Backup respiratory rate during noninvasive positive pressure ventilation in obesity hypoventilation syndrome: Can this difficult puzzle be resolved?

摘要

To the Editor: Obesity hypoventilation syndrome (OHS) refers to sleep-related hypoventilation with repetitive episodes of complete and partial obstructions of the upper airway.1 Some finesse is required to determine the appropriate ventilator settings to prevent such episodes, which can alter the efficacy of noninvasive positive pressure ventilation (NPPV). In a recent article in CHEST (January2013), Contal et al2 analyzed the effects of three strategies: a spontaneous (S) mode, a low backup respiratory rate (BURR), and a high BURR. The S mode was worse than the SAT mode, and changing the BURR from an S/T mode with a high or low BURR to an S mode was associated with the occurrence of a highly significant increase in respiratory events and oxygenation desaturation index events. It is worth highlighting some features of this study, which help place the findings in context. First, the population selected had some interesting characteristics. The prior use of NPPV for at least 42.7 months (duration of NPPV) and a baseline BURR of 14 may have influenced the results. Specifically, patients who had already been acclimated to NPPV might have adjusted more easily to a range of BURR. Second, ahighBMI of 48.5 kg/m2 could also have reduced the efficacy of NPPV, making it difficult to generalize from these results to the entire spectrum of OHS.3 Third, the authors did not consider the potential effects of upper airway obstruction during sleep (obstructive apneas and hypopnea), which are common in severely obese patients and could further reduce the therapeutic efficacy,4 depending on the algorithm for setting the expiratory pressure. Fourth, it is difficult to determine the effect of the NPPV strategy on PaCO2 over the relatively short period of intervention in this study in the group that was not hypercapnic at baseline (pH, 7.44; Pco2, 41.3; bicarbonate, 28.1). Other outcomes would be required to assess the acute effects of NPPV in this group (Table 1 in Contal et al2).