Propofol Versus Alfentanil Versus Nitrous Oxide for Moderate Procedural Sedation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Propofol Versus Alfentanil Versus Nitrous Oxide for Moderate Procedural Sedation (NCT00997126), a randomized phase 4 study. The primary outcome is Number of Participants With Sub-clinical Respiratory Depression and Clinical Events Associated With Respiratory Depression During the Sedation Procedure.

2. Clinical Question

The question is about recorded events during sedation, not a direct comparison of every aspect of sedation quality or recovery. The primary endpoint combines language about sub-clinical respiratory depression and related clinical events, but its operational criteria are not reported in the registry record. The registry also lists outcomes concerning return to baseline mental status, depth of sedation, pain, and recall. These outcomes address other parts of the procedure experience and do not replace the primary respiratory-depression question.

The comparison is randomized, but it is unmasked. Randomization is intended to make the treatment groups comparable on average, while lack of masking can affect care, assessment, or participant reports. Whether those possibilities influenced these results cannot be determined from the registry record. The results therefore describe the comparison recorded for these two arms and should not be treated as evidence about a treatment arm that was not listed.

3. Trial Design

The registry record describes a randomized, parallel-group, Phase 4 trial sponsored by Hennepin Healthcare Research Institute. It is marked completed. The recorded start is 2009-10, and primary completion is recorded as 2015-04. Enrollment is listed as 126. The design has no masking, so participants and study personnel were not masked according to the registry entry.

The two listed arms are propofol and alfentanil. The primary outcome is recorded as the number of participants with sub-clinical respiratory depression and clinical events associated with respiratory depression during the sedation procedure. The registry describes its observation period as beginning one minute before the procedure and continuing until the patient returned to baseline mental status after sedation, with the duration dependent on the procedure. The specific thresholds, event definitions, and assessment procedures are not reported in the registry record.

The registry lists secondary outcomes for time to return of baseline mental status, depth of sedation measured using the OAAS scale, patient-reported pain, and patient-reported recall. Posted results include pain and recall counts. Results for the listed return-to-baseline and sedation-depth measures are not reported in the registry record. The trial title mentions nitrous oxide, but the listed randomized arms and outcome comparisons cover propofol and alfentanil only.

The registry record does not report the original sample-size justification, planned statistical analysis, eligibility details, or participant flow. It also does not report whether allocation was concealed, what analysis population was prespecified, or how missing outcome data were handled. Those details matter for evaluating design execution and inference, and cannot be inferred from the fact that the trial was randomized or completed.

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.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Sub-clinical Respiratory Depression and Clinical Events Associated With Respiratory Depression During the Sedation Procedure, measured over From one minute prior to start of procedure until the patient has returned to baseline mental status after the conclusion of the sedation procedure (~3-60 minutes depending on procedure duration).

The primary endpoint counts participants with sub-clinical respiratory depression and clinical events associated with respiratory depression during the sedation procedure. In the posted results, this is represented as a number of participants with an event in each arm. The observation window starts one minute before the procedure and extends until return to baseline mental status after sedation. The registry notes that the duration varies with procedure length.

This outcome is used to focus the comparison on respiratory events occurring around procedural sedation. Counting participants with an event gives a binary outcome at the participant level: a participant is counted as having met the endpoint or not. It does not convey how many events an affected participant experienced, how severe an event was, or how long it lasted. The registry does not report the criteria used to distinguish sub-clinical respiratory depression from associated clinical events, nor whether all components were required for a participant to be counted.

The endpoint is distinct from the listed secondary measures of recovery time, sedation depth, pain, and recall. Those outcomes concern other features of the procedure and its aftermath. A difference in one does not establish a difference in another. In particular, the primary count should be read as a registry outcome measure, not as a complete account of respiratory physiology or the overall sedation experience.

7. Results Posted in the Registry

• Alfentanil: 23.1% (12/52) versus 19.6% (11/56) on control; risk difference 3.4 percentage points (95% CI -12.0 to 18.9), risk ratio 1.17 (0.57–2.43); unadjusted two-proportion z-test p = 0.663.

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.

Patient Reported Pain

• 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:
  • Alfentanil: 48.1% (25/52) versus 12.5% (7/56) on control; risk difference 35.6 percentage points (95% CI 19.5 to 51.7), risk ratio 3.85 (1.82–8.13); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Alfentanil than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Patient Reported Recall of the 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:
  • Alfentanil: 75.0% (39/52) versus 23.2% (13/56) on control; risk difference 51.8 percentage points (95% CI 35.6 to 67.9), risk ratio 3.23 (1.96–5.33); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Alfentanil than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary outcomes address patient experience and other aspects of the sedation course, rather than the primary respiratory-depression endpoint. Across the posted patient-reported outcomes, the counts are higher in the alfentanil arm for pain and recall. This pattern is distinct from the primary comparison, where the event counts and estimated risk difference do not clearly separate the arms. These outcomes should not be collapsed into a single overall judgment: pain, recall, and respiratory events measure different things.

Secondary results can help describe the broader pattern of observations, but they generally carry less inferential weight than a prespecified primary result. Multiple outcomes create more opportunities for apparently notable findings, especially when analyses are unadjusted. The registry record does not report how many outcomes were included in the planned analysis, whether a hierarchy was specified, or whether any correction for multiple comparisons was used. Therefore, secondary p-values should not be treated as if they were the sole confirmatory test.

The registry's reported analysis for recall also differs from a simple unadjusted recalculation using its posted counts: the registry reports p = 0.657, while the recalculation gives p < 0.001. No explanation for that difference is reported. This limits confidence in a single inferential summary for recall and makes it especially important to distinguish posted counts, the reported analysis, and recalculated results. The secondary pattern is descriptive context, not a substitute for the primary outcome or a definitive explanation of the comparative effects.

Return to baseline mental status and depth of sedation are also listed as secondary outcomes, but their results are not reported in the registry record. Their absence from the posted results means that the secondary picture is incomplete; it does not show that those outcomes were not measured or that their results would match the reported patient-reported outcomes.

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

• Time to Return of Baseline Mental Status From Start of Procedure in Minutes
• Depth of Sedation Measured Using the OAAS Scale
• Patient Reported Pain
• Patient Reported Recall of the Procedure

9. Statistical Interpretation

10. Statistical Methods Explained

For a binary endpoint, each participant contributes an event status: the participant either meets the endpoint or does not. The posted primary results give event counts and arm denominators. A risk is the proportion with an event in an arm; a risk difference compares those risks by subtraction. The registry comparison is expressed as alfentanil relative to propofol, so a positive risk difference indicates a higher observed event risk in the alfentanil arm. The posted estimate is 0.034. This direction describes the point estimate, not a definitive treatment effect.

What does the confidence interval add?

A confidence interval gives a range of values compatible with the observed data under the statistical method used. It communicates uncertainty around an estimate rather than turning the estimate into a certainty. For the primary risk difference, the interval runs from -0.120 to 0.189. Because this range includes zero, the data do not rule out no difference under the stated comparison. It also extends on both sides of zero, so the data are compatible with effects favoring either arm. The confidence level and exact interval method are not reported in the registry record.

The relative measures express the comparison differently. A risk ratio compares the risks as a ratio, while an odds ratio compares the odds of an event. A value at the no-association point corresponds to equal risks for a risk ratio, or equal odds for an odds ratio. The posted primary risk ratio is 1.175, with interval 0.569 to 2.428; the odds ratio is 1.227, with interval 0.488 to 3.087. Both intervals include their respective no-association points. Relative measures can look less intuitive than a risk difference, and neither removes the uncertainty seen in the data.

How should the p-value be read?

A p-value measures how unusual the observed data, or data more extreme, would be under a specified null model and assumptions. It is not the probability that the null hypothesis is true, and it is not a measure of the size or clinical importance of an effect. The primary unadjusted p-value is 0.663. It does not provide strong evidence against the no-difference model, but it cannot prove equivalence or rule out meaningful effects. A conclusion about equivalence would require a prespecified equivalence margin and a design and analysis intended to assess it; such information is not reported in the registry record.

The primary comparison is an unadjusted comparison of the posted summary statistics. No covariate-adjusted estimate is reported. Adjustment can account for selected measured characteristics, but it does not automatically correct for unmeasured factors or poor outcome measurement. Since the trial is randomized, treatment groups are intended to be comparable on average; nevertheless, the registry does not report enough detail to assess allocation procedures or how the analysis handled deviations from assigned treatment.

Why can binary outcomes be uncertain?

Binary outcomes discard detail: the count records whether an event occurred, but not its duration, severity, repetition, or timing within the observation window. The primary endpoint also joins sub-clinical respiratory depression with clinical events associated with respiratory depression. Without its operational definition, readers cannot determine which events qualify or whether distinct event types are weighted equally. This limits the clinical interpretation of a difference in participant counts.

Small event counts can yield substantial uncertainty, even when the point estimate appears to favor one arm. Confidence intervals make that uncertainty visible. A non-significant p-value does not mean the observed arms are identical; it may reflect an estimate near the null, limited information, or both. Conversely, a small p-value does not by itself establish that an effect is large or important. Interpretation should consider the effect estimate, interval, outcome definition, design, and analysis together.

What is the role of the secondary analyses?

Patient-reported pain and recall are binary outcomes in the posted comparisons. Their risk differences and unadjusted p-values summarize differences in reported event proportions. These comparisons are secondary to the primary respiratory endpoint. If multiple outcomes are examined, the chance of at least one apparently unusual result can increase when each is assessed without accounting for the full set. The registry record does not report a multiplicity strategy or a prespecified hierarchy among secondary outcomes.

For recall, the registry reports a chi-squared analysis with p = 0.657. A separate unadjusted recalculation based on the posted counts gives p < 0.001. The registry record does not explain the difference. The recalculated value is a simple analysis of the posted summary counts, while the registry value is the listed analysis result; without further analysis details, the reason for the mismatch is not known. The discrepancy should be kept explicit rather than selecting whichever value better fits a preferred interpretation.

Statistical methods are only one part of an evaluation. The registry does not report the original analysis plan, the confidence-interval method, missing-data procedures, or details of the analysis populations. Those omissions make it harder to determine whether the posted analyses follow the intended plan or how robust the results are to alternative reasonable choices. General explanations of these methods do not fill in the missing study-specific information.

11. Confidence Intervals and Precision

The primary risk-difference estimate is 0.034, and its confidence interval extends from -0.120 to 0.189. The interval crosses zero, so it includes no difference as well as values on either side. This is a wide range relative to the point estimate and means the observed data do not pin down the direction or size of the underlying difference precisely. The interval should be read as uncertainty around the estimate, not as a range that guarantees the true effect lies within it.

The relative-effect intervals tell a similar story. The risk ratio is 1.175, with interval 0.569 to 2.428, and the odds ratio is 1.227, with interval 0.488 to 3.087. Both include the no-association value. These intervals allow for lower and higher event occurrence in the alfentanil arm relative to propofol, so a single point estimate should not be overinterpreted.

The registry record does not identify the confidence level or interval construction method. It also does not report enough detail about outcome ascertainment or missing observations to assess how those issues affect precision. Precision is not the same as validity: a narrow interval would not repair bias in measurement or analysis, and a wide interval does not prove that the treatment effects are equal. In general, more information can narrow uncertainty, while a limited number of events can leave considerable uncertainty. Here, the primary interval supports a cautious reading rather than a firm claim of a difference or equivalence.

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 events. They are illustrations computed from the observed effect, not the original trial design calculation. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set to the stated fraction of the observed effect. The trial's own original sample-size assumptions are not reported in the registry record.

The 80% power column describes the number of participants per arm that a future study would need, under those assumptions, to have an 80% chance of detecting the specified effect if that effect were the true one. The 90% power column gives the corresponding planning target for a 90% chance. These are design probabilities under an assumed effect and analysis; they are not probabilities that the observed result is true. The displayed figures are not observed power.

Rows for 100% of the observed effect use the full estimated effect as the planning target; the 75% and 50% rows use progressively smaller targets. Smaller effects are harder to distinguish from chance variation, so they require more participants per arm under the same assumptions. These illustrations are particularly sensitive to the observed effect: if that estimate is unstable, the projected enrollment can also be unstable. They should therefore be read as hypothetical planning scenarios, not as a recommendation or as evidence that the completed trial was designed to meet a particular power target.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.196; treatment proportion p₁ = 0.231; average p̄ = 0.214.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5796 = 1.1360.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5791 = 0.4874.
4. n = (1.1360 + 0.4874)² / (0.0343)² = 2,234.8, rounded up to 2,235 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
p0 <- 0.196428571428571                          # control proportion
p1 <- 0.230769230769231                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(997126)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 2,235 (80% power), 2,992 (90% power)
 75% of observed effect: n per arm = 3,916 (80% power), 5,241 (90% power)
 50% of observed effect: n per arm = 8,677 (80% power), 11,616 (90% power)
power.prop.test: 2234.8 
Simulated power at n = 2,235 per arm: 0.800 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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 a primary outcome and several secondary outcomes. Considering multiple endpoints increases the chance that at least one comparison will appear statistically notable by chance when each is tested separately. A multiplicity plan can address that issue through methods such as adjusting thresholds or defining a testing hierarchy. Whether such a plan was specified or used is not reported in the registry record. The unadjusted secondary comparisons should therefore be interpreted as exploratory or descriptive unless further documentation establishes their planned role.

Missing-data handling is also not reported. The arm denominators are listed for the posted outcomes, but the record does not explain whether every randomized participant had each outcome measured, how unavailable assessments were treated, or whether any participants were excluded from an analysis. The listed denominators alone do not establish that there were no missing outcome data. The record also does not describe an intention-to-treat or per-protocol analysis population, so neither should be assumed.

The statistical plan is not reported in enough detail to determine whether the posted analyses were prespecified. The primary comparison has an unadjusted result, and the registry lists a chi-squared analysis for recall. Adjustment for baseline characteristics, handling of repeated or correlated outcomes, and sensitivity analyses are not reported. These omissions matter because analysis choices can affect uncertainty and interpretation, particularly when outcomes are measured in different ways.

For recall, the listed chi-squared p-value is 0.657, whereas an unadjusted recalculation from the posted summary counts gives p < 0.001. The record does not explain why the values differ. The difference cannot be resolved from the registry information alone, so it should remain visible in any reading of that endpoint. No assumption about the reason, analytic population, or missing-data procedure can be made from the posted information.

15. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists zero serious adverse events in the propofol arm among 56 at risk and zero in the alfentanil arm among 52 at risk. These are counts recorded for the serious adverse-event category. They do not establish that no clinically relevant harm occurred: the record also lists other adverse events, and the serious-event totals are based on the observation and reporting recorded in the trial.

Other adverse events are listed for 25 participants in the propofol arm and 29 in the alfentanil arm. The registry does not provide a description of these events in the available record, so their types, severity, timing, and relationship to treatment cannot be characterized. Death counts are not reported in the registry record.

Safety counts should be interpreted alongside the trial's size, duration, event definitions, and completeness of reporting. The registry record does not provide enough information to determine how sensitive the trial was to uncommon harms or whether all events were captured consistently. A zero count for serious events is not proof that risk is absent.

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

The primary result shows similar observed counts of participants with respiratory-depression-related events in the two listed arms, with an estimated risk difference of 0.034 for alfentanil relative to propofol. Its confidence interval, -0.120 to 0.189, includes zero and spans effects in either direction. The data therefore do not establish a clear difference on the primary endpoint, but they also do not establish that the treatments are equivalent or that a meaningful difference is absent.

The posted secondary patient-reported outcomes show higher counts in the alfentanil arm for both pain and recall. Those outcomes concern different dimensions from the primary endpoint and have their own uncertainty and reporting limitations. In particular, the registry's reported chi-squared p-value for recall differs from a simple unadjusted recalculation based on the posted counts. The record does not explain this difference, so the apparent strength of evidence for that comparison requires caution.

The trial record supports statements about the listed randomized comparison and the outcomes recorded for it. It does not establish how results would generalize to other settings or populations, or to nitrous oxide, which is named in the title but not listed as a randomized arm. The record does not report important details such as eligibility criteria, analysis populations, missing-data handling, or the original statistical plan. Those gaps restrict conclusions about robustness and generalizability.

Statistical evidence is not medical advice. These results alone do not determine which sedation approach should be selected for an individual or setting. They describe estimated group-level outcomes with uncertainty; decisions require clinical context and evidence beyond this registry record.

17. Why This Trial Matters Statistically

This trial illustrates why a point estimate and its uncertainty should be read together. The primary point estimate is slightly positive for alfentanil relative to propofol, but the confidence interval crosses zero and spans a broad range of possible differences. Focusing only on the point estimate could overstate what the data resolve; focusing only on the non-significant p-value could incorrectly suggest that the arms are identical. The interval provides the more useful picture of precision.

It also shows how endpoints answer distinct questions. Respiratory-depression-related events, patient-reported pain, and recall are not interchangeable outcomes. A pattern in one cannot automatically be generalized to another. Statistical interpretation should stay tied to the outcome definition and observation period, both of which shape what the count means.

The difference between the reported recall analysis and a recalculation from posted counts is another useful reminder: analysis results should be traceable to their methods and data. When the registry does not explain a mismatch, readers should preserve that uncertainty rather than assume the cause. Clear reporting of prespecified analyses, missing-data procedures, outcome definitions, and multiplicity plans makes results easier to evaluate and reproduce.

Finally, planning illustrations based on an observed effect are not the same as the original design justification or the power of the completed trial. Their values change with the target effect and assumptions. Keeping those concepts separate prevents a planning calculation from being mistaken for evidence about what the trial did or did not detect.

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.

The registry record does not report detailed eligibility criteria, baseline characteristics, allocation concealment, or participant flow. Without these details, readers cannot assess the composition of the study population, how randomization was implemented, or whether departures from assignment affected the analysis. The record identifies the design as randomized and unmasked, but does not describe procedures that could clarify these issues.

The primary endpoint's operational definition is not reported. The registry names sub-clinical respiratory depression and associated clinical events, but does not give thresholds or explain how different event types were combined. The listed observation window depends on return to baseline mental status and procedure duration. Without event definitions and assessment detail, the clinical meaning and reproducibility of the endpoint are difficult to judge.

The title names nitrous oxide, while the listed randomized arms and comparisons concern propofol and alfentanil. The record does not list a nitrous oxide arm in the posted results, so conclusions should be confined to the two listed arms. Results for some listed secondary measures, including return to baseline mental status and depth of sedation, are not reported in the registry record.

Further limitations include unreported missing-data procedures, analysis populations, original sample-size justification, and multiplicity strategy. The registry's reported recall p-value also differs from an unadjusted recalculation from the posted counts, with no explanation recorded. These limitations constrain interpretation of secondary findings and prevent a full assessment of analytic robustness.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Propofol Versus Alfentanil Versus Nitrous Oxide for Moderate Procedural Sedation — NCT00997126.
• Registry record last updated 2017-01-27; status last verified 2016-12.
• Results first posted 2017-01-27.
• 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

This completed, randomized, unmasked, parallel-group Phase 4 trial compared propofol with alfentanil for moderate procedural sedation in the emergency department. The registry records enrollment of 126, a start of 2009-10, and primary completion in 2015-04. The primary outcome counted participants with sub-clinical respiratory depression and related clinical events during the sedation procedure.

The primary risk-difference estimate for alfentanil relative to propofol was 0.034, with a confidence interval from -0.120 to 0.189 and p = 0.663. The interval includes zero and indicates substantial uncertainty about the comparative effect. Posted secondary patient-reported outcomes show higher counts in the alfentanil arm, but the recall analysis has an unexplained difference between the registry's reported p-value and an unadjusted recalculation. Key design and analysis details, including missing-data procedures and multiplicity handling, are not reported in the registry record.