Effect of ATC on Tidal Volume with Varied Amplitude

Document Type

Student Presentation

Presentation Date


Faculty Sponsor

Lonny Ashworth



Automatic Tube Compensation (ATC) has been shown to assist patients’ ventilation during spontaneous breathing trials (SBT); however, the level of support offered by this feature in different ventilators has not been determined. This bench study aimed to determine how the ATC on the CareFusion Avea (AAC), Covidien PB 840 (TC), and the Dräger Evita XL (ATC) each affect tidal volumes at various inspiratory demand levels.


After calibrating each ventilator and the lung simulator, the Avea, Evita XL, and the PB 840 were joined with the Hans Rudolph 1101 Electronic Lung Simulator (HR 1101) using the same large bore circuit and a Teleflex Isis HVT 7.0 and 7.5 and a Rusch 8.0 ETT. The HR 1101 was setup to mimic a ‘normal’ pulmonary system: Resistance 10 cm H2O/L/s; Compliance 40 mL/cm H2O; Rate 20/minute, Inspiratory time Percent 30; Load Effort NORMAL; Maximum Volume 3000 mL. The HR 1101 amplitude or ‘patient effort’ was set at 5, 10, 20, 30, and 40 cm H2O with each ETT and with each ventilator with ATC off and then on. The Evita XL was assessed with ATC at 80% and 100%. Each ventilator was placed in CPAP, Pressure Support 0 cm H2O and PEEP 5 cm H2O. After allowing for stabilization, video recordings of the HR 1101 displayed values were made at each combination of settings. While reviewing the video playback, data for six consecutive breaths were recorded and averaged.


Using the 7.5 ETT as a median value, the Avea’s AAC resulted in minimal changes in the delivered tidal volume, with the largest percentage being 5.56% at Amplitude of 5 garnering an 8 mL change per breath. In contrast, the Evita XL at 100% ATC resulted in a 51.34% increase in delivered tidal volume, delivering an additional 487.25 mL per breath at the maximal Amplitude of 40.

Overall, the use of ATC increases delivered tidal volume by 2.92% on the Avea, 12.1% on the PB 840, 11.96% on the Evita XL at 80% and 24.96% on the Evita XL at 100%.


While a patient is undergoing an SBT, s/he may be receiving more support than initially thought or desired. ATC results in an increased tidal volume and a presumed reduction in work of breathing. Currently, the level of support to be used during an SBT is being questioned by other authors and it has now been shown that airway resistance may increase after extubation, rather than decrease. Therefore, the use of ATC, designed to reduce the work of breathing of the ETT, needs to be carefully considered during an SBT.

This document is currently not available here.