The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

DIFFERENCE BETWEEN CALCULATED AND MEASURED TRACHEAL PRESSURES AT PEAK INSPIRATORY FLOW DEMAND DURING ATC ON THE DRAGER XL VENTILATOR.

Mark S. Siobal, Gregory Burns, Roberto Bautista; Anesthesia, SFGH/UCSF, San Francisco, CA

Background: Automatic Tube Compensation (ATC) is dependant on the calculation of tracheal pressure. This study was done to determine the accuracy of the calculated tracheal pressure deflection during ATC with varying peak inspiratory flow demands. Method: A dual compartment test lung (Michigan Instruments TTL, Grand Rapids, MI) with the chambers locked together was powered on one side (muscle chamber) by a Drager XL ventilator, Vt 500mL, RR 12, PEEP 5cmH2O, Ti 1.2sec, with varying inspiratory flow rates. Another Drager XL ventilator attached to the other TTL compartment (lung chamber), set in the Pressure Support mode with ATC on, PIP 15cmH2O, PEEP 5cmH20, Slope 0.2, Trigger 3L/min, was connected to an ETT inserted into smooth bore aerosol tubing with the cuff inflated. A pressure monitoring port was placed at the end of the tubing and connected directly to the lung chamber. At varying inspiratory flow rates, the difference between the calculated tracheal pressure (PCalc) and the measured tracheal pressure (PMeas) was determined. PMeas was recorded with a VenTrak 1550 Respiratory Mechanics Monitor (Novametrix, Wallingford, CT). Measurements were performed at 30, 60, 90, and 120L/min inspiratory flow rate with ATC of 0% and 100% using three different endotracheal tubes sizes (6.0, 7.0, and 8.0 mm) at the point of maximum negative tracheal pressure deflection. Five sets of measurements were recorded at each test condition. Results: During each test condition the difference between PCalc and PMeas increased with increasing inspiratory flow demands. The difference between PCalc and PMeas was greater with ATC set at 100%. Conclusion: There is marked variability in the accuracy of the PCalc at the point of maximum negative tracheal pressure deflection during ATC at both 0% and 100% compensation.
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