Examkin

Question

Difficulty: Very hardMeasures of Association and Impact

A regional health authority is evaluating strategies to reduce the incidence of ventilator-associated pneumonia (VAP) across its intensive care units. A prospective cohort study within the region yields the following incidence data based on patient positioning:

- Incidence of VAP in patients maintained in a supine position: 30 cases per 1,000 ventilator-days
- Incidence of VAP in patients maintained in a semi-recumbent position: 5 cases per 1,000 ventilator-days

Recent clinical audits indicate that, despite existing guidelines, 60% of all mechanically ventilated patients in the region are currently maintained primarily in the supine position.

The health authority plans to implement a strict quality improvement protocol to eliminate the use of the supine position entirely, successfully transitioning all patients to the semi-recumbent position. Assuming the observed association is entirely causal, what percentage of the total current VAP cases in the region can be attributed to the use of the supine position (and thus would be prevented by this initiative)?

Enter your answer as a whole number.

Answer: 75 %

Answer

75
The question asks for the percentage of total VAP cases in the population that are attributable to the supine position. This corresponds to the Population Attributable Risk Percent (PAR\%), also known as the Population Attributable Fraction (PAF). To find it, first calculate the overall population incidence (IpopI_{pop}), which is the weighted average based on exposure prevalence: (30×0.60)+(5×0.40)=20(30 \times 0.60) + (5 \times 0.40) = 20 cases per 1,000 ventilator-days. Next, find the Population Attributable Risk (PAR) by subtracting the unexposed incidence from the overall population incidence: 20−5=1520 - 5 = 15. Finally, calculate the PAR\% by dividing the PAR by the overall population incidence: (15/20)×100=75%(15 / 20) \times 100 = 75\%.

Step-by-Step Solution

1
Calculate the overall incidence of VAP in the entire ICU population (IpopI_{pop}).
Ipop=20I_{pop} = 20 cases per 1,000 ventilator-days.
The population incidence is the weighted average of the incidences in the exposed and unexposed groups, based on the prevalence of the exposure in the population: Ipop=(Iexp×Pexp)+(Iunexp×Punexp)=(30×0.60)+(5×0.40)=18+2=20I_{pop} = (I_{exp} \times P_{exp}) + (I_{unexp} \times P_{unexp}) = (30 \times 0.60) + (5 \times 0.40) = 18 + 2 = 20.
2
Calculate the Population Attributable Risk (PAR).
PAR=15PAR = 15 cases per 1,000 ventilator-days.
PAR represents the excess incidence of disease in the total population that is attributable to the exposure. It is calculated as Ipop−Iunexp=20−5=15I_{pop} - I_{unexp} = 20 - 5 = 15.
3
Calculate the Population Attributable Risk Percent (PAR\%).
PAR%=75%PAR\% = 75\%.
PAR\% (also known as the Population Attributable Fraction) is the proportion of total cases in the population that could be prevented if the exposure were eliminated. It is calculated as (PAR/Ipop)×100=(15/20)×100=75%(PAR / I_{pop}) \times 100 = (15 / 20) \times 100 = 75\%.

Key Concept

Population Attributable Risk Percent (PAR\%) is the proportion of disease incidence in a total population that can be attributed to a specific exposure, calculated as (Ipop−Iunexp)/Ipop(I_{pop} - I_{unexp}) / I_{pop}.

Alternative Method

The Population Attributable Fraction (PAF) can also be derived directly using the prevalence of exposure (PexpP_{exp}) and the Relative Risk (RRRR) with Levin's formula: PAF=[Pexp×(RR−1)]/[Pexp×(RR−1)+1]PAF = [P_{exp} \times (RR - 1)] / [P_{exp} \times (RR - 1) + 1]. Here, RR=30/5=6RR = 30 / 5 = 6. Therefore, PAF=[0.60×(6−1)]/[0.60×(6−1)+1]=[0.60×5]/[0.60×5+1]=3/4=75%PAF = [0.60 \times (6 - 1)] / [0.60 \times (6 - 1) + 1] = [0.60 \times 5] / [0.60 \times 5 + 1] = 3 / 4 = 75\%.
Estimated Time:1m 30s
Rate this question

Topics

Measures of Association and Impact

More questions from this topic