Buffered Lidocaine in Paracervical Blocks: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Buffered Lidocaine in Paracervical Blocks (NCT03107754), a randomized phase 4 study. The primary outcome is Injection Pain.

2. Clinical Question

The clinical question concerns pain during injection of the block, rather than pain across the entire aspiration procedure. The trial description explains that providers use paracervical blocks for pain relief during first-trimester surgical aspiration, and that some use buffered lidocaine based on a belief that it decreases pain. The study was designed to compare that preparation with plain lidocaine.

The primary outcome was measured immediately after injection. Pain was recorded using a 100-mm visual analog scale, with scores from 0 to 100 and higher scores indicating worse pain. The registry reports a median for each group, along with an inter-quartile range. The results therefore describe the middle of each group’s observed score distribution and the range containing its central half, rather than an average score or the experience of every individual.

The record reports group-level results but does not report a statistical test or confidence interval for the between-group comparison. The posted medians can be described, but they do not by themselves establish whether the observed difference is compatible with chance variation or how precisely the group contrast has been estimated.

3. Trial Design

This was a randomized, quadruple-masked, parallel-group phase 4 trial. The registry lists enrollment of 98 and a completed status. The trial began on 2017-05-15, and primary completion was recorded on 2018-10-25. The sponsor was the University of Hawaii.

Participants were assigned to one of two paracervical-block approaches. The standard arm used 20 cc of 1% lidocaine, described as the standard office protocol. The buffered arm used 20 cc of 1% lidocaine buffered with 8.4% sodium bicarbonate. The registry classifies the interventions as Lidocaine and Lidocaine-Sodium Bicarbonate. It does not give further details about how the buffering was prepared or administered beyond the arm description.

Random allocation is intended to create groups that are comparable on average with respect to measured and unmeasured characteristics. In a parallel design, participants are assigned to one group and receive that group’s intervention. Masking can reduce the influence of expectations on care, reporting, and assessment, although the registry does not specify which roles were masked or how masking was maintained. Those details are not reported in the registry record.

The posted primary outcome is injection pain immediately after the block injection. A secondary outcome is pain after speculum placement, cervical dilation, and aspiration. The record lists two outcome measures and one posted secondary outcome. It does not report the timing or scale for that secondary outcome in the summary information presented.

The record identifies the trial as phase 4 and completed, but does not report the recruitment setting, eligibility criteria, allocation concealment procedures, treatment adherence, or the planned sample-size justification. It also does not describe protocol deviations or the analysis population. These omissions limit assessment of how closely the reported results correspond to the randomized comparison as originally intended.

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 Injection Pain, measured over Immediately after injection of the paracervical block.

The primary endpoint is pain immediately after injection of the paracervical block. The registry says pain was measured using a 100-mm visual analog scale, with a minimum score of 0 and a maximum score of 100. Higher scores indicate worse pain. This endpoint focuses on the discomfort associated with injecting the block, which is the specific experience the trial set out to compare between buffered and plain lidocaine.

A visual analog scale turns a subjective experience into a recorded score. The score is useful for comparing reports across randomized groups, but it remains a measurement of reported pain rather than a direct measurement of tissue injury or another physical quantity. The interpretation depends on the scale being administered and recorded consistently. The registry does not report additional details about how participants marked the scale or how measurements were collected.

The result is summarized with a median and inter-quartile range for each arm. The median describes the center of the ordered observations: half of the scores lie at or below it and half at or above it, subject to ties. The inter-quartile range describes the span from the lower to the upper quartile and contains the central half of the observations. These summaries are useful when scores are skewed or when a small number of values might disproportionately affect a mean.

The endpoint is specifically immediate injection pain. It should not be treated as a direct summary of pain at every later procedural step. The registry lists a separate secondary outcome covering pain after speculum placement, cervical dilation, and aspiration, but the posted primary endpoint remains the immediate post-injection measure.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The key statistical feature of the posted primary result is its use of medians and inter-quartile ranges. These are descriptive statistics: they summarize the observed scores within each randomized arm. The registry reports 48 participants in the standard paracervical-block arm and 50 in the buffered-lidocaine arm. The corresponding medians are 44.5 and 30.0, and the inter-quartile ranges are 18.25 to 65.0 and 15.25 to 64.5, respectively.

Why use a median and inter-quartile range?

A mean can be sensitive to unusually high or low values, while a median depends on the rank order of the observations. If scores are skewed, the median can provide a more representative description of the center. The inter-quartile range complements it by showing the middle spread of the data. These summaries do not show the full shape of the distributions, and they do not identify how many people reported any particular score.

The registry does not report why the investigators selected this summary, whether they assessed the distribution of scores, or what inferential procedure was planned. Those decisions are not reported in the registry record. It is therefore possible to explain what the posted summaries mean, but not to reconstruct the investigators’ statistical rationale.

What does randomization contribute?

Randomization is designed to balance prognostic characteristics across treatment groups on average. It supports a comparison between groups because assignment is not intentionally based on the participant’s characteristics. Randomization does not guarantee that groups will be identical, especially in a finite trial. Nor does it resolve issues that arise after assignment, such as missing outcome measurements, nonadherence, or departures from the planned analysis. The registry record does not report enough detail to assess those issues.

A parallel-group design compares outcomes between separate groups assigned to different approaches. The comparison is not a before-and-after measurement in the same participants. The trial is described as quadruple masked, but the registry does not say which four roles or parties were masked. General statistical reasoning suggests that masking may reduce expectation-related influences on recorded pain, but the record does not explain how masking was implemented or whether it was successful.

What can be inferred from the reported summaries?

The medians are descriptive centers for the observed group scores. The inter-quartile ranges describe variability among those scores. Neither statistic alone estimates uncertainty in the difference between group medians. To assess the comparison inferentially, one would usually need an analysis that accounts for the observed data and yields an uncertainty measure, such as a confidence interval, or a test result under a stated statistical model. No such result is reported in the registry record.

In general, a confidence interval helps distinguish a precisely estimated contrast from one that remains uncertain. A p-value, when reported, evaluates how compatible the data are with a specified null hypothesis under assumptions; it does not measure the probability that a treatment works. Neither is available for the primary comparison in this record. The posted medians should therefore not be converted into a claim of statistical significance.

General statistical methods also need to match the outcome and design. Pain scores are bounded by the scale’s endpoints, and their distribution may not be symmetric. A method based on means and normal approximations could require assumptions that differ from a rank-based or quantile-based comparison. The registry does not report which method was used or planned. No method should be attributed to the investigators without documentation.

How should planning illustrations be understood?

In general, a sample-size calculation asks how many participants might be needed to detect a specified effect under assumptions about variability, significance level, allocation, and statistical model. Planning illustrations based on an observed effect are not the same as the trial’s original design justification, and they are not observed power. The registry’s stated illustration assumptions use a two-sided significance level of 0.05, equal allocation, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. The registry does not report the trial’s own sample-size justification.

Over-dispersion, in general, means that variability is greater than a model expects. If a model understates variability, its standard errors may be too small and its confidence intervals too narrow. That concept does not establish that over-dispersion occurred in this trial. The record does not report a model for the primary outcome or a dispersion assessment.

Planning numbers are conditional on their assumptions and should not be read as observed outcomes, evidence of adequate power, or an estimate of treatment benefit. No numerical planning estimates are reported in the registry summary. The posted outcome summaries remain the medians and inter-quartile ranges for the two arms.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures: the primary injection-pain outcome and a secondary outcome covering pain after speculum placement, cervical dilation, and aspiration. One secondary outcome is posted. The record does not describe a multiplicity adjustment, a hierarchy of hypotheses, or a prespecified testing strategy. Those details are not reported in the registry record.

Multiplicity is a general concern when several outcomes or comparisons are tested. The more tests that are conducted, the greater the chance of obtaining an apparently notable result by chance if each is interpreted without accounting for the full set of tests. Whether an adjustment is appropriate depends on the trial’s objectives and analysis plan. Since no inferential analyses are reported, the registry results do not show how multiplicity was handled.

The record reports no analyses and does not provide a primary-outcome p-value or confidence interval. It also does not explain whether the secondary outcome was analyzed, how it was scored, or how any analysis was related to the primary question. A posted outcome description is not evidence that a corresponding analysis was completed or reported.

The registry does not describe missing primary-outcome observations, reasons for missingness, imputation, or sensitivity analyses. It also does not state whether the analysis included all randomized participants, participants who received the assigned block, or only those with recorded scores. These are important distinctions because excluding participants after randomization can affect the comparability created by random assignment. The handling of missing data and the analysis population are not reported in the registry record.

Without these details, the group summaries can be read as the posted descriptive results, but their relationship to all randomized participants cannot be established from the registry record. No assumption about complete follow-up or a particular analysis population should be made.

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 5% reporting threshold.

The registry reports serious adverse events and other adverse events separately for each arm. In the standard paracervical-block group, 0 serious adverse events were reported among 48 at risk, and 0 other adverse events were reported among 48 at risk. In the buffered-lidocaine group, 0 serious adverse events were reported among 50 at risk, and 0 other adverse events were reported among 50 at risk. The registry also reports 0 deaths in each group.

These entries describe what was recorded during the trial; they do not show that the interventions carry no risk. An event count of zero does not rule out events that are uncommon, occur outside the recorded observation period, or were not captured under the registry’s reporting process. The record does not describe adverse-event definitions, surveillance procedures, follow-up duration, or how events were attributed to an intervention.

The counts should not be converted into claims about comparative safety. With no reported events in either group, the registry provides no observed event contrast to interpret, and it does not report an inferential safety analysis. Serious-event and other-event entries are separate categories, and the absence of recorded events is limited to those categories and the information in the registry record.

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

The posted primary results describe injection-pain scores after paracervical block. The median was 44.5 in the standard-lidocaine group and 30.0 in the buffered-lidocaine group. Higher scores mean worse pain, so the center of the observed scores was lower in the buffered group. The inter-quartile ranges, from 18.25 to 65.0 for standard lidocaine and from 15.25 to 64.5 for buffered lidocaine, indicate considerable variation and overlap in the middle portions of the distributions.

This comparison is specific to the immediate post-injection endpoint, the two lidocaine preparations, and the trial population described in the registry. It is not a summary of pain during every stage of uterine aspiration. The registry lists a secondary measure addressing pain after speculum placement, cervical dilation, and aspiration, but the primary results do not answer that separate question.

The results do not establish statistical significance because the record does not report an inferential analysis for the primary comparison. They do not provide a confidence interval for the group contrast or otherwise quantify its precision. A difference in descriptive medians is not, by itself, proof of a reliable population-level difference. Nor can the overlapping inter-quartile ranges be used as a formal test of the difference.

The registry record also does not provide details about missing outcome data, analysis population, adherence, or the statistical analysis plan. These omissions limit assessment of how the reported summaries were produced and how they relate to the randomized groups. The results should therefore be interpreted as descriptive evidence, with uncertainty about the comparative effect left unresolved by the posted analysis information.

Finally, the record does not support a general conclusion about every use of buffered lidocaine or every setting in which paracervical blocks are administered. The described protocol uses 20 cc of 1% lidocaine in the standard arm and 20 cc of 1% lidocaine buffered with 8.4% sodium bicarbonate in the buffered arm. The reported outcome concerns pain immediately after injection. Broader conclusions are not established by these results alone.

13. Why This Trial Matters Statistically

This trial poses a focused statistical question: whether two preparations used for a paracervical block produce different immediate injection-pain scores in a randomized comparison. Keeping the question narrow matters because the intervention is intended for a specific procedural moment, and pain at that moment is not interchangeable with pain during later steps of aspiration.

The endpoint also illustrates why the summary measure matters. A visual analog score is bounded and reflects a subjective report. The registry presents medians and inter-quartile ranges, which communicate the center and middle spread of the observed scores without assuming that the mean is the best description. Seeing both the center and spread helps avoid treating a single summary value as a complete account of participants’ experiences.

The comparison further demonstrates the distinction between a descriptive contrast and an inferential conclusion. The two group medians differ, but the record does not report a confidence interval or test. Without such information, readers cannot assess the precision of the group contrast or evaluate a formal hypothesis. Reporting group-level summaries is valuable, but the summaries do not substitute for an analysis of uncertainty.

Randomization and masking are relevant design features, yet they do not remove the need to report how outcomes were analyzed and how missing data were handled. Details about the analysis population, multiplicity, and prespecified methods help readers judge whether the reported findings align with the trial’s question. Those details are not reported in the registry record.

For biostatistical interpretation, this record is a useful example of how much can be learned from endpoint definitions and descriptive summaries—and where interpretation must stop. It permits a careful account of the observed medians and score variation, while leaving the strength and precision of the between-group evidence unresolved.

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 registry’s primary results are limited to group medians and inter-quartile ranges. No confidence interval, p-value, or other inferential result for the primary contrast is reported. This prevents direct assessment of the uncertainty around the comparative result and leaves the descriptive difference without a formal statistical interpretation.

The registry does not report the primary analysis method, the statistical analysis plan, or the reason for using a median and inter-quartile range. It also does not report whether the analysis population followed an intention-to-treat approach or another definition. The relationship between the posted summaries and all randomized participants is therefore not clear from the record.

Missing data and follow-up are not described for the primary endpoint. The record does not state whether every randomized participant contributed an injection-pain score, whether any measurements were excluded, or how absent values were treated. Treatment adherence, protocol deviations, and the success of masking are also not reported in the registry record.

The population description is limited. The record identifies first-trimester uterine aspiration as the clinical context, but does not provide further eligibility criteria, setting details, or demographic characteristics. This limits assessment of how representative the trial participants may be of other clinical populations or practice settings.

The registry lists a secondary pain outcome but does not provide its result in the summary information used for these interpretations. The record also does not report a multiplicity strategy. Safety reporting is limited to zero recorded serious and other adverse events and zero deaths in each arm; event definitions, monitoring, and observation duration are not described. These limitations call for a narrow reading of the available results rather than broader conclusions.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Buffered Lidocaine in Paracervical Blocks — NCT03107754.
• Registry record last updated 2021-01-05; status last verified 2020-12.
• Results first posted 2020-05-15.
• 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

The completed phase 4 trial NCT03107754, sponsored by the University of Hawaii, randomized participants in a quadruple-masked, parallel-group design. The registry reports enrollment of 98. It compared a standard paracervical block using 20 cc of 1% lidocaine with a buffered block using 20 cc of 1% lidocaine and 8.4% sodium bicarbonate.

The primary endpoint was pain immediately after block injection, measured on a 100-mm visual analog scale from 0 to 100, with higher scores indicating worse pain. The median was 44.5 (inter-quartile range 18.25 to 65.0) for standard lidocaine and 30.0 (15.25 to 64.5) for buffered lidocaine. The registry does not report an inferential analysis or confidence interval for this comparison.

The record lists a secondary outcome concerning pain after speculum placement, cervical dilation, and aspiration. It reports zero serious adverse events, zero other adverse events, and zero deaths in each arm. Details about the analysis population, missing data, statistical plan, and adverse-event monitoring are not reported in the registry record.