Impact of Diagnostic Criteria on the Incidence of Ventilator-Associated Pneumonia

BACKGROUND: Ventilator-associated pneumonia (VAP) is a frequent complication of prolonged invasive ventilation. Because VAP is largely preventable, its incidence has been used as an index of quality of care in the ICU. However, the incidence of VAP varies according to which criteria are used to identify it. We compared the incidence of VAP obtained with different sets of criteria. METHODS: We collected data from all adult patients admitted to our 35-bed ICU over a 7-month period who had no pulmonary infection on admission or within the first 48 h and who required mechanical ventilation for >48 h. To diagnose VAP, we applied six published sets of criteria and 89 combinations of criteria for hypoxemia, inflammatory response, purulence of tracheal secretions, chest radiography findings, and microbiologic findings of varying levels of severity. The variables used in each diagnostic algorithm were assessed daily. RESULTS: Of 1,824 patients admitted to the ICU during the study period, 91 were eligible for inclusion. The incidence of VAP ranged from 4% to 42% when using the six published sets of criteria and from 0% to 44% when using the 89 combinations. The delay before diagnosis of VAP increased from 4 to 8 days with increasingly stringent criteria, and mortality increased from 50% to 80%. CONCLUSIONS: Applying different diagnostic criteria to the same patient population can result in wide variation in the incidence of VAP. The use of different criteria can also influence the time of diagnosis and the associated mortality rate.