Assessment of PaO₂/FiO₂ for stratification of patients with moderate and severe acute respiratory distress syndrome

Jesús Villar, Jesús Blanco, Rafael del Campo, David Andaluz-Ojeda, Francisco J Díaz-Domínguez, Arturo Muriel, Virgilio Córcoles, Fernando Suárez-Sipmann, Concepción Tarancón, Elena González-Higueras, Julia López, Lluis Blanch, Lina Pérez-Méndez, Rosa Lidia Fernández, Robert M Kacmarek, Spanish Initiative for Epidemiology, Stratification & Therapies for ARDS (SIESTA) Network, José López, Demetrio Carriedo, Ana María Domínguez, Javier Belda, Gerardo Aguilar, Francisco Martí, Armando Maruenda, José M Añón, María J Bruscas, Iñaki Saralegui, Lina Pérez-Méndez, Dario Toral, Miguel A Romera, Antonio Santos-Bouza, Eli Zavala, Ramón Adalia, Frutos del Nogal, Luís Ramos, Gumersindo González-Díaz, Antonia López-Martínez, Santiago Macías, Noelia Lázaro, Francisco Gandía, David Andaluz, Laura Parra, Javier Collado, José I Alonso, Antonio Álvarez, Noelia Albalá, Ángel Rodríguez-Encinas, Raúl Sánchez, Fabiola Tena, Alberto Indarte, María E Perea, Fernando Mosteiro, Eleuterio Merayo, Alfonso Ambrós, José Manuel Gutiérrez, Francisca Prieto, Ricardo Fernández, José Ignacio Lozano, Antonio García, Carmen Martín, Lluís Blanch, Gemma Gomá, Gisela Gili, Jesús Villar, Rosa Lidia Fernández, Robert M Kacmarek, Jesús Villar, Jesús Blanco, Rafael del Campo, David Andaluz-Ojeda, Francisco J Díaz-Domínguez, Arturo Muriel, Virgilio Córcoles, Fernando Suárez-Sipmann, Concepción Tarancón, Elena González-Higueras, Julia López, Lluis Blanch, Lina Pérez-Méndez, Rosa Lidia Fernández, Robert M Kacmarek, Spanish Initiative for Epidemiology, Stratification & Therapies for ARDS (SIESTA) Network, José López, Demetrio Carriedo, Ana María Domínguez, Javier Belda, Gerardo Aguilar, Francisco Martí, Armando Maruenda, José M Añón, María J Bruscas, Iñaki Saralegui, Lina Pérez-Méndez, Dario Toral, Miguel A Romera, Antonio Santos-Bouza, Eli Zavala, Ramón Adalia, Frutos del Nogal, Luís Ramos, Gumersindo González-Díaz, Antonia López-Martínez, Santiago Macías, Noelia Lázaro, Francisco Gandía, David Andaluz, Laura Parra, Javier Collado, José I Alonso, Antonio Álvarez, Noelia Albalá, Ángel Rodríguez-Encinas, Raúl Sánchez, Fabiola Tena, Alberto Indarte, María E Perea, Fernando Mosteiro, Eleuterio Merayo, Alfonso Ambrós, José Manuel Gutiérrez, Francisca Prieto, Ricardo Fernández, José Ignacio Lozano, Antonio García, Carmen Martín, Lluís Blanch, Gemma Gomá, Gisela Gili, Jesús Villar, Rosa Lidia Fernández, Robert M Kacmarek

Abstract

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/FiOv 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.

Keywords: RESPIRATORY MEDICINE (see Thoracic Medicine).

Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Figures

Figure 1
Figure 1
Flow diagram of the study. The percentages are a proportion of the total patients initially classified as moderate and severe, respectively. AECC, American-European Consensus Conference; ARDS, acute respiratory distress syndrome; PaO2/FiO2, ratio of arterial partial pressure of oxygen to fraction of inspired oxygen; PEEP, positive end-expiratory pressure; SVS, standardised ventilator setting.
Figure 2
Figure 2
Receiver operating curves for risk assessment using the ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) ratio of each patient under standardised ventilator setting (SVS) at 24 h, and compared to risk stratification at ARDS onset (baseline) and at 24 h (T24) without standardising the measurement of PaO2/FiO2 values.

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