© 2008 American Thoracic Society
Oxygenation Indexes and Degrees of Lung InjuryFrom the Authors:We appreciate the comments of Dr. El-Khatib regarding our article (1). We, of course, agree that the American-European Consensus Conference (AECC) definition of acute respiratory distress syndrome (ARDS) is not specific, and the lack of PEEP/FIO2 criteria results in the misclassification of the severity of lung injury in critically ill patients. As a result, this definition in its current form identifies widely disparate forms of acute lung injury and results in the identification of patients with highly variable clinical courses and outcomes. This lack of specificity must be of concern when the definition is used to enroll patients into randomized controlled trials (RCTs). As we have demonstrated, the AECC definition for ARDS could result in patients with very different mortalities being randomized into one arm of an RCT and potentially proving an ineffective therapy effective or an effective therapy ineffective. Dr. El-Khatib's oxygenation factor (2), which is similar to the oxygenation index (3) used in pediatrics, does help to identify the impact on oxygenation of the level of positive pressure therapy. However, our approach was not designed to assess the level of therapy applied during clinical practice but rather to ensure that a minimum level of therapy was applied during the assessment of the severity of lung injury. Theoretically, both approaches could end up with the same results, but they approach the issue from very different perspectives. Mean airway pressure (MAP) is a very nonspecific variable. A MAP of 20 cm H2O could be achieved by the use of a large tidal volume, a high PEEP, or an inverse inspiratory-to-expiratory ratio. However, as Dr. El-Khatib indicated, it would be interesting to determine if indices, such as the oxygenation factor or index, have predictive capabilities when applied early in the course of lung injury.
Harvard Medical School
Hospital Universitario Dr. Negrin FOOTNOTES Conflict of Interest Statement: R.M.K. was paid $1,000 by Maquet, Inc., in September 2006, $1,000 by Viasys, Inc., in October 2006, $1,500 by Respironics, Inc., in November 2006, and $3,500 by Puritan Bennett in July 2007, all for lectures; he has received research grants from Respironics ($60,000 and $25,000), Maquet ($60,000), and Hamilton Medical ($15,000). J.V. has no financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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