Changing Rate of Ventilator-Associated Pneumonia Throughout Duration of Mechanical Ventilation
Background: Patients undergoing mechanical ventilation have an increased risk for nosocomial pneumonia. While many studies assume a constant rate of ventilator-associated pneumonia (VAP), there are a few small studies that suggest the risk of VAP varies across ventilation duration.
Objective: Our primary objective was to determine whether the rate of VAP varies over ventilation duration, adjusting for changes in the distribution of risk factors. A secondary objective was to clarify risk factors of VAP over duration of ventilation.
Methods: We included 11,041 patients with ventilators in a tertiary care academic hospital between 2002-2007. Data were collected from electronic health records. Discrete-time hazards were used to model changing VAP rate and obtain odds ratios (OR) for gender, race, age, patient location, hospital service, and comorbidities.
Results: 456 VAP cases occurred in 86,130 ventilator-days. VAP rate (per 1,000 ventilator-days) increased from 3.27 (95% confidence interval (CI) 2.57, 4.15) to 8.42 (95%CI 6.83, 10.28) in the first week, dropped to 3.40 (95%CI 2.30, 5.03) over the second week, increased to 6.57 (95%CI 4.57, 9.43) over the third week, and ranged from 3.39 to 4.89 with longer ventilator duration (see figure). VAP risk was higher among patients with trauma (OR 1.50, 95%CI 1.15, 1.95), central venous catheters (OR 1.46, 95%CI 0.99, 2.16), or bloodstream infection (OR 2.14, 95%CI 1.58, 2.88). VAP risk was lower on the floor (OR 0.56, 95%CI 0.39, 0.80) compared to intensive care. After 11 days, medical (odds ratio (OR) 0.30, 95%CI 0.21, 0.43) and pediatric (OR 0.38, 95%CI 0.28, 0.50) patients had decreased VAP risk compared with surgical patients.
Conclusions: Rate of VAP varied across ventilator duration. Differences remained after adjusting for changes in the population at risk. Closely monitoring patients with increased risk and targeting timed interventions could reduce VAP rate.
Figure. Rate (with 95%CI) of ventilator-associated pneumonia across duration of ventilation from unadjusted model. (Solid line is changing rate; dotted line is constant rate.)