The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

Auto-Tube Compensation(ATC) on the Dräger E-2 Ventilator Reduces Work of Breathing (WOB) During CPAP

RH Kallet MS RRT, M SiobalBS RRT, RW Kraemer CRTT, J Tang MD Respiratory Care Services, Department of Anesthesia, San Francisco General Hospital,University of California San Francisco.

Background: ATC augmentsventilator inspiratory flow rate [I to achieve the proximal airwaypressure target at the distal tip of the endotracheal tube (ETT), thus counterbalancingthe imposed WOB of the artificial airway. ATC can be set to compensate for avariable percentage of tube resistance. We investigated the effects of 3 levelsof ATC on WOB as ETT size was varied.

Methods: A standard WOB lungmodel was constructed using a Michigan Instruments TTL set at a compliance of27 mL/cm H2O; powered by a Veolar ventilator set to create a VTdemand of 500 mL at a respiratory rate of 24 and a peak [I demandof 50 L/m. The Dräger E-2 treatment ventilator was set at CPAP of 5 cm H2Oand a flow trigger of 5 L/min. We measured WOB performed by the Dräger E-2 ventilator(WOBv) and WOB performed by the drive ventilator to displace the ?patient? compartment(WOBc). WOBc approximated the total imposed WOB (ETT + circuit). Experimentswere conducted with ATC turned off and at an ATC of 100%, 75% and 50% compensationset to the corresponding ET size used in the model (8.0 and 6.0 mm ID). Measurementswere made with a BICORE CP-100 monitor and 10 breaths were used for analysis.Data was analyzed using repeated-measures analysis of variance (ANOVA) and Tukey-Kramertests. Alpha was set at 0.05.

Results: At all levels ofATC, WOBc was significantly reduced compared to CPAP without ATC. The abilityto reduce WOB diminished as the ATC level was lowered to 50%. Also, ATC 100%was not as effective in reducing WOBc as ETT size decreased (45% vs. 26% at8.0 and 6.0 ETT size respectively). All comparisons were statistically significant.

ETT 8.0 WOBc (J/L) WOBv (J/L) [I (L/m) VT (mL)
ATC OFF 0.69 ± .01 0.23 ± .003 68 ± 1 563 ± 5
ATC 100% 0.38 ± .02 0.99 ± .03 91 ± 2 572 ± 6
ATC 75% 0.42 ± .02 0.73 ± .01 82± 1 569 ± 3
ATC 50% 0.49± .01 0.53 ± .01 77 ± 1 575 ± 5
ETT 6.0
ATC OFF 1.45 ±.02 0.28 ± .004 54 ± 0.7 552 ± 4
ATC 100% 1.07 ± .01 1.06 ± .01 64 ± 0.7 589 ± 3
ATC 75% 1.18 ± .02 0.83 ±.004 61 ± .07 580 ± 0
ATC 50% 1.28 ± .01 0.61 ± .005 58 ± .04 570 ± 0

Conclusion: ATC reduced totalimposed WOB by increasing peak delivery above flow demand and probably shouldbe used at 100% compensation. However, ATC?s effectiveness appears to be diminishedby the presence of a small ETT size

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