This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for GlideScope®Video Laryngoscope for Difficult Intubation: Implication of the Size of Blade (NCT01616771), a na na study. The primary outcome is The Differences in the Glottis View (C&L Grade) of Macintosh Laryngoscope and GVL Selected by Weight..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01616771 |
| Phase | NA |
| Condition | Intubation; Difficult |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 23 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Seoul National University Hospital |
| Results posted | Yes |
2. Clinical Question
Population
Patients whose airway management was anticipated to be difficult, described in the record as C&L grade ≥3. The study enrolled 23 participants. Further participant characteristics are not reported in the registry record.
Intervention
Glottic view was assessed using a GlideScope video laryngoscope blade selected according to the patient’s weight. A smaller-sized GlideScope blade was also assessed.
Comparator
The primary comparison was the Macintosh laryngoscope versus the GlideScope blade selected by weight. The secondary comparison was the weight-selected GlideScope blade versus the smaller-sized GlideScope blade. Assessments were described as occurring in the same patients.
Primary question
How did the modified C&L glottis-view grade with the weight-selected GlideScope compare with the grade using the Macintosh laryngoscope? The record also asks whether the smaller GlideScope blade differed in glottic view from the weight-selected blade.
The focus is the view of the glottis during laryngoscopy, rather than a reported measure of successful intubation or a patient health outcome. The record describes an assessment in patients with anticipated difficult airways and lists two glottis-view outcomes. It does not report numerical outcome estimates, so the direction and magnitude of either comparison cannot be established from the registry record.
3. Trial Design
This was a completed, single-group study sponsored by Seoul National University Hospital. The registry lists enrollment of 23 and study dates from 2011-02 to primary completion in 2012-01. The phase is listed as NA, allocation as NA, and masking as none. The record describes the assessments as being made in a single patient using a Macintosh laryngoscope, a GlideScope blade selected by weight, and a smaller-sized GlideScope blade.
This is not a randomized comparison. The record’s study description identifies assessments in the same patients, rather than separate randomized groups. Consequently, the device assessments should not be read as a comparison between independent treatment arms or as a like-for-like randomized control comparison. The order of device assessments, any rules governing that order, and whether the same sequence was used for every participant are not reported in the registry record.
The primary outcome was the difference in modified C&L grade between the Macintosh laryngoscope and the weight-selected GlideScope. The secondary outcome was the difference in grade between the weight-selected and smaller-sized GlideScope blades. The primary outcome timeframe was up to 1 day of surgery. The registry identifies two outcome measures and two analyses, but does not report a detailed statistical analysis plan, sample-size justification, or procedures for handling repeated measurements.
The enrollment figure and the safety denominators are not identical for all device assessments: the record lists 23 participants at risk for the Macintosh and weight-selected GlideScope groups, and 19 for the smaller-sized blade. The reason for the smaller denominator is 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.
Macintosh Laryngoscopy for 5 Sec
| Stage | Glottis View Assessment |
|---|---|
| STARTED | 23 |
| COMPLETED | 23 |
| NOT COMPLETED | 0 |
GVL Selected by Weight for 5 Sec
| Stage | Glottis View Assessment |
|---|---|
| STARTED | 23 |
| COMPLETED | 23 |
| NOT COMPLETED | 0 |
Smaller Sized GVL for 5 Sec
| Stage | Glottis View Assessment |
|---|---|
| STARTED | 23 |
| COMPLETED | 19 |
| NOT COMPLETED | 4 |
Reasons for not completing this period:
| Reason | Glottis View Assessment |
|---|---|
| lack of GVL size | 4 |
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.
| Characteristic | Unit | Glottis View Assessment |
|---|---|---|
| Participants analysed | 23 | |
| Age, Categorical: <=18 years | Participants | 23 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 |
| Age, Categorical: >=65 years | Participants | 0 |
| Age, Continuous | years | 7.9 (SD 4.8) |
| Sex: Female, Male: Female | Participants | 10 |
| Sex: Female, Male: Male | Participants | 13 |
6. Primary Endpoint
The registry lists the primary outcome as The Differences in the Glottis View (C&L Grade) of Macintosh Laryngoscope and GVL Selected by Weight., measured over up to 1 day of surgery.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | 95% Confidence Interval |
| Unit | units on a scale |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the difference in glottic view, scored with a modified C&L grade, between Macintosh laryngoscopy and the GlideScope blade selected by weight. The modified grades describe how much of the glottic aperture or surrounding structures can be seen. For analysis, grade 1 was assigned a score of 1; grade 2a, 2; grade 2b, 3; grade 3a, 4; grade 3b, 5; and grade 4, 6. The reported score range is 1 to 6, with 1 representing the best view and 6 representing no view.
A graded view is useful as an endpoint because it records the visibility encountered during laryngoscopy, including distinctions among partial views. The ordered categories carry a natural ranking, but the distances between adjacent categories are not necessarily equal. The registry specifies a median and 95% confidence interval as the summary format. It does not report the actual median, confidence interval, or numerical comparison for the primary outcome, so the observed view difference and its precision are not available from the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes a comparison of laryngoscopic views in patients with anticipated difficult airway management. Its primary question concerns modified C&L grades observed with a Macintosh laryngoscope and a weight-selected GlideScope blade. The secondary question concerns the weight-selected and smaller-sized GlideScope blades. The record states that these assessments were made in the same patients, making the within-patient nature of the study important when interpreting the comparisons.
Numerical results for the primary and secondary glottis-view outcomes are not reported in the registry record. Although the primary outcome is specified as a median with a 95% confidence interval, the reported median, interval limits, and any numerical contrast are absent. The record therefore does not establish whether the views differed, how large any observed difference was, or how precisely a difference was estimated. No direction of effect should be inferred from the outcome descriptions alone.
The scale is ordinal: lower scores represent better views, and higher scores represent poorer views. A difference in the score summarizes a change in ranked categories, not necessarily a uniform change in visual access. In general, a confidence interval describes the uncertainty around an estimate under the assumptions of the analysis; it is not a guarantee that the true value lies within the interval. Without the interval limits and the analysis details, the precision of the primary estimate cannot be assessed.
The study is listed as single-group, with no masking and allocation marked NA. It is not a randomized comparison, and the device assessments were made in the same patients. This design can describe the views recorded under each device assessment, but does not remove possible effects of assessment order, operator experience, or other procedural conditions. Whether such factors were controlled or accounted for is not reported in the registry record.
The adverse-event entries list zero serious adverse events for each device assessment, with 23 participants at risk for the Macintosh and weight-selected GlideScope assessments and 19 for the smaller-sized blade. These entries describe the recorded serious adverse-event counts; they do not supply the missing view outcomes or resolve the limitations of the non-randomized design. Death counts are not reported in the registry record.
9. Statistical Methods Explained
The endpoint uses an ordered categorical scale, converted to numerical scores from 1 to 6. The conversion preserves the ranking stated in the registry: 1 is the best view and 6 is no view. It makes the categories convenient to summarize, but does not by itself make the underlying scale continuous or establish that the change from one category to the next has a constant meaning.
What does a median represent for an ordered grade?
In general, the median identifies the middle of an ordered set of observations. For an ordinal endpoint, it can communicate a typical position in the category ranking without assuming that category intervals are equal. The registry specifies the median as the primary summary and a 95% confidence interval as its dispersion measure. The numerical median and confidence interval are not reported in the registry record, so the central grade and its uncertainty cannot be reviewed.
How should a confidence interval be read?
In general, a confidence interval expresses the uncertainty associated with an estimate under a specified statistical procedure and its assumptions. A narrower interval indicates greater precision than a wider interval for the same estimand and method. The interval does not represent the range of individual participant scores, and it does not by itself show whether the comparison is clinically important. Here, the interval limits and the precise estimate are not reported in the registry record. The method used to calculate the interval is also not reported.
Why does the within-patient structure matter?
The study description says that the device assessments were performed in the same patients. In general, measurements on one person are often related: a participant’s airway characteristics can affect more than one device assessment. A paired analysis can account for that relationship, whereas treating the observations as independent may give an inappropriate estimate of uncertainty. The registry record does not identify the statistical test or model used, nor does it explain how within-patient dependence was handled. It is therefore not possible to determine whether the reported analysis, if any, accounted for the repeated assessments in an appropriate way.
For an ordinal outcome, possible methods in general include paired procedures based on ranks, ordinal regression approaches, or summaries of within-person category changes. These are examples of general statistical approaches, not methods attributed to this study. The registry record does not identify which approach was used or report enough outcome data to reproduce an analysis.
What does over-dispersion mean in general?
Over-dispersion arises when observed variability is greater than a statistical model expects. In general, ignoring it can make standard errors too small and confidence intervals too narrow. It is most relevant when a model’s variance assumptions do not match the data. The registry record does not describe a count model, an over-dispersion assessment, or a variance adjustment for the glottis-view outcomes; no conclusion about over-dispersion in this study can be drawn.
The record describes the primary outcome as a difference in grades, but does not specify the exact estimand or its calculation. For example, it does not state whether the contrast was based on a difference between group-level medians, a paired participant-level summary, or another method. That distinction matters because different estimands answer different questions and can have different uncertainty estimates.
The record’s planning assumptions describe an illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. For time-to-event outcomes, the illustration gives total events; for other outcomes, it gives participants per arm. Such calculations are planning illustrations, not observed power, and the registry record does not report the specific illustration values or the trial’s own sample-size justification. The study’s actual assessment structure is single-group and within-patient, so the stated equal-allocation assumption should not be mistaken for a description of the study design.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists two outcome measures and two analyses: the primary comparison of Macintosh laryngoscopy with the weight-selected GlideScope and the secondary comparison of the two GlideScope blade sizes. Considering more than one outcome or comparison raises a multiplicity question because the chance of at least one apparently notable finding can increase when many tests are conducted. In general, studies may prespecify a hierarchy of outcomes or adjust for multiple comparisons, but whether either approach was planned or used is not reported in the registry record. No multiplicity-adjusted results or analysis procedures are reported.
The registry record does not report a statistical analysis plan, a prespecified analysis population, or rules for excluding or retaining observations. It also does not describe how missing outcome grades were handled, whether all enrolled participants contributed to each endpoint, or why the smaller-sized blade safety denominator is 19 while the other denominators are 23. The outcome-specific participant counts and any missing-data analysis are not reported in the registry record.
In general, missing observations can affect an estimate when their absence is related to participant characteristics or the outcome. The impact depends on how many observations are absent, why they are absent, and the analysis method. Those details are not available for these glottis-view outcomes. Consequently, the registry information does not support an assessment of missing-data bias or a determination of whether the analyzed participants corresponded to a prespecified population.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Macintosh Laryngoscope | 0 | 23 | 0.0% |
| GVL Selected by Weight | 0 | 23 | 0.0% |
| Smaller Sized GVL | 0 | 19 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Macintosh Laryngoscope | 0 of 23 |
| GVL Selected by Weight | 0 of 23 |
| Smaller Sized GVL | 0 of 19 |
The adverse-event entries list 0 serious adverse events among 23 participants at risk for the Macintosh laryngoscope assessment, and 0 among 23 for the weight-selected GlideScope assessment. For the smaller-sized GlideScope assessment, the entry lists 0 serious adverse events among 19 participants at risk. These are the recorded counts and denominators for the respective device assessments; they should not be treated as evidence that the risk is absent.
In general, an event count of zero in a limited group does not establish that an event cannot occur. The amount of uncertainty depends in part on the number of people observed and the completeness of event ascertainment. The registry record does not report further detail about adverse-event definitions, monitoring procedures, or follow-up beyond the listed assessment context. Death counts are not reported in the registry record. The safety entries also do not answer the primary question about comparative glottic view.
12. What the Result Does, and Does Not, Mean
The record documents a study of laryngoscopic view assessments using a Macintosh laryngoscope and two GlideScope blade choices in patients with anticipated difficult airway management. It identifies modified C&L grade as the primary endpoint, describes how the ordered grades were converted to scores, and specifies a median with a 95% confidence interval as the primary summary. It also identifies a secondary comparison between the two GlideScope blade sizes.
Those descriptions define the questions and the measurement approach, but do not show the observed answers. Numerical results for either glottis-view comparison are not reported in the registry record. There is therefore no basis in this record for stating which device produced a better view, whether the difference was large or small, or how precise an estimate was. The absence of numerical outcome estimates is not evidence of no difference.
The study’s single-group, same-patient description is relevant to how the assessments may be compared. In general, within-person comparisons can reduce the influence of stable differences between participants, but assessment order or procedural conditions can still matter. The record does not report those details or the statistical method used to account for repeated measurements. The findings also cannot be treated as a randomized comparison, because allocation is listed as NA and the study is not randomized.
The adverse-event counts are zero in the listed assessment groups, but the record does not report deaths or further safety details. These entries should be read as recorded counts, not as proof that no risk exists. Overall, the registry establishes the study questions and some design and safety details, while leaving the main comparative outcome results unavailable.
13. Why This Trial Matters Statistically
This study is statistically notable for using repeated assessments within a single group rather than assigning participants to separate randomized device groups. That structure makes the relationship between measurements important: each participant was assessed with the Macintosh laryngoscope and the weight-selected GlideScope, with a smaller-sized GlideScope also assessed. The registry description says the assessments were made in the same patients, but does not report how the paired observations were analyzed.
The endpoint also illustrates a common issue in clinical measurement. The modified C&L grades are ordered categories, and the registry maps them onto scores from 1 to 6. That numerical coding preserves the grade ranking, but analysis should still respect the ordinal character of the underlying measure. The record names a median and confidence interval, yet does not report their values or the method used to calculate them.
Transparency about outcome estimates and analysis methods is essential for judging both the size and precision of a comparison. In this case, the registry lists two view outcomes but does not report numerical results, the analysis procedure, or multiplicity handling. This limits what can be concluded, even though the study question and outcome scale are described. The record is therefore useful for understanding the intended comparisons and their design context, while not allowing statistical evaluation of the primary or secondary effect estimates.
14. 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 central limitation is that numerical results for the primary and secondary glottis-view outcomes are not reported in the registry record. The median, 95% confidence interval, numerical contrast, and details needed to interpret either comparison are absent. As a result, effect direction, magnitude, and precision cannot be assessed.
The study is described as single-group and non-randomized, with all device assessments made in the same patients. This structure does not provide a randomized control comparison. The assessment sequence, operator details, and whether order or other procedural factors were addressed are not reported in the registry record. Nor is the statistical method for accounting for repeated observations identified.
The registry lists enrollment of 23, while the smaller-sized blade safety denominator is 19. The reason for this difference and the endpoint-specific analysis populations are not reported. Missing-data definitions and handling are also not reported. The record does not give a sample-size justification or a detailed statistical analysis plan, and it does not describe multiplicity procedures for the two outcomes. These omissions limit assessment of both the reliability of any comparison and the possibility of selective or incomplete reporting.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: GlideScope®Video Laryngoscope for Difficult Intubation: Implication of the Size of Blade — NCT01616771.
- Registry record last updated 2014-11-04; status last verified 2014-11.
- Results first posted 2014-11-03.
- 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.
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18. Record Summary
NCT01616771 is a completed, single-group study sponsored by Seoul National University Hospital, with enrollment of 23. It evaluated modified C&L glottic-view grades using a Macintosh laryngoscope, a weight-selected GlideScope blade, and a smaller-sized GlideScope blade in patients with anticipated difficult airway management. The primary comparison was Macintosh versus weight-selected GlideScope; the secondary comparison was between GlideScope blade sizes.
The primary endpoint was specified as a median with a 95% confidence interval, using scores from 1 to 6, where 1 represents the best view and 6 represents no view. Numerical results for the view outcomes and the analysis methods are not reported in the registry record. The listed serious adverse-event counts are 0 for each assessment group; deaths are not reported.