Impact of expiratory trigger setting on delayed cycling and inspiratory muscle workload

Rationale: During pressure-sup port ventilation, the ventilator cycles into expiration when inspiratory flow decreases to a given percentage of peak inspiratory flow (expiratory trigger). In obstructive disease, the slower rise and decrease of inspiratory flow entails delayed cycling, an increase in intrinsic positive end-expiratory pressure, and nontriggering breaths. Objectives: We hypothesized that setting expiratory trigger at a higher than usual percentage of peak inspiratory flow would attenuate the adverse effects of delayed cycling. Methods: Ten intubated patients with obstructive disease undergoing pressure support were studied at expiratory trigger settings of 10, 25, 50, and 70% of peak inspiratory flow. Measurements: Continuous recording of diaphragmatic EMG activity with surface electrodes, and esophageal and gastric pressures with a dual-balloon nasogastric tube. Main Results: Compared with expiratory trigger 10, expiratory trigger 70 reduced the magnitude of delayed cycling (0.25 +/- 0.18 vs. 1.26 +/- 0.72 s, p < 0.05), intrinsic positive end-expiratory pressure (4.8 +/- 1.9 vs. 6.5 +/- 2.2 cm H2O, p < 0.05), nontriggering breaths (2 +/- 3 vs. 9 +/- 5 breaths/min, p < 0.05), and triggering pressure-time product (0.9 +/- 0.8 vs. 2.1 +/- 0.7 cm H2O center dot s, p < 0.05). Conclusions: Setting expiratory trigger at a higher percentage of peak inspiratory flow in patients with obstructive disease during pressure support improves patient-ventilator synchrony and reduces inspiratory muscle effort. Further studies should explore whether these effects can influence patient outcome.