Auto-Tube Compensation
(ATC) on the Dräger E-2 Ventilator Reduces Work of Breathing (WOB) During CPAP
RH Kallet MS RRT, M Siobal
BS RRT, RW Kraemer CRTT, J Tang MD
Respiratory Care Services, Department of Anesthesia, San Francisco General Hospital,
University of California San Francisco.
Background: ATC augments
ventilator inspiratory flow rate [I to achieve the proximal airway
pressure target at the distal tip of the endotracheal tube (ETT), thus counterbalancing
the imposed WOB of the artificial airway. ATC can be set to compensate for a
variable percentage of tube resistance. We investigated the effects of 3 levels
of ATC on WOB as ETT size was varied.
Methods: A standard WOB lung
model was constructed using a Michigan Instruments TTL set at a compliance of
27 mL/cm H2O; powered by a Veolar ventilator set to create a VT demand of 500 mL at a respiratory rate of 24 and a peak [I demand
of 50 L/m. The Dräger E-2 treatment ventilator was set at CPAP of 5 cm H2O
and 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). Experiments
were conducted with ATC turned off and at an ATC of 100%, 75% and 50% compensation
set to the corresponding ET size used in the model (8.0 and 6.0 mm ID). Measurements
were 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-Kramer
tests. Alpha was set at 0.05.
Results: At all levels of
ATC, WOBc was significantly reduced compared to CPAP without ATC. The ability
to 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% at
8.0 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 total
imposed WOB by increasing peak delivery above flow demand and probably should
be used at 100% compensation. However, ATC?s effectiveness appears to be diminished
by the presence of a small ETT size
