Pendelluft in Patients with Acute Respiratory Distress Syndrome during Spontaneous breathing

Background: Pendelluft occurs in patients with acute respiratory distress syndrome (ARDS) during spontaneous breaths. Quantifying pendelluft in ARDS patients has not been performed before. We combined electrical impedance tomography (EIT) and respiratory mechanics monitoring to quantitatively examine pendelluft in trigger and reverse triggering breaths in mechanically ventilated patients with ARDS. Methods EIT and respiratory mechanics measurements were analyzed in 20 mechanically ventilated patients with ARDS during transitioning from controlled to spontaneous breaths following discontinuance of myorelaxant under volume-cycled ventilation. Breath selection was based on 4 levels of esophageal pressure swing (∆P es ). These were rest (0 cm H 2 O, breaths = 200), low (< 5cm H 2 O, breaths = 471), moderate (≥ 5, < 10cm H 2 O, breaths = 906), and high effort (≥ 10cm H 2 O, breaths = 565). A total of 2,142 breaths were analyzed. Results The pendelluft response to breathing efforts varied and was significantly greater in trigger versus reverse triggering breaths (3.9 ± 6.8 vs 1.9 ± 2.8 ml, respectively, p < 0.0001). There were two distinct patterns of effort-related pendelluft (high vs. low pendelluft group) in trigger and reverse triggering breaths based on pendeluft- ∆P es slope (ml/cmH 2 O). For trigger breaths, high pendelluft group (n = 9, slope 0.7 to 2.4 ml/cmH 2 O) was significantly associated with lower peak airway/plateau pressure and lower respiratory system/lung elastance than low pendelluft group (n = 11, slope − 0.1 to 0.3 ml/cmH 2 O). For reverse triggering breaths, there was no difference in respiratory mechanics between high (n = 4, 0.49 to 2.53 ml/cmH 2 O) and low pendelluft (n = 12, -0.22 to 0.25 ml/cmH 2 O) groups. The prediction of pendelluft by ∆P es was characterized by a low positive predictive value. ARDS cases with high effort-related pendelluft were uncommon. The prediction of pendelluft was not significant in reverse triggering breaths. Conclusions Effort-related pendelluft should be individualized. Pendelluft is higher in trigger breaths than reverse triggering breaths. For trigger breaths, high pendelluft is likely to occur in ARDS patients with lower lung elastance and lower peak airway/plateau pressure. However, ARDS cases with high effort-related pendelluft were uncommon in our study population.