IMPACT OF PREVIOUS ANTIMICROBIAL THERAPY ON THE ETIOLOGY AND OUTCOME OF VENTILATOR-ASSOCIATED PNEUMONIA

Objective: To define the influence of prior antibiotic use on the etio logy and mortality of ventilator-associated pneumonia (VAP). Setting: A university hospital medical-surgical ICU. Design: Prospective clinic al study. Methods: Over a 35-month period, we prospectively studied 12 9 consecutive episodes of VAP. Etiologic diagnosis was established usi ng a protected specimen brush and quantitative culture techniques. We examined prognostic factors by univariate and multivariate analyses us ing a statistical software package (SPSS).Results: The rate of VAP cau sed by Gram-positive cocci or Haemophilus influenzae was statistically lower (p<0.05) in the patients who had received antibiotics previousl y, while the rate of VAP caused by Pseudomonas aeruginosa was statisti cally higher (p<0.01). Patients died of causes directly related to the infection in 18 (14.0 percent) episodes, P aeruginosa being isolated in 9 of these fatal cases. Indeed, we found that 27.7 percent (15/54) of patients who had received prior antimicrobial therapy before the on set of pneumonia died, compared with only 4.0 percent (3/75) of those who did not. In the univariate analysis, the variables significantly a ssociated with attributable mortality were age older than 45 years, us e of corticosteroids, presence of shock, hospital day of VAP over 9, a ntecedent COPD, and a prior antibiotic use. A step-forward logistic re gression analysis defined only prior antibiotic. use (p<0.0001, OR = 9 .2) as significantly influencing the risk of death from VAP. The same result was obtained when severity was included in the model. However, prior antibiotic use entirely dropped out as a significant risk factor when the etiologic agent was included in the regression equation. Con clusions: Distribution of infecting microorganisms responsible for VAP differs in patients who received prior antimicrobial therapy, and thi s factor determines a higher mortality rate. We suggest a restrictive antibiotic policy in mechanically ventilated patients with the purpose of reducing the risk of death from VAP.