Volume 14
Number 3
Aug 2010
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SJH Heines, U Strauch, PMHJ Roekaerts, B Winkens, DCJJ Bergmans

Introduction Previous research on automatic tube compensation (ATC) mainly investigated work of breathing in spontaneously breathing patients. However, ATC also compensates the increase in resistance in a controlled mechanical ventilation mode. We designed an experimental study to investigate the effects of ATC on pressures and inspiratory rise time during controlled ventilation. Methods A ventilator was connected to an artificial lung. Two sets of experiments were performed: ‘Pressure constant experiment’: fixed inspiratory pressure (Pinsp) (25 mbar), three respiratory rates (10, 30 and 50 breaths min –1). ‘Frequency constant experiment’: fixed respiratory rate (15 breaths min –1), three Pinsp (15, 30 and 45 mbar). Measurements of maximum pressure on the ventilator, proximal and distal of the endotracheal tube were performed. In addition, mean pressure and inspiratory rise time distal of the endotracheal tube were determined. All measurements were performed at each setting with ATC on and ATC off, and with an endotracheal tube with an internal diameter ID of 7.0 and 9.0 mm. Results The pressure distal of the tube never exceeded the set pressure level on the ventilator. The time needed to reach the set inspiratory pressure distal of the tube was shorter with ATC than without ATC. (668±2.9 msec versus 1694±2.5 msec respectively for tube ID 7.0 and Pinsp 30 mbar and 1070±4.7 msec versus 1435±2.2 msec respectively for tube ID 9.0 and Pinsp 30 mbar). On ATC the pressure at the distal end of the endotracheal tube did not exceed the set inspiratory pressure on the ventilator. Moreover, ATC resulted in a shorter inspiratory pressure rise time at the tracheal level and a significantly higher mean airway pressure as compared to mechanical ventilation without using ATC.

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