© 2006 American Thoracic Society
Is Maximal Lung Recruitment Worth It?From the Authors:We thank Drs. Bugedo and Bruhn for their comments on our recent article (1). We do not share, however, their concerns about the levels of PaCO2 and pH reported. After an extensive review of the literature, we concluded that it is impossible to delimit safety boundaries: no systemic or physiologic harm has been directly associated with hypercapnia or respiratory acidosis. On the contrary, there are data suggesting a direct benefit of such a strategy in situations of acute lung injury (2). The benefit seems to extend beyond its original purpose (i.e., the minimization of mechanical stress), and is a direct consequence of intracellular acidosis. Obviously, there is a strong rationale precluding us from using hypercapnia when facing an unstable cardiovascular system (especially arrhythmias) or high intracranial pressures. These recommendations were followed in our study. But it is interesting to recall, in this context, some past studies on diabetic ketoacidosis, in which patients have repeatedly presented uncomplicated recovery from pH values as low as 6.73, without any specific intervention (like bicarbonate infusion) (3, 4). Concerning the minimal gain in reversing collapse at pressures beyond 45 cm H2O, we must emphasize that our Figure 2 is an averaged graph. By considering only those patients not yet fully recruited at the first recruitment step (7 patients), we observed a mean reduction in the amount of collapsed units from 15 to 5%. In the most extreme case, the collapsed mass decreased from 25 to 6%. Whether one-fifth of the parenchyma is worth the challenge is a matter for future studies. Finally, we must agree with Bugedo and Bruhn that the transient overdistension promoted by the maximum-recruitment maneuver may cause further damage to the parenchyma. Our data demonstrated, however, that whenever we were able to obtain massive recruitment, there was a marked decrease of overdistension in the nondependent zones, likely due to an overall increase in pleural pressures (5). In any case, we should keep our focus on the long-term benefit of the strategy. The medical literature is full of examples of now well-accepted treatments that caused transient harm to patients, from chemotherapy for cancer to pulse therapy for lupus. The key issue is the overall balance and not the short-term concerns and fears. In this regard, we must point out that two recent series of patients with severe ARDS who were treated according to a maximum-recruitment strategy showed an overall mortality less than 22% (6).
Universidade de São Paulo, São Paulo, Brazil FOOTNOTES Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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