LAUSR

becoming a common finding in mechanically ventilated patients. Second, despite some data in support of the use of NIV among patients with obesity at high risk of extubation failure, NIV is rarely implemented after extubation (2). Although the current study does not represent a definitive trial, we believe that there are solid physiologic reasons that explain why NIV is beneficial after extubation in obesity. In a recent ambulatory study (3) of patients with obesity and normal-range BMI, we characterized the effects of NIV on work of breathing. Our study rationale stemmed from prior observations that patients with obesity have elevated pleural pressures when mechanically ventilated and have recruitable lungs if adequate positive end-expiratory pressure (PEEP) is set to match resting pleural pressure after a recruitment maneuver (4). We found that applying noninvasive continuous positive airway pressure (CPAP) set to match pleural pressure as measured through esophageal manometry led to a dramatic reduction in work of breathing in ambulatory patients with obesity but not in patients with normalrange BMI. At baseline before CPAP initiation, patients with obesity demonstrated large inspiratory swings in pleural pressure—both for achieving airways opening as well as for VTs— representing a tremendous work of breathing in this population even outside of acute illness. CPAP matching end-expiratory pleural pressure in subjects with obesity dramatically reduced pleural pressure swings, reduced occlusion to airways opening, improved peripheral oxygen saturation, and led to a more homogeneous distribution of ventilation as observed through electrical impedance tomography. In an intubated patient with BMI of 43 kg/m, we observed failure of spontaneous breathing trial when performed according to the hospital standard of care (i.e., low degrees of PEEP, 5 cm H2O) (5). At 5 cm H2O PEEP, esophageal manometry revealed both high amounts of end-expiratory pleural pressure and large swings during the inspiratory phase, which is expected in subjects with obesity. When PEEP was set to counterbalance the high degree of pleural pressure, a threefold reduction in inspiratory work of breathing was observed. Furthermore, the analysis of lung ventilation by electrical impedance tomography showed a more homogeneous distribution of ventilation at higher degrees of PEEP and disappearance of a Pendelluft phenomenon (6). Taken together, these studies suggest that a titrated degree of PEEP to overcome airway occlusion and excessive work of breathing during weaning frommechanical ventilation and the application of postextubationNIVmight lead to improved outcomes. Although the goal of a spontaneous breathing trial is to simulate postextubation conditions (baseline work of breathing and respiratorymechanics), NIVmight help this subset of patients with obesity readapt to spontaneous breathing conditions, clear lingering anesthetics, and sit awake in the upright position. On the contrary, extubation to atmospheric pressuremight promote lung derecruitment and hemodynamic derangement owing to large transthoracic pressure swings, especially in those patients who are not fully awake and/or sitting fully upright. Although future studies should test the present hypothesis, Thille and colleagues should be complimented for demonstrating improved outcomes in this vulnerable and understudied population. Author disclosures are available with the text of this letter at www.atsjournals.org.