Accupressure of P6 to Reduce Nausea During Cesarean Section: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Accupressure of P6 to Reduce Nausea During Cesarean Section (NCT04799587), a randomized na study. The primary outcome is Presence of Intraoperative Vomiting.

2. Clinical Question

The trial focused on intraoperative and postoperative nausea and vomiting, with the primary endpoint specifically defined as the presence of intraoperative vomiting. The registry’s description states that the study evaluated whether adding P6 pressure-point stimulation, rather than sham-point stimulation, would reduce these symptoms. Its stated hypothesis concerned a reduction in intraoperative emesis.

The registry describes the study in the context of an institutional standard of care that included a phenylephrine infusion, an intravenous fluid bolus, and ondansetron as needed during the operation. These details describe the stated background to the research question; the record does not establish which components each participant received. The central comparison is the assigned P6 magnet versus the sham-point magnet, with the outcome being whether vomiting occurred during the intraoperative period.

3. Trial Design

This was a randomized, parallel-group trial listed as completed. The registry lists an enrollment of 200. The posted results give 100 participants in the sham-pressure-point group and 99 in the P6 acupressure group for the primary outcome. The record does not explain the difference between the enrollment figure and the total shown in these two outcome groups.

The two groups received different placements of a magnet: at P6 for the intervention group, and at a sham point distal to P6 for the comparator group. The trial is listed as single-masked, but the registry record does not identify which people were masked or explain how masking was maintained. The study is listed as having no applicable phase designation.

The primary endpoint was the presence of intraoperative vomiting during scheduled cesarean delivery. The posted secondary outcomes include the number of intraoperative emesis episodes and the number of rescue antiemetic doses given for intraoperative nausea and vomiting. The record lists 22 outcome measures and 2 analyses, but does not describe the full analysis plan or the relationship among all listed outcomes.

The original sample-size rationale, target effect, and assumptions used to design the trial are not reported in the registry record. The sample-size illustrations accompanying the posted results are based on the observed effect and are separate from the trial’s original design rationale.

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:

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 Presence of Intraoperative Vomiting, measured over Intraoperative Period.

The primary endpoint counts participants who experienced any vomiting during the intraoperative period. It is a binary outcome: for each participant, the recorded status is whether vomiting was present or absent during that defined period. It does not measure how many vomiting episodes occurred; the registry lists episode count as a separate secondary outcome.

This endpoint addresses the trial’s stated question about intraoperative emesis during scheduled cesarean delivery. A participant-level presence-or-absence outcome can be compared between randomized groups using the proportion of participants with the event. That comparison summarizes how frequently the event was observed in each group, without distinguishing between participants who had one episode and those who had multiple episodes. The separate secondary measure of episode count is relevant to that distinction.

The registry lists 17 participants with vomiting among 100 in the sham group and 17 among 99 in the P6 group. These are the posted counts for the primary endpoint. The endpoint definition does not establish whether nausea occurred, how severe symptoms were, or whether vomiting was accompanied by nausea; those are distinct clinical details and are not captured by this binary measure alone.

7. Results Posted in the Registry

• P6 Accupressure Group: 17.2% (17/99) versus 17.0% (17/100) on control; risk difference 0.2 percentage points (95% CI -10.3 to 10.6), risk ratio 1.01 (0.55–1.86); unadjusted two-proportion z-test p = 0.974.

8. Statistical Interpretation

9. Statistical Methods Explained

What kind of outcome is being compared?

General: A binary outcome records whether each participant experienced an event. In this trial, the event was vomiting during the intraoperative period. The group-level event proportion is based on the number with the event and the number assessed. Comparing these proportions is one way to describe the difference between randomized groups.

The registry reports a risk-difference estimate, which expresses the absolute separation between the group risks, and also reports risk-ratio and odds-ratio estimates. These measures describe the same binary outcome on different scales. A risk difference is expressed as an absolute difference in risk; a risk ratio compares risks multiplicatively; and an odds ratio compares the odds of the event. Their numerical values should not be treated as interchangeable. The posted risk ratio is 1.01 and the odds ratio is 1.012.

What does a p-value say?

General: A p-value is calculated under a null hypothesis, often one that assumes no difference between groups. It indicates how compatible the observed data are with that hypothesis under the test’s assumptions. A small p-value can be evidence against the null hypothesis, but a large p-value does not establish that the null is true. It also does not quantify the probability that a treatment works or fails to work.

The sponsor’s posted analysis is described as a chi-squared test and reports p = .94. A separate unadjusted recalculation from the posted counts reports p = 0.974. The methods and assumptions used in the sponsor’s test beyond the named test are not reported in the registry record.

Why report an interval as well?

General: A confidence interval gives a range of values compatible with the data and the method used to calculate the interval. It conveys uncertainty around an estimate and is often more informative than a p-value alone. An interval that spans zero for a risk difference includes no absolute difference, but it can also include differences on either side of zero. That does not prove equivalence. The registry record does not state the confidence level for the interval associated with the recalculated risk difference.

Interval width reflects both the observed data and the amount of information available. With a limited number of observed events, plausible values can remain far apart even when the point estimate is close to zero. The estimate should therefore be read together with its interval, rather than interpreted as a precise statement based only on the point estimate.

Why can analyses differ slightly?

General: Analyses of the same outcome can produce different p-values or estimates if they use different test procedures, continuity corrections, adjustments, analysis populations, or rounding conventions. These are possible general reasons; the registry record does not identify a specific reason for the difference between the posted chi-squared p-value and the unadjusted recalculation. The reported comparison is not marked as discrepant, so the numerical results can be described together without asserting that one value corrects the other.

The recalculation is unadjusted and uses the posted summary counts. It does not reproduce an analysis of individual participant data, adjust for additional covariates, or account for details not present in the registry record. The sponsor’s reported result remains the record of the sponsor’s own analysis.

What does randomization contribute?

General: Random allocation aims to make the comparison groups similar, on average, with respect to factors that could affect the outcome. It supports a causal comparison when the trial is conducted and analyzed appropriately, but it does not guarantee that the groups are identical in every characteristic. The registry lists randomized allocation and a parallel model. It does not describe the randomization sequence, allocation concealment, or balance of baseline characteristics.

The study is listed as single-masked. Masking can reduce the influence of expectations on care or outcome assessment, depending on who is masked and how the outcome is measured. The registry record does not identify the masked party or provide details about masking procedures. Those omissions limit what can be inferred about protection against possible performance or assessment effects.

How should the other outcomes be viewed?

The registry lists 22 outcome measures, while 2 secondary outcomes are posted: intraoperative emesis episode count and rescue antiemetic doses for intraoperative nausea and vomiting. These outcomes address different aspects of symptoms and treatment than the primary presence-or-absence endpoint. Their results are not included in the registry record described for the primary comparison, so no conclusion about their observed values can be drawn.

General: When many outcomes or comparisons are examined, the chance of at least one apparently notable result can increase. A prespecified hierarchy or multiplicity adjustment can help define how such results should be interpreted. Whether the trial used such an approach, and how the remaining outcomes were analyzed, are not reported in the registry record.

10. Confidence Intervals and Precision

The point estimate for the primary comparison is close to no difference, but precision depends on the range of values compatible with the observed data, not just on how close the estimate is to zero. The reported interval for the risk difference crosses zero, so it includes the possibility of a difference in either direction. Its endpoints are not repeated because the record’s interval confidence level is not stated.

General: A confidence interval is a way to express uncertainty from sampling under a specified statistical method. A wide interval indicates that the data do not pin down the effect tightly. It is not a range that guarantees where the true value lies, and it does not assign a probability to a particular effect after the data have been observed.

The primary outcome counts were 17 in each group, with 100 participants in the sham group and 99 in the P6 group. The count of events and the denominators provide limited information about the comparison, and the recalculated interval reflects that uncertainty. The registry does not report the confidence level associated with this recalculated interval, so it should not be labeled with a particular level on the basis of the record alone.

The risk ratio is 1.01, but the reported interval for that measure is also broad. A point estimate near one is not proof that the underlying risks are identical. The interval should be read as evidence that the study’s estimate is not highly precise, rather than as confirmation of a null effect. Equivalence or non-inferiority would require an appropriate design and prespecified margin; such a margin is not reported in the registry record.

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 original trial design calculation. For this binary endpoint, the figures mean participants per arm. The total-events convention applies to time-to-event outcomes, not this endpoint.

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 registry record does not report the trial’s own original sample-size assumptions or justification.

The 80% power column describes the number of participants per arm that the planning calculation would require for an 80% chance of detecting the specified effect under those assumptions, if that effect were the true effect and the analysis conditions held. The 90% power column uses a higher target probability of detection and therefore calls for more participants per arm. These are design targets, not probabilities that the completed study has demonstrated its result.

Planning for 75% or 50% of the observed effect means targeting a smaller effect than the observed estimate. Smaller effects are harder to distinguish from random variation, so the planning figures rise as the target effect gets smaller. Because the observed risk difference is close to zero, these calculations produce very large sample-size requirements. They are not observed power: they are conditional illustrations of what a future study’s size might look like under the stated assumptions, not a measure of how likely this completed trial was to detect an effect after its results were known.

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 = 0.170; treatment proportion p₁ = 0.172; average p̄ = 0.171.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5323 = 1.0433.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5323 = 0.4480.
4. n = (1.0433 + 0.4480)² / (0.0017)² = 754,179.9, rounded up to 754,180 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 <- 0.17                          # control proportion
p1 <- 0.171717171717172                          # 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(4799587)
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 = 754,180 (80% power), 1,009,633 (90% power)
 75% of observed effect: n per arm = 1,339,428 (80% power), 1,793,113 (90% power)
 50% of observed effect: n per arm = 3,010,702 (80% power), 4,030,475 (90% power)
power.prop.test: 754179.9 
Simulated power at n = 754,180 per arm: 0.800 (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. Analyses Reported by the Sponsor

The registry’s sponsor-reported analysis is a chi-squared test with p = .94. The unadjusted recalculation from the posted summary counts gives p = 0.974, alongside a risk-difference estimate close to zero. Both p-values indicate that the respective test did not distinguish the observed groups at conventional significance thresholds, but neither p-value establishes equality or equivalence.

The two values need not be identical because the record does not provide enough detail to reproduce every feature of the sponsor’s analysis. Potential general sources of variation include the precise test implementation, adjustments, or rounding, but no specific explanation for this comparison is reported in the registry record. The recalculation is an unadjusted calculation from group-level summary statistics; it is not a replacement for an analysis of individual participant data.

The sponsor’s result should be understood as the trial’s posted analysis. The recalculated result provides a supplementary description based on the posted counts and should not be treated as evidence that the sponsor’s result is invalid. The registry does not provide a fuller analysis specification or identify whether the sponsor’s test used any additional procedures.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists 22 outcome measures, and 2 secondary outcomes are posted: intraoperative emesis episode count and the number of rescue antiemetic doses administered for intraoperative nausea and vomiting. The primary endpoint is the presence of intraoperative vomiting. These outcomes differ in what they measure and should not be treated as interchangeable endpoints.

General: Testing multiple outcomes can increase the chance of observing a nominally unusual result even when no underlying effects exist. Researchers may address this through prespecified primary and secondary outcome hierarchies, adjusted significance thresholds, or other methods. The registry record does not report whether such an approach was used, whether outcomes were prioritized, or whether the listed outcomes were all analyzed.

The posted results list 2 analyses. The full statistical analysis plan, including any multiplicity strategy, is not reported in the registry record. It is also not reported whether the analysis populations were defined as intention-to-treat, per-protocol, or another population, or how participants with incomplete outcome data were handled.

The number enrolled is 200, while the primary outcome groups list 100 and 99 participants. The record does not explain this difference or state whether an outcome was missing for a participant, whether any participant was excluded, or why the outcome denominators differ from the enrollment figure. No missing-data method, imputation procedure, or sensitivity analysis is described in the registry record.

These omissions do not establish that missing data or multiplicity affected the result. They mean that readers cannot assess those aspects of the analysis from the registry information alone. The primary comparison should therefore be read as the posted group-level result, without assuming an unreported analysis population, adjustment, or data-handling procedure.

15. 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.

Most frequent non-serious adverse event terms

The serious adverse event figures list 0 affected participants among 100 at risk in the sham-pressure-point group and 0 among 99 at risk in the P6 group. The record also lists 0 deaths in each group. These figures describe the serious adverse event counts recorded for the groups; they do not demonstrate that serious events are impossible or that the interventions have no safety risks.

The record lists other, non-serious adverse events for 57 participants in the sham group and 56 in the P6 group. Those figures are distinct from the serious adverse event counts. No serious adverse event terms are listed in the posted information. The registry record does not provide further detail about event types, severity, timing, relatedness, or the method used to collect adverse events.

Safety counts should be interpreted in the context of the number of participants observed and the information reported. Zero recorded serious events in these groups is a description of the posted data, not proof that an event could not occur. The figures alone also do not establish a difference in safety between groups.

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

The primary endpoint results show 17 participants with intraoperative vomiting in each group: 17 of 100 assigned to the sham pressure point and 17 of 99 assigned to P6 acupressure. The recalculated point estimate is close to no difference, and the sponsor-reported chi-squared analysis gives p = .94. The posted results do not identify a statistically clear difference on this primary endpoint.

That finding should not be translated into proof that the approaches are equivalent. The estimated interval includes differences in both directions and is not precise enough to rule out a potentially meaningful effect. The registry does not report an equivalence margin or a design intended to establish equivalence. A non-significant test is not evidence that the true effect must be zero.

The primary result addresses the presence of vomiting during the intraoperative period. It does not by itself answer whether the groups differed in nausea, the number of emesis episodes, rescue medication use, or postoperative nausea and vomiting. Although the record lists some of these as outcomes, the corresponding numerical results are not part of the primary comparison.

The trial involved women undergoing non-emergent cesarean delivery and compared magnets placed at P6 or a sham point. The result should be interpreted within that study context. The registry does not provide the detailed participant characteristics or analysis information needed to judge how broadly the findings apply.

In statistical terms, the observed counts are similar, but the uncertainty remains important. The data do not establish a clear difference on the primary endpoint, nor do they establish that no difference exists. They describe what was observed in the posted groups and the limits on precision around the comparison.

17. Why This Trial Matters Statistically

This trial illustrates why a point estimate and a significance test are not enough to interpret a randomized comparison. The event counts were 17 in each group, making the observed groups look similar on the primary outcome. However, the reported interval for the effect spans values on both sides of no difference. The uncertainty therefore matters alongside the similarity in counts.

It also illustrates the distinction between absence of evidence for a difference and evidence of equivalence. The posted chi-squared p-value is .94, and the unadjusted recalculation is 0.974. Neither result establishes that the groups have identical risks. To establish equivalence, a study would need an appropriate objective and prespecified margin; the registry record does not report such a margin.

The primary endpoint is binary and participant-based, while the listed secondary outcomes capture episode counts and rescue medication use. Those measures answer related but different questions. A clear statistical interpretation depends on keeping the endpoint definition, estimate, interval, and analysis method in view rather than treating all nausea-and-vomiting outcomes as one measure.

Finally, the sample-size illustrations show how planning calculations depend on the effect chosen for detection. Smaller target effects require more participants, and calculations based on an observed effect near zero can produce especially large planning figures. Such illustrations are useful for understanding precision and future design, but they are not retrospective evidence of the trial’s power.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary outcome is limited to whether vomiting occurred during the intraoperative period. It does not capture symptom severity, duration, timing within the operation, or the number of episodes. Episode count is listed separately as a secondary outcome, but its posted numerical result is not included in the primary comparison.

The registry lists 200 enrolled participants, whereas the primary outcome groups contain 100 and 99 participants. The reason for the difference is not reported in the registry record. The record also does not explain missing outcomes, exclusions, or the analysis population. These details matter when assessing whether all randomized participants contributed to the comparison and how incomplete information was handled.

The masking designation is single, but the registry does not identify who was masked or describe the procedures. The randomization sequence and allocation-concealment methods are also not reported in the registry record. Without those details, the extent to which allocation and outcome assessment were protected from potential bias cannot be fully evaluated from the registry entry.

The record lists 22 outcome measures but posts 2 secondary outcomes and 2 analyses. The full statistical plan, multiplicity strategy, and detailed results for other outcomes are not reported in the registry record. The original sample-size justification and design assumptions are also not reported. Consequently, the planning illustrations should not be mistaken for the trial’s original design calculation.

Finally, the reported confidence-interval level for the recalculated comparison is not identified in the registry record. The interval still communicates uncertainty, but the missing specification limits how completely its construction can be evaluated. These are limits of the information reported, not proof that the trial methods were inadequate.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Accupressure of P6 to Reduce Nausea During Cesarean Section — NCT04799587.
• Registry record last updated 2025-06-06; status last verified 2025-05.
• Results first posted 2025-06-06.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

The completed randomized, parallel-group trial compared a magnet placed at P6 with a magnet placed at a sham point distal to P6 among women undergoing non-emergent cesarean delivery. The registry lists an enrollment of 200 and a primary outcome of intraoperative vomiting.

The primary outcome counts were 17 of 100 in the sham group and 17 of 99 in the P6 group. The sponsor-reported chi-squared analysis gives p = .94; an unadjusted recalculation gives p = 0.974 and a risk ratio of 1.01. The results do not show a clear difference, while the reported interval indicates uncertainty in both directions.

The record lists intraoperative emesis episodes and rescue antiemetic doses as secondary outcomes. Details about missing data, analysis populations, multiplicity procedures, the original sample-size rationale, and the identity of the masked party are not reported in the registry record.