The Effect of Goal-directed Therapy Guided by Stroke Volume Variation and Cardiac Index in Non-severe Surgical Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Goal-directed Therapy Guided by Stroke Volume Variation and Cardiac Index in Non-severe Surgical Patients (NCT02841046), a randomized na study. The primary outcome is Number of Days Needed for Anal Exsufflation After Surgery.

2. Clinical Question

In statistical terms, the question is whether the recorded distribution of time to this postoperative milestone differed between the randomized treatment groups. The endpoint is reported as a mean with standard deviation, so the primary summary focuses on average days rather than the proportion reaching the milestone by a specified day. The registry record does not report a separate threshold-based primary comparison or a time-to-event analysis.

3. Trial Design

The record describes a randomized, single-masked, parallel-group trial, with enrollment of 50. It lists the status as completed and the condition as fluid therapy. The study start date is 2016-07-27 and the primary completion date is 2019-05-18. The phase is listed as NA. The registry names First Affiliated Hospital, Sun Yat-Sen University as the sponsor.

The two groups differed in their stated goal-directed fluid-therapy targets. Group Cardiac Index used CI as the primary judgment and targeted CI no less than 2.5L•min-1•m-2. Group Stroke Volume Variation used SVV and CI together, targeting SVV less than 12% and CI no less than 2.5L•min-1•m-2. The registry record does not describe the details of fluid administration beyond these treatment schemes.

There were 25 participants listed in each arm for the primary endpoint. The registry describes random allocation, but the method used to generate the sequence, conceal allocation, and implement randomization is not reported in the registry record. Masking is recorded as single; who was masked and how masking was maintained are not reported in the registry record.

The primary outcome was number of days needed for anal exsufflation after surgery, with a timeframe of up to 8 weeks. The record also names secondary outcomes: incidence of adverse cardiovascular events, oxygen delivery, oxygen consumption, oxygen extraction rate, and number of days in hospital. Five secondary outcomes are posted, while the record lists nine outcome measures overall. Results for the named secondary outcomes are not included in the registry record described for this analysis.

The registry record does not report the trial's original sample-size justification, its detailed statistical analysis plan, or whether interim analyses were planned or performed. It also does not provide a fuller account of participant flow, deviations from assigned treatment, or analysis populations. These omissions limit what can be concluded about design and analysis procedures beyond the recorded allocation, masking, parallel structure, and arm descriptions.

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 Number of Days Needed for Anal Exsufflation After Surgery, measured over up to 8 weeks.

The primary endpoint is the number of days needed for anal exsufflation after gastrointestinal tumor surgery. The record describes recording this number in non-severe patients and gives a measurement timeframe of up to 8 weeks. The endpoint is reported as a continuous measure summarized by its mean and standard deviation: Group Cardiac Index has a mean of 3.8 days and standard deviation of 1.1, while Group Stroke Volume Variation has a mean of 2.7 days and standard deviation of 1.2.

As a general explanation, a postoperative recovery milestone can be summarized as elapsed time, allowing comparison of the average timing across groups. A mean gives the arithmetic average of the observed values, while a standard deviation describes how spread out values are around that average. The mean alone does not show the full distribution: participants may reach a milestone at different times, and a small number of relatively long times can influence an average.

The registry record does not define the clinical or operational criteria for anal exsufflation, explain how the event time was recorded, or state how observations without a recorded milestone by the end of the timeframe were handled. It also does not report whether any endpoint observations were missing. Those details matter for interpreting precisely what the recorded day count represents and how it was analyzed. The posted result should therefore be read as a comparison of the recorded group means, with the stated timeframe and outcome definition, rather than as a complete description of every aspect of postoperative recovery.

7. Results Posted in the Registry

• Group Stroke Volume Variation: mean 2.70 versus 3.80 on control; difference -1.10 (95% CI -1.74 to -0.46), standardized effect d = -0.96; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous and summarized by a mean and standard deviation. For that kind of outcome, an unadjusted comparison can express the difference between group means in the outcome's original units. In this trial the unit is days, and the posted mean difference compares Group Stroke Volume Variation with Group Cardiac Index. The stated estimate is -1.1 days. A negative value means the first group's mean is lower than the comparison group's mean under that ordering; it does not mean that every participant had a lower value.

As a general explanation, an unadjusted analysis compares the groups without incorporating additional covariates into the estimate. Adjustment can be useful in some settings, but the registry record does not describe an adjusted primary analysis. It does not report the exact test or model used for the sponsor's primary analysis. The result therefore should be described using the posted comparison and not attributed to a specific test or model that the record does not name.

The standard deviation describes variation among participant-level measurements around a group mean. It is different from the standard error, which concerns precision of an estimated quantity such as a group mean. The registry comparison lists standard errors for the group means as 0.22 and 0.24. As a general concept, a standard error tends to be smaller when an estimate is more precise, while a standard deviation characterizes variation in the observed outcome. Neither measure on its own describes the full shape of the endpoint distribution.

A confidence interval for a mean difference conveys uncertainty about the estimated contrast under its statistical assumptions. Its position relative to zero is relevant when considering whether the data are compatible with no mean difference under that framework. The reported interval lies below zero, and the unadjusted p-value is <0.001. These are related summaries of evidence, but they answer different presentation needs: the p-value summarizes compatibility with a null model, while the interval conveys a range of estimates compatible with the data and assumptions. Neither determines clinical importance.

As a general statistical caution, methods based on means can be sensitive to skewness and unusually high or low observations. The registry record does not report the outcome distribution, diagnostics, transformations, or robust analyses. It is therefore not possible to assess from the record whether distributional assumptions were checked or whether an alternative analysis was considered. The record also does not specify whether the stated mean difference and interval were adjusted for any design features.

Randomized parallel-group allocation means participants were assigned to one of the two treatment schemes, rather than receiving both schemes in a crossover sequence. Randomization supports a group comparison by aiming to balance prognostic factors, but it cannot guarantee balance in a particular trial. The registry record does not report sequence-generation details, allocation concealment, baseline outcome values, or baseline characteristics. Single masking is recorded, but the masked party and masking procedures are not reported in the registry record.

The registry lists the endpoint timeframe as up to 8 weeks. A measure of days until a milestone can, in general, have a feature of time-to-event data: some observations may be incomplete if the event is not recorded within the observation period. The posted primary result is characterized as a mean, not as a time-to-event estimate. The record does not say whether participants who did not reach the milestone within the timeframe were censored, assigned another value, excluded, or handled in another way. It also does not report the number of such observations, if any. This uncertainty is relevant because different approaches to incomplete event times can change the interpretation of a mean.

The registry identifies nine outcome measures overall and five posted secondary outcomes. Multiple outcomes can create a multiplicity issue if many hypotheses are tested and interpreted together. As a general explanation, the more comparisons made, the greater the chance that some results may appear statistically notable by chance when no adjustment or prespecified hierarchy is used. The registry record does not report a multiplicity strategy, a prespecified hierarchy, or which outcomes were designated as primary beyond the posted primary endpoint. The p-value for the primary comparison is explicitly unadjusted, so it should not be presented as multiplicity-adjusted evidence.

There are no analyses listed in the registry entries for this record. That absence does not demonstrate that no analyses were carried out; it means analysis details are not reported in the registry record. The exact handling of missing data, protocol deviations, adherence, and analysis populations is likewise not reported. These items affect how closely an analysis reflects randomized assignment and how broadly its estimate can be interpreted.

Effect-size planning figures use the observed effect as a reference and then consider specified fractions of that effect. As a general explanation, planning at a smaller target effect requires more participants for the same power assumptions, because a smaller group difference is harder to distinguish from sampling variation. These figures are prospective planning illustrations, not a description of the original trial design. The trial's own design assumptions and sample-size justification are not reported in the registry record.

Finally, statistical significance should not be used as a substitute for estimating the size and precision of an effect. The estimated difference, its interval, the endpoint's definition, trial conduct, missingness, and relevance to the intended population are all part of interpretation. The posted summaries make the direction and size of the mean comparison legible, but they do not answer every methodological question needed for a full independent appraisal.

10. Confidence Intervals and Precision

The posted mean difference is -1.1 days for Group Stroke Volume Variation relative to Group Cardiac Index. The registry also reports a confidence interval for this comparison; both endpoints are below zero. The interval therefore indicates that the estimates supported by this calculation remain in the direction of a lower mean in the SVV-plus-CI group. The interval's exact endpoint values are not repeated because they are recorded with more than three decimal places.

As a general explanation, a confidence interval combines an estimate with information about its uncertainty under a statistical model. A relatively narrow interval indicates greater precision than a wide interval, while an interval that spans a range of values signals uncertainty about the exact size of the underlying effect. A confidence interval is not a guarantee that the true effect lies within its limits, and it does not describe the spread of individual participant outcomes.

The group summaries show standard deviations of 1.1 days and 1.2 days. These describe observed variability within each group, whereas the confidence interval concerns uncertainty in the between-group estimate. The registry comparison also lists standard errors of 0.22 and 0.24 for the group means. These quantities serve different purposes and should not be read interchangeably.

Precision is conditional on the analysis and its assumptions. The record does not report distributional diagnostics, the method used to construct the interval, missing-data handling, or an adjusted analysis. It also does not provide enough information to assess how representative the trial participants are of populations beyond those described. The interval gives useful statistical information about the reported mean comparison, but it cannot account for uncertainties that are not represented in that calculation.

11. 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 for 80% power and participants per arm for 90% power. They are not total-event counts. The assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for planning is the stated fraction of the observed effect. These are planning illustrations based on the observed trial effect, not observed power.

For planning at 100% of the observed effect, the figures are 18 participants per arm for 80% power and 24 participants per arm for 90% power. Planning for 75% of the observed effect gives 31 participants per arm for 80% power and 41 participants per arm for 90% power. Planning for 50% of the observed effect gives 69 participants per arm for 80% power and 93 participants per arm for 90% power.

In plain language, the 80% power column gives the planned number in each arm under which the calculation would have an 80% chance of detecting the chosen effect if the assumptions and effect were correct. The 90% power column expresses the corresponding planning target for a higher chance of detection. Neither column is a statement about the probability that the observed finding is true, and neither describes the trial's achieved power.

Smaller effects need more participants to be detectable under the same planning assumptions. The lower-fraction rows illustrate this pattern. The original trial's sample-size justification and original planning assumptions are not reported in the registry record, so these illustrations should not be mistaken for the basis on which enrollment was set.

12. 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 = -1.100; pooled standard deviation σ = 1.151.
2. n = 2 × (1.96 + 0.842)² × 1.151² / -1.100² = 17.2, rounded up to 18 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 <- -1.1                      # observed difference in means
sigma <- 1.15108644332213                     # 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(2841046)
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 = 18 (80% power), 24 (90% power)
 75% of observed effect: n per arm = 31 (80% power), 41 (90% power)
 50% of observed effect: n per arm = 69 (80% power), 93 (90% power)
power.t.test: 18.2 
Simulated power at n = 18 per arm: 0.789 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists nine outcome measures overall and five posted secondary outcomes. The primary endpoint is number of days needed for anal exsufflation after surgery. The secondary outcomes named in the record are incidence of adverse cardiovascular events, oxygen delivery, oxygen consumption, oxygen extraction rate, and number of days in hospital. Results for those secondary outcomes are not included in the registry record described for this analysis.

As a general statistical issue, testing multiple outcomes can increase the chance of obtaining at least one apparently notable result by chance. Researchers may address this through prespecified outcome hierarchies, adjusted significance thresholds, or other methods. The registry record does not report whether any such approach was planned or used. The posted primary comparison is labeled unadjusted, and no multiplicity adjustment is reported.

The record lists zero analyses. This does not establish whether analyses were performed; the analysis details are not reported in the registry record. It does not describe the statistical analysis plan, the primary test, the handling of protocol deviations, or whether an intention-to-treat, per-protocol, or other analysis population was used. The population contributing to each outcome is not described beyond the arm counts posted for the primary endpoint.

Missing-data procedures are not reported in the registry record. The primary outcome timeframe is up to 8 weeks, but the record does not explain how observations were handled when the milestone was not recorded or when follow-up was incomplete. The number of missing endpoint observations, if any, is not reported. Baseline characteristics, participant flow, treatment adherence, and withdrawal information are also not provided in the registry record described for this analysis.

These omissions do not show that there were missing observations or that a particular analysis method was inappropriate. They mean that readers cannot determine from the registry record how completeness, multiplicity, and analysis-population choices may have affected the posted comparison. A transparent report of those decisions would help distinguish the intended analysis from any analyses undertaken after examining the data.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 4% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: abdominal infection (16.0%), ileus (12.0%).

The adverse-event figures list serious events affecting 5 of 25 participants in Group Cardiac Index and 1 of 25 in Group Stroke Volume Variation. Other adverse events affected 2 of 25 participants in Group Cardiac Index and 1 of 25 in Group Stroke Volume Variation. Deaths are listed as 0 in each group.

The registry lists abdominal infection at 16.0% and ileus at 12.0% among the top serious-event terms. The denominator and the relationship of these terms to individual participants are not reported in the registry record. These percentages should therefore be read as the registry's listed term frequencies, not converted into participant counts or interpreted as a complete account of all events.

As a general explanation, event counts describe what was recorded during the trial and are not, by themselves, estimates of comparative risk with known precision. The listed figures do not provide event timing, severity grading details, causal attribution, follow-up completeness, or statistical comparisons. The registry record does not explain the definitions used for serious and other adverse events. The small group counts also mean that the posted numbers alone give limited information about the range of possible underlying event rates. These data describe reported safety events; they do not establish that one strategy is safer or more hazardous.

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

The posted result is a comparison of mean days to anal exsufflation after gastrointestinal tumor surgery. Group Cardiac Index had a mean of 3.8 days, and Group Stroke Volume Variation had a mean of 2.7 days. The reported mean difference, defined as the SVV-plus-CI group relative to the CI group, is -1.1 days. The unadjusted p-value is <0.001, and the reported confidence interval lies below zero.

This result describes the endpoint as recorded in the randomized groups. It does not establish that the combined SVV-and-CI strategy caused the observed difference. The registry record does not provide enough detail on randomization procedures, masking, outcome assessment, missing data, or analysis populations to resolve every potential source of uncertainty. The result also cannot be assumed to apply to patients who differ from the described study population.

The primary endpoint is one measure of postoperative recovery, not a complete account of recovery or health. The record names secondary outcomes, including adverse cardiovascular events, oxygen delivery, oxygen consumption, oxygen extraction rate, and hospital days, but their results are not included in the registry record described for this analysis. The posted primary comparison therefore cannot be used to infer the direction or size of effects on those outcomes.

Statistical evidence and clinical importance are separate considerations. The p-value and interval describe evidence and precision under statistical assumptions, while the registry does not state what size of difference would be considered clinically important. The endpoint's operational definition is also not reported. No medical advice or conclusion about treatment choice follows from these statistics alone.

The safety counts should be considered separately from the primary efficacy endpoint. They record adverse events and deaths by group, but do not include enough information to estimate comparative safety with precision or determine causality. Taken together, the record supports a description of the posted group summaries, not a complete assessment of benefits and harms.

16. Why This Trial Matters Statistically

This trial illustrates how treatment strategies can be defined by different monitoring targets while sharing a broader goal-directed fluid-therapy framework. One group used CI as its primary judgment; the other used SVV alongside CI. The statistical contrast therefore concerns the two recorded strategies and their associated targets, not an isolated measurement considered outside the treatment schemes.

Its primary result also shows why reporting an effect estimate matters alongside a significance test. The posted mean difference is expressed in days, and the confidence interval lies below zero. Those summaries communicate direction and uncertainty in a way that a p-value alone cannot. At the same time, the registry does not report a threshold for clinical importance, so statistical evidence should not be equated with practical importance.

The record is also a useful example of the difference between an observed result and a design calculation. Enrollment was 50, while the sample-size illustrations use specified fractions of the observed effect and explicit planning assumptions. Those illustrations cannot explain the original design because the trial's own sample-size justification is not reported. Nor can they be interpreted as observed power.

Finally, registry results need to be read with attention to completeness. The primary endpoint summaries and adverse-event figures are posted, but the analysis plan, missing-data procedures, analysis populations, and results for the named secondary outcomes are not reported in the registry record. Identifying those limits is part of statistical interpretation: estimates can be informative while still leaving important questions unanswered.

17. 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 record gives limited detail on how randomization and masking were implemented. It records randomized allocation and single masking, but sequence generation, concealment, and the identity of the masked party are not reported in the registry record. These details affect assessment of the trial's conduct and potential bias.

The endpoint is described as number of days needed for anal exsufflation, but its operational definition and recording procedures are not reported. Although the timeframe is up to 8 weeks, the record does not explain how participants without a recorded milestone or with incomplete follow-up were handled. Missingness and participant flow are not reported.

The record does not provide baseline characteristics, details of adherence to assigned fluid-therapy targets, protocol deviations, or the analysis population. It also does not identify the precise statistical test or provide the original statistical analysis plan. These omissions limit assessment of whether the posted mean comparison reflects the planned analysis and how broadly the result can be generalized.

Only the primary outcome and adverse-event summaries are described in the registry record used for this analysis. Results for the listed secondary outcomes are not included. The registry also does not report a strategy for addressing multiple outcomes or the original sample-size justification. Finally, the adverse-event terms do not include a reported denominator or detailed event-level context. These are reporting limitations; they do not establish that particular problems occurred during the trial.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: The Effect of Goal-directed Therapy Guided by Stroke Volume Variation and Cardiac Index in Non-severe Surgical Patients — NCT02841046.
• Registry record last updated 2020-03-03; status last verified 2020-02.
• Results first posted 2020-03-03.
• 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.

21. Record Summary

NCT02841046 is a completed, randomized, single-masked, parallel-group trial with enrollment of 50. It compares goal-directed fluid therapy using CI as the primary judgment with therapy using SVV and CI together. The primary outcome is number of days needed for anal exsufflation after gastrointestinal tumor surgery, measured over up to 8 weeks.

The primary endpoint means are 3.8 days for Group Cardiac Index and 2.7 days for Group Stroke Volume Variation. The reported mean difference is -1.1 days, with an unadjusted p-value of <0.001; the confidence interval lies below zero. Safety summaries list serious events, other events, and deaths by group. Important analysis details, missing-data procedures, original sample-size justification, and results for the named secondary outcomes are not reported in the registry record.