2001 OPEN FORUM Abstracts
INTERACTIONSBETWEEN AUTO-TUBE COMPENSATION (ATC) AND VOLUME CONTROL-AUTO FLOW (VC-AF) ONWORK OF BREATHING (WOB) DURING LOW TIDAL VOLUME (VT) VENTILATION.
RH Kallet MS RRT, EL WarneckeBS RRT, M Siobal BS RRT, RW Kraemer CRTT, J Tang MD. Respiratory Care Services, Departmentof Anesthesia, San Francisco General Hospital, University of California SanFrancisco.
Background:ATC augments ventilator inspiratory flow rate () to achieve the proximal airwaypressure target at the distal tip of the endotracheal tube (ETT), thus counterbalancingthe imposed WOB of the artificial airway. VC-AF incorporates a variable, deceleratingflow pattern to deliver the target VT at the lowest airway pressure,and thus, may reduce WOB during patient-triggered breaths. We studied the combinedeffects of ATC and VC-AF on peak , VT and WOB during simulated patient-triggered,low VT ventilation.
Methods: A standardWOB lung model was constructed using a Michigan Instruments TTL set at a complianceof 27 mL/cm H2O; powered by a Veolar ventilator set to create a VTdemand of 400 mL at a respiratory rate (f) = 24, a peak demand = 39 L/m andinspiratory time (TI) of 0.8 s. The Dräger E-2 treatment ventilatorwas set in VC-AF at a target VT of 400 mL, f = 20; TI= 0.9 s and flow trigger = 5 L/m. We measured WOB performed by the drive ventilatorto displace the ?patient? compartment (WOBc). WOBc approximated total imposedWOB (ETT + circuit). Experiments were done with ATC off and at ATC of 100, 75and 50% compensation set to the ETT sizes used in the model (7.0 and 6 mm ID).Measurements were made with a BICORE CP-100 monitor. After stabilization ofVT delivery, 10 breaths were used for analysis. Data was reportedas mean ± standard deviation and analyzed using repeated-measures analysis ofvariance and both Dunnett or Tukey-Kramer tests. Alpha was set at 0.05.
Results: A VT-overshootoccurred as VT demand equaled the pre-set target VT. AddingATC increased peak delivery and caused a slightly greater VT-overshoot.This resulted in a 36-38% reduction in WOBc for ETT sizes of 6 and 7 mm respectively.Only 3 comparisons were not statistically significant (*, ?, ?; p > 0.05).
|ETT = 7.0mm||ATC OFF||ATC 100||ATC 75||ATC 50|
|WOBc (J/L) (L/m) VT(mL)||0.24 ± .01 58 ±1 470 ±0||0.15 ± .01* 71± 0.9 486 ±5||0.16 ± .02* 66 ±1 480 ±0?||0.18 ± .01 63 ±0.7 480 ±0?|
|ETT = 6.0mm||ATC OFF||ATC 100||ATC 75||ATC 50|
|WOBc (J/L) (L/m) VT(mL)||0.56 ± .01 45 ±0.4 450 ±0||0.36 ± .01 51 ±0.6 470 ±0?||0.41 ± .01 50 ±0.6 470 ±0?||0.45 ± .01 48 ±0.6 461 ±3|
Conclusion:Our results suggest that ATC enhances the WOB-reducing effects of VC-AF. Reducingthe level of ATC support caused a minor increase in imposed WOB, and therefore,ATC should be used at 100% compensation.