Pulmonary Function and Interscalene Block: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pulmonary Function and Interscalene Block (NCT02181296), a randomized na study. The primary outcome is Number of Patients With Paradoxical Diaphragmatic Movement.

2. Clinical Question

The clinical question concerns whether the concentration of ropivacaine used for an ultrasound-guided interscalene brachial plexus block is associated with different rates of paradoxical diaphragmatic movement after the block. The registry describes this movement as an indication of phrenic nerve blockade. The primary outcome was assessed 30 minutes after the block by ultrasonographic evaluation of the diaphragm.

The registry summary states the hypothesis that a lower concentration would result in a lesser degree of phrenic nerve block. The posted primary outcome addresses that question through an ultrasound finding, not through a direct measure of every aspect of nerve function. Pulmonary function and analgesia were also part of the study's stated interests, with secondary outcomes covering changes in forced vital capacity, changes in forced expired volume in the first second, and opioid requirements after surgery.

3. Trial Design

The registry describes a randomized, double-masked, parallel-group trial sponsored by the University of Pennsylvania. The trial status is completed. The listed start was 2014-07, and primary completion was 2016-02. The phase is recorded as NA. The comparison assigned participants to a block using either 0.1% or 0.2% ropivacaine.

The registry enrollment field gives 50. However, the brief summary says that 40 patients will be enrolled and describes an intended equal split between the concentrations. Those are different enrollment figures within the registry record. The posted primary-outcome groups contain 24 participants in the high-concentration group and 23 in the lower-concentration group. The primary-outcome description also notes missing ultrasound data for 3 participants: 2 from the 0.1% group and 1 from the 0.2% group. The record does not explain the difference between its enrollment figure, the brief-summary target, and the group counts used for the posted outcome.

Random allocation and double masking describe important features of the design, but the registry record does not report the allocation-generation method, how allocation was concealed, who was masked, or how masking was maintained. It also does not report detailed eligibility criteria, the setting, or the block procedure beyond describing it as ultrasound-guided. These details should not be inferred from the design labels.

The primary outcome was paradoxical diaphragmatic movement assessed 30 minutes after the block. The listed secondary outcomes were percentage change in forced vital capacity from pre-block to the post-block measurement in the post-anesthesia care unit, percentage change in forced expired volume in the first second after the block, and opioid requirements for 72 hours after surgery. Results for those secondary outcomes are not reported in the registry record. No protocol details or explanation of the original sample-size planning are reported in the registry record.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Paradoxical diaphragm movement at 30 min after the block. we had missing data on 3 patients ( 2 from the 0.1% group and 1 from the 0.2% group)

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 Patients With Paradoxical Diaphragmatic Movement, measured over 30 minutes after the block.

The primary endpoint is the number of participants with paradoxical diaphragmatic movement 30 minutes after the block. The registry describes the movement as an indication of phrenic nerve blockade and says it was assessed by ultrasound visualization of the diaphragm. The posted results give 16 participants with the outcome in the high-concentration group, whose group denominator was 24, and 8 in the lower-concentration group, whose denominator was 23.

This endpoint makes a physiological effect of the block observable through diaphragm movement. It is not itself a complete account of pulmonary function, pain relief, or all consequences of phrenic nerve blockade. The study listed separate secondary outcomes for changes in forced vital capacity and forced expired volume in the first second, as well as opioid requirements after surgery. Their results are not reported in the registry record.

The endpoint's interpretation also depends on the ultrasound assessment being available. The registry notes missing data for 3 participants, with 2 missing from the lower-concentration group and 1 from the high-concentration group. The group denominators in the posted primary results are therefore the counts to use when reading the outcome, rather than treating the registry enrollment figure as the denominator for this endpoint. The record does not report how the missing measurements were handled in the analysis or whether any additional outcome definitions were used.

7. Results Posted in the Registry

• Lower Concentration Group: 34.8% (8/23) versus 66.7% (16/24) on control; risk difference -31.9 percentage points (95% CI -59.0 to -4.8), risk ratio 0.52 (0.28–0.98); unadjusted two-proportion z-test p = 0.029.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted primary comparison is an unadjusted comparison of a binary outcome: each participant either had paradoxical diaphragmatic movement recorded or did not. For a binary outcome, the group count with the event is read alongside the group denominator. The registry reports 16 events among 24 participants in the high-concentration group and 8 among 23 in the lower-concentration group. The denominator matters because the group sizes differ and because ultrasound data were missing for some participants.

What does the risk difference describe?

General statistical explanation: a risk difference subtracts the event proportion in one group from the event proportion in the other. Its sign depends on the order of the groups. In the posted comparison, the lower-concentration group is contrasted with the high-concentration group, and the estimated risk difference is negative. That sign indicates that the observed event proportion was lower in the lower-concentration group. The risk difference is an absolute contrast in proportions, rather than a relative measure. It does not indicate how important the difference is for patients or how outcomes beyond this endpoint compare.

What does the p-value tell us?

The posted p-value is unadjusted and equals 0.029. General statistical explanation: a p-value describes how unusual data at least as incompatible with a specified null comparison would be if that null model and the analysis assumptions held. It is not the chance that the null is true, and it is not a measure of the probability that the finding will be replicated. The registry record does not name the exact test or report enough detail to identify all computational choices behind the p-value. Those choices should not be guessed.

What does the confidence interval add?

General statistical explanation: a confidence interval gives a range of values compatible with the data and the method used to construct it. It presents uncertainty about the estimated contrast, including the direction and possible magnitude of the difference. The posted interval for the risk difference lies below zero, while still spanning a range of possible effect sizes. The interval's construction method and confidence level are not reported in the registry record, so they cannot be specified from the record.

Why distinguish absolute and relative comparisons?

General statistical explanation: a risk difference gives an absolute contrast in event proportions. Relative measures instead compare one group's event frequency with the other's by a ratio. The posted comparison also includes a risk ratio and an odds ratio with confidence intervals. These measures express the contrast on different scales and are not interchangeable. A ratio can look different from an absolute difference, even when both are calculated from the same group counts. Each should be interpreted with its own definition and uncertainty interval. The registry record does not report a preferred measure or a clinical threshold for interpreting these contrasts.

How should randomization be understood?

General statistical explanation: random allocation is intended to make the comparison between assigned groups less dependent on participant characteristics that could influence the outcome. It does not ensure that every feature is balanced in the realized groups, nor does it remove uncertainty from a trial with finite data. Here, the registry identifies the study as randomized, double-masked, and parallel-group. The sequence-generation and concealment procedures are not reported in the registry record. The analysis population and whether participants were analyzed according to assignment are also not reported in the registry record.

What does over-dispersion mean for this outcome?

General statistical explanation: over-dispersion is a concern when observed variability exceeds what a statistical model expects. It often arises in count or rate outcomes when observations are more heterogeneous than the model allows. The primary outcome is reported as participants with an event, rather than as a repeated count or rate with an exposure time. The registry record does not report an over-dispersion assessment or a model that would permit one to evaluate. It would be inappropriate to assume that an over-dispersion adjustment was used.

What remains unknown about the analysis?

The registry record does not report the exact statistical test, any covariate adjustment, the confidence-interval method, an analysis plan, or the original sample-size justification. The record lists three secondary outcomes, but results for them are not reported. It also lists zero analyses, despite including posted group results and a comparison for the primary outcome. These record details do not explain how the results were generated. The primary comparison should therefore be described using its reported, unadjusted estimate, confidence interval, and p-value, without attributing unreported methods to the investigators.

10. Confidence Intervals and Precision

The risk-difference confidence interval is an important part of the interpretation because it conveys uncertainty beyond the single point estimate. The interval reported for the lower-concentration group relative to the high-concentration group remains below zero. This is consistent with a lower event proportion in the lower-concentration group, while allowing a range of possible differences. The interval is not so narrow that the exact size of the difference can be treated as settled.

Precision is distinct from whether a p-value crosses a conventional threshold. The posted unadjusted p-value is 0.029, but the p-value alone does not show the range of effects compatible with the data. The interval communicates that range, subject to the method used to calculate it. The registry record does not report the interval's construction method or confidence level, so those details cannot be assessed from the record.

The endpoint counts are based on 24 participants in the high-concentration group and 23 in the lower-concentration group. The primary outcome description notes missing ultrasound data for 1 participant in the 0.2% group and 2 in the 0.1% group. The record does not say whether the missingness could be related to participant characteristics or outcomes, or whether any imputation or sensitivity analysis was performed. If missingness is related to the endpoint, uncertainty may be affected in ways that the reported interval alone does not capture.

The interval concerns the registered primary outcome and this unadjusted group comparison. It does not express uncertainty for the unreported pulmonary-function or analgesia outcomes, and it does not resolve questions about analysis populations or multiplicity. Its interpretation should remain tied to the specific endpoint and available data.

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 estimates are planning illustrations based on the observed effect, not a report of the trial's original design calculation. They assume a two-sided significance level of 0.05, equal allocation between the arms, and a normal approximation. Each planning scenario uses a stated fraction of the observed effect as the effect to detect. For this binary outcome, the figures are participants per arm, not total events.

The row for 100% of the observed effect gives 38 participants per arm for 80% power and 50 participants per arm for 90% power. The row for 75% of the observed effect gives 67 participants per arm for 80% power and 89 participants per arm for 90% power. The row for 50% of the observed effect gives 149 participants per arm for 80% power and 199 participants per arm for 90% power. The planning table and curve express the same relationship in different formats.

In plain language, the 80% power column gives the estimated participants per arm for a study designed to have an 80% chance of detecting the specified effect under the stated assumptions if that effect is real. The 90% power column gives the corresponding estimate for a 90% chance. These are design probabilities under assumptions, not probabilities that the observed finding is true. Smaller effects require more participants to detect, which is why the estimates rise as the assumed fraction of the observed effect falls.

This is not observed power. The registry record does not report the trial's original sample-size justification or its original design assumptions. The planning figures should be read as illustrations tied to the observed endpoint contrast and the stated assumptions, not as evidence about the trial's actual power or as a record of its planned 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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.667; treatment proportion p₁ = 0.348; average p̄ = 0.507.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.7070 = 1.3858.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6701 = 0.5640.
4. n = (1.3858 + 0.5640)² / (-0.3188)² = 37.4, rounded up to 38 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
p0 <- 0.666666666666667                          # control proportion
p1 <- 0.347826086956522                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2181296)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 38 (80% power), 50 (90% power)
 75% of observed effect: n per arm = 67 (80% power), 89 (90% power)
 50% of observed effect: n per arm = 149 (80% power), 199 (90% power)
power.prop.test: 37.4 
Simulated power at n = 38 per arm: 0.810 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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 lists three secondary outcomes in addition to the primary outcome. They concern percentage change in forced vital capacity, percentage change in forced expired volume in the first second, and opioid requirements for 72 hours after surgery. Results for those secondary outcomes are not reported in the registry record. The record does not report whether the outcomes were tested as a family, whether any multiplicity adjustment was planned, or how the primary endpoint was prioritized if several results were considered.

General statistical explanation: when several outcomes or comparisons are examined, the chance of finding at least one apparently unusual result can increase if each is assessed separately. Methods that account for multiple testing can change how inferential evidence is interpreted. Whether such methods are needed depends on the analysis plan and the claims being made. Since the registry record does not report a multiplicity strategy, the primary comparison's p-value should be treated as unadjusted rather than assumed to reflect any correction.

The primary outcome description explicitly reports missing ultrasound measurements for 3 participants: 2 from the 0.1% group and 1 from the 0.2% group. The posted primary counts use denominators of 23 and 24, respectively. The record does not report why the measurements were missing, whether the missingness was related to the outcome, how missing data were handled, or whether sensitivity analyses were conducted. It also does not report imputation.

The analysis population is not described. The registry identifies randomized allocation, but does not say whether the posted outcome analysis included all randomized participants, only participants with an observed ultrasound assessment, or another defined population. The group denominators indicate which participants contribute to the posted outcome counts, but do not establish the analysis rule used. Interpretation should therefore distinguish the randomized design from the unreported details of the analysis set and missing-data approach.

The enrollment field gives 50, while the brief summary says 40 patients will be enrolled. The primary outcome groups have denominators of 24 and 23, with missing measurements noted separately. The record does not reconcile these figures. No further explanation should be inferred from the posted results.

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 5% reporting threshold.

The serious adverse event figures list 25 participants at risk in each group, with 0 serious events in the high-concentration group and 0 in the lower-concentration group. The record also lists 0 other adverse events in each group and 0 deaths in either group. These are the registry's reported figures for the adverse-event categories; they should not be treated as evidence that no adverse effects of any kind occurred.

General statistical explanation: a zero count in a study does not establish that the underlying event risk is zero. The amount of information depends on the number of participants observed, the completeness of safety reporting, and the duration and method of follow-up. The registry record does not describe the safety-collection period, definitions, ascertainment procedures, or whether all participants contributed safety data. It also does not provide event-level descriptions.

The safety figures are separate from the primary diaphragm-movement outcome, which had reported events in both groups. The adverse-event summary does not supply a comparison estimate or confidence interval. The registry lists no serious adverse-event terms. These figures should therefore be read narrowly as the reported counts, not as a comprehensive characterization of safety.

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

The posted primary result is a comparison of paradoxical diaphragmatic movement after interscalene block with 0.1% versus 0.2% ropivacaine. The event count was lower in the lower-concentration group: 8 of 23 compared with 16 of 24 in the high-concentration group. The reported risk-difference interval lies below zero, and the unadjusted p-value is 0.029. Taken together, these statistics describe an observed group contrast whose direction is consistent with fewer recorded events in the lower-concentration group, while leaving uncertainty about the contrast's exact size.

This result does not establish the effect on every aspect of phrenic nerve function, pulmonary function, analgesia, or recovery. The registry listed forced vital capacity, forced expired volume in the first second, and opioid requirements as secondary outcomes, but their results are not reported in the registry record. The primary endpoint is an ultrasound finding at a specified post-block time, not a complete account of those other outcomes.

The record also leaves uncertainty about missing ultrasound data, analysis populations, and multiplicity. The registry's enrollment field and brief-summary enrollment statement differ, and the record does not reconcile those figures with the outcome denominators. The randomized, double-masked design is relevant context, but procedural details and the analysis plan are not reported in the registry record.

The result is therefore best understood as the posted unadjusted comparison for the registered diaphragm-movement endpoint, in the groups and denominators reported. It does not establish broader clinical benefit or harm, nor does it show what would happen in other settings or populations. It should not be used on its own to make an individual treatment decision.

16. Why This Trial Matters Statistically

This trial illustrates how a physiological endpoint can be represented as a binary outcome: whether a participant had paradoxical diaphragmatic movement at a specified time after the block. That makes the primary comparison accessible through event counts and denominators. It also shows why interpretation should retain the endpoint's exact meaning. A diaphragm movement finding is related to the study's stated interest in phrenic nerve blockade, but it does not substitute for the separately listed pulmonary-function and analgesia outcomes.

The contrast is reported in several forms, including an absolute risk difference and relative measures. General statistical explanation: different effect measures answer related but distinct questions. Absolute contrasts communicate the difference in event proportions, while relative measures compare event frequencies on a ratio scale. Reading the estimate together with its confidence interval is more informative than relying on a single significance test.

The registry record also illustrates the importance of transparent reporting. It identifies a randomized, double-masked design and gives group outcome counts, yet does not report the exact test, interval method, analysis population, missing-data approach, or multiplicity plan. The enrollment field and the brief summary give different enrollment figures. Such details affect how confidently readers can connect the planned design to the analyzed outcome.

Finally, planning estimates based on the observed effect are not a substitute for an original design justification. They show how participant requirements change under stated assumptions and smaller target effects, but do not reveal what the investigators planned before observing trial data. Keeping these distinctions clear helps readers separate the observed result, the uncertainty around it, and hypothetical future-study planning.

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 primary outcome has missing ultrasound measurements for 3 participants, with 2 from the lower-concentration group and 1 from the high-concentration group. The registry does not report the reasons for missingness, how those measurements were handled, or whether the missingness could be related to diaphragm movement. The reported denominators therefore describe the posted endpoint data, but the record does not explain how missing outcomes were addressed in the analysis.

The registry enrollment field is 50, while the brief summary states that 40 patients will be enrolled. The posted primary outcome denominators are 24 for the high-concentration group and 23 for the lower-concentration group. The record does not reconcile the enrollment statement, enrollment field, missing measurements, and analyzed denominators. The discrepancy limits what can be concluded about participant flow from the registry record alone.

The registry identifies randomization and double masking but does not report the sequence-generation or allocation-concealment methods, who was masked, or how masking was maintained. Detailed eligibility criteria and the precise procedure are also not reported in the registry record. These omissions prevent a fuller assessment of design implementation and the population to which the findings may apply.

Several outcomes were listed, but secondary-outcome results are not reported. The registry also does not report the statistical test, confidence-interval method, analysis population, multiplicity plan, or original sample-size rationale. The posted p-value is unadjusted. Together, these reporting gaps limit assessment of the complete analysis strategy and the extent to which the primary result was selected or interpreted alongside other outcomes.

The safety summary reports zero serious adverse events, other adverse events, and deaths in each group, but it does not describe safety follow-up or ascertainment. These figures should not be taken as a complete safety assessment. The limitations are specific to what the registry record reports and do not establish that unreported procedures or analyses did not occur.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Pulmonary Function and Interscalene Block — NCT02181296.
• Registry record last updated 2019-02-20; status last verified 2018-05.
• Results first posted 2018-11-02.
• 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 describes a completed, randomized, double-masked, parallel-group comparison of 0.1% and 0.2% ropivacaine for ultrasound-guided interscalene block in patients undergoing shoulder arthroscopy. The listed start was 2014-07 and primary completion was 2016-02. The primary endpoint was paradoxical diaphragmatic movement assessed by ultrasound 30 minutes after the block.

The posted counts were 8 of 23 participants in the lower-concentration group and 16 of 24 in the high-concentration group. The unadjusted risk-difference confidence interval lies below zero, and the unadjusted p-value is 0.029. The primary-outcome description notes missing ultrasound data for 3 participants.

The registry lists three secondary outcomes, but their results are not reported in the registry record. It also gives different enrollment figures in the enrollment field and brief summary, and does not explain the analysis population, missing-data handling, multiplicity strategy, or original sample-size justification. The posted safety figures report zero serious adverse events, other adverse events, and deaths in either group.