The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

Automatic Tube Compensation (ATC)

Richard Branson BA, RRT University of Cincinnati Medical Center, Cincinnati, Ohio

Automatic Tube Compensation is a technique used on both the Drager Evita 4 and Mallinckrodt 840 ventilators which overcomes the imposed work due to the artificial airway automatically based on the known resistive characteristics of the endotracheal tube and the measured inspiratory flow. This technique is similar to the resistive component of proportional assist ventilation (PAV). ATC has been shown to reduce the imposed work of breathing due to the artificial airway more reliably than pressure support ventilation.
Proposed Advantages
1. Overcomes the imposed work of breathing caused by the endotracheal tube during spontaneous breathing.
2. Adjusts the level of support according to patient flow, allowing improved patient ventilator synchrony.
3. Can simulate the patient's workload following extubation - 'electronic extubation'.
Settings
1. Input the endotracheal or tracheostomy tube size.
2. Set the % of tube compensation desired (1 to 100%).
3. Set other parameters as required (SIMV rate, tidal volume, etc.)
Operation
1. The ventilator uses known constants for different size endotracheal and tracheostomy tubes in a look-up table.
2. The operator inputs the tube size and % compensation. The ventilator uses the mathematical model to simulate tracheal pressure control.
3. The ventilator also displays the calculated tracheal pressure.
4. The equation for tube compensation is PTRACHEA = PAW - KTUBE X Flow2 PTRACHEA = tracheal pressure, PAW = pressure at the Y-piece, KTUBE = tube coefficient, Flow2 = airway flow.
Pitfalls
1. Airway secretions or position changes may result in under compensation.
2. In vivo resistance is greater than ex vivo resistance.
3. Following extubation upper airway changes may effect work of breathing unanticipated by tube compensation.
4. Inexperience.

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