2001 OPEN FORUM Abstracts
EFFECTOF TUBE COMPENSATION (TC) VS PRESSURE SUPPORT (PS)ON CARINAL PRESSURE ANDWORK INDICES: A BENCH STUDY
CarlHaas, MLS, RRT and Paul Loik, RRT University of MichiganHealth System, Ann Arbor MI
BACKGROUND:PS provides a constant pressure assist, regardless of patient effort to overcomeresistance of an artificial airway while TC provides a variable pressure assistlevel in direct proportion to patient effort. With the ventilator tested, TCattempts to maintain carinal pressure at set-PEEP.
STUDY QUESTIONS:1) What impact does TC have on minimizing carinal pressure changes, and on otherindices of inspiratory work compared to PS; and 2) What influence does endotrachealtube size (ETT) have on PS and TC?
Methods: Lungmodel: A computerized lung simulator (ASL-5000, Igmar Medical) was set toa single lung model with C=50 mL/cm H2O, R=10 cm H2O/L/s,RR=20, an inspiratory effort of ?15 cm H2O and settings resultingin an I:E of ~1:3.0. Ventilator settings: A PB-840 ventilator (CarlsbadCA) was set to PEEP=0 cm H2O, FIO2=0.21, and trigger of?1 cm H2O. For PS breaths, flow acceleration=50% and expiratory sensitivity=10%.The ventilator was tested at: PS=0, 5, and 10 cm H2O; and TC=50 and100%. Airways: ETT of an ID of 6, 7, 8, and 9 mm were studied. The distalend was attached to the lung simulator and the proximal end to the circuit wyewith identical adapters. Measurements: The simulator measured flow, volume,and pressure. These measurements were taken immediately distal to the airwaytested, therefore airway pressure is considered to reflect ?carinal? pressure.Minimum pressure (Pmin) after trigger, time to Pmin aftertrigger, and work done from the onset of flow to Pmin were calculatedby the lung simulator. Data: Ten breaths of data were analyzed for eachdata set. Results are mean values; p<0.005 (+) was consideredsignificant comparing all levels of support (0.05/10 comparisons=0.005); onlyp values for PS=0 vs other levels are reported.
Pmin (cm H2O)
|ETT=6 ETT=7 ETT=8 ETT=9||-7.34 -5.79 -5.24 -5.25||-6.61+ -5.65 -5.42 -5.17+||-5.93+ -5.47+ -5.17 -4.96+||-6.63+ -5.50+ -5.19 -4.94+||-6.23+ -5.44+ -5.23 -4.93+|
Time to Pmin (msec)
|ETT=6 ETT=7 ETT=8 ETT=9||198.2 188.8 49.0 49.4||180.2+ 50.4+ 46.8 48.4||46.6+ 44.0+ 41.2+ 38.8+||186.8 49.2+ 46.8 44.6+||64.6+ 49.2+ 48.6 44.4+|
Work, flowonset to Pmin (J)
|ETT=6 ETT=7 ETT=8 ETT=9||33.86 32.30 0.22 0.17||24.64+ 0.12+ 0.03 0.09+||-0.19+ -.015+ -0.14+ -0.08+||27.45 0.07+ 0.08 0.10||0.38+ 0.06+ 0.18 0.12|
CONCLUSIONS:1) Under current test conditions, ETT=8 & 9 had minimal effect on the 3measured parameters; 2) Pmin was reduced with both TC levels andPS=10 in all airways but ETT=8; 3) Pmin never exceeded -4.93 cm H2O(target=0); 4) time to Pmin was reduced most with PS=10 and TC=100;5) work from onset of flow to Pmin was reduced in small airways with TC=100and PS=5 and in all airways by PS=10. PS=10 may have provided excessive work(negative values). The clinical relevance of these findings remains to be determined.