Impact of Expiratory Trigger Setting on Delayed Cycling and Inspiratory Muscle Workload

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Abstract
During pressure-support 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. We hypothesized that setting expiratory trigger at a higher than usual percentage of peak inspiratory flow would attenuate the adverse effects of delayed cycling. 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. Continuous recording of diaphragmatic EMG activity with surface electrodes, and esophageal and gastric pressures with a dual-balloon nasogastric tube. 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 H(2)O, 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 . s, p < 0.05). 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.

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