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

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Abstract
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. Prospective physiological study in a 13-bed medical intensive care unit in a university hospital. Twelve intubated patients with more than 10% of ineffective breaths while receiving pressure-support ventilation. 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. Reducing pressure support from 20.0 cm H2O (IQR 19.5–20) to 13.0 (12.0–14.0) reduced tidal volume [10.2 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 breaths/min (23.1–31.9) vs. 29.4 (24.6–34.5)], patient effort, or arterial PCO2. Shortening the insufflation time reduced ineffective triggering events and patient effort, while applying positive end-expiratory pressure had no influence on asynchrony. Markedly reducing pressure support or inspiratory duration to reach a tidal volume of about 6 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.

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