ICU-acquired pneumonia and PaO2/FIO2value accuracy: A new paradigm?

Introduction: ICU-acquired pneumonia (ICUAP) is the leading infection in critically ill patients. Lacking gold standard diagnostic criteria, clinical criteria are used to suggest diagnosis. A worsening oxygenation (PaO 2 /F I O 2 ≤240 mmHg) is proposed as diagnostic criterion of ICUAP. Objectives: To assess the adequacy of PaO 2 /F I O 2 ≤240 mmHg to diagnose ICUAP. Methods: We prospectively assessed 426 consecutive patients with clinical diagnosis of ICUAP, clustered according to PaO 2 /F I O 2 ≤240 vs. >240 mmHg at onset of pneumonia. Results: PaO 2 /F I O 2 was 195±82 mmHg at onset of pneumonia; 307 (73%) cases had PaO 2 /F I O 2 ≤240 mmHg. Patients with PaO 2 /F I O 2 ≤240 mmHg had less frequently positive microbiologic confirmation (181;59% vs .90;78%, p vs .26; 23%,p=0.063), compared to those with PaO 2 /F I O 2 >240 mmHg. A sub-group analysis of patients without antibiotics before ICUAP diagnosis (99; 22%) also showed less positive microbiology (20;59% vs. 21;88%,p=0.010) in those with worse oxygenation. Severity scores such as SAPS-II, CPIS and SOFA, were higher in patients with worse oxygenation. However, they had similar initial non-response to the empiric treatment (165;53% vs .67;58%,p=0.38), hospital stay (43±35 vs .44±35 days,p=0.54) and hospital mortality (126;41% vs .39;34%,p=0.22) than those with better oxygenation. Conclusion: PaO 2 /F I O 2 ≤240 mmHg does not predict microbiologic confirmation of clinically suspected ICUAP or mortality, suggesting that this is not appropriate for ICUAP diagnosis. Funding: 2009-SGR-911, IDIBAPS, ICREA academia 2013, Juan de la Cierva 2012 (JCI-2012-14801), MEyC, PN I+D (SAF2012-33744), CibeRes (CB06/06/0028)-ISCiii, ERS Fellowship.