Morphine Added to Ropivacaine for FICB for Postoperative Analgesia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Morphine Added to Ropivacaine for FICB for Postoperative Analgesia (NCT03875274), a randomized phase 4 study. The primary outcome is Duration of Analgesia.

2. Clinical Question

The record identifies postoperative pain as the condition and describes the study as investigating morphine as an adjuvant to ropivacaine for FICB. The comparison therefore concerns the reported duration of analgesia under the two block regimens, rather than a broad assessment of all postoperative pain outcomes. The primary endpoint is defined as the period in minutes when a patient is free of pain. The record does not report a more detailed definition of pain freedom, the assessment schedule, or the method used to determine when the pain-free period ended.

The posted group means were 634 minutes for ropivacaine with morphine and 541 minutes for ropivacaine with saline. The reported mean difference is 93 minutes, with the comparison expressed as ropivacaine with morphine relative to ropivacaine alone. The statistical question is whether the observed difference is compatible with no difference in the underlying group means, and how precisely the data estimate the mean difference. These are questions about the posted trial results, not a guarantee that the same difference would occur in another study or setting.

3. Trial Design

The registry record describes a completed, randomized, parallel-group phase 4 trial with triple masking. The enrollment recorded is 70. The brief summary calls the study prospective and randomized, and describes it as double blinded; the registry’s masking classification is triple. Which people or roles were masked, and how masking was maintained, are not reported in the registry record.

The two groups received FICB with ropivacaine 0.375% 20 ml plus either Morphine 2 ml or Normal saline 2 ml. The listed control group is the ropivacaine group. The primary outcome was duration of analgesia, a continuous measure reported as a mean and standard deviation, with a 24-hour timeframe. The record includes one outcome measure and no posted analysis entries.

The registry lists the study start as 2017-04-01, primary completion as 2017-12-31, and overall status as completed. The sponsor is B.P. Koirala Institute of Health Sciences. The record does not report the recruitment setting, eligibility criteria, participant characteristics, allocation method beyond randomization, or details of the masking process. It also does not report the trial’s original sample-size justification or the statistical analysis plan. Those omissions limit what can be inferred about the design beyond the characteristics explicitly recorded. In particular, the enrollment figure should not be treated as evidence about the trial’s planned power, because that design rationale is not 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.

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 Duration of Analgesia, measured over 24 hours.

The primary endpoint is duration of analgesia, measured in minutes over a 24-hour timeframe. The registry defines it as the period when a patient is free of pain. It is a continuous outcome, summarized using a mean and standard deviation for each group. The reported mean is 541 minutes in the ropivacaine group and 634 minutes in the ropivacaine-and-morphine group; the corresponding standard deviations are 167 and 164 minutes.

This type of endpoint is used to describe how long pain relief is reported to persist, rather than to count whether a single event occurred. Comparing group means gives a measure of the difference in average duration between the regimens. The standard deviations describe the spread of individual observations around each group’s mean; they are not confidence intervals and do not show the precision of the comparison by themselves.

The registry record does not specify how pain freedom was assessed, how often assessments were made, or whether the duration was determined by participant report, clinical assessment, or another method. It also does not report the outcome population in further detail. These missing definitions matter when interpreting what a difference in minutes represents and how consistently the endpoint could be measured.

7. Results Posted in the Registry

• Ropivacaine and Morphine Group: mean 634.00 versus 541.00 on control; difference 93.00 (95% CI 15.46 to 170.54), standardized effect d = 0.56; z-test p = 0.019.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports group means and standard deviations for a continuous outcome, along with a mean difference, a confidence interval, and an unadjusted p-value. The comparison is between ropivacaine with morphine and ropivacaine with saline. The reported estimate is the difference in group means, with the ropivacaine-and-morphine group as the first group in the comparison. The mean difference of 93 minutes is therefore oriented toward the higher mean in that group.

What does a mean difference represent?

In general, a mean is the arithmetic average of the recorded outcome values in a group. A mean difference compares the two group averages on the outcome’s original scale. Here the scale is minutes, so the difference is also expressed in minutes. This makes the estimate interpretable in the same units as the endpoint. It does not mean that each participant’s pain-free period differed by that amount: it is a summary of the group averages.

The standard deviations describe variation among observations within each group. In general, a larger standard deviation indicates more spread around that group’s mean. The reported standard deviations are 167 minutes for ropivacaine and 164 minutes for ropivacaine with morphine. They are not measures of uncertainty in the mean difference. The confidence interval is the reported measure that conveys uncertainty about that comparative estimate.

How should the p-value be read?

The unadjusted p-value is 0.019. In general, a p-value is calculated under a null hypothesis and statistical model, and describes how unusual data at least as incompatible with that null model would be if the model’s assumptions held. It is not a probability that the treatment difference is real, nor a direct measure of the magnitude of the observed difference. “Unadjusted” indicates that the posted value is not presented as adjusted for multiple comparisons. The registry record does not report whether any additional or sponsor-specific analyses were conducted.

A p-value is most useful when read alongside the estimated difference and its confidence interval. The estimate describes the direction and size of the observed group-average difference, while the interval describes a range of values compatible with the data under the interval method and its assumptions. Neither alone establishes whether the difference is important in a clinical or practical sense; the registry record does not report a threshold for interpreting the endpoint’s importance.

What assumptions underlie the comparison?

In general, methods for comparing means rely on assumptions about the data and sampling process. Common considerations include whether observations are independent, whether the analysis handles the distribution and variability of the outcome appropriately, and whether missing observations affect the estimate. The registry record does not report the specific statistical test or model used for the posted comparison, the distribution of individual durations, or any missing-data method. The reported summaries do not allow those details to be reconstructed.

Randomization and a parallel-group design describe important features of the comparison, but they do not provide the full analysis method. The record does not describe sequence generation, allocation concealment, masking roles, or whether the outcome analysis followed an intention-to-treat or another population definition. The arm counts and summary statistics alone cannot establish how every randomized participant was handled in the analysis.

What can the posted analysis establish?

The registry reports one primary outcome measure and no analysis entries. The stated comparison provides an estimate, interval, and unadjusted p-value for the mean difference in duration of analgesia. It does not report adjusted analyses, subgroup analyses, sensitivity analyses, or an analysis plan. Their conduct or absence should not be inferred from the lack of posted entries; they are not reported in the registry record.

In general, statistical uncertainty and study design are distinct considerations. The confidence interval quantifies uncertainty in the estimated difference under a statistical method; it does not account for every possible source of bias, such as measurement limitations or incomplete reporting. The randomized design is relevant to interpretation, while the unreported procedural and analytical details limit a fuller appraisal of how the result was obtained. The record does not report a sample-size justification or interim-analysis plan, so neither should be inferred from the enrollment or the p-value.

10. Confidence Intervals and Precision

The estimated mean difference in duration of analgesia is 93 minutes, with a 95% confidence interval from 15.46 to 170.5 minutes. The interval summarizes uncertainty about the comparative mean under the method used to calculate it. In general, a confidence interval is a range produced by a procedure that, over repeated studies under its assumptions, would cover the underlying quantity at the stated rate. It is not a range that contains a specified proportion of individual participants’ outcomes.

The interval’s lower end is above zero, while its upper end is substantially farther from zero. Thus, the posted estimate is compatible with a range of positive mean differences, rather than identifying one exact value. Its width signals that the precise size of the mean difference is uncertain. It does not indicate that every value inside the interval is equally likely, and it does not address possible bias or limits in outcome measurement.

The standard deviations of 167 minutes and 164 minutes describe the variability of observed durations within the groups; they should not be confused with the confidence interval for the difference. The unadjusted p-value of 0.019 is another summary of the data under a null model, but it does not replace the interval’s information about the range of estimates compatible with the analysis.

The registry record does not report the exact statistical method used to calculate the interval, details of missing-data handling, or analysis-population definitions. Those omissions prevent a complete assessment of the interval’s assumptions. The interval also does not establish whether the observed difference is clinically important; no threshold for an important difference is reported.

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 sample-size figures are planning illustrations based on the observed effect, not the trial’s original design assumptions. They are stated as participants per arm, not as a total across groups or as total events. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect.

The 80% power column gives the illustrative number of participants per arm for a design with an 80% chance of detecting the specified effect under those assumptions, if the assumed effect and statistical model hold. The 90% power column gives the corresponding illustration for a 90% chance. These are planning concepts, not guarantees of what a future study would detect. This is not observed power.

For planning for 100% of the observed effect, the figures are 50 participants per arm for 80% power and 67 participants per arm for 90% power. For planning for 75% of the observed effect, they are 89 and 119 participants per arm. For planning for 50% of the observed effect, they are 199 and 267 participants per arm. The pattern illustrates a general principle: smaller effects are harder to detect and require more participants for the same target power, under otherwise unchanged assumptions.

The curve is a visual aid for the relationship between the assumed effect and the planning requirement; it should be read as an illustration based on these assumptions, not as a report of the trial’s actual power. The registry record does not report the original sample-size calculation or its design assumptions. These figures should therefore not be treated as evidence about the adequacy of the trial’s original enrollment.

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 = 93.000; pooled standard deviation σ = 165.507.
2. n = 2 × (1.96 + 0.842)² × 165.507² / 93.000² = 49.7, rounded up to 50 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 <- 93                      # observed difference in means
sigma <- 165.506797443489                     # 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(3875274)
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 = 50 (80% power), 67 (90% power)
 75% of observed effect: n per arm = 89 (80% power), 119 (90% power)
 50% of observed effect: n per arm = 199 (80% power), 267 (90% power)
power.t.test: 50.7 
Simulated power at n = 50 per arm: 0.795 (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 one outcome measure and no posted analysis entries. It does not list secondary outcomes. The primary endpoint is duration of analgesia, and the comparison includes an unadjusted p-value. Whether the trial investigators assessed additional outcomes or performed analyses not posted in the record is not reported in the registry record.

In general, multiplicity arises when a study makes several statistical comparisons or tests several outcomes. Repeated testing can increase the chance of at least one apparently noteworthy result under a null model. A statistical plan may address this through a prespecified hierarchy, adjustment, or another approach. The registry record does not report a multiplicity plan, any adjustment procedure, or whether the primary comparison was treated as the sole confirmatory test. The term “unadjusted” describes the posted p-value and should not be taken to imply how any unreported analyses were handled.

The record does not describe missing data, withdrawals, exclusions after randomization, or the number of participants included in the endpoint analysis. It lists 35 participants in each group for the primary outcome summaries, but does not state whether these counts represent all randomized participants, all treated participants, or a defined analysis population. The approach to missing endpoint observations is not reported in the registry record.

Similarly, the record does not identify an intention-to-treat, per-protocol, or other analysis population. The method used to handle protocol deviations or participants without a measured endpoint is also not reported. These details matter because an analysis can depend on who is included and how unavailable observations are treated. No specific method should be inferred from the posted group summaries.

In general, missing-data and multiplicity information help readers assess how robust a result may be to analytic choices. Their absence from the registry record is a reporting limitation; it does not demonstrate that the investigators did or did not use particular methods. The available result can be described as posted, but the analysis cannot be fully reconstructed from the record.

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 0% reporting threshold.

The adverse-event record lists 0 serious adverse events, 0 other adverse events, and 0 deaths in the ropivacaine group. For the ropivacaine-and-morphine group, it also lists 0 serious adverse events, 0 other adverse events, and 0 deaths. Each group’s adverse-event record lists 35 participants at risk for serious and other adverse events. No serious adverse-event terms are listed.

These are the counts recorded in the registry, not proof that no adverse effects occurred. In general, zero recorded events means that none were reported in the specified category and group in the available record. It does not rule out events that were not captured, not reported, or not classified in that category. The registry record does not describe the method or duration of adverse-event surveillance, criteria for event classification, or completeness of reporting.

The counts should be interpreted as safety reporting for this trial and not as a comprehensive comparison of every possible harm. The record does not provide event-level descriptions or additional safety analyses. These figures alone do not establish that either regimen is free of risk.

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

The posted results show a higher mean duration of analgesia in the ropivacaine-and-morphine group than in the ropivacaine group: 634 minutes compared with 541 minutes. The reported mean difference is 93 minutes, with a 95% confidence interval from 15.46 to 170.5 minutes and an unadjusted p-value of 0.019. These statistics describe the comparison observed for the registry’s primary endpoint.

The result does not show that every participant had a longer pain-free period, nor does it specify the outcome for any individual. The group standard deviations, 164 minutes and 167 minutes, indicate variation in recorded duration within each group. The confidence interval communicates uncertainty about the group-average difference; it is not a prediction interval for individual outcomes.

The result also does not by itself establish the practical importance of the difference. The registry record does not report a threshold for a clinically important change in minutes, nor does it provide other postoperative outcomes that would place this endpoint in a broader context. It reports one outcome measure and no analysis entries, so conclusions about outcomes beyond duration of analgesia cannot be drawn from these results.

The randomized design is relevant to the comparison, but the registry record does not report key details of sequence generation, allocation concealment, analysis populations, missing-data handling, or the statistical plan. The adverse-event record lists zero serious adverse events, zero other adverse events, and zero deaths in both groups; that record does not establish that there were no risks or unrecorded events.

Overall, the posted estimate is one trial’s comparison of the two specified FICB regimens for the defined pain-free duration. The interval and unadjusted p-value describe statistical uncertainty under the reported analysis, while missing design and analysis details limit a fuller assessment. The result should not be read as a guarantee of the same difference in other populations or settings.

16. Why This Trial Matters Statistically

This trial offers a useful statistical example of how a randomized comparison can be summarized on a continuous outcome. Duration of analgesia is reported in minutes, and the mean difference preserves those original units. The estimate of 93 minutes is more directly interpretable than a test result alone because it conveys the direction and size of the observed difference in group averages.

The confidence interval adds important context: the estimated mean difference is not known exactly, and the interval spans from 15.46 to 170.5 minutes. The reported p-value of 0.019 does not convey that range or indicate whether the estimate is clinically important. Reading the estimate, interval, and p-value together demonstrates why statistical significance and precision are related but distinct ideas.

The sample-size illustrations also show how planning depends on the effect a future study aims to detect. Under the stated assumptions, smaller target effects correspond to larger participant requirements per arm. These figures are not the original design calculation and are not observed power. This distinction matters because a planning illustration based on an observed effect cannot establish whether the original trial was adequately designed.

Finally, the record makes visible the limits of summary reporting. It supplies group-level outcome statistics but does not report the analysis plan, missing-data approach, analysis population, or multiplicity strategy. The safety counts are also limited to the adverse-event categories recorded. Together, these features make the trial a case study in both interpreting an estimated treatment contrast and recognizing what aggregate registry results leave unresolved.

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 does not report participant eligibility criteria, baseline characteristics, recruitment setting, or detailed descriptions of the population contributing to the primary outcome. As a result, the extent to which the observed group summaries apply to particular patient groups or settings cannot be assessed from this record.

There is a difference in masking wording within the record: the design classification says triple masking, while the brief summary describes a double-blinded study. The people or roles masked, and the procedures used, are not reported. Details of random sequence generation and allocation concealment are also not reported, limiting appraisal of how assignment was carried out.

The endpoint definition is brief. Although duration of analgesia is defined as minutes free of pain, the record does not state how pain freedom was assessed, how often it was assessed, or how the end of the pain-free period was determined. The specific statistical method, analysis population, handling of missing observations, and treatment of protocol deviations are not reported. The registry also provides no original sample-size justification or statistical plan.

Only one outcome measure is posted, and the record contains no analysis entries. It therefore does not provide a broader outcome profile or additional analyses that might clarify the robustness of the primary estimate. The adverse-event record lists no events in the reported categories, but surveillance details and event definitions are not reported. These limitations concern what can be evaluated from the registry record and should not be taken as evidence that unreported procedures or outcomes were absent from the study.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Morphine Added to Ropivacaine for FICB for Postoperative Analgesia — NCT03875274.
• Registry record last updated 2023-03-24; status last verified 2022-06.
• Results first posted 2023-03-24.
• 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

The registry record describes a completed, randomized, parallel-group phase 4 trial sponsored by B.P. Koirala Institute of Health Sciences. It lists an enrollment of 70, a study start of 2017-04-01, and primary completion on 2017-12-31. The two FICB regimens were ropivacaine with saline and ropivacaine with morphine.

The primary outcome was duration of analgesia, defined as minutes free of pain within a 24-hour timeframe. The reported means were 541 minutes for ropivacaine and 634 minutes for ropivacaine with morphine. The mean difference was 93 minutes, with a 95% confidence interval from 15.46 to 170.5 minutes and an unadjusted p-value of 0.019. The registry lists zero serious adverse events, zero other adverse events, and zero deaths in both groups. Analysis-plan details, missing-data methods, and the trial’s original sample-size assumptions are not reported in the registry record.