Propofol and Dexmedetomidine Versus a Propofol Only Regimen for Sedation During Colonoscopy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Propofol and Dexmedetomidine Versus a Propofol Only Regimen for Sedation During Colonoscopy (NCT03139279), a randomized phase 4 study. The primary outcome is Percentage of Subjects Ready for Discharge in Each Group at 30 Minutes Post Procedure.

2. Clinical Question

The clinical context in the registry is a concern that dexmedetomidine might prolong recovery or readiness for discharge when used with propofol. The registry summary also describes the rationale for combining sedatives with different mechanisms as potentially reducing the amount of each agent used. Those statements explain the question; they are not findings from the posted primary comparison. The result describes readiness at the specified assessment time, not overall recovery, all potential benefits or harms, or the experience of every person undergoing colonoscopy.

3. Trial Design

The registry identifies this as a Phase 4, randomized, double-masked, parallel-group trial. The listed condition is colonoscopy, and the study status is completed. The sponsor is State University of New York - Downstate Medical Center. The record lists a start date of 2017-05-05 and a primary completion date of 2018-05-04.

The two regimens shared propofol, with propofol doses titrated at the anesthesiologist’s discretion to a target BIS range between 60-70. The dexmedetomidine group received intravenous dexmedetomidine 0.3 ug/kg followed by propofol. The comparison group received intravenous saline placebo followed by propofol. The registry labels the study double-masked but does not report further details of how masking was maintained.

Enrollment is recorded as 122. For the posted primary outcome, the arm-level denominators are 51 for dexmedetomidine and propofol and 50 for saline placebo and propofol. The registry record does not report why these outcome denominators differ from the enrollment figure, nor does it provide participant flow or an explanation of missing primary outcome data. These figures should therefore be read as separately reported enrollment and outcome information, not as a complete account of participant disposition.

The primary outcome description specifies assessment of readiness for discharge at 10, 20 and 30 minutes after the procedure using MPADSS, with scores of 9-10 classified as ready. The primary outcome title identifies the 30-minute measure, and that is the time point represented by the posted comparison. The record lists four secondary outcomes: average total propofol consumption per group, sustained bradycardic episodes, lowest intraoperative percentage change in MAP from baseline, and apneic episodes requiring positive pressure ventilation. Results for those secondary outcomes are not reported in the registry record. The original statistical analysis plan and the trial’s own sample-size assumptions 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.

Before assignment: We consented 122 patients of which 8 were immediately excluded for the following reasons: procedure began prior to randomization (3), inclusion criteria not met (3), anesthesiologist declined (1), patient withdrew consent (1); 114 were randomized into the treatment and placebo groups.

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: 114 were randomized into the treatment and placebo groups. Seven additional patients in the propofol-dexmedetomidine group and 6 in the propofol-saline group were excluded. Final n = 101

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Subjects Ready for Discharge in Each Group at 30 Minutes Post Procedure, measured over 30 minutes.

The primary endpoint concerns readiness for discharge after the colonoscopy procedure. Readiness was assessed with the Modified Post-Anesthesia Discharge Scoring System (MPADSS); the registry defines an MPADSS score of 9-10 as ready for discharge. The title of the primary outcome specifies the percentage ready in each group at 30 minutes post procedure. The description says assessments were made at 10, 20 and 30 minutes, but the posted comparison is for the 30-minute measure.

This endpoint is used to represent a practical recovery milestone: whether participants meet a specified discharge-readiness threshold at a fixed time after the procedure. It is a binary classification for the analysis—ready or not ready according to the stated score threshold—rather than a direct measurement of every aspect of recovery. General statistical context: converting a score into a threshold-based outcome can make group proportions easier to compare, but it does not show the distribution of scores within either category or how quickly people became ready between assessment times.

The posted arm results are counts: 26 participants in the dexmedetomidine and propofol group and 44 in the saline placebo and propofol group were reported ready at the primary time point, with denominators of 51 and 50, respectively. The registry’s title calls the outcome a percentage, but the posted arm-level values are participant counts. The record does not report the individual MPADSS scores, results at 10 or 20 minutes, or time-to-readiness data. The 30-minute endpoint therefore answers a narrower question than whether recovery trajectories differed throughout the post-procedure period.

7. Results Posted in the Registry

• Dexmedetomidine and Propofol: 51.0% (26/51) versus 88.0% (44/50) on control; risk difference -37.0 percentage points (95% CI -53.4 to -20.6), risk ratio 0.58 (0.43–0.77); unadjusted two-proportion z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The main effect measure is a risk difference. In general, a risk difference subtracts one group’s outcome probability from the other’s, so zero represents equal probabilities and the sign gives the direction of the contrast. The posted estimate is -0.370 for dexmedetomidine and propofol relative to saline placebo and propofol. The negative direction means the observed probability of being ready at 30 minutes was lower in the first group. This absolute measure directly describes the difference between group probabilities, unlike a relative measure that expresses one probability in relation to another.

What do the risk ratio and odds ratio add?

The registry also posts a risk ratio and an odds ratio. In general, a risk ratio compares the probability of an outcome between groups. An odds ratio compares the odds, where odds describe the probability of an event relative to the probability of no event. Both are relative measures, so their numerical scale and interpretation differ from the risk difference. The posted risk ratio is 0.579, with interval 0.434 to 0.773; the posted odds ratio is 0.142, with interval 0.051 to 0.391. These measures do not replace the absolute group counts or the risk-difference estimate.

How should the p-value be understood?

The posted unadjusted p-value is p < 0.001. General statistical explanation: a p-value describes how incompatible the observed data are with a specified null hypothesis under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The registry record does not identify the test or model used for this p-value, and it does not report an adjusted p-value. The result should therefore be described as the unadjusted value in the record rather than attributed to a particular analysis procedure.

What does an interval estimate describe?

The posted interval for the risk difference runs from -0.534 to -0.206. General statistical explanation: an interval estimate communicates uncertainty around an estimated contrast. A narrower interval indicates greater precision than a wider interval on the same scale, while the interval’s location indicates the range of effect values compatible with the method used. The registry record does not state the confidence level or the method used to construct this interval, so neither should be inferred. The interval is not a range containing a known fixed percentage of individual outcomes.

Why do several effect measures appear?

Different effect measures answer related but distinct questions. The risk difference is an absolute contrast between probabilities. The risk ratio is relative to the comparator probability, and the odds ratio is based on odds rather than probabilities. For a binary endpoint such as ready versus not ready, the arm counts are also important: they keep the measure connected to the observed event information and the denominators. General statistical context: relative measures can appear more or less dramatic than absolute measures because they use different scales. A reader should identify the scale before interpreting an estimate and should not compare numerical values across scales as if they meant the same thing.

Why can over-dispersion matter?

General statistical explanation: over-dispersion occurs when the variability in observed data is greater than a model assumes. If a model underestimates variability, standard errors may be too small and intervals may be too narrow; tests can then give stronger evidence than the data warrant. This concept is relevant when count or grouped data are modeled, but the posted primary outcome is a binary readiness classification and the registry record does not report a model or any over-dispersion assessment. It is not possible to say whether over-dispersion was considered in the sponsor’s analysis.

The primary outcome has a stated threshold and assessment time, but many details of the statistical analysis are not reported in the registry record. These include the test or model, the confidence level and interval method, adjustment for any prespecified covariates, and the treatment of missing observations. The posted comparison and its uncertainty can be interpreted as reported, while these unreported details constrain independent reconstruction of the analysis. The registry lists zero analyses, so no analysis descriptions are available there to clarify those choices.

10. Confidence Intervals and Precision

The risk-difference estimate is -0.370, with an interval from -0.534 to -0.206. This interval communicates uncertainty about the estimated contrast: its endpoints span a range of values compatible with the interval procedure used. The entire posted interval is below zero, consistent with a lower estimated readiness probability for dexmedetomidine and propofol than for saline placebo and propofol at 30 minutes. The registry record does not report the interval’s confidence level or construction method.

Precision is not the same as clinical importance. An estimate can be statistically precise yet still require context to judge what its magnitude means for recovery and discharge processes. The risk difference is an absolute-scale measure, so it relates directly to the difference in group probabilities; it does not quantify a time delay. The interval also does not describe variation in individual recovery times, which are not reported.

The relative estimates have their own intervals: the risk ratio is 0.579, with interval 0.434 to 0.773, and the odds ratio is 0.142, with interval 0.051 to 0.391. These intervals are on different scales from the risk-difference interval. Each should be interpreted in relation to its corresponding effect measure, not as an alternative expression of the same numerical magnitude.

Although the interval and p-value indicate a clear statistical contrast in the posted 30-minute outcome, precision is also affected by what is not described. The registry record does not report missing outcome handling, analysis populations, or the specific interval method. Enrollment is recorded as 122, while the arm denominators for the primary outcome are 51 and 50; the record does not explain the relationship between those figures. These gaps make it harder to assess how robustly the reported precision reflects the full enrolled population.

11. 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 illustrations based on the observed effect, not a description of the trial’s original design. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set at a stated fraction of the observed effect. The trial’s own original sample-size assumptions are not reported in the registry record.

For this binary outcome, the planning values are participants per arm. At 100% of the observed effect, the figures are 24 participants per arm for 80% power and 31 participants per arm for 90% power. At 75% of the observed effect, they are 38 participants per arm for 80% power and 51 participants per arm for 90% power. At 50% of the observed effect, they are 76 participants per arm for 80% power and 101 participants per arm for 90% power. These are planning illustrations, not observed power.

In general, power is the probability that a planned analysis will detect an effect of a specified size under its assumptions when that effect is present. The 80% column represents a design targeting 80% power under the stated assumptions; the 90% column represents a design targeting 90% power. A higher target generally requires more participants for the same assumed effect. Smaller effects are harder to distinguish from random variation and therefore require more participants, as reflected by the increasing figures across the listed effect fractions.

A sample-size curve is read by relating the assumed effect size to the number of participants required under the planning assumptions. It does not show the number actually analyzed or establish that the original trial had a particular probability of finding a result. The listed figures are per arm, not total participants. The time-to-event convention about total events does not apply to this binary endpoint.

12. 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 = 0.880; treatment proportion p₁ = 0.510; average p̄ = 0.695.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6512 = 1.2763.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5962 = 0.5018.
4. n = (1.2763 + 0.5018)² / (-0.3702)² = 23.1, rounded up to 24 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 <- 0.88                          # control proportion
p1 <- 0.509803921568627                          # 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(3139279)
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 = 24 (80% power), 31 (90% power)
 75% of observed effect: n per arm = 38 (80% power), 51 (90% power)
 50% of observed effect: n per arm = 76 (80% power), 101 (90% power)
power.prop.test: 23.1 
Simulated power at n = 24 per arm: 0.834 (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.

13. Multiplicity, Missing Data and Analysis Populations

The primary outcome description includes assessments at 10, 20 and 30 minutes, while the primary outcome title singles out the 30-minute result. The record also lists four secondary outcomes. When several outcomes or assessment times are examined, the chance of at least one apparently unusual result can increase if each is tested separately. General statistical explanation: multiplicity procedures can control this issue by adjusting testing or by defining a hierarchy of questions in advance. The registry record does not report whether any such strategy was planned or used, and the posted primary p-value is explicitly unadjusted.

The registry lists zero analyses and does not include an analysis plan. It therefore does not report whether the 30-minute time point was selected in advance for the primary comparison, how the other assessment times were handled, or whether secondary outcomes were analyzed inferentially. Results for the four listed secondary outcomes are not reported in the registry record. The available information does not support conclusions about those outcomes or about any correction for multiple comparisons.

Missing data and analysis populations are also not described. The record reports enrollment of 122 and primary outcome denominators of 51 and 50. It does not report whether every enrolled participant was assessed, the reasons for any absent outcomes, how missing observations were handled, or whether the analysis followed an intention-to-treat principle. Those details matter because exclusions or missing outcome data can affect the population represented by an estimate and may introduce bias if their occurrence is related to group assignment or readiness.

Baseline characteristics, participant flow, and the number screened or randomized are not reported in the registry record. The listed enrollment and outcome denominators should not be taken as a substitute for those details. Without the analysis population and missing-data methods, the result can be interpreted as the posted group comparison, but the record does not allow a full assessment of how the analyzed participants were selected or how robust the findings are to missingness.

14. 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 reports serious adverse events for 0 of 51 participants in the dexmedetomidine and propofol group and 0 of 50 participants in the saline placebo and propofol group. It also reports 0 other adverse events in each group and 0 deaths in each group. These are event counts for the groups and categories recorded in the registry.

General statistical context: observing zero events does not establish that an event is impossible or that the underlying risk is zero. With no events recorded, the data do not provide a direct comparison of event rates between the groups for that category. The amount of information about rare outcomes depends on the number observed and the number at risk, as well as how events were defined and collected.

The registry lists secondary outcomes concerning sustained bradycardic episodes, intraoperative MAP change, and apneic episodes requiring positive pressure ventilation, but it does not report their results in the outcome results. Those measures should not be treated as equivalent to the registry’s adverse-event counts. The record also does not report event definitions, follow-up procedures, or detailed safety analyses. The figures therefore describe only the adverse-event categories and counts posted, not all possible side effects or the full safety profile of either regimen.

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

The result establishes what the registry reports for one defined comparison: at 30 minutes after colonoscopy, fewer participants in the dexmedetomidine and propofol group were classified as ready for discharge than in the saline placebo and propofol group. The estimated risk difference is -0.370, with interval -0.534 to -0.206, and the unadjusted p-value is p < 0.001. This is evidence of a statistical difference in the posted binary outcome at that time point.

It does not establish how many minutes later participants became ready, whether readiness differed at the 10- or 20-minute assessment, or whether the groups differed in other aspects of recovery. The posted outcome is based on the MPADSS threshold of 9-10, not a continuous measure of recovery time. The registry record does not report the underlying scores or individual trajectories.

It also does not establish the results of the secondary outcomes. Although the registry lists propofol consumption, sustained bradycardic episodes, MAP change, and apneic episodes requiring positive pressure ventilation, their results are not reported in the registry record. The recorded zero adverse-event counts are limited to the posted adverse-event categories and do not show that no other events occurred.

The result should not be taken as a universal estimate for every colonoscopy setting or sedation regimen. It comes from a randomized, double-masked, parallel-group Phase 4 trial with the regimens and outcome definition described in the record. Details about participant characteristics, missing outcomes, the statistical analysis plan, and the relationship between enrollment and outcome denominators are not reported in the registry record. Those omissions limit assessment of generalizability and of how the reported analysis was conducted.

Statistical evidence alone does not determine clinical importance. The estimate and interval quantify the posted contrast on a probability-difference scale, while clinical interpretation also depends on the relevance of the endpoint, the timing of discharge decisions, and other benefits and harms. Those broader judgments are not resolved by the 30-minute result.

16. Why This Trial Matters Statistically

This trial is statistically informative because it frames a practical recovery question as a randomized comparison with a clear binary endpoint and a defined assessment time. The MPADSS threshold of 9-10 specifies what counts as ready for discharge, making the outcome operational rather than dependent on an undefined impression of recovery. The posted result can be expressed as both arm-level counts and an absolute risk difference, allowing readers to connect the effect estimate to the observed groups.

The distinction between the endpoint and the broader clinical question matters. Readiness at 30 minutes is not the same as time to readiness, and it does not capture every feature of recovery. The record’s description notes other assessment times and secondary outcomes, but their results are not reported. This illustrates why a statistically clear result for one outcome cannot automatically be extended to related outcomes or to the overall balance of treatment effects.

The interval is also central to interpretation. It gives a range of estimates compatible with the reported procedure, rather than leaving the reader with a point estimate alone. The p-value indicates strong evidence against the tested null under the analysis assumptions, but the analysis method and adjustment for multiple testing are not reported. Effect size, precision, endpoint meaning, and analysis transparency all contribute to a careful interpretation.

Finally, the record illustrates the difference between a trial’s observed results and planning calculations derived from them. The sample-size illustrations use fractions of the observed effect and stated planning assumptions; they do not reconstruct the original design or measure observed power. Keeping these concepts separate prevents a post hoc planning display from being mistaken for evidence about the trial’s design or its probability of detecting an effect.

17. 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 offers limited information for judging how well the result applies beyond the trial. It identifies colonoscopy as the condition and gives the sedation regimens, but it does not report participant characteristics or further eligibility details. The primary outcome population field is blank, and details about the clinical setting and participant flow are not reported in the registry record.

The enrollment figure is 122, while the primary outcome denominators are 51 and 50. Reasons for the difference, withdrawals, exclusions, and missing outcome data are not reported in the registry record. Without those details, it is not possible to determine how the outcome groups relate to all enrolled participants or to assess the potential effect of missing observations.

The outcome is a threshold classification at a fixed time. Although the registry description states that assessments occurred at 10, 20 and 30 minutes, the posted primary comparison concerns 30 minutes. Results for the earlier assessments, individual MPADSS scores, and time-to-readiness are not reported in the registry record. A difference in the binary 30-minute outcome therefore does not by itself describe the full recovery course.

The record lists several secondary outcomes, but their results are not reported. The statistical analysis plan, test or model for the primary result, interval construction method, confidence level, and any multiplicity strategy are also not reported in the registry record. These omissions restrict independent evaluation of the analysis and prevent a complete account of evidence across outcomes. The posted zero adverse-event counts are limited to the categories shown and do not replace detailed safety results.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Propofol and Dexmedetomidine Versus a Propofol Only Regimen for Sedation During Colonoscopy — NCT03139279.
• Registry record last updated 2019-07-29; status last verified 2019-07.
• Results first posted 2019-07-16.
• 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.

21. Record Summary

The registry record describes a completed, randomized, double-masked, parallel-group Phase 4 trial of dexmedetomidine plus propofol versus saline placebo plus propofol for colonoscopy sedation. Enrollment is recorded as 122. The primary endpoint is readiness for discharge at 30 minutes, defined as an MPADSS score of 9-10.

At that assessment, 26 of 51 participants in the dexmedetomidine and propofol group and 44 of 50 in the saline placebo and propofol group were reported ready. The risk difference is -0.370, with interval -0.534 to -0.206; the unadjusted p-value is p < 0.001. The record lists four secondary outcomes, but their results are not reported. Serious adverse events, other adverse events, and deaths are recorded as 0 in both groups.

Participant flow, missing-data handling, the statistical analysis plan, and the trial’s original sample-size assumptions are not reported in the registry record.