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

Byline: Arnaud W. Thille (1), Belen Cabello (1), Fabrice Galia (1), Aissam Lyazidi (1), Laurent Brochard (1) Keywords: Patient-ventilator asynchrony; Patient-ventilator interaction; Assisted mechanical ventilation; Pressure-support ventilation; Work of breathing Abstract: 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 20.0a-cm [H.sub.2]O (IQR 19.5--20) to 13.0 (12.0--14.0) reduced tidal volume [10.2a-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 [26.5a-breaths/min (23.1--31.9) vs. 29.4 (24.6--34.5)], patient effort, or arterial PCO.sub.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 6a-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. Author Affiliation: (1) Medical Intensive Care Unit, Henri Mondor Teaching Hospital, AP-HP, INSERM U841, Paris XII University, 51 avenue du Marechal de Lattre de Tassigny, 94010, Creteil, France Article History: Registration Date: 31/03/2008 Received Date: 15/11/2007 Accepted Date: 27/03/2008 Online Date: 24/04/2008