Assessment of PaO₂/FiO₂for stratification of patients with moderate and severe acute respiratory distress syndrome

Abstract

ObjectivesA recent update of the definition of acute respiratory distress syndrome (ARDS) proposed an empirical classification based on ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) at ARDS onset. Since the proposal did not mandate PaO2/FiO2 calculation under standardised ventilator settings (SVS), we hypothesised that a stratification based on baseline PaO2/FiO2 would not provide accurate assessment of lung injury severity.DesignA prospective, multicentre, observational study.SettingA network of teaching hospitals.Participants478 patients with eligible criteria for moderate (100<PaO2/FiO2≤200) and severe (PaO2/FiO2≤100) ARDS and followed until hospital discharge.InterventionsWe examined physiological and ventilator parameters in association with the PaO2/FiO2 at ARDS onset, after 24 h of usual care and at 24 h under a SVS. At 24 h, patients were reclassified as severe, moderate, mild (200<PaO2/FiO2≤300) ARDS and non-ARDS (PaO2/FiO2>300).Primary and secondary outcomesGroup severity and hospital mortality.ResultsAt ARDS onset, 173 patients had a PaO2/FiO2≤100 but only 38.7% met criteria for severe ARDS at 24 h under SVS. When assessed under SVS, 61.3% of patients with severe ARDS were reclassified as moderate, mild and non-ARDS, while lung severity and hospital mortality changed markedly with every PaO2/FiO2 category (p<0.000001). Our model of risk stratification outperformed the stratification using baseline PaO2/FiO2 and non-standardised PaO2/FiO2 at 24 h, when analysed by the predictive receiver operating characteristic (ROC) curve: area under the ROC curve for stratification at baseline was 0.583 (95% CI 0.525 to 0.636), 0.605 (95% CI 0.552 to 0.658) at 24 h without SVS and 0.693 (95% CI 0.645 to 0.742) at 24 h under SVS (p<0.000001).ConclusionsOur findings support the need for patient assessment under SVS at 24 h after ARDS onset to assess disease severity, and have implications for the diagnosis and management of ARDS patients.Trial registration numbersNCT00435110 and NCT00736892.

Association between ventilatory settings and development of acute respiratory distress syndrome in mechanically ventilated patients due to brain injury

“…In our study, diagnostic criteria for ARDS must be met in two consecutive days to get a more consistent diagnosis. This is supported by recent reports [20,21]. In an observational study, the use of a standardized ventilatory setting at 24 h of ARDS onset allowed a more precise and clinically relevant stratification of ARDS patients [20].…”

“…In an observational study, the use of a standardized ventilatory setting at 24 h of ARDS onset allowed a more precise and clinically relevant stratification of ARDS patients [20]. And, in other large, observational study demonstrated that risk stratification of ARDS patients based on PaO2/FiO2 recorded at ARDS onset (baseline) is not clinically useful [21].…”

“…Otherwise, both definitions have serious limitations [20]. As the Berlin criteria, similar to the AECC criteria, did not mandate the assessment of hypoxemia under standardized ventilatory conditions, the values of PaO2/FiO2 recorded at the time of ARDS diagnosis do not provide accurate assessment of ARDS severity and outcome [21]. Even for patients with severe ARDS by the Berlin definition, only 58% demonstrated diffuse alveolar damage on autopsy [35].…”

The Berlin definition met our needs: no

“…Otherwise, it becomes difficult-if not impossible-to interpret trial results [11]. Villar et al [18] studied 478 patients with moderate and severe ARDS and examined the PaO 2 /FiO 2 at ARDS onset, after 24 h of usual care, and at 24 h under standardized ventilator settings. Their standardized model outperformed the Berlin criteria and non-standardized PaO 2 /FiO 2 at 24 h. More than 60 % of patients with severe ARDS according to Berlin criteria were reclassified as moderate, mild or non-ARDS after 24 h of usual care, while hospital mortality changed significantly with every PaO 2 /FiO 2 category under the standardized method.…”

The APPS: an outcome score for the acute respiratory distress syndrome

“…However, no simple and reliable index quantifying the clinical condition of ARDS patients predicts hospital outcome at 24 hours of usual care (including lung protective ventilation and hemodynamic stabilization) until the recent description and validation of an ARDS score by Villar et al (5). Current definitions of ARDS are incapable of properly identifying or stratifying ARDS patients in terms of severity and prognosis (4). It is increasingly recognized that our understanding of the definition of ARDS and its outcome has been limited by the failure to accept that ARDS is a syndrome with different phenotypes that are independent of each other (1,4).…”