Efficacy Study of a Novel Device to Clean the Endotracheal Tube: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy Study of a Novel Device to Clean the Endotracheal Tube (NCT01765530), a randomized na study. The primary outcome is Percentage of Occlusion Assessed Using a High Definition Computed Tomography Imaging of the Extubated ETTs.

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group study of a device-based endotracheal-tube cleaning maneuver. Its listed phase is NA, and its status is completed. Massachusetts General Hospital is listed as the sponsor. The registry enrollment is 74. The reported primary-outcome arms each have an analyzed count of 36; the record does not explain the relation between the enrollment figure and those arm counts.

Patients assigned to the cleaning group were to receive the endOclear maneuver three times a day (every 8 hours) for the whole intubation period, alongside standard care. The control group had no planned study intervention and was to receive blind suctioning as determined by caregiver clinical decision. The registry identifies the masking as single, but does not report who was masked or how masking was maintained. Allocation concealment and other implementation details are not reported in the registry record.

The primary outcome was measured at extubation, with an expected average timeframe of 5 days. The registry also lists endotracheal-tube microbiology as a secondary outcome at the same expected timeframe. The record does not report the original statistical design assumptions, the planned sample size, or whether there were interim analyses. It lists no reported analyses for the secondary outcome. These omissions limit what can be inferred about the study's prespecified analytical procedures.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Occlusion Assessed Using a High Definition Computed Tomography Imaging of the Extubated ETTs, measured over At extubation (An expected average of 5 days).

The primary endpoint is the percentage of occlusion in the lumen of an endotracheal tube after extubation. The registry says the investigators assessed this by imaging extubated tubes with high-definition computed tomography, analyzing the whole tube through CT slices. The measure represents secretion accumulation within the tube lumen. The registry defines 0% as absence of occlusion and 100% as total occlusion.

This endpoint was selected to quantify the physical condition of the tube lumen at the end of intubation, rather than to directly measure a patient-centered clinical outcome. A continuous measure can retain information about variation in occlusion across tubes instead of reducing the observation to a simple present-or-absent category. The group means describe average occlusion, while the standard deviations describe how dispersed individual observations were around those averages.

The measurement is tied to extubation: it captures the tube's observed condition when it is removed, not a continuously monitored change over time. The registry gives the expected average timeframe as 5 days. It does not report how imaging measurements were read, whether readers were blinded to assignment, or how reproducibility of the measurement was assessed.

7. Results Posted in the Registry

• ETT Cleaning Manuver: mean 10.60 versus 17.70 on control; difference -7.10 (95% CI -12.20 to -2.00), standardized effect d = -0.64; z-test p = 0.006.

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.

ETT Microbiology

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • ETT Cleaning Manuver: mean 2.89 versus 3.35 on control; difference -0.46 (95% CI -1.80 to 0.88), standardized effect d = -0.16; z-test p = 0.502.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between ETT Cleaning Manuver and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists endotracheal-tube microbiology, measured as log colony-forming units per milliliter at extubation, as a secondary outcome. Across the primary and secondary outcomes, the reported group means have the same broad direction: the cleaning arm has a lower mean than standard care. The uncertainty and inferential support differ across outcomes, however, so this directional pattern should not be treated as equally strong evidence for each measure.

The secondary outcome is related to the primary question because both concern endotracheal tubes at extubation, but they measure different features. The primary endpoint quantifies physical lumen occlusion from secretion accumulation; microbiology concerns organisms measured in a sample. A lower value on one measure does not establish a corresponding change in the other, and neither measure alone establishes an effect on clinical outcomes.

The registry reports no analyses for the secondary endpoint in its analysis listings. The posted summary comparison is unadjusted, and the record does not report whether secondary testing was prespecified, how many hypotheses were considered in the full study, or how multiplicity was handled. When several outcomes are tested, the chance of observing a seemingly notable result by chance can increase. Without a reported strategy for controlling that issue, secondary findings generally warrant more cautious interpretation than a prespecified primary comparison.

Accordingly, the secondary result can be viewed as contextual information that may help describe the pattern of measured outcomes, but it should not be used as independent confirmation of the primary endpoint. A coherent direction across measures can motivate further study, yet the distinct constructs, uncertainty, and unreported analysis details remain important.

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

• ETT Microbiology

9. Statistical Interpretation

10. Statistical Methods Explained

The main outcome is continuous: each assessed tube has a percentage-occlusion measurement, and the registry reports the mean and standard deviation for each arm. A mean difference compares the arm averages on the original measurement scale. Here, the estimate is expressed as cleaning minus standard care, so a negative difference corresponds to a lower mean percentage of occlusion in the cleaning arm.

What does the standard deviation describe?

The standard deviation summarizes how spread out observations are around a group mean. It is not the uncertainty of the mean itself, and it is not a range containing every observed tube. A larger standard deviation indicates greater variation among the observations in that arm. The primary outcome standard deviations are 8.0 in the cleaning arm and 13.4 in standard care. This difference in spread is worth noting when reading the mean contrast: averages compress the distribution of observations into a single summary.

Standard error and standard deviation answer different questions. The standard deviation characterizes variation among observations. A standard error characterizes the estimated uncertainty of a statistic, such as an arm mean. The registry reports standard deviations for the primary outcome and standard errors for the secondary microbiology outcome. These measures should not be read interchangeably. In particular, the primary outcome's standard deviations do not directly give the confidence interval for the mean difference.

How should the mean difference be read?

The estimated difference is a contrast between two group means, not a measure of the change experienced by each participant. Its sign depends on the order of subtraction. Because the comparison is stated as cleaning minus standard care, a negative value indicates a lower mean in the cleaning arm. The estimate of -7.1 is in percentage points of occlusion, not a relative percentage change. No ratio or relative reduction is reported in the registry record.

The confidence interval around the estimate represents uncertainty under the calculation method used. It gives a range of plausible values for the mean difference under the model and sampling assumptions behind the interval. It should not be interpreted as the range of individual outcomes, nor as a guarantee that the true difference lies inside it. The reported interval is from -12.2 to -2.002. Since zero is outside this interval, the interval is consistent with a negative mean difference under that method.

What does the p-value contribute?

The unadjusted p-value is 0.006. A p-value describes how incompatible the observed data, or data more extreme, would be with a specified no-difference model, assuming the model and its assumptions hold. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of the observed contrast. The word unadjusted matters: the registry does not report whether this result was adjusted for testing multiple outcomes or other analyses. Thus, it should not be mistaken for a multiplicity-adjusted result.

The posted comparison is an unadjusted comparison based on summary statistics. The registry does not report a covariate-adjusted model for this endpoint, or a detailed statistical analysis plan. It also does not report whether any model checks or alternative analyses were prespecified. Without those details, interpretation should stay close to the reported arm summaries and comparison rather than assume a more elaborate model.

Why can spread and distribution matter?

Mean-based methods summarize group differences efficiently when their assumptions are suitable, but a mean alone may conceal skewness, outliers, or clusters of observations. The registry does not report distribution plots or details that would allow those features to be evaluated. Greater spread in one group can also affect the precision of a contrast. The posted confidence interval reflects the calculation used for the comparison; the registry does not provide enough methodological detail to independently assess all its assumptions.

In general, over-dispersion means that observed variability is greater than a model assumes. If a model understates variability, its standard errors can be too small and confidence intervals too narrow. This is a general statistical consideration, not a finding that over-dispersion occurred in this trial. The record does not describe a count model for the primary endpoint; the endpoint is reported as a continuous percentage and summarized with means and standard deviations.

What is and is not established by randomization?

Random allocation can support a fair comparison by reducing systematic differences between groups on average, but it does not ensure that every aspect of conduct is free from bias. Information about allocation procedures, the identity of masked personnel, adherence to the assigned maneuver, and missing observations is not reported in the registry record. The available summaries therefore support interpretation of the posted randomized comparison, while leaving important implementation and analysis questions unresolved.

11. Confidence Intervals and Precision

The primary mean difference is -7.1 percentage points, with a confidence interval from -12.2 to -2.002. The interval expresses uncertainty around the estimated average contrast, conditional on the calculation method and its assumptions. It is distinct from the observed spread among tubes, which is described by the arm standard deviations.

Because the confidence interval does not include zero, the reported data are compatible with a negative average difference under the interval method. The width of the interval also matters: it includes values representing differences of varying magnitude, rather than identifying a single exact effect. Precision is therefore not the same as certainty about the exact difference. The point estimate is the center of the reported comparison, while the interval communicates how much uncertainty remains around it.

The registry does not state the confidence level or provide detailed calculation methods for the interval, so those should not be inferred beyond the posted values. It also does not report a prespecified threshold for a clinically meaningful change. Statistical evidence of a difference and evidence that a difference matters clinically are separate questions. The imaging endpoint alone cannot resolve the latter.

For the secondary microbiology outcome, the reported interval includes values on both sides of no difference. That means the posted estimate is less precise about the direction and magnitude of the contrast. Its uncertainty should be considered alongside the lack of a reported multiplicity plan and the registry's statement that no analyses are listed for that outcome.

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, not the original design assumptions for this trial; those original assumptions are not reported in the registry record. The illustration uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect.

The 80% power column gives the number of participants per arm estimated to provide an 80% chance of detecting the specified effect under those planning assumptions, if that effect is the true one and the assumptions hold. The 90% power column uses a higher target chance of detection, which generally requires more participants per arm for the same assumed effect. The figures are planning estimates, not observed power; observed power is not a way to establish the strength or reliability of the completed trial result.

Rows for planning at 100%, 75%, and 50% of the observed effect illustrate how the assumed target changes the required sample size. Smaller effects are harder to distinguish from random variation and need more participants to detect at a given power target. The estimates are not evidence that the trial was designed around these effect fractions, nor do they establish that the actual trial had a particular chance of finding a result. The registry record does not report the trial's own sample-size justification or design assumptions.

These calculations also rely on a simplified normal approximation and equal allocation. They should be treated as planning aids rather than an exact forecast of performance under every possible trial design or analysis. The primary outcome and secondary microbiology outcome have different observed effects and variability, so their planning illustrations need not be alike.

13. How the Sample Size Is Derived

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

Formula

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

Worked calculation for this trial

1. Observed difference Δ = -7.100; pooled standard deviation σ = 11.035.
2. n = 2 × (1.96 + 0.842)² × 11.035² / -7.100² = 37.9, rounded up to 38 participants per arm for 80% power.

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

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -7.1                      # observed difference in means
sigma <- 11.0353975913875                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

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

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1765530)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 38 (80% power), 51 (90% power)
 75% of observed effect: n per arm = 68 (80% power), 91 (90% power)
 50% of observed effect: n per arm = 152 (80% power), 204 (90% power)
power.t.test: 38.9 
Simulated power at n = 38 per arm: 0.795 (20000 replicates)

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

14. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when statistical tests are conducted across multiple outcomes, time points, subgroups, or analytical choices. If each test is judged separately without adjustment, the chance of at least one apparently notable finding can rise. The registry identifies a primary outcome and a secondary microbiology outcome, but does not report a family of hypotheses or a plan for controlling multiplicity. It is therefore not possible to determine whether the posted unadjusted p-values reflect a prespecified testing hierarchy or an adjustment strategy.

The primary result is reported with an unadjusted p-value. No multiplicity-adjusted result is reported in the registry record. The secondary outcome has no reported analysis listing, and its comparison is also described as unadjusted in the posted summary. The absence of a reported adjustment does not prove that none was considered outside the registry, but the registry record does not establish one. The results should be interpreted with that uncertainty in mind.

Missing-data procedures are also not reported in the registry record. The posted arm summaries include 36 observations for each arm, but the record does not explain whether all randomized participants contributed outcome data, whether any measurements were excluded, or how missing outcomes were handled. The enrollment figure is 74, and the registry does not reconcile it with the outcome arm counts. It would be inappropriate to infer the reason for that difference from the record alone.

The analysis population is not reported in the registry record. In particular, the available information does not identify whether the reported summaries follow an intention-to-treat population, a per-protocol population, or another defined set of participants. The record also does not describe adherence, crossovers, or exclusions after randomization. These details can affect how closely an estimate represents the effect of assignment versus the effect among those who received or completed the maneuver.

The listed single masking designation does not specify who was masked. The registry does not describe masking of CT image readers or microbiology assessors, and it does not provide an assessment of measurement reliability. These are uncertainties about reporting, not evidence that masking or measurement procedures were inadequate.

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.

The adverse-event record lists zero serious adverse events and zero other adverse events in the cleaning arm, with 36 participants at risk for each category. It also lists zero serious adverse events and zero other adverse events in standard care, with 36 participants at risk for each category. Deaths are not reported in the registry record.

These entries describe what the registry reports for the defined adverse-event categories and at-risk groups. They do not establish that no adverse events of any kind occurred, since the record may not include every event type or detail of ascertainment. Nor do zero recorded events prove that the intervention carries no risk. With no serious events recorded in either arm, the registry does not provide an observed between-arm difference for that category.

The record does not describe the adverse-event collection period, definitions, monitoring process, or handling of events after extubation. Those details would be needed to assess the completeness and sensitivity of safety surveillance. The adverse-event figures should therefore be read narrowly as registry-reported counts, not as a definitive safety conclusion.

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

The result describes a randomized comparison of mean endotracheal-tube lumen occlusion at extubation. The cleaning group had a lower reported mean than the standard-care group, and the posted unadjusted mean difference and confidence interval are consistent with a negative average contrast. This is evidence about the measured tube outcome in the reported study arms.

It does not demonstrate that every tube in the cleaning group was less occluded, or that the cleaning maneuver changed an individual patient's course. Group averages do not show the full distribution of outcomes, and the registry does not provide individual-level data. The result also does not directly answer whether the device changes rates of pneumonia, airway obstruction, duration of ventilation, or other clinical outcomes. Although these conditions appear in the registry, they are not the primary endpoint described in the posted results.

The finding should not be translated into a claim of clinical benefit or lack of benefit. The endpoint is a CT-based measure of tube occlusion, and the registry does not report a threshold that defines a clinically important difference. It also does not report patient-centered outcomes that would connect the measured lumen condition to symptoms or subsequent health events.

The inference is limited by information not reported in the registry record, including the original sample-size justification, detailed analysis plan, missing-data handling, analysis population, and multiplicity strategy. The registry reports a single masking designation without identifying who was masked. These omissions make it difficult to assess the full robustness and generalizability of the findings. They do not erase the reported comparison, but they limit how far it can be extended beyond the specific outcome and analysis presented.

Overall, the posted data indicate a lower mean occlusion measurement in the endOclear group at extubation, with uncertainty expressed by the confidence interval. That statistical result is not equivalent to proof of improved clinical outcomes, nor does it by itself establish the balance of benefits and risks. Any broader interpretation would require evidence beyond this endpoint and fuller reporting of trial conduct and analysis.

17. Why This Trial Matters Statistically

This study is statistically useful because it applies a randomized parallel-group design to a device intended to remove secretions from endotracheal tubes, and it defines a measurable physical endpoint at extubation. A continuous percentage-occlusion measure retains distinctions in degree, which allows group means and their uncertainty to be compared rather than recording only whether a tube met a threshold.

The results also illustrate why an effect estimate should be read alongside its uncertainty and the variability of the observations. The mean difference summarizes the average contrast, the confidence interval conveys uncertainty in that contrast, and the standard deviations describe variation among tube measurements. These quantities answer related but different questions. A p-value alone cannot replace them or communicate clinical importance.

The registry's primary and secondary outcomes address different aspects of the tube. Considering more than one measure may help describe the evidence, but interpretation depends on knowing which comparisons were planned and how multiplicity was handled. The record does not report that strategy. This makes the study a useful example of why a clear hierarchy of outcomes and transparent analysis reporting matter for interpreting a set of results.

Finally, the record shows the value of separating a device-related physical measurement from clinical outcomes. The posted result concerns occlusion assessed on extubated tubes. It does not automatically establish changes in patient outcomes. Making that distinction is important in biostatistical reporting: a precise description of what was measured, what was estimated, and what remains unreported helps prevent an endpoint result from being overstated.

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 does not report detailed eligibility criteria, participant characteristics, or the clinical settings in which the study was conducted. As a result, the applicability of the reported comparison to other patient groups or care settings cannot be fully assessed from this record. The enrollment figure and outcome arm counts are both listed, but the record does not explain their relationship.

The intervention was specified as repeated cleaning throughout intubation, but adherence to that schedule, the actual number of maneuvers received, and deviations from the assigned approach are not reported. The control description allows blind suctioning according to caregiver clinical decision, so the record does not characterize the frequency or timing of that care. These details could be relevant to understanding the contrast between assigned groups.

The primary measurement relies on CT imaging of extubated tubes. The registry does not report who assessed the images, whether readers were masked to group, how the imaging protocol was standardized, or whether measurement reliability was evaluated. It also does not report whether the full tube could be assessed in every case or how incomplete imaging would have been handled.

Additional limitations are the lack of reported missing-data methods, analysis population, original design assumptions, and multiplicity plan. The record lists a secondary microbiology outcome but no reported analyses for it. The masking designation does not identify which people were masked, and deaths are not reported in the adverse-event record. These are reporting gaps; they should not be converted into assumptions about what occurred.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Efficacy Study of a Novel Device to Clean the Endotracheal Tube — NCT01765530.
• Registry record last updated 2017-10-18; status last verified 2017-04.
• Results first posted 2017-03-29.
• 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

The registry record describes a completed, randomized, single-masked, parallel-group device study sponsored by Massachusetts General Hospital. It lists enrollment of 74 and identifies endoClear endotracheal-tube cleaning as the intervention, compared with standard care.

The primary outcome was percentage of tube-lumen occlusion measured from extubated tubes using high-definition CT. The reported mean was 10.6 in the cleaning arm and 17.7 in standard care; the unadjusted mean difference was -7.1, with a confidence interval from -12.2 to -2.002 and an unadjusted p-value of 0.006. Endotracheal-tube microbiology is listed as a secondary outcome.

The registry reports no serious or other adverse events in either arm, while deaths are not reported in the registry record. The original sample-size assumptions, analysis population, missing-data procedures, multiplicity plan, and detailed masking procedures are also not reported in the registry record.