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Difficulty: MediumEpidemiologic Study Designs

A group of surgical researchers at a university hospital is evaluating the relationship between intraoperative fluid administration strategies and postoperative renal complications. They hypothesize that utilizing a restrictive fluid strategy during elective colorectal surgery increases the incidence of acute kidney injury (AKI). Utilizing the hospital's centralized electronic health records from the last five years, the researchers identify 600 patients who received a restrictive fluid protocol and 600 patients who received a liberal fluid protocol during their operations. The investigators then analyze the subsequent postoperative laboratory results and clinical notes within the same database to determine the rate of AKI development in each group within 7 days of surgery. Which of the following best describes the design of this epidemiologic study?

  1. Retrospective cohort studyAnswer
  2. B
    Case-control study
  3. C
    Cross-sectional study
  4. D
    Prospective cohort study
  5. E
    Nested case-control study

Answer

The correct answer is Retrospective cohort study.
The correct answer accurately identifies the methodology described. By searching the medical records for patients who had a specific exposure (restrictive vs. liberal fluids) and then reviewing their subsequent charts to see if they developed a disease (AKI), the investigators are utilizing a retrospective cohort design. They are looking forward in time from the point of exposure, even though all events occurred in the past.

Step-by-Step Solution

1
Identify the independent variable (exposure) and dependent variable (outcome) in the study.
Exposure is the intraoperative fluid strategy (restrictive vs. liberal). Outcome is acute kidney injury (AKI).
Understanding what is being measured is required to determine how the groups were assembled.
2
Determine the criteria used to assemble the initial patient groups.
The researchers initially identified 600 patients with the restrictive protocol and 600 with the liberal protocol. They were selected based on their EXPOSURE status.
The defining feature of a cohort study is selecting patients based on exposure, whereas a case-control study selects based on outcome.
3
Determine the timing of the study data collection relative to the investigator's present time.
The researchers are using electronic health records from the past five years. Both the exposure (surgery) and the outcome (postoperative AKI) have already occurred before the study began.
Because the events have already occurred and historical data is used, the cohort is retrospective rather than prospective.

Key Concept

Retrospective cohort studies group subjects based on their past exposure status and use historical data to determine the subsequent incidence of an outcome.
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Epidemiologic Study Designs

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