The response of flow-triggered infant ventilators.

Patient-triggered ventilation (PTV) has not been feasible for infants because of large trigger pressures and long delay times with pressure-triggered systems. Recently, four infant ventilators with flow triggering have become available. We questioned if delay times, trigger pressures, and trigger work with these ventilators would be acceptable for PTV in infants. All ventilators were attached via 3-, 4-, and 5-mm endotracheal tubes to a spontaneously breathing infant lung model. The lung simulator was set at an inspiratory time of 0.65 s, tidal volume of 15, 30, and 45 ml, and 0 and 5 cm H2O positive end-expiratory pressure (PEEP). Delay time, trigger pressure, and trigger work were determined from pressure measured at the proximal airway, trachea, and alveolus. There were significant differences between the endotracheal tube sizes, sites of measurement, ventilatory demand and ventilator brand at each PEEP level for delay time, trigger pressure, and trigger work (p < 0.001). Delay time was greatest with the 3-mm endotracheal tube at high ventilatory drive (maximum 138.2 +/- 2.1 ms). Both trigger pressure (minimum 0.23 +/- 0.02 cm H2O) and trigger work (minimum 0.05 +/- 0.01 g.ml) increased with decreasing endotracheal tube size, increasing ventilatory demand, use of PEEP, and site of measurement: alveolus > trachea > airway (maximum: trigger pressure 5.04 +/- 0.02 cm H2O; trigger work 114.48 +/- 0.88 g.ml). PTV may not be appropriate under conditions of increased ventilatory drive and small endotracheal tube size in infants.