The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

RESISTANCE TO SPONTANEOUS BREATHING WITH OSCILLATION VERSUS CPAP BY A CONVENTIONAL MECHANICAL VENTILATOR.

Craig Black, PhD, RRT, Mike Troxell, PhD, RRT, Respiratory Care Program, The University of Toledo.

Background: With increased interest in oscillatory ventilation in adult areas as well as pediatric and neonatal areas, understanding the spontaneous work of breathing during oscillation would be beneficial. In most cases of oscillation, patients are sedated and/or chemically paralyzed to avoid the work of spontaneous breathing. Patients are then placed on conventional ventilation for weaning to effective spontaneous breathing. This practice of switching to conventional mechanical ventilation may not be necessary. The hypothesis of this project is: The work of spontaneous breathing with oscillation is no greater than during conventional ventilation.

Methods:
A Sensormedics 3100a ventilator and a VIP Bird ventilator were each connected to an IngMar ASL5000 Lung Simulator. Simulator settings were as follows: Respiratory rate = 30, tidal volume = 25ml, peak flow = 125ml/sec. Spontaneous tidal volume measured at the airway was 25 mls. Bird VIP parameters were: CPAP = 3 cmH2O, peak flow = 10 L/min, Assist sensitivity = 1. Oscillator parameters = bias flow 15 L/min, Amplitude = 10 cmH2O, Paw = 7 cmH2O, Frequency = 5 Htz.

Results:
With spontaneous breathing simulated for each ventilator, the resistance to expiratory flow was significantly greater (p < 0.05) with the oscillator than with the conventional ventilator (6.70 cmH2O/L/s vs. 1.75 cmH20/L/s).

Conclusion:
The resistance to expiratory flow and the simulated spontaneous work of breathing is significantly greater for the oscillator than for the conventional mechanical ventilator in the CPAP mode. Therefore the current practice of changing patients to conventional ventilators for weaning purposes should continue in order to minimize work of spontaneous breathing during mechanical ventilation.

Work of and resistance to simulated spontaneous breathing:

VIP Bird/ CPAP Sensormedics 3100a Oscillator

Inspiratory work (mj) 11.35 23.88
Expiratory work (mj) 8.79 43.40
Median expiratory resitance (cmH2O/L/sec) 1.75 6.70
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