The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

COMPARINGWORK OF BREATHING (WOB) DURING CPAP AND PRESSURE SUPPORT (PS), WITH AND WITHOUTAUTO-TUBE COMPENSATION (ATC)

RH Kallet MS RRT,M Siobal BS RRT, EL Warnecke 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 [I to achieve the proximalairway pressure target at the distal tip of the endotracheal tube (ETT), thuscounterbalancing the imposed WOB of the artificial airway. Low to moderate levelsof PS often are used for the same purpose. We compared the effects of ATC onWOB, VT and peak [I during CPAP and PS.

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 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 then with PS of 5 and 10 cm H2O. The flow trigger was set at5 L/m. We measured the WOB performed by the drive ventilator to displace the?patient? compartment (WOBc). WOBc approximated total imposed WOB (ETT + circuit).Experiments were done with ATC turned off and at 100% ATC compensation set tothe corresponding ETT sizes used in the model (7.0 and 6.0 mm ID). Measurementswere made with a BICORE CP-100 monitor; 10 breaths were used for analysis. Datawas reported as mean ± standard deviation and analyzed using repeated-measuresanalysis of variance and Tukey-Kramer tests. Alpha was set at 0.05.

Results: AddingATC to CPAP increased peak [I more than adding 5-10 cm H2Oof PS. CPAP with ATC reduced WOBc more than PS of 5 cm H2O. For eachlevel of PS, adding ATC increased peak [I and substantially reducedWOBc at both ETT sizes. Only 3 comparisons were not statistically significant(*, ?, ?; p > 0.05).

ETT 7.0

[I(L/m)VT(mL) WOBc (J/L)% WOB

CPAP

62 ± 1581 ± 30.97 ± .01 

CPAP ATC

96 ± 1* 641 ± 60.46± .0153%

PS 5

67 ± 1630 ± 00.66± .02 

PS 5 ATC

97 ± 2*712 ± 60.32 ± .0152%

PS 10

77 ± 1676 ± 50.38 ± .03

PS 10 ATC ON

109 ± 2766 ± 50.19± .0150%

ETT 6.0

CPAP

54 ± 0.7552 ± 4 1.45 ± .02

CPAP ATC

64 ± 0.7? 589 ± 31.07 ± .01 26%

PS 5

56 ± 0.5 585 ± 51.15 ± .01 

PS 5 ATC

65 ± 2??630 ± 00.80 ± .0230%

PS 10

59± 0.4620 ± 0 0.80 ± .02 

PS 10 ATC ON

66 ± 0.6?642 ± 40.51 ± .0136%

Conclusion: Adding100% ATC to CPAP was more effective in reducing total imposed WOB than adding5 cm H2O PS, but not as effective as adding 10 cm H2OPS. ATC was less effective in reducing WOBc when a small ETT size (6.0 mm ID)was in place, possibly becauseof less flow augmentation.

OF-01-197

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