IV Acetaminophen for Postoperative Pain Analgesia After Laparoscopic Hysterectomy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for IV Acetaminophen for Postoperative Pain Analgesia After Laparoscopic Hysterectomy (NCT02400580), a randomized phase 4 study. The primary outcome is Postoperative Pain.

2. Clinical Question

The trial focused on pain after laparoscopic hysterectomy and also included narcotic medication use as a secondary outcome. The primary question concerns the difference in reported pain between randomized groups, not whether every participant experienced a particular level of pain. The posted results give a mean and 95% confidence interval for each arm. They do not report a direct between-group estimate, a hypothesis test, or a p-value for the primary outcome. The arm-level results therefore describe the observed scores and their uncertainty, but do not by themselves establish whether a between-group difference is statistically significant.

3. Trial Design

This was a phase 4, randomized, parallel-group, triple-masked trial comparing intravenous acetaminophen with normal saline in people undergoing laparoscopic hysterectomy. The registry record describes the study as double blind and placebo controlled in its official title; the structured masking description is triple. It does not specify which trial roles were masked, so the masking procedure cannot be characterized further from the record.

The trial enrolled 183 participants. The posted primary outcome includes 91 participants in the intravenous acetaminophen arm and 92 in the normal saline arm. The intervention description identifies the acetaminophen dose as 1000mg and normal saline as the placebo. Although the study summary describes pre- and post-operative administration, exact administration times and the number of doses are not reported in the registry record.

The study status is completed. The recorded start was 2015-02 and the primary completion was 2016-09. These dates describe the trial record and do not provide details about recruitment duration or follow-up beyond the stated primary outcome timeframe.

The primary outcome was postoperative pain at 24 hours, expressed as a mean score on a visual analog scale. Narcotic medication use is named as a secondary outcome. The registry record lists six outcome measures and one posted secondary outcome, but further details about the other measures and their results are not reported in the registry record. Allocation concealment, the randomization sequence method, protocol deviations, and the analysis population are not reported in the registry record. The record also does not give a detailed statistical analysis plan or explain how participants were handled if outcome data were unavailable.

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 Postoperative Pain, measured over 24 hours.

The primary endpoint is postoperative pain reported at 24 hours on a visual analog scale ranging from 0 to 10. The scale is described as running from no pain at all to the worst pain a person can imagine. The registry record states that less pain is preferable to more pain. This endpoint captures patients’ own assessments of pain at the specified follow-up time.

The posted summary statistic is the mean in each randomized arm, accompanied by a 95% confidence interval. A mean gives an overall summary of the scores in a group; it does not show the full distribution of participants’ scores or how many people experienced each level of pain. The confidence interval conveys uncertainty around the estimated group mean. It is not a range containing most individual patients’ scores.

A 24-hour measurement provides a defined time point for comparing the arms, but it does not describe pain at other times. The registry record does not report whether pain was measured repeatedly, how the 24-hour assessment was timed relative to surgery or medication, or how missing assessments were handled. Those details matter when interpreting what the endpoint represents and how broadly it reflects postoperative pain over time.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean summarize?

A mean is an average of the observed scores in a group. For this trial, the reported means summarize visual analog scale pain scores at 24 hours separately for the intravenous acetaminophen and normal saline arms. A mean is useful for a concise group comparison, but it does not show the spread or shape of the scores. Participants may have reported values across the scale even when a group mean is similar to another group’s mean. The registry record does not provide a standard deviation, a distribution of individual scores, or other detail about within-arm variability.

The scale’s direction is important for interpretation: the registry record says that less pain is preferable. The means should therefore be read with the scale definition in mind, rather than treated as measures where a larger value is automatically favorable. The mean remains a group summary, not an individual prediction.

What does a 95% confidence interval mean?

A confidence interval expresses uncertainty about an estimated quantity, such as a group mean. In general statistical terms, a 95% confidence procedure is constructed so that, over repeated use under its assumptions, intervals would cover the target quantity at the stated rate. For an individual study, the interval gives a range of values compatible with the estimate under the procedure’s assumptions. It does not mean that 95% of participants’ scores fall inside the interval, and it does not establish that an effect is clinically important.

The posted intervals are for the mean within each arm. A direct comparison would ordinarily focus on a between-group contrast and the uncertainty around that contrast. Separate arm intervals do not provide the same information as an interval for the contrast. The registry record does not post a contrast estimate or a primary-outcome p-value, so neither can be described from these results.

How should the arm comparison be read?

The reported arm means are 3.55 for intravenous acetaminophen and 3.11 for normal saline. Because lower scores are described as preferable, the observed mean in the acetaminophen arm is not lower than the observed mean in the saline arm. This descriptive direction is not, by itself, an inferential conclusion. A randomized comparison is interpreted using the estimate of the between-group effect, its uncertainty, and the prespecified analysis. The direct estimate and the analysis details are not reported in the registry record.

Overlapping confidence intervals are not a definitive test of whether two means differ. A test or interval for the contrast uses the comparison itself and its uncertainty. The two arm-level intervals also should not be read as if they describe the range of possible scores for an individual. Their breadth indicates uncertainty about the group means, but the record does not provide enough information to reconstruct a formal comparison.

What can be inferred from the participant counts?

The primary outcome lists 91 participants in the intravenous acetaminophen arm and 92 in the normal saline arm. The trial’s total enrollment is 183. The record does not state whether all randomized participants contributed a 24-hour pain score, whether any participants were excluded from the analysis, or how incomplete measurements were treated. It is therefore not possible to identify the analysis population from these counts alone.

Randomization is intended to support a fair comparison by assigning participants to groups through a chance process. The record identifies the study as randomized, but does not describe sequence generation, allocation concealment, or the analysis approach used to preserve the randomized comparison. Those implementation details are not reported in the registry record. No adjusted or unadjusted treatment estimate is posted for the primary endpoint.

What does the planning illustration represent?

Planning illustrations based on an observed effect are different from observed trial results and from the trial’s original sample-size justification. The stated approach uses a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect defined as a stated fraction of the observed effect. Such calculations illustrate the participant numbers that might be required under those assumptions; they do not show the probability that this completed trial detected an effect. They are not observed power.

The registry record does not report the trial’s original sample-size justification, the assumptions used when the trial was designed, or the target effect and power used in its planning. Nor does it report enough primary-comparison details to explain a trial-specific power calculation. A planning calculation based on the observed result is retrospective and should not be used to replace the primary analysis.

What is not available about the analysis?

The record lists outcome measures and analyses, but it does not describe the statistical model, the test used for the primary comparison, any covariate adjustment, or a prespecified hierarchy of outcomes. It also does not report interim analyses, multiplicity adjustments, or a detailed missing-data method. These omissions limit the ability to assess whether the posted arm summaries correspond to the planned primary analysis. Without those details, interpretation should remain anchored to the stated endpoint and the arm-level estimates, rather than assuming unreported methods.

10. Multiplicity, Missing Data and Analysis Populations

The registry record identifies postoperative pain as the primary outcome and narcotic medication use as a secondary outcome. It lists six outcome measures, while one secondary outcome is posted by name. The details and results for the remaining measures are not reported in the registry record. The record does not explain whether outcomes were organized into a testing hierarchy, whether multiple comparisons were planned, or whether any adjustment for multiplicity was used.

Multiplicity matters when several outcomes or comparisons are examined because repeated testing can increase the chance of a chance-positive finding. That general concern does not establish that an error occurred in this trial. The posted information is insufficient to determine how multiplicity was addressed, so no adjustment or absence of adjustment should be assumed.

The registry record lists 91 participants for the primary outcome in the intravenous acetaminophen arm and 92 in the normal saline arm, but does not state whether these are all randomized participants or only those with usable outcome data. It does not report the number or reasons for missing pain scores, any imputation method, or sensitivity analyses for missing data. The analysis population and whether the analysis followed randomized assignment are also not reported in the registry record.

These omissions matter because missing outcomes can affect the estimate if their occurrence is related to treatment assignment or pain. The available arm means remain interpretable as posted summaries, but the record does not establish how representative they are of all randomized participants.

11. 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: in patient hospitalization (1.1%).

The serious-adverse-event figures record 1 affected participant among 91 at risk in the intravenous acetaminophen arm and 0 among 92 at risk in the normal saline arm. The listed serious term is “In patient hospitalization,” reported as 1.1%. No deaths are recorded in either arm. These are counts in the registry record, not estimates of a comparative safety effect.

The other adverse-event counts are 10 among 91 participants in the intravenous acetaminophen arm and 11 among 92 in the saline arm. The record distinguishes these counts from the serious-event counts. It does not provide event-level descriptions, timing, duration, severity grading beyond the serious classification, or judgments about whether events were related to treatment. The listed serious term should not be assumed to explain every adverse event.

Small event counts are descriptive and can be imprecise. A count of zero in an arm means no event was recorded there in this dataset; it does not establish that an event cannot occur. The registry record does not post a formal between-arm safety comparison or further detail about how adverse events were collected. These figures should therefore be read as reported counts, not as proof of a treatment-related cause or a complete account of safety.

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

The posted results describe mean pain scores at 24 hours for a randomized comparison of intravenous acetaminophen and normal saline after laparoscopic hysterectomy. The acetaminophen arm mean was 3.55, with a 95% confidence interval from 1.08 to 6.02; the saline arm mean was 3.11, with a 95% confidence interval from 0.89 to 5.33. These values summarize group-level outcomes on a scale from 0 to 10, where lower pain scores are described as preferable.

Those figures do not establish whether the groups differed statistically. The registry record does not report a direct estimate of the between-group difference, a confidence interval for that contrast, or a p-value for the primary outcome. Arm-level means and their separate confidence intervals are not a substitute for those quantities. The available results also do not state a threshold for a clinically important difference, so the clinical importance of any contrast cannot be assessed from the posted information.

The findings are specific to the recorded 24-hour endpoint and the participants included in the posted summaries. They do not establish what pain was like at other time points, whether every participant had a measured outcome, or how narcotic medication use differed between arms. Although narcotic medication use is named as a secondary outcome, its numerical result is not reported in the registry record.

The trial’s randomized, parallel-group design provides a framework for comparing assigned groups, but important analytical details are absent. The record does not describe the primary statistical test, missing-data handling, or analysis population. The data therefore support a limited account of the posted arm means, confidence intervals, and adverse-event counts. They do not support a broader claim about treatment benefit, lack of benefit, or comparative safety.

13. Why This Trial Matters Statistically

This trial illustrates why the form of a posted result matters as much as the direction of an arm mean. A randomized study can report a mean for each group, but the main inferential question concerns the between-group contrast and its uncertainty. Without that contrast, readers can describe the observed arm summaries but cannot determine from the registry record whether the primary comparison was statistically distinguishable from no difference.

The 95% confidence intervals also demonstrate the distinction between uncertainty around group means and variability among individual participants. They are intervals for estimates, not ranges of patient scores. The intervals are broad and overlap, but that observation does not replace a formal comparison of groups. Clear reporting of an effect estimate and its confidence interval would make the primary result easier to interpret.

The trial record also highlights the importance of documenting analysis populations and missing-data methods. The group counts attached to the primary outcome do not, by themselves, explain whether all randomized participants were analyzed. Without that information, readers cannot fully assess how the outcome summaries relate to the randomized cohort.

Finally, a planning illustration based on an observed effect has a different role from the original design justification. It can show how assumptions about an effect and allocation relate to a hypothetical sample-size calculation, but it is not observed power and does not explain the original design. Distinguishing those purposes helps prevent retrospective calculations from being mistaken for evidence about the success of the trial’s planned analysis.

14. 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 available primary results are arm-level means and confidence intervals. A direct between-group estimate, its confidence interval, and a p-value are not reported in the registry record. This restricts interpretation to descriptive comparisons and prevents a direct assessment of statistical uncertainty around the contrast.

The record does not describe the analysis population, whether participants were analyzed according to randomized assignment, or how missing 24-hour pain scores were handled. Although the outcome counts are listed by arm, their relationship to all randomized participants is not explained. The record also does not report individual-score distributions or a standard deviation, limiting assessment of variability within each arm.

Details of randomization and masking procedures are limited. The trial is identified as randomized and triple masked, while its official title describes it as double blind; the identities of masked trial roles and the masking procedures are not reported in the registry record. The exact timing and schedule of acetaminophen administration are also not specified, despite the summary’s reference to pre- and post-operative treatment.

The 24-hour pain endpoint does not describe outcomes at other times. The named secondary outcome, narcotic medication use, has no numerical results in the registry entries. The record does not provide a threshold for clinical importance, a detailed statistical analysis plan, or information about interim analyses and multiplicity. Adverse-event counts are posted, but event timing, relatedness, and fuller event descriptions are not reported in the registry record. These limits constrain the conclusions that can be drawn from the available summaries.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: IV Acetaminophen for Postoperative Pain Analgesia After Laparoscopic Hysterectomy — NCT02400580.
• Registry record last updated 2018-06-13; status last verified 2018-05.
• Results first posted 2017-12-21.
• 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.

18. Record Summary

NCT02400580 is a completed phase 4 randomized, parallel-group trial sponsored by the University of Pittsburgh. It compared intravenous acetaminophen with normal saline after laparoscopic hysterectomy and enrolled 183 participants. The acetaminophen arm description specifies 1000mg; the study summary refers to pre- and post-operative administration, but its schedule is not reported in the registry record.

The primary outcome was mean postoperative pain at 24 hours on a visual analog scale from 0 to 10. The recorded means were 3.55 for intravenous acetaminophen and 3.11 for normal saline, with a 95% confidence interval for each arm. A direct between-group estimate and p-value are not reported in the registry record. Narcotic medication use is named as a secondary outcome, but numerical results are not available in the registry entries.

The record lists one serious adverse event in the acetaminophen arm and none in the saline arm, no deaths, and other adverse-event counts of 10 and 11, respectively. Further analytical and outcome details are not reported in the registry record.