2001 OPEN FORUM Abstracts
INTERACTIONS BETWEENAUTO-TUBE COMPENSATION (ATC), MODERATE LEVEL PRESSURE SUPPORT (PS), AND PRESSURE-RISETIME (PRT) ON WORK OF BREATHING (WOB)
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 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. A moderate level of PS often is usedfor the same purpose. PRT prolongs the time to achieve the PS level, and mayincrease WOB. We studied the interactions of ATC and PRT on peak [I,VT and WOB during PS.
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, a peak [I demand of50 L/m and inspiratory time of 0.8 s. The Dräger E-2 treatment ventilator wasset at CPAP of 5 cm H2O with PS of 10 cm H2O. The PRTwas set at 0.25 s; the flow trigger was set at 5 L/m. We measured WOB performedby the drive ventilator to displace the ?patient? compartment (WOBc). WOBc approximatedtotal imposed WOB (ETT + circuit). Experiments were done with ATC turned offand at an ATC of 100, 75 and 50% compensation set to the ETT size used in themodel (7.0 mm ID). Experiments were done with and without PRT. 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 both Dunnett and Tukey-Kramer tests. Alpha was setat 0.05.
Results: Compared to PS alone,adding ATC increased both peak [I, and VT, and reducedWOBc. However, adding PRT increased WOBc at all levels of ATC, but did not appreciablyaffect peak [I and VT. Decreasing ATC support caused asmall increase in WOBc. Only 5 discreet comparisons were not statistically significant(p > 0.05): peak [I (*), WOBc (?, ?;), and VT (§,||)
|PRT = 0||ATC OFF||ATC 100||ATC 75||ATC 50|
|WOBc (J/L) (L/m) VT(mL)||0.38 ± .03? 77 ±1.0* 676 ±5||0.19 ± .01 109 ±1.9 766 ±5§||0.23 ± .02? 96 ±1.1 719 ±6||||0.25 ± .02? 102 ±0.3 707 ±5|
|PRT = 0.25s||ATC OFF||ATC 100||ATC 75||ATC 50|
|WOBc (J/L) (L/m) VT(mL)||0.58 ± .01 78 ±1.0* 660 ±0||0.34 ± .01 114 ±1.3 769 ±6§||0.38 ± .01? 101 ±1.2 720 ±7||||0.42 ± .02 92 ±1.3 700 ±0|
Conclusion:Our results suggest that ATC enhances the WOB-reducing effects of moderate levelPS. Decreasing the % ATC support caused a minor increase in imposed WOB andtherefore, ATC should be used at 100% support. PRT counters the effects of ATCand should not be used in conjunction with ATC.