Ventilator-Associated Pneumonia and PaO(2)/F(I)O(2) Diagnostic Accuracy: Changing the Paradigm?

Background: Ventilator-associated pneumonia (VAP) is associated to longer stay and poor outcomes. Lacking definitive diagnostic criteria, worsening gas exchange assessed by PaO(2)/F(I)O(2) ≤ 240 in mmHg has been proposed as one of the diagnostic criteria for VAP. We aim to assess the adequacy of PaO(2)/F(I)O(2) ≤ 240 to diagnose VAP. Methods: Prospective observational study in 255 consecutive patients with suspected VAP, clustered according to PaO(2)/F(I)O(2) ≤ 240 vs. > 240 at pneumonia onset. The primary analysis was the association between PaO(2)/F(I)O(2) ≤ 240 and quantitative microbiologic confirmation of pneumonia, the most reliable diagnostic gold-standard. Results: Mean PaO(2)/F(I)O(2) at VAP onset was 195 ± 82; 171 (67%) cases had PaO(2)/F(I)O(2) ≤ 240. Patients with PaO(2)/F(I)O(2) ≤ 240 had a lower APACHE-II score at ICU admission; however, at pneumonia onset they had higher CPIS, SOFA score, acute respiratory distress syndrome criteria and incidence of shock, and less microbiological confirmation of pneumonia (117, 69% vs. 71, 85%, p = 0.008), compared to patients with PaO(2)/FIO(2) > 240. In multivariate logistic regression, PaO(2)/FIO(2) ≤ 240 was independently associated with less microbiological confirmation (adjusted odds-ratio 0.37, 95% confidence interval 0.15–0.89, p = 0.027). The association between PaO(2)/F(I)O(2) and microbiological confirmation of VAP was poor, with an area under the ROC curve 0.645. Initial non-response to treatment and length of stay were similar between both groups, while hospital mortality was higher in patients with PaO(2)/F(I)O(2) ≤ 240. Conclusion: Adding PaO(2)/F(I)O(2) ratio ≤ 240 to the clinical and radiographic criteria does not help in the diagnosis of VAP. PaO(2)/F(I)O(2) ratio > 240 does not exclude this infection. Using this threshold may underestimate the incidence of VAP.