NR 714 Week 3 Epidemiologic Rates Write-Up Example

Rates, Denominators and Their Limits: Peripheral IV Catheter Failure on a 36-Bed Medicine Unit, January to June 2026

Student Name

College of Nursing, Chamberlain University

NR 714: Application of Analytic Methods II

Instructor Name

Month Day, Year

Rates, Denominators and Their Limits: Peripheral IV Catheter Failure on a 36-Bed Medicine Unit, January to June 2026

The Counts Behind Every Rate

All figures in this write-up come from the same six months, 1 January to 30 June 2026, on 4 North, a 36-bed adult general medicine unit. The numerator in every case is the number of peripheral catheters removed before the end of therapy for infiltration, occlusion, dislodgement, phlebitis or leakage: 437. Four candidate denominators were available from the unit's records: 1,412 catheters, 4,236 catheter-days, 5,940 patient-days and 1,186 admissions. The choice among them is the main argument of this paper, because each answers a different question and only one answers the question the project asks (Celentano & Szklo, 2019).

The Exposure Underneath the Count

The risk of a catheter failing exists only while a catheter is in place, and it accrues with each day the catheter stays. The exposure that matches that risk is catheter-days.

Incidence density = 437 failures divided by 4,236 catheter-days, multiplied by 1,000 = 103.2 failures per 1,000 catheter-days.

The same events can also be expressed per catheter, which answers a simpler question, what share of catheters fail:

Cumulative incidence = 437 divided by 1,412 catheters, multiplied by 100 = 30.9 failures per 100 catheters.

Both are legitimate. The first is the one the project will use for comparison, because if the bundle lengthens how long catheters last, each catheter will be exposed for longer and the per-catheter figure could stay flat even as each day becomes safer.

Two Denominators That Look Reasonable and Are Not

Per patient-day: 437 divided by 5,940 patient-days, times 1,000 = 73.6 per 1,000 patient-days. Per admission: 437 divided by 1,186, times 100 = 36.8 per 100 admissions.

Neither should be used. Patient-days include every day a patient had no catheter. On 4 North the proportion of patient-days on which a catheter was in place, known as the device utilization ratio, was 4,236 over 5,940, or 0.71. If the unit began removing idle catheters more promptly and the ratio fell to 0.60, failures per patient-day would fall by about 16% with no change in how often any catheter failed. Admissions are worse still, because a patient may have three catheters in one stay and the risk depends on length of stay, which varies widely on a medicine unit. A falling rate on either denominator could mean the bundle worked, or fewer catheters, or shorter stays, and nobody could tell which.

Rates by Reason

Table 1

Premature Peripheral Catheter Failure by Reason, 4 North, January to June 2026

Note. Note. Denominator for every rate is 4,236 catheter-days. Shares are rounded and may not sum exactly.

Infiltration and occlusion together account for two failures in three. Dislodgement, the reason a securement device is most directly designed to address, accounts for about one in five.

Incidence Against Prevalence

On 18 March 2026 at 10:00, the project lead assessed every patient on the unit. Of 33 patients, 25 had a peripheral catheter in place, and 4 of those 25 sites showed signs of infiltration or phlebitis on the unit's assessment scales. The point prevalence of site complications was therefore 4 of 25, or 16.0% of catheters in place at that moment.

Prevalence answers a different question from incidence. It describes how many sites are in trouble at one time, which is useful for planning how long a site-check round will take and for showing staff what a once-a-shift check is likely to find. It cannot show whether the bundle prevents new failures, because a site that has been infiltrating for an hour and one that has been fine for four days look the same in a single snapshot. A prevalence survey also overrepresents long-dwelling catheters, since they are more likely to be in place on the survey day. The project will use incidence density to test the change and repeat the prevalence survey once a quarter as a process check (Celentano & Szklo, 2019).

How Far One Event Moves the Rate

The unit records about 700 catheter-days a month. One failure more or less moves a monthly rate by about 1.4 per 1,000 catheter-days, so the overall rate is reasonably stable month to month. The reason-specific rates are not. In May the unit recorded 5 phlebitis removals on 706 catheter-days, 7.1 per 1,000; a sixth would have raised it to 8.5, an apparent rise of 20% from a single site.

Over six months the picture is steadier but still uncertain. Treating the 437 failures as a Poisson count gives an approximate 95% interval of about 396 to 478 events, or 93.5 to 112.8 per 1,000 catheter-days. For phlebitis, 31 events give an exact interval of about 21 to 44, or 5.0 to 10.4 per 1,000 catheter-days, so the true phlebitis rate could plausibly be half or double what was observed. The project will therefore report reason-specific rates as description only, and test the bundle on all failures together and on dislodgement, which has enough events to be read (Provost & Murray, 2022). In practice, this means a staff meeting will not hear that phlebitis doubled in a month. It will hear the six-month count with its interval, and a reminder that a handful of sites decides the monthly figure for the smaller reasons.

Comparison, With Its Reference Named

Large adult cohorts have reported that roughly a third of peripheral catheters fail before therapy ends (Marsh et al., 2018). The unit's 30.9 per 100 catheters sits in that range. The comparison is made per catheter because that is how the cohort reported it; comparing the unit's per-catheter-day rate with a published per-catheter figure would mix denominators. Even then, the populations differ in age, illness and who inserts the catheters, so the comparison shows the unit is not unusual, not that its practice is adequate. A unit can sit in the middle of a published range and still have room to improve, since the range itself describes what hospitals have accepted rather than what is achievable.

A Sentence a Colleague Could Repeat

On 4 North in the first half of 2026, about one peripheral IV in three came out early because it stopped working, roughly one failure for every ten days that catheters were in place, and infiltration was the most common reason.

References

Celentano, D. D., & Szklo, M. (2019). Gordis epidemiology (6th ed.). Elsevier.

Marsh, N., Webster, J., Larsen, E., Cooke, M., Mihala, G., & Rickard, C. M. (2018). Observational study of peripheral intravenous catheter outcomes in adult hospitalized patients: A multivariable analysis of peripheral intravenous catheter failure. Journal of Hospital Medicine, 13(2), 83-89. https://doi.org/10.12788/jhm.2867

Provost, L. P., & Murray, S. K. (2022). The health care data guide: Learning from data for improvement (2nd ed.). Jossey-Bass.