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 Cognitive Effects of Inhalational Versus Intravenous General Anesthesia in the Elderly (NCT00788008), a randomized na study. The primary outcome is Change in Neurocognitive Performance (Z-score).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00788008 |
| Phase | NA |
| Condition | Lumbar Spondylosis, Cervical Spondylosis, Hip Osteoarthritis |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 200 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Duke University |
| Results posted | Yes |
2. Clinical Question
Population
Elderly people undergoing surgery in the context of lumbar spondylosis, cervical spondylosis, hip osteoarthritis, or knee osteoarthritis. The registry record does not report an age range or other detailed eligibility criteria.
Intervention
General anesthesia using inhaled isoflurane.
Comparator
Total intravenous anesthesia using propofol.
Primary question
Does mean change in composite neurocognitive performance, measured as a z-score, differ between the anesthesia approaches at 3 months post operatively?
The clinical question focuses on postoperative cognition rather than surgical outcomes or immediate recovery. The registry’s brief description frames the comparison as whether cognition after surgery will be better with inhaled anesthesia or intravenous anesthesia. The registered primary measure is change in neurocognitive performance, with memory and executive-function measures contributing to composite scores. A positive change is described as improvement in function.
The record identifies the treatment approaches and assessment timeframe, but it does not report the observed cognitive changes in either group, a between-group difference, or an uncertainty interval. It therefore establishes what the trial set out to compare, but the registry record does not give the numerical result needed to judge the direction, size, or precision of any difference. The primary question is identifiable; its answer is not reported in the registry record.
3. Trial Design
The registry describes a randomized, parallel-group trial with no masking. Participants were assigned to inhalational anesthesia with isoflurane or total intravenous anesthesia with propofol. The listed enrollment is 200, and the study status is completed. The phase is listed as not applicable. Duke University is identified as the sponsor.
The study start is recorded as 2008-11 and primary completion as 2013-12. The record places the trial in the context of lumbar spondylosis, cervical spondylosis, hip osteoarthritis, and knee osteoarthritis. These conditions indicate the surgical context, but the record does not provide detailed eligibility criteria, the specific operations performed, or how many participants underwent each type of surgery.
Randomization is intended to support a fair comparison by assigning treatment without choosing the group according to participant characteristics. That design can reduce systematic differences between groups, although it does not guarantee that the groups are identical. The record does not describe the randomization sequence, allocation concealment, or procedures used to maintain assignment concealment before treatment.
The trial is listed as unmasked. Participants and clinicians may therefore have known which anesthetic approach was used, but the registry record does not describe who knew assignments or whether outcome assessors were masked. This matters when outcomes involve cognitive testing, because knowledge of treatment assignment could potentially influence how assessments are administered or interpreted. No such influence can be established from the registry record.
The parallel design means the two approaches were assigned to separate groups rather than being compared within the same participant. The record does not report the protocol, the planned statistical analysis, or a sample-size justification. Completion status and enrollment do not by themselves establish that the primary outcome was analyzed or reported.
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: 200 patients were consented. One person dropped out prior to baseline testing.
Overall Study
| Stage | Isoflurane | Propofol |
|---|---|---|
| STARTED | 98 | 101 |
| COMPLETED | 98 | 101 |
| NOT COMPLETED | 0 | 0 |
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 | Isoflurane | Propofol | Total |
|---|---|---|---|---|
| Participants analysed | 98 | 101 | 199 | |
| Age, Continuous | years | 73.38 (66 to 86) | 73.13 (65 to 91) | 73.25 (65 to 91) |
| Sex: Female, Male: Female | Participants | 32 | 39 | 71 |
| Sex: Female, Male: Male | Participants | 66 | 62 | 128 |
| Region of Enrollment: United States | participants | 98 | 101 | 199 |
6. Primary Endpoint
The registry lists the primary outcome as Change in Neurocognitive Performance (Z-score), measured over 3 months post operatively.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | z score |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled “Change in Neurocognitive Performance (Z-score)” and is described as mean change on composite scores for memory and executive function measures. The assessment timeframe is 3 months post operatively. Memory measures are the Hopkins Verbal Learning Test-Revised and the Brief Visuospatial Memory Test-Revised. Executive-function measures include the Trail Making Test, Digit-symbol substitution and Symbol Search subtests of the Processing Speed Index of the Wechsler Adult Intelligence Scale-III, and the Controlled Oral Word Association subtest of the Multilingual Aphasia Examination.
The registry describes the outcomes as summed z-score composites scaled in standard deviations. A score of 0 is central on each composite; the record states that 95% of scores would fall within -2.0 and +2.0, and that it is rare for a score to fall outside the -3.0 to +3.0 range (<1%). Higher scores, and positive change values, indicate improvement in function. These properties make a composite score a way to express results from cognitive measures on a common scale and to summarize performance across multiple tasks.
The record does not give the observed mean change in either group, the full range for either group, or a comparison between groups. Although “Full Range” is listed as the dispersion type, the corresponding values are not reported in the registry record. Thus the endpoint and its intended interpretation are described, but its observed results are unavailable.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a randomized comparison of isoflurane and propofol anesthesia and a primary cognitive endpoint assessed 3 months post operatively. It does not report numerical results for that endpoint. No group-specific mean changes, difference between groups, dispersion values, confidence interval, or p-value are reported in the registry record. The posted information therefore does not establish which group had a higher mean change, how large any difference was, or how precisely it was estimated.
The endpoint is a change score built from composite measures of memory and executive function. Its description gives the intended scale and direction: positive change indicates improvement, and higher scores indicate better function. Those definitions explain how an observed value would be read, but they do not substitute for the observed values. In particular, the scale description cannot show whether either group changed, whether the groups differed, or whether a difference was compatible with random variation.
There is also no reported analysis to interpret. The registry lists one outcome measure and zero analyses. An outcome definition describes what researchers planned to measure; an analysis would connect observed participant data to an estimate and its uncertainty. Without the latter, statistical significance, clinical importance, consistency, and precision cannot be assessed from this record.
General statistical interpretation distinguishes an estimated effect from the uncertainty around it. A confidence interval, when reported, describes a range of values compatible with the data and the analysis assumptions; it is not a guarantee that the true value lies in that range. A p-value, when reported, summarizes how unusual data at least as extreme as the observed data would be under a specified null model. Neither quantity is reported for the primary outcome in the registry record, so neither can be used to characterize this comparison.
The sample-size assumptions describe planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such illustrations are not evidence of an observed treatment effect and are not the trial’s own design justification. The record does not provide a single reduced outcome comparison for these calculations, so a specific planning result cannot be interpreted as a trial finding. Any planning sample sizes are illustrations, not observed power.
The safety record reports zero serious adverse events and zero other adverse events in the listed groups, with 98 participants at risk in the isoflurane group and 101 in the propofol group. Death counts are not reported in the registry record, and no serious event terms are listed. These entries describe the registry’s safety reporting; they do not resolve the missing primary cognitive results.
Overall, the registry record documents the trial’s question, design, endpoint definition, and selected safety counts. It does not provide enough outcome information to estimate the cognitive comparison or draw a statistical conclusion about it.
9. Statistical Methods Explained
The registered design is randomized and parallel, with no masking. Random assignment is a design method intended to make treatment groups comparable on average with respect to both measured and unmeasured characteristics. Its value comes from the assignment process, not from a guarantee that every characteristic will balance. The registry record does not describe the sequence-generation or allocation-concealment methods, so those procedures cannot be evaluated from this information.
What does a mean change represent?
A mean is an average across participant measurements. A mean change summarizes the average difference between an individual’s starting measurement and a later measurement, then aggregates those changes within a group. The registered endpoint is mean change in a cognitive composite at 3 months post operatively. The registry does not report baseline values, group mean changes, or the method used to handle participants without measurements at both time points. Consequently, the endpoint’s definition is available, but the estimated changes are not.
Using change scores can focus analysis on how measurements move over time. Interpretation still depends on how baseline and follow-up values were collected, how composite scores were constructed, and how incomplete observations were handled. The registry describes summed z-score composites but does not report the full scoring algorithm, baseline characteristics, or missing-data procedures. Those details are not reported in the registry record.
Why use a composite z-score?
A z-score expresses a measurement relative to a reference distribution in standard-deviation units. In general, converting multiple measures to a common scale can make it possible to combine tasks that have different original units. A composite can then summarize performance across several related tasks. The registry states that memory and executive-function measures were combined as summed z-score composites, with 0 central on each composite and positive change indicating improvement.
Composite outcomes also require careful interpretation. A single summary can conceal different patterns across component tests: improvement on one task and little change on another may contribute to the same overall composite. The registry lists the component tests but does not report component-level results. It is therefore not possible to determine whether the composite reflects a consistent pattern across tasks or variation among them.
What does a range add?
Dispersion describes variation among participant values rather than the average alone. A full range records the lowest and highest observed values, so it can indicate the span of the data and the presence of extreme observations. Unlike a standard error or confidence interval, a range does not directly describe the precision of a group mean or a between-group effect. The record lists full range as the dispersion type but does not give the actual group ranges.
In general, a small range does not automatically imply a precise estimate, and a wide range does not by itself show that a group mean is unreliable. Precision depends on the distribution of values and the amount of information contributing to the estimate. The registry does not report the outcome distributions, standard errors, or confidence intervals needed to assess precision for this endpoint.
How should a confidence interval or p-value be read?
In general, a confidence interval communicates uncertainty around an estimated effect under the chosen statistical model. Its width reflects precision, while its location gives the plausible direction and magnitude of the estimate under that model. A p-value addresses compatibility between the observed data and a specified null hypothesis, given the model assumptions. Neither is a measure of the probability that a treatment works, and neither conveys the practical importance of an effect by itself. No confidence interval or p-value for the primary endpoint is reported in the registry record.
The record lists zero analyses. That means there is no reported estimate to which these general interpretive tools can be applied. The randomization and outcome definition alone do not reveal the results.
What do the planning assumptions mean?
The registry’s planning description refers to an illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. It describes detecting a stated fraction of the observed effect. These are assumptions for planning calculations, not evidence that the trial achieved a particular power or detected an effect. Sample-size calculations are planning illustrations, never observed power.
The record does not provide a trial-specific sample-size justification or the values needed to interpret an individual planning scenario. It also indicates that the primary outcome has several categories or time points and was not reduced to one comparison. For that reason, the planning description cannot be treated as a single, directly interpretable calculation for the cognitive endpoint. Any reference to participants per arm for a chosen power level would describe a planning target under assumptions, not the number observed in the trial or a result of the trial.
More broadly, statistical conclusions require both a clearly defined estimand—the quantity the analysis is intended to estimate—and a reported analysis using participant data. The record identifies a mean change endpoint but does not specify the comparative estimand, adjustment variables, model, or approach to incomplete data. These methods are not reported in the registry record. No particular model or analysis procedure should therefore be inferred.
10. Multiplicity, Missing Data and Analysis Populations
The primary endpoint draws on multiple cognitive tests and describes composite scores for memory and executive function. The registry does not report whether the composites were treated as separate outcomes in analysis, whether component tests were analyzed individually, or whether any adjustment for multiple comparisons was planned or used. An adjustment for multiplicity can help control the chance of false-positive findings when many statistical questions are tested, but the appropriate approach depends on which outcomes and comparisons are treated as confirmatory. That analysis plan is not reported in the registry record.
The record lists one outcome measure and zero analyses, and states that the primary outcome has several categories or time points and was not reduced to one comparison. No results for alternative time points, outcome categories, or component tests are reported. It is therefore not possible to reconstruct the number of tests performed or determine how multiplicity was handled.
Missing-data handling is not reported in the registry record. The available information does not state how many participants completed cognitive testing at baseline or at 3 months post operatively, whether any observations were excluded, or how missing measurements were treated. The analysis population is also not reported: there is no description of whether participants were analyzed according to randomized assignment, treatment received, or another population definition.
These omissions matter because different choices about the analysis population and missing observations can affect an estimate and its uncertainty. No direction or size of such an effect can be inferred without the data and methods. The registry record does not provide a participant flow account, a missing-data strategy, or a multiplicity plan, so these aspects of the evidence remain unresolved.
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 |
|---|---|---|---|
| Isoflurane | 0 | 98 | 0.0% |
| Propofol | 0 | 101 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Isoflurane | 0 of 98 |
| Propofol | 0 of 101 |
The registry lists serious adverse event counts of 0 for isoflurane, among 98 participants at risk, and 0 for propofol, among 101 participants at risk. It also lists 0 other adverse events in each group, using the same at-risk counts. No serious adverse event terms are listed. These are the safety figures recorded for the groups; they do not provide event-level descriptions or additional detail about how adverse events were defined, collected, or monitored.
The death fields are null, so death counts are not reported in the registry record. A missing death count should not be read as a reported count of zero. The record also does not explain the relationship between the listed at-risk populations and the overall enrollment, or provide a participant flow description that would clarify who contributed to each safety count.
Zero reported events in these categories means that the registry lists no events in the relevant count fields. It does not establish that no event of any kind occurred, nor does it establish that the groups had identical safety experiences. The counts should be interpreted within the limits of what the registry records, without extending them to unlisted events, unreported deaths, or the primary cognitive outcome.
12. What the Result Does, and Does Not, Mean
The trial’s registered question is whether postoperative cognitive performance differs after inhalational isoflurane anesthesia compared with total intravenous propofol anesthesia. Its primary endpoint is mean change in composite z-scores for memory and executive function, assessed 3 months post operatively. The endpoint description explains the direction of the scale, but the registry record does not report the outcome estimates or a statistical comparison.
As a result, the record cannot show whether either group had a positive or negative mean change, whether the observed groups differed, or how large and precise any difference might have been. It also cannot establish whether a possible difference would be important in practice. A completed trial status is not itself evidence of a positive, negative, or null result.
This absence should not be interpreted as proof that the approaches produce the same cognitive outcome. Demonstrating similarity or equivalence generally requires a prespecified margin and an analysis sufficiently precise to rule out differences outside that margin. Such a margin and analysis are not reported in the registry record. Nor can the absence of a reported result be interpreted as evidence favoring either approach.
The listed safety counts are limited to the adverse event fields in the record. Zero serious and zero other adverse events are recorded in the two groups, while deaths are not reported. These entries do not answer the cognitive question and should not be expanded into a general claim about safety.
The appropriate reading is therefore narrow: the registry describes a randomized comparison, specifies its cognitive endpoint, and reports selected safety counts, but it does not report the primary outcome analysis. Without comparative estimates, their uncertainty, and fuller methods, a statistical conclusion about the cognitive effect cannot be drawn from this record.
13. Why This Trial Matters Statistically
This trial illustrates the difference between registering a research question and reporting evidence that answers it. The record clearly identifies the two anesthetic approaches, a randomized parallel design, and a cognitive endpoint at 3 months post operatively. Those details make the intended comparison understandable. However, a defined endpoint is not a result: without group estimates and a comparison, readers cannot assess direction, magnitude, or uncertainty.
The cognitive outcome also demonstrates why measurement choices matter. The registered composite combines several memory and executive-function tasks on a z-score scale. A composite can create a common summary from measures with differing original scales, while also making component-level patterns less visible. Because the record does not report composite estimates or component results, neither the overall pattern nor the contribution of individual tests can be assessed.
The unmasked design is another interpretive consideration. Randomization supports a comparison by assignment, but lack of masking may matter for subjective or assessor-influenced processes. The registry record does not say whether outcome assessors were masked, so the practical implications cannot be determined. This is a design consideration, not evidence that the measurements were biased.
Finally, the record shows why planning quantities must remain separate from findings. A sample-size illustration based on an observed effect is not a substitute for a reported treatment-effect estimate, and it is not observed power. Without a reported analysis, planning assumptions cannot establish what the trial found. The statistical value of the record is in defining the question and methods that are known, while making clear that the primary comparative result is not reported in the registry record.
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 main limitation for interpretation is that the primary cognitive outcome has no reported group results or comparative analysis. The registry defines mean change in composite z-score at 3 months post operatively, but does not give group means, ranges, an effect estimate, or a measure of uncertainty. This prevents assessment of the observed direction, magnitude, and precision of the comparison.
The outcome is based on multiple cognitive measures, yet the registry does not report component-level values, the detailed composite construction, or whether memory and executive function were analyzed separately. The record also does not state how repeated measurements, baseline scores, or incomplete assessments were handled. These details limit the ability to evaluate the meaning and robustness of any eventual estimate.
The trial is listed as unmasked. The registry record does not specify whether outcome assessors were masked or describe safeguards around cognitive testing. It also does not provide details about allocation concealment, participant eligibility beyond the listed conditions, or the types and distribution of surgeries. These are unreported design details, not evidence of a particular flaw.
There is no reported statistical analysis plan, sample-size justification, missing-data method, analysis population, or multiplicity procedure. The record lists zero analyses and notes that the outcome was not reduced to one comparison. Accordingly, the planning description cannot supply the missing result, and it is not possible to judge whether the analysis followed a prespecified plan.
For safety, deaths are not reported in the registry record, and the adverse-event entries do not include event terms or collection details. The reported counts should be read as limited registry entries rather than a complete characterization of safety. Taken together, these reporting gaps constrain interpretation of both efficacy-related outcomes and safety.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Cognitive Effects of Inhalational Versus Intravenous General Anesthesia in the Elderly — NCT00788008.
- Registry record last updated 2015-03-26; status last verified 2015-03.
- Results first posted 2015-03-26.
- 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
The record describes a completed, randomized, unmasked, parallel-group trial sponsored by Duke University, with enrollment listed as 200. It compares inhalational isoflurane anesthesia with total intravenous propofol anesthesia in the context of lumbar spondylosis, cervical spondylosis, hip osteoarthritis, and knee osteoarthritis.
The primary endpoint is mean change in neurocognitive performance, expressed as composite z-scores for memory and executive function, at 3 months post operatively. Higher scores and positive change indicate improvement. The registry record does not report comparative endpoint estimates or analyses, and it does not report the statistical plan, missing-data methods, or analysis populations.
The listed safety counts are zero serious and zero other adverse events in both groups; death counts are not reported in the registry record. The trial question and endpoint are identifiable, but the record does not provide the primary results needed to assess the cognitive comparison.