Displacement Between PVC and Silicon DLT: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Displacement Between PVC and Silicon DLT (NCT02691468), a randomized na study. The primary outcome is the Incidence of Clinically Significant Displacement of DLTs During Change of Patient Position.

2. Clinical Question

The clinical question is about tube position during a specified procedural transition, rather than about a general comparison of all aspects of the devices. Measurements were based on distances involving the tracheal carina and the tube tips. The primary outcome classified participants according to whether displacement crossed the registry's stated threshold. That binary definition supports a direct comparison of event occurrence, but it does not describe the full size or direction of each participant's displacement.

The registry record identifies thoracic surgery and a change from supine to lateral position as the setting and timeframe. It does not report participant characteristics such as age, or further details about surgical procedures. Results therefore describe the posted trial groups and the stated positioning context; the record does not establish how well they apply to other populations, procedures, tube uses, or positioning transitions.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group trial comparing PVC and silicon double-lumen endobronchial tubes. Its phase is listed as NA, and its status is completed. The recorded enrollment is 108. The study start is listed as 2016-02, and primary completion as 2017-04-01. Yeungnam University College of Medicine is identified as the sponsor.

The two arms used left-sided tubes after induction of general anesthesia. In each arm, an anesthesiologist placed the tube using direct laryngoscopy, and position was confirmed with a fiberoptic bronchoscope. The posted arm descriptions begin to describe tracheal and bronchial distance measurements, but the descriptions are incomplete. The record does not report which people were masked, how randomization was generated or concealed, or how treatment assignment was implemented.

The primary endpoint concerns clinically significant displacement during the change from supine to lateral decubitus position during surgery. The posted results give outcome denominators of 48 for the PVC arm and 52 for the silicon arm. The registry does not explain the relationship between those endpoint denominators and the recorded enrollment, nor does it state how participants without endpoint data, if any, were handled.

The record also includes a secondary outcome for critical malposition during the change from supine to lateral position. No detailed protocol, eligibility criteria, recruitment setting, analysis population, or planned statistical analysis is reported in the registry record. Consequently, features beyond the randomized parallel-group structure and the posted endpoint descriptions cannot be inferred from the 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: Patients with emergency surgery, difficult intubation, poor lung function to accomplish one-lung ventilation (OLV) during surgery were excluded.

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: 108 adult patients scheduled for elective thoracic surgery were enrolled. They were randomly allocated into two groups using a computer-generated random assignment scheme; group P (Polyvinyl chloride (PVC) double lumen tube (DLT)) and group S (Silicone DLT).

6. Primary Endpoint

The registry lists the primary outcome as the Incidence of Clinically Significant Displacement of DLTs During Change of Patient Position, measured over from supine to lateral decubitus position during surgery.

The primary endpoint counts participants with clinically significant displacement of a double-lumen tube during the change from supine to lateral decubitus position. The registry defines displacement using changes in tracheal and bronchial distances. Tracheal distance is the distance between the distal tip of the tracheal lumen and the tracheal carina; bronchial distance is the distance between the bronchial carina and the distal tip of the endobronchial lumen. The described comparisons use measurements taken in different positions and at different points during surgery.

For the primary endpoint, displacement was considered clinically significant when the tube deviated by more than 10 mm from the initial correct position, regardless of direction. The outcome therefore reduces measurements to whether the stated threshold was crossed. This makes the endpoint interpretable as an event count in each arm, while discarding detail about the exact distance and direction of displacement among participants classified as having an event.

A threshold-based endpoint is used to focus on a prespecified degree of positional change rather than every measured movement. However, the registry record does not explain how the threshold was selected, whether measurements were assessed by masked personnel, or how measurement variability was addressed. It also does not report the detailed timing of each measurement beyond the stated positional transition and the described start- and end-of-surgery measurements. Interpretation should therefore remain tied to the operational definition and timeframe in the record.

7. Results Posted in the Registry

• Silicon DLT: 34.6% (18/52) versus 35.4% (17/48) on control; risk difference -0.8 percentage points (95% CI -19.5 to 17.9), risk ratio 0.98 (0.57–1.67); unadjusted two-proportion z-test p = 0.933.

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.

the Incidence of Critical Malposition of DLTs

• 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:
  • Silicon DLT: 7.7% (4/52) versus 8.3% (4/48) on control; risk difference -0.6 percentage points (95% CI -11.3 to 10.0), risk ratio 0.92 (0.24–3.49); unadjusted two-proportion z-test p = 0.906.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Silicon DLT and the control. The interval gives the range of effects that remain compatible with the data.

The secondary endpoint concerns critical malposition during the change from supine to lateral decubitus position. The overall pattern of posted results is consistent with the primary comparison in that the observed event frequencies are similar across the PVC and silicon groups, and the comparison does not provide clear evidence of a between-group difference. This qualitative alignment does not independently confirm the primary result; the endpoints describe different classifications of tube position.

Secondary outcomes can help show whether the primary finding sits within a broader pattern, but they generally carry less weight when they are not the central prespecified question or when multiple outcomes are examined. Testing several outcomes creates more opportunities for apparently noteworthy findings to arise by chance. In general, multiplicity procedures can address this issue by controlling the interpretation across a family of tests. The registry record does not report a multiplicity plan or adjustment, and the posted secondary analysis is unadjusted.

The secondary result should therefore be treated as supporting context rather than as a separate confirmatory conclusion. Its interpretation is constrained by the same broad issues that affect the primary comparison: uncertainty in the group estimates, limited information about analysis methods, and incomplete reporting of participant accounting and endpoint assessment. The record does not state whether the secondary endpoint was prioritized in a formal testing hierarchy, or whether its definition and analysis were fixed before outcome data were examined.

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

• the Incidence of Critical Malposition of DLTs

9. Statistical Interpretation

10. Statistical Methods Explained

The results are counts of participants meeting a binary endpoint: clinically significant displacement either occurred or did not occur according to the registry definition. For this kind of outcome, the group event proportions provide a direct description of how frequently the recorded event occurred in each arm. The primary comparison presents an absolute measure, the risk difference, as well as relative measures, the risk ratio and odds ratio.

What does the risk difference mean?

The risk difference subtracts the event proportion in the PVC group from the event proportion in the silicon group. With that direction of comparison, a negative estimate means the observed event proportion was lower in the silicon group; a positive estimate means it was higher. The estimated difference is -0.008. This is an absolute-scale measure: it describes the difference between group proportions, not a proportional change relative to one group. The confidence interval from -0.195 to 0.179 communicates the range of values compatible with the data under the interval method. Because it crosses zero and extends in both directions, it does not identify a clear direction of difference.

How do relative measures differ?

The risk ratio compares the event proportion in the silicon group with the event proportion in the PVC group. A value corresponding to no relative difference is 1. The posted risk ratio is 0.977, and its interval, 0.573 to 1.668, includes 1. The odds ratio compares the odds of the event rather than the proportions themselves. Its posted estimate is 0.965, with an interval from 0.424 to 2.197, also including 1. These measures use different scales, so their numerical magnitudes are not directly interchangeable with a risk difference. In this case, their broad intervals likewise allow results in either direction.

What does the p-value contribute?

The unadjusted p-value for the primary comparison is 0.933. In general, a p-value measures how compatible the observed data are with a specified null model, assuming that model and the test's conditions. It is not the probability that the null hypothesis is true, nor does it measure the probability that the result occurred by chance. It does not convey the size or clinical importance of a difference. The estimate and confidence interval are needed to see the direction and range of uncertainty.

The record does not name the test used to obtain the posted p-value or report a model specification. It is therefore not appropriate to attribute a particular test, adjustment, or covariate structure to the sponsor. The comparison is described as unadjusted in the posted statistical summary.

Why does the endpoint definition matter?

The endpoint is a count of participants whose tube deviation exceeded the threshold of more than 10 mm from the initial correct position. In general, converting a measured quantity into a binary outcome can simplify interpretation around a defined threshold, but it also loses information. Participants just on opposite sides of the threshold are categorized differently despite potentially similar measurements; participants on the same side may have quite different displacement distances. The posted event comparison does not reveal those underlying distances or their direction.

The registry also describes measurements involving tracheal and bronchial distances and subtraction across positions and surgical time points. The available description does not fully specify the measurement protocol or how discordant measurements were treated. Details about assessor masking and measurement reliability are not reported in the registry record.

What can randomization support?

Random allocation is intended, in general, to reduce systematic differences between treatment groups at assignment. It does not guarantee that all observed characteristics are balanced, especially in a trial with limited endpoint counts, and it cannot address missing or unmeasured information by itself. The registry identifies the trial as randomized but does not report the sequence-generation method, concealment procedures, or planned analysis population. Without those details, the strengths and implementation of the allocation process cannot be assessed from this record.

Overall, the posted statistics compare event frequency between the randomized arms and quantify uncertainty around the observed difference. They do not establish equivalence, identify the underlying pattern of measured distances, or resolve limitations in reporting about analysis methods and participant accounting.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.008, and its 95% confidence interval ranges from -0.195 to 0.179. A confidence interval is an uncertainty summary around an estimate: under the method's assumptions, intervals constructed in this way would capture the target parameter at the stated rate over repeated studies. It is not a guarantee that the true effect lies in this particular interval, and it does not assign probabilities to individual values after observing the data.

Because the interval includes zero, the primary result is compatible with no absolute difference. Its negative and positive limits also allow differences in either direction. The limits are far from the point estimate, so the observed data do not pin down the size or direction of a possible difference precisely. The relative-effect intervals are also broad: 0.573 to 1.668 for the risk ratio and 0.424 to 2.197 for the odds ratio. Each includes the relative no-difference value of 1.

Precision depends in part on the amount of outcome information, not merely the size of the point estimate. The endpoint counts are limited in the posted groups, and the confidence interval reflects substantial uncertainty around the estimated comparison. The registry record does not report a precision target or a prespecified clinically important difference against which to judge the interval.

A non-significant p-value is not evidence that an effect is absent. Likewise, a point estimate near zero does not by itself demonstrate equivalence. To support an equivalence interpretation, a suitable margin and analysis would need to be stated in advance; these are not reported in the registry record. The most defensible reading is that the estimated difference is small in the observed groups, while the interval leaves meaningful uncertainty about the underlying difference.

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 based on the observed effect, rather than the trial's original design assumptions. The calculation assumptions listed for these illustrations are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect targeted is the stated fraction of the observed effect.

For the primary outcome, the row for planning around 100% of the observed effect gives 55,633 participants per arm for 80% power and 74,477 participants per arm for 90% power. Planning for 75% of the observed effect gives 99,034 participants per arm for 80% power and 132,578 participants per arm for 90% power. Planning for 50% of the observed effect gives 223,118 participants per arm for 80% power and 298,691 participants per arm for 90% power.

The 80% power column represents the planned probability of detecting the specified effect under the stated assumptions if that effect is real; the 90% column uses a higher target probability under those same assumptions. These are design targets, not guarantees for a future study. The curve should be read in the same planning context: smaller target effects require more participants to detect under otherwise unchanged assumptions. The displayed values are not observed power. The registry record does not report the assumptions or justification used for the trial's original design.

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 = 0.354; treatment proportion p₁ = 0.346; average p̄ = 0.350.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6746 = 1.3222.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6746 = 0.5677.
4. n = (1.3222 + 0.5677)² / (-0.0080)² = 55,632.8, rounded up to 55,633 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 <- 0.354166666666667                          # control proportion
p1 <- 0.346153846153846                          # 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(2691468)
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 = 55,633 (80% power), 74,477 (90% power)
 75% of observed effect: n per arm = 99,034 (80% power), 132,578 (90% power)
 50% of observed effect: n per arm = 223,118 (80% power), 298,691 (90% power)
power.prop.test: 55632.8 
Simulated power at n = 55,633 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 record identifies a primary endpoint and a secondary endpoint, but it does not report a formal statistical analysis plan, a testing hierarchy, or a method for controlling multiplicity. In general, when several outcomes are tested, the chance of at least one apparently unusual result can increase. Prespecifying which outcome is primary and how secondary outcomes will be interpreted helps distinguish confirmatory questions from supportive or exploratory ones. The registry identifies the primary outcome, but it does not supply enough detail to determine how the full outcome family was handled.

The record does not report whether interim analyses were planned or conducted. It also does not report the method used to generate or conceal the randomization sequence, the exact analysis population, covariate adjustment plans, or procedures for handling protocol deviations. These omissions do not demonstrate that such procedures were absent; they mean their use cannot be established from the registry record.

Missing outcome data and participant flow are not described in enough detail to assess. The recorded enrollment is 108, while the primary endpoint results use denominators of 48 for PVC and 52 for silicon. Safety results list 54 participants at risk in each arm. The registry record does not explain the difference among these reported quantities, identify exclusions or withdrawals, or state how missing observations were treated. No imputation method or sensitivity analysis is reported.

For a randomized trial, analyzing participants according to their original assignment can preserve the benefits of randomization, while other analysis populations may answer different questions. The record does not state which approach was used for the posted endpoint comparisons. Without this information, the influence of missing data, exclusions, or changes after randomization cannot be evaluated. The interpretation should remain focused on the posted denominators and the analyses actually described in the record.

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 registry reports zero serious adverse events and zero deaths in both device groups. It also reports zero other adverse events in each group. For the adverse-event summaries, 54 participants are listed at risk in each arm. No serious adverse-event terms are listed.

These figures mean that the registry record contains no recorded events in the listed categories for the stated groups. They do not show that adverse events are impossible, and they cannot establish comparative safety on their own. The record does not provide details about adverse-event definitions, surveillance procedures, severity grading, relatedness assessment, or the period of safety follow-up. It also does not explain why the safety denominators differ from the primary endpoint denominators.

Zero reported events should therefore be interpreted as a feature of the posted safety data, not as proof that either device has no risk. The available record supports only a limited description of reported serious events, other events, and deaths.

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

The posted primary result is a comparison of clinically significant displacement during a defined positioning transition in a randomized trial of PVC and silicon double-lumen tubes. The event proportions were similar in the observed groups, and the estimated absolute difference was close to zero. The confidence interval, however, spans values on both sides of no difference, so the data do not determine a precise comparative effect.

This finding does not demonstrate that the devices are equivalent. Equivalence requires a prespecified margin defining what differences would be acceptably small, together with an analysis designed to evaluate that margin. Such a margin and analysis are not reported in the registry record. Nor does the unadjusted p-value establish that the groups are identical or that a difference is absent.

The result also does not describe all features of displacement. The primary outcome applies a threshold of more than 10 mm from the initial correct position, regardless of direction. It does not show the distribution of measured distances, the direction of movement, or how often measurements fell near the cutoff. The secondary endpoint addresses critical malposition, but its presence does not overcome the uncertainty in the posted comparisons.

These results should not be generalized beyond the recorded context without additional evidence. The trial concerns thoracic surgery and a change from supine to lateral decubitus position. Details about participant characteristics, other procedures, measurement reliability, and follow-up are not reported. The registry record also does not explain the endpoint and safety denominator accounting or provide enough detail to assess missing-data handling.

In summary, the posted data show similar observed event proportions and an imprecise comparison. They do not establish a clinically important advantage, equivalence, or absence of risk for either tube. The scope of interpretation is limited to the stated endpoints, recorded groups, and registry information.

17. Why This Trial Matters Statistically

This trial illustrates the distinction between an estimate and the certainty attached to it. The observed risk difference is close to zero, but the confidence interval extends in both directions and includes values that could represent a difference favoring either group. Statistical interpretation therefore depends on the interval as well as the point estimate and p-value.

It also shows why a non-significant comparison should not be translated into equivalence. A test that does not provide evidence against no difference does not establish that meaningful differences have been ruled out. Equivalence requires a clearly defined margin and an appropriate design and analysis; the registry record does not report those features.

The endpoint itself provides a useful lesson in measurement. A threshold can make a clinical outcome easier to count and compare, but binary classification compresses information about distance and direction. Readers should understand the operational definition before assigning meaning to event rates. The registry describes a threshold of more than 10 mm, while the posted outcome comparison does not expose the underlying continuous measurements.

Finally, the record highlights the role of reporting completeness. Randomization is stated, but important details about implementation, analysis populations, missing data, multiplicity, and the original design assumptions are not reported. These gaps do not invalidate the numerical results, but they limit the conclusions that can be drawn from them. Careful reporting is essential for distinguishing a precise negative finding from an inconclusive comparison.

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 limitations specific to this trial affect interpretation. The primary endpoint is threshold-based: displacement is counted as clinically significant only when deviation exceeds 10 mm from the initial correct position. The posted results do not include the underlying distance measurements or directions of displacement, so differences in the pattern or magnitude of movement cannot be assessed from the event counts.

The registry's descriptions of the measurement process are incomplete. They identify tracheal and bronchial distances and describe comparisons across positions and surgical time points, but do not give a complete measurement protocol. Information about assessor masking, measurement reliability, and handling of inconsistent measurements is not reported in the registry record.

Participant accounting is another limitation. The record lists enrollment as 108, gives primary endpoint denominators of 48 and 52, and reports safety groups with 54 at risk in each arm. It does not explain how these numbers relate, whether participants were excluded or lacked endpoint measurements, or how any missing observations were handled. This prevents assessment of possible selection or missing-data effects.

The record provides limited information about trial conduct and analysis. It does not report detailed eligibility criteria or participant characteristics, randomization procedures, who was masked, the analysis population, covariate adjustment, or the statistical analysis plan. It also does not state how secondary outcomes and multiplicity were handled. The applicability of results beyond the stated thoracic-surgery positioning context is consequently difficult to assess.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Displacement Between PVC and Silicon DLT — NCT02691468.
• Registry record last updated 2021-08-10; status last verified 2021-08.
• Results first posted 2019-12-23.
• 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

NCT02691468 is a completed randomized, single-masked, parallel-group trial comparing PVC and silicon double-lumen endobronchial tubes during a change from supine to lateral position in thoracic surgery. Yeungnam University College of Medicine is listed as the sponsor. The registry records enrollment of 108, a study start of 2016-02, and primary completion on 2017-04-01.

The primary endpoint is the incidence of clinically significant displacement, defined as deviation of more than 10 mm from the initial correct position. The posted event proportions were similar, with an estimated risk difference of -0.008 and a 95% confidence interval from -0.195 to 0.179. The interval includes no difference and remains broad.

The record also includes critical malposition as a secondary outcome and reports no serious adverse events, other adverse events, or deaths in the listed safety groups. Details about participant accounting, missing data, analysis methods, and the original sample-size rationale are not reported in the registry record.