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An Early PEEP/FI_O2 Trial Identifies Different Degrees of Lung Injury in Patients with Acute Respiratory Distress Syndrome

¹ Multidisciplinary Organ Dysfunction Evaluation Research Network, Hospital Universitario Dr. Negrin, Las Palmas de Gran Canaria, Canary Islands, Spain; ² Division of Clinical and Genetic Epidemiology, Hospital Universitario N.S. de Candelaria, Tenerife, Spain; ³ Intensive Care Unit, Hospital General de Leon, Leon, Spain; ⁴ Department of Anesthesia, Hospital Clínico de Valencia, Valencia, Spain; ⁵ Intensive Care Unit, Hospital Universitario Rio Hortega, Valladolid, Spain; ⁶ Hospital Santiago Apóstol, Vitoria, Spain; ⁷ Intensive Care Unit, Fundación Jimenez Diaz, Madrid, Spain; ⁸ Intensive Care Unit, Hospital Universitario La Paz, Madrid, Spain; ⁹ Intensive Care Unit, Hospital Universitario N.S. de Candelaria, Santa Cruz de Tenerife, Spain; and ¹⁰ Respiratory Care, Massachusetts General Hospital, Harvard University, Boston, Massachusetts

Correspondence and requests for reprints should be addressed to Robert M. Kacmarek, Ph.D., R.R.T., Director, Respiratory Care, Massachusetts General Hospital, 55 Fruit Street, Ellison 401, Boston, MA 02114. E-mail: rkacmarek{at}partners.org

Rationale: Current American-European Consensus Conference definitions for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are inadequate for inclusion into clinical trials due to the lack of standardization for measuring the oxygenation defect.

Objectives: We questioned whether an early assessment of oxygenation on specific ventilator settings would identify patients with established ARDS (persisting over 24 h).

Methods: At the time of meeting ARDS criteria (Day 0) and 24 hours later (Day 1), arterial blood gases were obtained on standard ventilator settings, VT 7 ml/kg predicted body weight plus the following positive end-expiratory pressure (PEEP) and FI_O2 settings in sequence: (1) PEEP 5 cm H₂O and FI_O2 0.5, (2) PEEP 5 cm H₂O and FI_O2 1.0, (3) PEEP 10 cm H₂O and FI_O20.5, and (4) PEEP 10 cm H₂O and FI_O2 1.0.

Measurements and Main Results: One hundred seventy patients meeting ARDS criteria (Pa_O2/FI_O2 128 ± 33 mm Hg) were enrolled. Overall hospital mortality was 34.1%. The standard ventilator settings that best identified patients with established ARDS and predicted differences in intensive care unit (ICU) mortality were PEEP 10 cm H₂O and FI_O2 0.5 at Day 1 (P = 0.0001). Only 99 (58.2%) patients continued to meet ARDS criteria (Pa_O2/FI_O2, 155.8 ± 29.8 mm Hg; ICU mortality, 45.5%), whereas 55 patients were reclassified as having ALI (Pa_O2/FI_O2, 246.5 ± 25.6 mm Hg; ICU mortality, 20%) and 16 patients as having acute respiratory failure (Pa_O2/FI_O2, 370 ± 54 mm Hg; ICU mortality, 6.3%) (P = 0.0001) on these settings.

Conclusions: Patients meeting current American-European Consensus Conference ARDS criteria may have highly variable levels of lung injury and outcomes. A systematic method of assessing severity of lung injury is required for enrollment of patients with ARDS into randomized controlled trials.

Clinical trial registered with www.clinicaltrials.gov (NCT 00435110).

Key Words: acute respiratory distress syndrome • acute lung injury • positive end-expiratory pressure • standard ventilator settings • definitions • inclusion criteria

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are currently defined without reference to the positive end-expiratory pressure (PEEP) and FIO2 applied. The impact of various PEEP and FIO2 levels on the classification of patients as having ARDS/ALI is unknown. What This Study Adds to the Field The definitions of ARDS and ALI require the use of standard ventilator settings to ensure that patients with consistent levels of lung injury are properly classified as having ARDS or ALI.

 

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