Protective ventilation of patients with ARDS

N. George1, M. Griffiths2 and E. Moloney2

1 Kettering, UK 2 London, UK

Editor—I read with interest the review article on protective ventilation of patients with acute respiratory distress syndrome (ARDS).1 In their comments on the use of prone ventilation in patients with ARDS, the authors have quoted the study by Gattitoni and colleagues2 published in 2001, and have commented that, at present, although prone positioning may help improve oxygenation and pulmonary mechanics, it has not been shown to improve outcome in ARDS.

Subsequent to this publication, Gattitoni’s group of investigators have retrospectively analysed their data from the previous study. They have also included 73 patients from the pilot study, and have reached the conclusion that a decrease in PaCO2 with the prone position is predictive of an improved outcome in ARDS.3 The reason for this decrease in PaCO2 is alveolar recruitment resulting in an increase in alveolar ventilation. They have suggested that this probably indicates some difference in the underlying pathology, which results in a higher potential for recruitment in the PaCO2 responders compared with the non-responders.

This paper may not have been available at the time of submission of the review article.1

N. George

Kettering, UK

Editor—Thank you for these comments. The article3 referred to was not available when our review was submitted (as you suggested). Despite its limitations,4 reanalysis of the multi-centre study of prone positioning in acute respiratory failure2 suggests that a PaCO2 response (decrease of >=1 mm Hg or 0.133 kPa after 6 h of the first pronation) is associated with survival, whereas a change in PaO2/FIO2 is not. Increased carbon dioxide clearance is likely to have been caused by recruitment of unventilated lung in responders, for which there are several plausible explanations. These observations are concordant with others that have correlated the dead space fraction with survival in patients with ARDS,5 and tempt speculation as to the pathophysiological basis that underlies this correlation.

However, it is worth noting that the mean tidal volume used to ventilate these patients would now be considered to be undesirably high1 (10.4 ml kg–1 ideal body weight), and that the effects of prone positioning are dependent on alveolar pressure.6 Clearly, there is still much to be learnt about the complex interactions between ventilatory strategy and non-ventilatory adjunct used in supporting patients suffering from acute lung injury.

M. Griffiths

E. Moloney

London, UK

References

1 Moloney ED, Griffiths MJD. Protective ventilation of patients with acute respiratory distress syndrome. Br J Anaesth 2004; 92: 261–70[Abstract/Free Full Text]

2 Gattitoni L, Togoni G, Pesenti A, et al. Effect of prone positioning on the survival of patients with acute respiratory failure. N Engl J Med 2001; 345: 568–73[Abstract/Free Full Text]

3 Gattitoni L, Vaginelli F, Carlesso E, et al. Decrease in PaCO2 with prone position is predictive of improved outcome in patients with acute respiratory distress syndrome. Crit Care Med 2003; 31: 2727–33[CrossRef][ISI][Medline]

4 Bein T. Prone position, carbon dioxide elimination, and survival: a turn for the better? Crit Care Med 2003; 31: 2804–5[CrossRef][ISI][Medline]

5 Nuckton TJ, Alonso JA, Kallet RH, et al. Pulmonary dead-space fraction as a risk factor for death in the acute respiratory distress syndrome. N Engl J Med 2002; 346: 1281–6[Abstract/Free Full Text]

6 Walther SM, Domino KB, Glenny RW, Hlastala MP. Positive end-expiratory pressure redistributes perfusion to dependent lung regions in supine but not in prone lambs. Crit Care Med 1999; 27: 37–45[ISI][Medline]





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