© 2008 American Thoracic Society
Tidal Volume in Mechanical Ventilation: The Importance of Considering Predicted Body WeightTo the Editor:The important study by Dr. Esteban and colleagues (1) concludes that previous randomized clinical trials have advanced ventilation practice and, in particular, that the ARDS Network trial on low versus traditional tidal volumes (ARMA) (2) may have led to increased use of low-stretch ventilation. However, the data provided to support their conclusions are not completely clear. The authors state in the abstract that the tidal volume decreased from 9.1 to 7.4 ml/kg in patients with ARDS, but do not indicate the parameter (mean?) or the precise unit (ml/kg actual body weight [BW]?). Furthermore, the results present tidal volume data as ml/kg actual BW in two categories: "higher, median" and "lower, median." It would be useful to clarify the meaning of these categories. Also, it would be particularly relevant to present the tidal volume values as ml/kg predicted BW, as has been reported previously (2). Such presentation would yield higher tidal volumes than those presented, and so might provide a further explanation for the lack of improved outcome in patients with ARDS. We have conducted a study on the efficacy of rSP-C surfactant in patients with pneumonia or aspiration of gastric contents requiring invasive mechanical ventilation comprising a total of 843 patients. Although the study protocol requested adherence to the ARDS Network ventilation protocol, we still observed a median tidal volume of 7.8 ml/kg predicted BW for the first 200 patients, with considerable differences among the 23 participating countries (3). To increase use of low-stretch ventilation, we then implemented intensified training measures, including evaluation of the ventilation strategy employed for each patient at enrollment, regular communication with study sites, and educational programs. These efforts resulted in a significant reduction of the applied median tidal volume to 6.7 ml/kg predicted BW, corresponding to 5.6 ml/kg actual BW, for the last cohort of 200 patients. While Estaban and coworkers certainly discussed why patients with ARDS did not exhibit an improved outcome between 1998 and 2004, we suggest that their conclusions would be greatly enhanced if values for tidal volume in ml/kg predicted BW were provided. In light of our experience, we believe that many more patients with acute respiratory failure could still benefit from low-stretch ventilation, as measured using ml/kg predicted BW, and that intensified training measures are required to more efficiently incorporate study findings into clinical practice.
Justus-Liebig-University
Nycomed GmbH FOOTNOTES Conflict of Interest Statement: A.G. is an advisory board member of the mentioned surfactant study and has received consultancy fees from Nycomed GmbH. F.T. is a full-time employee of Nycomed GmbH, the sponsor of the rSP-C surfactant study cited in this letter. REFERENCES
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