Reduction of patient-ventilator asynchrony by reducing tidal volume during pressure-support ventilation

OBJECTIVE: To identify ventilatory setting adjustments that improve patient-ventilator synchrony during pressure-support ventilation in ventilator-dependent patients by reducing ineffective triggering events without decreasing tolerance. DESIGN AND SETTING: Prospective physiological study in a 13-bed medical intensive care unit in a university hospital. PATIENTS AND PARTICIPANTS: Twelve intubated patients with more than 10% of ineffective breaths while receiving pressure-support ventilation. INTERVENTIONS: Flow, airway-pressure, esophageal-pressure, and gastric-pressure signals were used to measure patient inspiratory effort. To decrease ineffective triggering the following ventilator setting adjustments were randomly adjusted: pressure support reduction, insufflation time reduction, and change in end-expiratory pressure. MEASUREMENTS AND RESULTS: Reducing pressure support from 20.0[Symbol: see text]cm H(2)O (IQR 19.5-20) to 13.0 (12.0-14.0) reduced tidal volume [10.2[Symbol: see text]ml/kg predicted body weight (7.2-11.5) to 5.9 (4.9-6.7)] and minimized ineffective triggering events [45% of respiratory efforts (36-52) to 0% (0-7)], completely abolishing ineffective triggering in two-thirds of patients. The ventilator respiratory rate increased due to unmasked wasted efforts, with no changes in patient respiratory rate [26.5[Symbol: see text]breaths/min (23.1-31.9) vs. 29.4 (24.6-34.5)], patient effort, or arterial PCO(2). Shortening the insufflation time reduced ineffective triggering events and patient effort, while applying positive end-expiratory pressure had no influence on asynchrony. CONCLUSIONS: Markedly reducing pressure support or inspiratory duration to reach a tidal volume of about 6[Symbol: see text]ml/kg predicted body weight eliminated ineffective triggering in two-thirds of patients with weaning difficulties and a high percentage of ineffective efforts without inducing excessive work of breathing or modifying patient respiratory rate.