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Assessment of PaO2/FiO2 for stratification of patients with moderate and severe acute respiratory distress syndrome
  1. Jesús Villar1,2,
  2. Jesús Blanco1,3,
  3. Rafael del Campo4,
  4. David Andaluz-Ojeda5,
  5. Francisco J Díaz-Domínguez6,
  6. Arturo Muriel3,
  7. Virgilio Córcoles7,
  8. Fernando Suárez-Sipmann1,8,
  9. Concepción Tarancón9,
  10. Elena González-Higueras10,
  11. Julia López11,
  12. Lluis Blanch1,12,
  13. Lina Pérez-Méndez1,13,
  14. Rosa Lidia Fernández1,2,
  15. Robert M Kacmarek14,15,
  16. for the Spanish Initiative for Epidemiology, Stratification & Therapies for ARDS (SIESTA) Network
  1. 1CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain
  2. 2Multidisciplinary Organ Dysfunction Evaluation Research Network, Research Unit, Hospital Universitario Dr Negrín, Las Palmas, Spain
  3. 3Intensive Care Unit, Hospital Universitario Río Hortega, Valladolid, Spain
  4. 4Intensive Care Unit, Hospital General de Ciudad Real, Ciudad Real, Spain
  5. 5Intensive Care Unit, Hospital Clínico Universitario de Valladolid, Valladolid, Spain
  6. 6Intensive Care Unit, Hospital Universitario General de León, León, Spain
  7. 7Intensive Care Unit, Complejo Hospitalario Universitario de Albacete, Albacete, Spain
  8. 8Department of Surgical Sciences, Anesthesiology & Critical Care, Hedenstierna Laboratory, Uppsala University Hospital, Uppsala, Sweden
  9. 9Intensive Care Unit, Hospital Virgen de la Concha, Zamora, Spain
  10. 10Intensive Care Unit, Hospital Virgen de la Luz, Cuenca, Spain
  11. 11Intensive Care Unit, Hospital Universitario La Paz, Madrid, Spain
  12. 12Critical Care Center, Corporació Sanitaria Parc Taulí, Sabadell, Spain
  13. 13Research Unit, Hospital Universitario NS de Candelaria, Tenerife, Spain
  14. 14Department of Respiratory Care, Massachusetts General Hospital, Boston, Massachusetts, USA
  15. 15Department of Anesthesiology, Harvard University, Boston, Massachusetts, USA
  1. Correspondence to Dr Jesús Villar; jesus.villar54{at}


Objectives A 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.

Design A prospective, multicentre, observational study.

Setting A network of teaching hospitals.

Participants 478 patients with eligible criteria for moderate (100<PaO2/FiO2≤200) and severe (PaO2/FiO2≤100) ARDS and followed until hospital discharge.

Interventions We 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 outcomes Group severity and hospital mortality.

Results At 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).

Conclusions Our 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 numbers NCT00435110 and NCT00736892.

  • RESPIRATORY MEDICINE (see Thoracic Medicine)

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