The Effect of Remote Ischemic Preconditioning Applied in Children the Day Before Open Heart Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Remote Ischemic Preconditioning Applied in Children the Day Before Open Heart Surgery (NCT00868101), a randomized phase 1, phase 2 study. The primary outcome is IkB-alpha Expression.

2. Clinical Question

3. Trial Design

The registry lists NCT00868101 as a completed, randomized, single-masked, parallel-group phase 1 and phase 2 study sponsored by the University of Sao Paulo. Its title identifies remote ischemic preconditioning applied in children the day before open-heart surgery as the subject. The enrollment is recorded as 22. The study start is listed as 2008-01, and primary completion as 2009-11.

Children receiving the preconditioning stimulus were compared with children who did not receive it. The brief study description frames the research as examining whether brief episodes of limb ischemia applied the day before surgery might protect against myocardial injury induced by extracorporeal circulation. That description states the research question; it is not evidence that protection occurred.

The primary outcome was IkB-alpha expression at 24 hours. The registry identifies the measure as a mean with standard deviation and describes the result as expression in arbitrary units, relative to an endogenous protein expression. NT-proBNP and Troponin I, each measured at 24 hours, are listed as secondary outcomes. Specific measurement procedures for those secondary markers are not reported in the registry record.

Single masking is reported, but the identity of the masked parties and the procedures used to maintain masking are not reported in the registry record. Details of the randomization sequence, allocation concealment, eligibility criteria, and the original sample-size justification are also not reported in the registry record. The registry status is completed. Its posted outcome information includes group means and standard deviations, but the registry lists no analyses. That distinction matters: descriptive summaries can be reported even when a formal analysis is not listed.

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 IkB-alpha Expression, measured over 24 hours.

The primary endpoint is IkB-alpha expression at 24 hours. The registry describes IkB-alpha as an inhibitory protein associated with regulation of the inflammatory response protein called kappa-B nuclear factor. It states that expression was assessed using real-time protein chain reaction (RT-PCR), compared with an endogenous protein expression treated as invariable. The reported value is therefore described as arbitrary units: how much greater the IkB-alpha expression is than the endogenous reference.

As a laboratory measure, this endpoint can be used to examine a biological response connected in the registry description to inflammation. It is not itself a direct measure of a child’s clinical condition, the extent of myocardial injury, or recovery after surgery. Its interpretation depends on the assay, reference expression, timing, and the way the outcome is summarized. The registry reports a group mean and standard deviation for each arm at 24 hours, but further assay-validation details and a clinically meaningful threshold are not reported in the registry record.

The comparison is therefore best read as a contrast in the measured marker between the randomized groups at the specified time. The posted summaries do not establish whether any difference in expression corresponds to a meaningful difference in clinical outcomes.

7. Results Posted in the Registry

• Preconditioning: mean 4.10 versus 3.60 on control; difference 0.50 (95% CI -1.84 to 2.84), standardized effect d = 0.17; z-test p = 0.676.

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.

NT-proBNP

• 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 deviations.
• Result:
  • Preconditioning: mean 8.56 versus 12.68 on control; difference -4.12 (95% CI -8.76 to 0.52), standardized effect d = -0.75; z-test p = 0.082.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Preconditioning and the control. The interval gives the range of effects that remain compatible with the data.

Troponin I

• 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 deviations.
• Result:
  • Preconditioning: mean 33.70 versus 22.30 on control; difference 11.40 (95% CI -5.66 to 28.46), standardized effect d = 0.56; z-test p = 0.190.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Preconditioning and the control. The interval gives the range of effects that remain compatible with the data.

NT-proBNP and Troponin I are reported as secondary outcomes at 24 hours. Their group contrasts point in opposite directions: the posted NT-proBNP mean is lower in the preconditioning group than in control, while the posted Troponin I mean is higher. The unadjusted confidence intervals for both comparisons include no difference, so neither provides a precise distinction between the groups in these summaries.

This mixed directional pattern does not reinforce a single, consistent change across the two secondary markers. It also does not establish that the markers disagree in a formal statistical sense; the record does not report a direct comparison between them, and their units and biological meanings differ. These secondary results are best treated as descriptive context alongside the primary IkB-alpha result, rather than as independent confirmation of it.

In general, secondary outcomes often help explore whether a primary finding is accompanied by related signals. Their evidential weight depends on whether they were prespecified, how many outcomes or analyses were considered, and whether an appropriate multiplicity strategy was used. The registry lists NT-proBNP and Troponin I as secondary outcomes but does not report a multiplicity adjustment or sponsor-reported analyses. When several outcomes are examined, unadjusted p-values do not account for the broader set of comparisons, and a nominal result can be less persuasive as confirmatory evidence.

The registry lists no reported secondary analyses. The contrasts and intervals associated with these endpoints are unadjusted recalculations from the posted group summaries. They do not establish an overall treatment effect, do not resolve uncertainty in the primary endpoint, and do not provide evidence about clinical outcomes beyond the laboratory measurements recorded.

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

• NT-proBNP
• Troponin I

9. Statistical Interpretation

10. Statistical Methods Explained

In general, a randomized parallel-group design assigns participants to separate groups and compares their outcomes. Randomization is intended to make treatment groups comparable on average, including for factors that may not be measured. It does not guarantee that groups are balanced in a small study, and its value depends on how the sequence is generated and assignment is concealed. Those procedures are not reported in the registry record. The record says the study was single-masked, but does not identify who was masked or describe how masking was maintained.

What does a group mean describe?

The primary outcome and the listed secondary outcomes are continuous measures summarized using means and standard deviations. A mean describes the central value of the observations in a group. A standard deviation describes variation among observations around that group’s mean; it is not the uncertainty of the estimated mean and is not a confidence interval. The registry gives the group summaries for preconditioning and control separately.

For a comparison of means, the posted contrast is defined as the preconditioning mean minus the control mean. A positive estimate means the observed mean is higher in the preconditioning group; a negative estimate means it is lower. This is a direction-of-difference convention, not a judgment about whether a value is beneficial or harmful. The endpoint’s clinical meaning requires context that is not reported in the registry record.

How should the confidence interval be read?

In general, a confidence interval describes the range of effect estimates reasonably compatible with the data and the method used to calculate it. A narrower interval represents greater precision, while a wider interval leaves more uncertainty about the size and direction of the contrast. When an interval includes no difference, the data do not rule out no difference at the corresponding confidence level. That does not prove that there is no effect; it indicates that the estimate is not precise enough to exclude that possibility using the stated method.

The confidence intervals associated with these contrasts are unadjusted recalculations from the posted group summaries. They do not incorporate adjustment for other variables, and the registry does not list adjusted analyses. The calculations also rely on assumptions appropriate to comparisons of means. The registry does not report tests of those assumptions or alternative analyses.

What does a p-value add?

In general, a p-value measures how unusual the observed data, or data more extreme, would be under a specified null model and its assumptions. It is not the probability that the null model is true, and it does not measure the size or clinical importance of a difference. A large p-value can arise when the estimated difference is small, when measurements are variable, or when information is limited. A small p-value does not by itself establish that a result is clinically important or free of bias.

The posted p-values are unadjusted. The planning assumptions specify a two-sided significance level of 0.05, but that planning value does not establish which formal testing procedure the original investigators used. The registry lists zero analyses, and the secondary outcomes have no reported analyses. The original statistical analysis plan, including any prespecified hypotheses or adjustment strategy, is not reported in the registry record.

Why does variability matter?

In general, estimates become less precise when the measurements vary widely relative to the amount of information available. This is reflected in the standard errors and confidence intervals. Standard errors describe the estimated sampling variability of a statistic under its calculation assumptions. They should not be confused with the standard deviation, which describes spread among individual measurements. The posted summaries indicate substantial variability, particularly for the primary outcome and Troponin I. The registry does not provide individual-level data, so the summaries cannot show the shape of the outcome distributions or identify unusual observations.

Some continuous outcomes can be skewed or contain unusually high values. When such features are present, the mean and standard deviation may not fully describe the distribution, and methods based on a normal approximation may be less suitable. This is a general consideration; the registry does not report distribution checks or an alternative modeling strategy for these outcomes.

What can be learned from recalculated results?

The unadjusted contrasts are recalculated from the posted means, standard deviations, and group sizes. Such calculations offer a transparent way to describe the difference and its uncertainty when a registry record includes summary statistics but no listed analysis. They are not a substitute for a prespecified sponsor analysis, which could use a different method or include additional information. No discrepancy with a sponsor analysis is flagged, but the registry record does not list a sponsor-reported analysis for these outcomes.

These recalculations cannot account for individual-level features, missing observations, covariates, repeated measurements, or changes to the analysis population unless those details are available and incorporated. The record does not report whether covariate adjustment was planned or conducted, whether missing values occurred, or which analysis population was used. The posted numbers should therefore be read as unadjusted group summaries and comparisons, rather than as estimates from a fully described statistical model.

The planning illustrations use a normal approximation and equal allocation between the arms, with a two-sided significance level of 0.05. Those are assumptions for the illustrations, not confirmed features of the original trial design. The original design assumptions and sample-size justification are not reported in the registry record. Planning estimates based on an observed effect are especially sensitive to uncertainty in that effect; they should be considered scenarios rather than evidence about the trial’s achieved ability to detect an effect.

11. Confidence Intervals and Precision

Precision concerns how much uncertainty surrounds an estimated contrast. The primary mean difference is 0.5, and its confidence interval extends from -1.844 to 2.844. This interval includes zero and values in either direction, so the primary estimate does not pin down whether the population contrast is positive, negative, or close to no difference. The width is important: the point estimate is only one value among many that remain compatible with the posted data and calculation.

For NT-proBNP, the unadjusted mean difference is -4.116, with a confidence interval from -8.756 to 0.524. For Troponin I, the unadjusted mean difference is 11.4, with a confidence interval from -5.661 to 28.46. Each interval includes zero. These intervals likewise leave uncertainty about the direction and size of the corresponding group contrast. The endpoints use pg/mL, while the primary outcome is reported in arbitrary units, so the effect estimates are not directly comparable across markers.

In general, a confidence interval is not a guarantee that the true effect lies within its limits. Its interpretation depends on the statistical method and assumptions, and repeated use of the method under those assumptions would yield intervals that cover the target effect at the method’s nominal rate. The registry does not state a confidence level for the displayed intervals. They are unadjusted recalculations from posted summaries and do not reflect a multiplicity adjustment.

The modest enrollment and variation in the posted measurements contribute to uncertainty. The record does not provide individual observations or information to assess whether the variability is driven by a few values. The estimates should therefore be read as imprecise descriptions of this study’s group contrasts, not as precise measurements of a stable underlying effect.

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. The registry’s planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each scenario uses the stated fraction of the observed effect as the effect to detect. Those are planning assumptions for the illustrations; the original trial’s design assumptions and sample-size justification are not reported in the registry record.

The 80% power column describes the number of participants per arm estimated, under those assumptions, to give an 80% chance of detecting the specified effect if that effect were the true one. The 90% power column uses a higher target chance of detection and therefore gives larger planning requirements for the same effect scenario. These are design calculations, not results observed in the trial.

Rows that plan for a smaller fraction of the observed effect require more participants per arm than rows planning for the full observed effect. This follows because smaller differences are harder to distinguish from ordinary sampling variation. For example, the primary-outcome illustrations list 555 participants per arm for 80% power at 100% of the observed effect and 2,218 participants per arm at 50% of the observed effect. The corresponding 90% figures are 743 and 2,969. These are planning illustrations based on the observed estimate, not the study’s original target and not observed power. The registry does not report the assumptions used to set the original enrollment.

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 = 0.500; pooled standard deviation σ = 2.972.
2. n = 2 × (1.96 + 0.842)² × 2.972² / 0.500² = 554.4, rounded up to 555 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 <- 0.5                      # observed difference in means
sigma <- 2.97153159162072                     # 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(868101)
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 = 555 (80% power), 743 (90% power)
 75% of observed effect: n per arm = 986 (80% power), 1,320 (90% power)
 50% of observed effect: n per arm = 2,218 (80% power), 2,969 (90% power)
power.t.test: 555.4 
Simulated power at n = 555 per arm: 0.797 (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 researchers consider more than one outcome, comparison, time point, or analysis. In general, the more statistical tests considered, the greater the chance that at least one result appears noteworthy by chance if each is interpreted without regard to the full set. A prespecified strategy may define which result is primary, whether secondary outcomes are exploratory, and whether any adjustment is needed. Such a strategy is not reported in the registry record.

The registry identifies IkB-alpha expression as the primary outcome and NT-proBNP and Troponin I as secondary outcomes. It records four outcome measures, but the additional outcome details are not reported in the registry record. The registry lists zero analyses, and the secondary outcomes have no reported analyses. Consequently, the posted unadjusted comparisons should not be interpreted as multiplicity-adjusted or as a complete account of the original analysis plan. The record does not report whether further outcomes, time points, or analyses were considered by the investigators.

Missing-data information is also limited. The registry does not report whether any outcome measurements were missing, how missing values were handled, or whether the group summaries include all enrolled children. The posted group sizes are 12 for preconditioning and 10 for control, but without a participant flow account these figures do not establish why any enrolled participant may or may not have contributed an outcome. The record does not report exclusions after randomization or reasons for exclusion.

The analysis population is not reported in the registry record. It is therefore not possible to determine from the record whether the analyses followed an intention-to-treat principle, included only participants with available measurements, or used another definition. Similarly, covariate adjustment, protocol deviations, and sensitivity analyses are not reported. These omissions limit assessment of how robust the estimates are to missing outcomes or analysis choices. They do not demonstrate that such issues occurred; they mean the registry record does not give enough detail to assess them.

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 registry lists zero serious adverse events in the preconditioning group, with 12 at risk, and zero in the control group, with 10 at risk. It also lists zero other adverse events in each group, using the same at-risk counts. These are the adverse-event figures recorded for the study. The registry does not provide serious adverse-event terms.

A zero count in a posted record means that no events of that category are recorded for the specified group; it does not prove that the risk is absent. With limited enrollment, the information may be insufficient to characterize uncommon events. The record does not report the event definitions, collection process, surveillance period, or whether adverse events were actively solicited. Deaths are not reported in the registry record; the death entries are null, which is different from a reported count of zero.

These figures should be read as registry safety reporting, not as a comprehensive estimate of risk. They do not establish that every possible adverse outcome was assessed or captured.

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

The posted results describe laboratory markers measured at 24 hours in children assigned to receive the preconditioning stimulus or to control. For the primary marker, the group means differ by an unadjusted estimate of 0.5 units, with a confidence interval from -1.844 to 2.844 and an unadjusted p-value of 0.676. The interval includes no difference and allows values in either direction. Thus, the estimate is not precise enough to establish the direction or size of a group difference from these summaries.

The secondary marker comparisons are also uncertain, and their directions do not align with one another. Taken together, the posted outcomes do not provide a consistent pattern of precise group contrasts. That is a description of the data and their uncertainty, not a conclusion that the intervention has no effect. A study with limited information can fail to distinguish among possibilities that remain compatible with its confidence intervals.

These laboratory results do not by themselves establish effects on myocardial injury, complications, recovery, or other clinical outcomes. The study description presents protection from myocardial injury as the research motivation, but the posted primary measure is IkB-alpha expression, and the secondary measures are NT-proBNP and Troponin I. The registry does not report a clinical endpoint linking these marker measurements to patient-important outcomes.

The record also does not supply enough information to assess the original statistical analysis plan, missing data, analysis population, or multiplicity handling. The unadjusted recalculations are useful for describing the posted summaries, but they cannot replace a complete prespecified analysis. The results should therefore be understood as uncertain estimates from this completed randomized study, rather than as definitive evidence for or against a clinical benefit or harm.

17. Why This Trial Matters Statistically

This study is statistically informative because it illustrates the difference between a point estimate and the precision of that estimate. The primary group means are close, but the main interpretive issue is not simply the distance between them. The confidence interval is broad and includes contrasts in both directions, so the posted data leave considerable uncertainty. Reporting the interval alongside the estimate prevents a single number from being mistaken for a precise answer.

The study also illustrates why variability and enrollment matter when interpreting continuous outcomes. The registry reports standard deviations for each group, and the primary outcome shows substantial variation relative to its mean. With limited information, estimates can remain uncertain even when a numerical contrast is available. A non-significant result is not evidence that the groups are equivalent; equivalence would require a defined margin and a design and analysis suited to that question, neither of which is reported in the registry record.

Another statistical lesson is the distinction between primary and secondary outcomes. A primary outcome provides the central comparison, while secondary outcomes may add context. When several markers are considered, unadjusted results warrant caution unless their role and multiplicity plan are clear. The record names secondary markers but does not list their analyses or any multiplicity adjustment.

Finally, this record shows the limits of registry summaries. Group means and standard deviations permit unadjusted recalculations, but cannot reveal individual distributions, missingness, or the details of the original analysis. Clear reporting of analysis populations, missing-data handling, and prespecified methods would make the results easier to assess. The posted information supports careful description, while leaving important questions about design and analysis unanswered.

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 trial-specific limitations restrict interpretation. The enrollment recorded in the registry is 22, and the outcome summaries are based on group sizes of 12 for preconditioning and 10 for control. The measurements show appreciable variation, while the primary confidence interval spans values on both sides of no difference. The resulting estimates are therefore uncertain and should not be treated as precise estimates of the underlying contrasts.

The registry does not report detailed eligibility criteria, ages, baseline characteristics, or participant flow. It is not possible to assess from the record whether the groups were balanced on relevant characteristics, whether participants were excluded after randomization, or whether all randomized children contributed to each outcome. The analysis population and missing-data handling are not reported.

Details of random sequence generation and allocation concealment are not reported. The study is described as single-masked, but the masked party and masking procedures are not identified. The registry also does not report assay validation details, distribution checks, adjusted analyses, or sensitivity analyses. The posted comparisons are unadjusted recalculations from summary statistics, while no sponsor-reported analyses are listed.

The registry identifies secondary markers but does not report the multiplicity strategy or analyses for them. It records four outcome measures, while details for all measures are not included in the available outcome descriptions. Follow-up beyond the stated 24-hour measurements is not reported for these outcomes. Finally, adverse-event collection details and death counts are not reported in the registry record. These are reporting limitations; they do not establish that particular problems occurred, but they constrain what can be concluded from the posted record.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: The Effect of Remote Ischemic Preconditioning Applied in Children the Day Before Open Heart Surgery — NCT00868101.
• Registry record last updated 2012-01-09; status last verified 2011-12.
• Results first posted 2012-01-09.
• 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

NCT00868101 is a completed randomized, single-masked, parallel-group phase 1 and phase 2 study sponsored by the University of Sao Paulo. It enrolled 22 children and examined remote ischemic preconditioning applied the day before open-heart surgery. The primary outcome was IkB-alpha expression at 24 hours; NT-proBNP and Troponin I were listed as secondary outcomes at the same timeframe.

The primary unadjusted recalculated mean difference was 0.5, with a confidence interval from -1.844 to 2.844 and p = 0.676. The interval includes no difference and remains compatible with contrasts in either direction. Secondary comparisons are also uncertain and point in different directions. No sponsor-reported analyses are listed, and important details about missing data, analysis populations, multiplicity, and the original design assumptions are not reported in the registry record.

The results support cautious description of the posted laboratory measurements, not a definitive conclusion about clinical effects.