The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

LABORATORY EVALUATION OF DUAL CONTROL MODES (DCM) OF VENTILATION OF THREE ADULT VENTILATORS

Gary Banks* RRT, Robert S. Campbell RRT, FAARC, Jay A. Johannigman MD, Fred A. Luchette MD, Kenneth Davis Jr. MD, Sandra L. Miller MD, Scott B. Frame MD, Richard D. Branson RRT. Respiratory Care Department*, University Hospital and Division of Trauma/Critical Care, University of Cincinnati College of Medicine

Introduction: DCMs are designed to combine the benefits of pressure control (PC) and volume control (VC) ventilation. We evaluated DCMs of 3 vents in the lab with respect to tidal volume (VT) and pressure delivery at different and varying combinations of lung impedance (LI). Function of DCMs was compared to that of PC and VC for and between each vent.

Methods:
Each vent (Drager Evita4, Hamilton Galileo, Siemens 300) was set to ventilate one side of a two-chambered test lung (TTL) at all combinations of resistance (R) and compliance (C) characteristics: R10 and 20 cmH2O/L/sec, C 20 and 40 ml/cmH2O. Constant settings included: PEEP - 5 cmH2O, inspiratory time - 1.0 sec, 21% O2, and a rate - 15. VT was set to 500 ml during DCM and VC. During PC, inspiratory pressure was adjusted to an exhaled VT of 500 ml. Exhaled VT was measured proximally using a variable orifice flow transducer (Bicore) and used as the standard from which to compare VT delivered and measured by each vent. Time to stabilization (TS) of vent output was measured with each vent as the time elapsed from initiation of DCM to delivery of VT within 10% of set value. DCM response to changing LI conditions was assessed by changing C and R acutely from C40/R10 to C20/R20 and visa versa. VT and pressure delivery to the lung in response to the changed LI and TS (VT within 10% of set) with each DCM were recorded and compared to the VT and pressure delivery measured with PC and VC.

Results:
TS from DCM initialization varied between each vent (300 = 22.5 sec, E4 = 17.4 sec, Galileo = 60.5 sec). Each DCM responded to changed LI with appropriate pressure changes to maintain the target VT. TS varied between vents (300 = 29 sec, E4 = 26 sec, Galileo = 42 sec) and was determined by the max pressure change per breath allowed by each DCM algorithm. The first VT delivered after each change in LI are as follows (low/high): 300 = 220/745, E4 = 240/880, Galileo = 270/900. Each vent performed similarly in PC and VC during changing LI. During PC, VT changed from 500 to 263 and 963 ml following respective increased and decreased LI. During VC, PIP changed from 33 to 19 cmH2O and visa versa while maintaining VT delivery of 500 ml. Actual VT delivery during DCM was within 10% of set VT at each lung condition with a mean difference of: 300 = -3%, E4 = -7%, Galileo = +5%. Mean vent measured VT was within 10% of actual VT delivered to test lung (300 = -8.2%, E4 = +7.2%, Galileo = -5.6%). Conclusion: Although there are subtle differences between each DCM tested, all function acceptably and are monitored appropriately.

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