Acute hypoxemic respiratory failure in acquired immune deficiency syndrome: effects of noninvasive ventilation: the highest PEEP may not be best.

Acquired immune deficiency syndrome (AIDS) isa severehealthproblem,and,acute hypoxemic respiratory failure (AHRF) a major complication.1 Early noninvasive ventilation (NIV) may improve gas exchange and outcome in selected patients during AHRF.2 Anjos CF et al3 describe noninvasive PEEP effects on gas exchange and clinical variables in 30 AIDS patients during AHRF, in randomized sequence. They observed that oxygenation improves linearly with increasing levels of PEEP. We read with great interest the paper and their results. The study confirms previous concepts about NIV effects in AHRF. That is, implementation of incremental PEEP may improve oxygenation, irrespective of causative factors and related with PEEP level (Fig. 2A in Anjos et al3). We don’t understand what is the authors’ expectancy about the application of“sequentialPEEP”as it isdescribed.Some issues are very interesting to analyze for their practical implications related to PEEP effects during NIV in AIDS patients with ARDS criteria. First, the periods during which PEEP is applied may be too short to achieve a complete and effective alveolar recruitment, and zero end-expiratory pressure periods doesn’t allow for a sequence effect. It could then be that there is no real “sequential effect” of PEEP with this protocol, and so it is hard to analyze their results. Second, as the authors describe in Figure 2B, 2C, and 2D, there was a slight elevation of PCO2 levels, with a simultaneous increase in tidal volume and respiratory rate when increasing levels of PEEP. The more reasonable explanation for this finding would be the Haldane effect and the changes in the ventilation/perfusion ratio secondary to improvement in PaO2. 4