The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

Intravascular pressure wire transducer system maintains accuracy over many days, an in vitro experiment

Brian K. Walsh, RRT, Billy Clem,Allan Doctor, MD, Virginia ChildrenÕs Heart Center, University of Virginia,Charlottesville, VA

Introduction: It is desirableto be able to monitor pulmonary artery and cardiac chamber pressures followingcomplex congenital heart defect repairs in small infants. Conventional monitoringdevices are large, have embolic risk, and require large fluid infusions. Also,removal of these devices is occasionally complicated by significant hemorrhage.Solid state wire-mounted micro transducer devices have been available for shortterm use during catheterization (RADI Pressure Wire¨ XT, RADI Medical Systems,Reading, MA) and have a proven accuracy. Because the transducer is intravascular,however, re-zeroing after the initiation of monitoring is not possible. Thepossibility of longer-term use following cardiac surgery led us to evaluatetheir precision over time (drift) in an in vitro test system.

Methods: A piece of Tygontubing (0.25 inch internal diameter) approximately 12 inches long was sealedat end with a three way stop-cock. From one end, a conventional saline filledtransducer (Transpac¨ Abbott Critical Care Systems, Chicago, Illinois) was attachedto the stopcock and Zeroed to atmosperic pressure. From the other a RADI PressureWire¨ was attached to the free port of the stopcock and floated 5 inches intothe tubing following zeroing to atmospheric pressure and calibration with itÕsmonitor unit. A 60 cc syringe was used to fill the test system with normal salineand to pressurize it between 25 and 35 torr. The pressure was maintained atthis level for 96 hours in one experiment and 144 hours in a second experimentwith a second wire. Temperature was not controlled and remained passively between20 and 23° C. Following the experimental period, each wire was compared to thestandard transducer. A calibration curve was created between 0 and 100 mmHgwith 5 mmHg steps.

Results: The maximum deviationwas 3 mmHg at any point and there was no tendency to larger deviation at eitherextreme of the scale.


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