Using Electrical Bioimpedance Assessments to Estimate Perioperative Total Body Water and Postoperative Fluid Need: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Using Electrical Bioimpedance Assessments to Estimate Perioperative Total Body Water and Postoperative Fluid Need (NCT02200055), a na na study. The primary outcome is Bioimpedance Assessment.

2. Clinical Question

3. Trial Design

This is a completed, single-group study registered as NCT02200055. The registry describes the only group as patients undergoing major intra-abdominal surgical procedures and names the Bodystat Quadscan 4000 as the device intervention. The record lists enrollment of 86. It does not describe a randomized allocation or a parallel control group.

The study start is recorded as 2012-05, and primary completion as 2015-07. The sponsor is United States Naval Medical Center, Portsmouth. Phase is listed as NA, allocation as NA, and masking as NONE. These registry labels describe the record; they do not establish additional design details beyond those explicitly stated.

The primary outcome concerns bioimpedance measurements recorded before the surgical procedure. It is described as the mean, with standard deviation, in ohms, among participants with preoperative bioimpedance measurements. The record also lists secondary measures concerning extracellular and intracellular water volume, daily fluid balance, urine output, body mass index, and American Society of Anaesthesiologists Physical Status Classification Scale. The specific results for those measures are not reported in the registry record.

The study summary describes comparing bioimpedance data with traditional measures of fluid status, including urine output and central venous catheter measurements. However, the full measurement schedule, analysis details, and comparative findings are not reported in the registry record. No randomized treatment comparison can be inferred from this single-group design.

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

Analysis population for the primary outcome, as defined in the registry: This is the population of participants with bioimpedance measurements taken preoperative

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.

Population: The number of participants meeting study eligibility requirements

6. Primary Endpoint

The registry lists the primary outcome as Bioimpedance Assessment, measured over preoperative measurement.

The primary endpoint is the preoperative bioimpedance assessment, recorded in ohms and summarized using a mean and standard deviation. The registry describes this outcome population as participants with bioimpedance measurements taken preoperatively. It does not provide the numerical mean, standard deviation, or number of participants contributing to that outcome.

Bioimpedance uses small electrical currents, according to the registry’s study summary, to estimate aspects of body water. The study’s broader rationale is to assess whether these measurements can help characterize fluid shifts associated with major intra-abdominal surgery. The primary outcome itself is specified in ohms; it should not be mistaken for a direct reported volume of total body water or for a measured postoperative fluid requirement.

In general, a mean describes the average value of a continuous measurement, while a standard deviation describes how spread out individual measurements are around that average. Those summaries can help characterize the measurement distribution, but their interpretation depends on the actual values and the population measured. Because the primary numerical result is not reported in the registry record, the endpoint’s observed level and variability cannot be described.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a bioimpedance measurement reported in ohms. The registry specifies a mean as the summary parameter and standard deviation as the dispersion measure. The outcome timeframe is preoperative measurement. These details identify the type of endpoint and the intended summary, but they do not provide the observed mean, standard deviation, or analysis population size.

What does a mean describe?

In general, the mean is the arithmetic average of the measured values. It provides a central summary, but it can be affected by unusually high or low observations. The standard deviation describes how much individual values vary around the mean. It is not the same as the standard error, which describes the estimated precision of a sample mean. A standard deviation and a mean alone would not establish a relationship with another measure or demonstrate that the measurement is useful for predicting fluid need.

What would a comparison of measurements require?

The study summary says bioimpedance data were to be compared with traditional measures of body-fluid status. In general, the choice of analysis depends on the question: association, agreement, or prediction are distinct aims. Association asks whether values tend to vary together. Agreement asks whether two methods produce sufficiently similar values for the intended use. Prediction asks how well one measure forecasts another variable or outcome. A correlation alone, for example, does not establish agreement between methods. The registry record does not report which comparison analysis was used, its assumptions, or its results.

Why can repeated measurements matter?

In general, measurements taken from the same participant at different times are related rather than independent. An analysis of repeated measurements may need to account for within-participant correlation and changes over time. The study’s broad aim concerns fluid shifts during and after surgery, but the primary endpoint listed is a preoperative measurement. The timing and analysis of any additional measurements are not reported in the registry record, so the statistical handling of repeated observations cannot be assessed.

What does the planning illustration mean?

The registry includes assumptions for a planning illustration based on an observed effect: 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 non-time-to-event outcomes, the illustration is expressed as participants per arm for 80% power or another stated power level; time-to-event illustrations use a total number of events. These are planning assumptions, not a description of this study’s single-group design.

In general, a sample-size illustration estimates how many participants might be needed under specified assumptions to detect a target effect with a chosen probability, if those assumptions hold. It is not an observed study result or evidence that the completed study had a particular probability of detecting an effect. The registry record does not report a trial-specific sample-size justification, and the planning assumptions should not be treated as the study’s design plan.

What cannot be evaluated from the record?

The registry record does not report the primary outcome values, a confidence interval, a test statistic, or a p-value. It also does not report the statistical model, any covariate adjustment, the handling of missing measurements, or a detailed analysis population. Without those details and results, it is not possible to reproduce the primary analysis or assess its assumptions. General statistical concepts can clarify what the stated summaries mean, but they cannot fill in unreported study findings.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Bioimpedance Assessment")
n   <- c(45)
m   <- c(0.53)
sp  <- c(0.06)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Bioimpedance Assessment  45  0.530  0.060  0.512  0.548

11. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple outcome types, including extracellular and intracellular water-volume percentages, daily fluid balance, urine output, body mass index, and physical-status classification. It does not report a statistical plan describing which outcomes were designated for formal hypothesis testing, whether comparisons were prioritized, or how multiplicity was handled. A multiplicity adjustment or testing hierarchy is therefore not reported in the registry record.

In general, examining many outcomes or making many statistical tests can increase the chance of finding an apparently notable result by chance. Methods for addressing that issue depend on the study questions and analysis plan. Without a reported plan and outcome results, it is not possible to determine whether multiplicity affects interpretation in this study.

The record does not describe missing-data methods, reasons for missing measurements, or how participants with incomplete data were handled. It identifies the primary population as participants with preoperative bioimpedance measurements, but does not state how many contributed to the primary analysis. The analysis population and any exclusions from the registered enrollment are not reported in the registry record.

In general, missing measurements can affect interpretation if their availability is related to participant characteristics or measurement values. The pattern and handling of missing data are needed to assess that possibility. No assumptions about missingness or imputation can be inferred from the outcome description.

12. 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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: perineal wound infection (1.1%), bronchospasm (1.1%), upper gastrointestinal bleed (1.1%).

The registry reports a serious adverse event group titled Bioimpedance Assessment. It records 90 participants at risk, 3 affected by serious adverse events, and 0 deaths. These are the registry’s reported figures; the record’s enrollment figure is 86, and the different at-risk figure should be retained as recorded rather than reconciled by assumption.

The listed serious adverse event terms are perineal wound infection, Bronchospasm, and upper gastrointestinal bleed, each reported as 1.1%. These terms and percentages describe the registry’s serious-event listing. The record does not provide further event narratives, timing, severity details beyond the serious-event classification, or an explanation of how the percentages were calculated.

In general, an adverse-event count describes events recorded under the registry’s reporting definitions; it does not by itself establish that an event was caused by the device or study procedures. The registry figures also do not answer the primary question about the relationship between bioimpedance and fluid status. Safety reporting and measurement performance are separate considerations.

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

The study addresses whether electrical bioimpedance assessments can be related to perioperative fluid shifts in people undergoing major intra-abdominal surgery. It records a single-group design and identifies the Bodystat Quadscan 4000 as the device. Its primary outcome is a preoperative measurement in ohms, with mean and standard deviation specified as the summary approach. These details clarify what the study set out to measure.

The registry record does not report the primary outcome’s numerical findings. It also does not report quantitative comparisons between bioimpedance and traditional fluid-status measures, or results showing how the device relates to postoperative fluid need. The purpose statement should not be read as evidence that the device accurately estimates fluid status or changes clinical management.

In general, a measurement’s practical value depends on more than its ability to produce a numerical reading. Researchers may need to assess reliability, agreement with an appropriate reference, performance across relevant patient groups, and whether the measurement informs decisions or outcomes. Those questions require suitable data and analyses. The registry record does not report those findings.

The record’s single-group structure also limits what can be concluded about comparative effects. Without a separate control group, it does not provide a randomized comparison between strategies. The listed safety figures describe reported serious adverse events, but they do not establish a causal relationship with the device or answer the primary measurement question.

Accordingly, the record supports describing the study’s rationale, device, broad population, outcome definition, and reported safety figures. It does not support a conclusion about the magnitude, precision, or clinical importance of the primary result. Those outcome findings are not reported in the registry record.

14. Why This Trial Matters Statistically

This study raises a statistical question about measurement: whether a noninvasive electrical bioimpedance assessment can provide information about body-fluid status around major intra-abdominal surgery. The registry’s primary endpoint is a preoperative reading in ohms. Distinguishing that device reading from an estimate of body-water volume or a postoperative fluid requirement is important. They are related concepts in the study rationale, but they are not interchangeable endpoint definitions.

In general, evaluating a new measurement method involves more than reporting an average. The distribution of readings, their repeatability, their association with reference measures, and their agreement with those measures can all matter. If measurements are repeated over time, analyses may also need to account for their within-person relationship. The registry record does not report the analyses or results needed to assess these questions.

The study’s single-group design is also relevant. It can describe measurements within the enrolled group, but it does not by itself create a randomized comparison of competing management strategies. The registry’s planning assumptions, which describe equal allocation between two arms, are illustrations and not evidence that the completed study used that design.

The record therefore illustrates why statistical interpretation depends on both the endpoint definition and the analysis results. The numerical primary outcome, uncertainty estimate, and method-comparison findings are not reported in the registry record. Without them, the measurement question remains quantitatively unresolved in the posted results.

15. 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 most direct limitation for interpreting the registry record is that it does not report the primary outcome’s numerical mean or standard deviation. It also does not report an uncertainty interval or a test result. As a result, the size and precision of the primary measurement cannot be assessed from the record.

The study is listed as single-group, with no randomized control group. Although the summary describes an intended comparison with traditional measures of fluid status, the registry record does not report the comparison method or results. The record therefore does not establish agreement, predictive performance, or comparative benefit.

The primary endpoint is a preoperative bioimpedance measurement in ohms, while the broader study rationale concerns perioperative fluid shifts and postoperative fluid need. The registry record does not report the detailed timing and results of measurements relevant to those broader questions. The intervention description is also incomplete in the registry record, so further procedural details cannot be assessed.

The record does not report a trial-specific sample-size justification, a detailed statistical analysis plan, missing-data methods, or a description of the primary analysis population size. It lists multiple secondary outcome types without reporting a multiplicity strategy or their numerical findings. These omissions limit assessment of analytic choices and the robustness of any conclusions.

The registry lists 86 enrolled and an adverse-event group with 90 at risk. It does not explain this difference. The figures should be treated as separately recorded values, not reconciled through an assumption about participants or analysis populations.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Using Electrical Bioimpedance Assessments to Estimate Perioperative Total Body Water and Postoperative Fluid Need — NCT02200055.
• Registry record last updated 2018-08-28; status last verified 2018-08.
• Results first posted 2018-08-28.
• 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.

19. Record Summary

NCT02200055 is a completed, single-group study sponsored by United States Naval Medical Center, Portsmouth. The registry records enrollment of 86, a study start of 2012-05, and primary completion of 2015-07. Masking is listed as NONE, allocation as NA, and phase as NA.

The study concerns use of the Bodystat Quadscan 4000 for bioimpedance assessment in people undergoing major intra-abdominal surgery. Its primary outcome is a preoperative measurement in ohms, summarized as a mean with standard deviation. Numerical primary results and reported method-comparison findings are not reported in the registry record.

The record lists secondary measures relating to body-water compartments, fluid balance, urine output, and participant characteristics. It also records serious adverse event figures for the Bioimpedance Assessment group. Those safety figures do not provide the missing primary endpoint results.