The Effect of Bedside Ultrasound Assistance on the Proportion of Successful Infant Spinal Taps: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effect of Bedside Ultrasound Assistance on the Proportion of Successful Infant Spinal Taps (NCT02133066), a randomized na study. The primary outcome is Percentage of Successful First Attempt Lumbar Punctures in the Ultrasound-assisted Group as Compared to the Non-ultrasound Assisted Group.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group trial comparing ultrasound-assisted site marking with routine lumbar puncture. The registry lists masking as none, so the trial was not masked according to the record. It lists the study as completed and reports enrollment of 128. The registry gives a start date of 2014-05 and primary completion in 2016-02. The phase is recorded as NA.

Participants assigned to the ultrasound-assisted group received site marking with a Mindray M7 ultrasound device before lumbar puncture. Participants in the routine group received no ultrasound-assisted site marking before the procedure. The registry describes the routine procedure as a standard-of-care spinal tap performed by the clinician. The trial therefore compares a marking approach against routine practice; it does not describe a comparison of ultrasound-guided needle placement with another needle-placement technique.

The registry lists 64 participants in each group for the primary outcome. Random allocation can help balance known and unknown participant characteristics across groups on average, but it does not guarantee that groups are identical, especially in a particular trial. The record does not report the randomization sequence method, allocation concealment, stratification, or details of how assignment was implemented. Those aspects of trial conduct cannot be evaluated from the registry information.

The primary outcome was the percentage of successful first-attempt lumbar punctures, assessed within 30 minutes. Three secondary outcomes are listed: overall lumbar puncture success, length of hospitalization, and length of antibiotic use. The registry does not provide posted results for these secondary outcomes in the record described. Details such as the exact definition of a successful attempt, the criteria for counting attempts, and the handling of procedures that were not completed within the stated timeframe are not reported in the registry record.

The record names Children's Hospital of Philadelphia as sponsor. It does not report further details about clinician training, procedural standardization, participant flow, or the characteristics of enrolled participants. These gaps limit assessment of how closely the procedures were conducted across clinicians and how broadly the results may apply to other settings.

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 Percentage of Successful First Attempt Lumbar Punctures in the Ultrasound-assisted Group as Compared to the Non-ultrasound Assisted Group, measured over 30 minutes.

The primary endpoint is the percentage of successful first-attempt lumbar punctures in each group, comparing ultrasound-assisted site marking with routine lumbar puncture. The stated timeframe is 30 minutes. This is a binary procedural outcome at the participant or procedure level: a first attempt is categorized as successful or not successful, and the group result is expressed as a percentage.

First-attempt success is used because it focuses on whether the procedure succeeded without needing another attempt. It is a direct measure of the procedural outcome targeted by the trial question. As a general statistical point, binary endpoints can be summarized as proportions, but their interpretation depends on a clear and consistent definition of success and a specified denominator. The precise operational definition of success, including what counted as an attempt and how incomplete or unassessable procedures were handled, is not reported in the registry record.

The posted group estimates are 58.0% for ultrasound-assisted site marking and 31.0% for routine lumbar puncture. Their respective 95% confidence intervals are 50.0% to 70.0% and 19.0% to 39.0%. These intervals describe uncertainty around each group’s estimated percentage; they are not themselves a confidence interval for the difference between groups. The registry record does not report a formal contrast estimate or its confidence interval.

First-attempt success captures one aspect of procedural performance. It does not, on its own, describe overall success, length of hospitalization, antibiotic use, or other consequences of the procedure. Those topics are represented among the listed secondary outcomes, but their results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports a percentage for each randomized group and a 95% confidence interval for each percentage. It does not report a formal estimate of the between-group contrast or an inferential analysis for the primary comparison. This distinction is central: descriptive statistics summarize what was observed within groups, while a comparative analysis estimates how outcomes differ between assigned strategies and quantifies uncertainty in that contrast.

What does a confidence interval describe?

In general, a confidence interval is constructed using a statistical procedure that, under its assumptions, will cover the underlying quantity at the stated rate across repeated applications of the procedure. For an individual trial, it gives a range of estimates consistent with the observed data and the specified method. A narrower interval generally indicates greater precision for the quantity being estimated; a wider interval indicates less precision. Precision is not the same as freedom from bias. A precise estimate can still be affected by problems in trial conduct, outcome measurement, or analysis.

Here, the registry reports 50.0% to 70.0% for the ultrasound-assisted group and 19.0% to 39.0% for the routine group. These intervals attach to the separate percentages. To make a direct comparative claim, readers would generally look for an estimate of the between-group contrast and its confidence interval, or a clearly specified test of the primary comparison. Such a contrast and test are not reported in the registry record. The group-specific intervals should not be treated as if either were the interval for the difference.

Why is the endpoint a proportion?

First-attempt success is a binary outcome: a procedure is classified as either successful or not successful under the endpoint definition. A proportion summarizes the share of assessed procedures classified as successful. The meaning of that proportion depends on the denominator and on consistent outcome classification. The registry lists 64 participants in each group, but does not describe the exact operational rules for success, the handling of missing assessments, or whether any participants were excluded from the reported denominator. Those details are not reported in the registry record.

As a general concept, binary data can be analyzed using methods that model event probabilities or compare proportions. Different valid methods may yield different estimates or uncertainty measures, especially in smaller samples or when the event is uncommon. A choice of method should be specified before interpreting a p-value or interval. The registry record does not report the method used to construct the posted confidence intervals or a statistical analysis plan for the primary outcome.

What does randomization contribute?

Random allocation is intended to reduce systematic differences between groups at the point of assignment. In general, it supports causal comparisons when allocation is implemented as intended, participants are analyzed appropriately, outcome measurement is sufficiently reliable, and post-assignment events are handled transparently. Randomization does not ensure exact balance in all participant features, eliminate measurement error, or address missing data by itself. The record identifies the trial as randomized, but does not report the sequence-generation or allocation-concealment procedures.

The record lists no masking. That fact is relevant because knowledge of the assigned approach can influence care, procedural decisions, or outcome assessment in some settings. Whether such influences occurred cannot be determined from the registry record. It also does not report whether the person classifying first-attempt success was masked to assignment.

How should planning calculations be read?

The registry describes its sample-size planning illustration as based on the observed effect, with a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. It describes the effect to detect as a stated fraction of the observed effect. Such planning figures, when presented, are illustrations based on assumptions rather than observed trial outcomes. They are not observed power and do not establish that the study had a particular probability of detecting an effect. The numerical planning counts and any target power are not reported in the registry record.

As a general statistical principle, planning calculations depend on assumptions about the outcome, the effect considered meaningful, the chosen error rate, allocation, and the analysis method. Calculations that use an effect estimated from the same trial can be especially uncertain because that estimate is itself subject to sampling variation. A planning exercise is most useful when its assumptions are explicit and its purpose is kept separate from interpretation of the observed results.

Why can over-dispersion matter?

This primary endpoint is reported as a percentage, not as a count of repeated events per participant. Over-dispersion is a general concern in count or proportion models when observed variability exceeds what a chosen model assumes. If present, it can make standard errors too small and intervals too narrow unless the analysis accounts for it. The registry record does not report an over-dispersion assessment or an analysis model for the primary endpoint, so it is not possible to say whether this issue arose or how it was addressed.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists three secondary outcomes: overall success of lumbar punctures, length of hospitalization, and length of antibiotic use. It also reports four outcome measures in total. Results for the listed secondary outcomes are not reported in the registry record. Their absence means readers cannot assess whether the primary outcome was accompanied by consistent findings on other measured outcomes.

When a study evaluates multiple outcomes or multiple comparisons, the chance of at least one apparently unusual result can increase if each is interpreted separately without a plan for multiplicity. As a general concept, researchers may specify one primary endpoint, adjust for multiple testing, or treat secondary analyses as exploratory. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or whether any adjustment was used. No conclusion about adjustment should be inferred from the presence of one primary outcome and several secondary outcomes.

The record reports no analyses in its analysis listing. It does not describe the primary analysis population, whether participants were analyzed according to randomized assignment, or whether a per-protocol or other population was used. Missing outcome data, exclusions, protocol deviations, and methods for handling missing observations are not reported in the registry record. These omissions limit evaluation of whether the posted group percentages reflect all randomized participants or a subset with assessed outcomes.

The record provides group-specific percentages and confidence intervals but no p-value or formal comparative estimate for the primary outcome. It also does not report a statistical analysis plan. Consequently, it is not possible to determine from the registry record whether the posted analysis was prespecified, whether other analyses were conducted, or how decisions about analysis were made. These are reporting limitations; they do not establish that a particular method was or was not used.

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.

The registry reports no serious adverse events, other adverse events, or deaths in either group. For the ultrasound-assisted group, 64 participants are listed as at risk for serious adverse events and 0 as affected; 64 are listed as at risk for other adverse events and 0 as affected; deaths are reported as 0. The routine group has the same reported figures: 64 at risk for each adverse-event category, 0 affected in each category, and 0 deaths.

These figures describe the safety events recorded in the registry. A zero count means no events were reported in the listed categories; it does not establish that no event occurred outside the reporting process or timeframe. The registry record does not report the adverse-event collection period, event definitions, severity grading details, relatedness assessments, or completeness of follow-up. It also does not provide individual event narratives. Those omissions limit interpretation of what was monitored and how comprehensively.

As a general statistical point, when no events are observed, the data still allow uncertainty about the underlying event risk. The zero counts should not be read as proof that a procedure has no risk. They also do not by themselves support a comparison of safety between groups. The registry’s safety figures are a report of observed and recorded counts, not medical advice.

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

The posted result describes first-attempt lumbar puncture success in a randomized comparison of ultrasound-assisted site marking and routine lumbar puncture. The reported percentage is 58.0% in the ultrasound-assisted group and 31.0% in the routine group. The accompanying 95% confidence intervals are 50.0% to 70.0% and 19.0% to 39.0%, respectively. In this trial’s posted data, the group estimate is higher for ultrasound-assisted marking.

The results do not provide a formal estimate of the between-group contrast or its uncertainty. They therefore do not show how precise the comparative effect is according to a direct contrast analysis. Separate confidence intervals for the two groups answer a different question from a confidence interval for the difference. The registry record also does not report a p-value for the primary comparison, and the available information does not establish whether any comparison met a prespecified criterion for statistical significance.

The endpoint concerns first-attempt success within 30 minutes. It does not, by itself, establish the effect on overall lumbar puncture success, length of hospitalization, or length of antibiotic use. These are listed secondary outcomes, but their results are not reported in the registry record. Nor do the primary results establish the intervention’s performance in populations or settings beyond those represented by this trial.

Several details needed for a fuller interpretation are not reported in the registry record, including the exact success definition, the primary analysis population, missing-data handling, and the method used to construct the confidence intervals. The trial is listed as randomized and unmasked, but details of allocation implementation and outcome assessment are absent. Such information can affect how confidently the observed percentages can be interpreted.

The result is therefore best read as a report of the observed group-specific primary outcome estimates, with their stated uncertainty intervals. It is not a guarantee of future procedural outcomes, a complete account of all trial outcomes, or medical advice.

13. Why This Trial Matters Statistically

This trial is statistically useful because it asks a focused procedural question and reports a binary primary outcome in two randomized groups. Reporting the percentage of first-attempt successes makes the outcome understandable in clinical terms, while confidence intervals give information about the precision of each group estimate. The randomized design is relevant because it aims to make the assigned strategies comparable at the start of follow-up.

The record also illustrates why descriptive group results and comparative estimates should not be conflated. A percentage in each group tells readers what was observed within each group. A direct contrast would summarize the estimated difference between strategies and quantify uncertainty for that comparison. The registry reports the former, but not the latter. This distinction helps prevent overinterpretation of group-level percentages as if they were a complete inferential analysis.

The intervention itself is specifically site marking with ultrasound before the procedure. Naming the intervention precisely matters: the registry does not describe ultrasound-guided needle placement. Clear intervention definitions make it easier to understand what was randomized and what a result can reasonably address.

The trial also highlights the importance of reporting outcome definitions, analysis populations, missing-data methods, and the handling of multiple outcomes. These details support reproducibility and help readers assess whether a reported endpoint captures the intended clinical question. Three secondary outcomes are listed, but their results and the approach to multiplicity are not reported in the registry record. The primary result can still be described, while these missing details remain relevant limits on interpretation.

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 record leaves important aspects of the trial population and conduct unspecified. Although the study concerns infants in a pediatric emergency department, specific age eligibility, baseline characteristics, clinical severity, and participant flow are not reported. The degree to which the enrolled participants represent other clinical settings or patient groups therefore cannot be assessed from the record.

Procedural details are also limited. The intervention is described as ultrasound-assisted site marking, but the record does not report the precise marking protocol, clinician training, operator experience, or how routine procedures were standardized. The exact definition of first-attempt success and the rules for counting attempts are not reported. Without those definitions, it is difficult to judge how consistently the endpoint was measured across participants and clinicians.

The trial is listed as randomized and unmasked, but sequence generation, allocation concealment, and outcome-assessor masking are not reported in the registry record. The record also does not describe the primary analysis population, missing-data handling, exclusions, or protocol deviations. These omissions limit assessment of the risk of bias and the robustness of the posted percentages.

Finally, the registry provides group-specific primary outcome estimates and confidence intervals without a reported between-group estimate, p-value, or analysis method. The three listed secondary outcomes do not have posted results in the record described, and multiplicity handling is not reported. Safety counts are available, but the adverse-event definitions and observation period are not. These are reporting limitations and should not be interpreted as evidence that an unreported procedure or analysis did or did not occur.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Effect of Bedside Ultrasound Assistance on the Proportion of Successful Infant Spinal Taps — NCT02133066.
• Registry record last updated 2017-08-31; status last verified 2017-08.
• Results first posted 2017-08-31.
• 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 registry record describes a completed, randomized, parallel-group trial comparing ultrasound-assisted site marking before lumbar puncture with routine lumbar puncture without ultrasound-assisted marking. It lists no masking and reports enrollment of 128. The study start is recorded as 2014-05, with primary completion in 2016-02.

The primary outcome was percentage of successful first-attempt lumbar punctures within 30 minutes. The registry reports 58.0% success in the ultrasound-assisted group, with a 95% confidence interval of 50.0% to 70.0%, and 31.0% in the routine group, with a 95% confidence interval of 19.0% to 39.0%. A direct comparative estimate and p-value are not reported in the registry record.

Three secondary outcomes are listed, but their results are not reported. The record lists 0 serious adverse events, 0 other adverse events, and 0 deaths in each group. Details about the primary analysis, missing data, endpoint definition, and multiplicity are not reported in the registry record.