025-07-24.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT04171037 is a completed randomized, open-label, parallel-group pilot study sponsored by M.D. Anderson Cancer Center. It compared Optiflow THRIVE with a non-rebreather facemask for oxygen delivery during total intravenous anesthesia in patients undergoing interventional radiology procedures. The registry records an enrollment of 108.

The primary outcome was mean total duration of desaturation episodes during a 60-minute observation window beginning with propofol infusion. The posted mean difference was -63.0 minutes, with a 95% confidence interval from -63.95 to -62.05 and an unadjusted p-value of <0.001. One secondary outcome has posted results; results for BIS episodes and PACU observation time are not reported in the registry record. The original sample-size justification, detailed analysis methods, missing-data approach, and multiplicity plan are not reported.