April 9, 2004BME 272/2731 Investigation of Bubble Formation in Tuohy-Borst Adaptors Department of Biomedical Engineering Melanie Bernard, Isaac Clements, & Jason Hirshburg Advisor: Ted Larson III, M.D.

April 9, 2004BME 272/2732 Problem Statement Bubbles are seen within the Tuohy-Borst Adaptor –Origin/cause unknown Consequences –Can get stuck in small arteries, inhibiting blood and oxygen to the brain –Causes stroke in 0.1% of procedures (bubbles > 1ml) Accessory Problems –Bubbled are hard to remove; they stick to inner surface of tubing/adaptor –Occurs in adaptors of different length, angle of arm –May be from multiple sources

April 9, 2004BME 272/2733 Problem Definition Find the cause of the bubbles and correct it! –Constraints Solution must apply to all adaptor types Any system changes must not significantly change adaptor cost or the catheterization procedure. Must eliminate problem without introducing new ones –Limitations Time – 6 months Money – have only a reasonable budget. Equipment – don’t have access to blood or ultra- sound machines cardio/cathlab.htm

April 9, 2004BME 272/2734 Background Dr. Larson has 15 years of experience in interventional neuroradiology Catheter uses: –Angiography –Embolization of arteriovenous fistulas –Aneurysms –Preoperative embolization of neck and intracranial tumors Bubbles are consistently observed in catheterization procedures (but have not been formally documented by Dr. Larson). Dr. Larson reverses flow 3 times without bubbles before proceeding.

April 9, 2004BME 272/2735 Background cont. Bubble Traps –Used when blood is routed outside the body with pumps Cost Analysis –$45k/procedure $25k Radiology ~4-6 min. to clear bubbles ~3 hour procedure =$700!!

April 9, 2004BME 272/2736 Market Potential Target group –Operating rooms worldwide Will meet customer needs –Catheterization procedures will be safer Is technologically feasible –Physical principles and/or methods can be changed to eliminate bubble formation Is economically viable –Adaptor costs should not rise after our changes –Could save up to $700 per procedure (not including saving money that would be lost for inducing a stroke)

April 9, 2004BME 272/2737 Primary Objective Our task is to discover the cause of bubble formation and correct it Observations from Dr. Larson’s procedures: Bubbles… –Up to 10-20% of tube diameter –Stick to inner surface of adaptor –Appear at the edge of the Y-junction –Occur before microcatheter is inserted –Typically occur when catheter flow is reversed and blood hits the edge of the Y-junction and interfaces with the saline

April 9, 2004BME 272/2738 Previous Work Observed device in a medical procedure on 11/18/03 Literature Search Innovation WorkBench (revised 3/2) Conducted experiments –Primary: tested equipment –Secondary: simulated pressures and temperatures of entire system –Tertiary: testing individual components to different conditions Filmed procedures on 2/2/04 and 3/31/04; obtained new supplies Performed calculations based on actual and worst-case scenario parameters

April 9, 2004BME 272/2739 Possible Sources of Bubbles 1. Leaks From 3-way valve From rotating hemostatic valve Between adaptor and catheter 2. Introduced during adjustments In flushing process Injecting contrast agent Reversing fluid flow 3. Adaptor Angle of arm causes local pressure drop Microbubbles pool at connections 4. Temperature differences N 2, O 2, or CO 2 coming out of blood Air coming out of saline 5. Initial flushing process In catheter In saline tube Pulling back saline syringe 6. Saline Air coming out of solution Pushed into system by pressure bag High flow rate and interaction with blood Pressure drop from 250 – 0 mmHg 7. Pressure change for N 2, O 2, & CO 2 in blood Local pressure drop at diameter change Pressure drop across catheter Pressure drop from 100 – 0 mmHg

April 9, 2004BME 272/27310 Experiments Conducted Primary Experiments: –Observed many bubbles throughout system Secondary Experiments: –Blood pressure = 120/80 (mmHg) –Saline pressure = 250 mmHg –Blood temp = 98.6 F –Saline temp = room Tertiary Experiments: –Tested connections for leaks 35 degree catheter turn –Air solubility in saline under pressure (250 mmHg) –Tested catheter for bubbles after flushing –Tested bubble occurrence after syringe pull-back

April 9, 2004BME 272/27311 Videotaping the procedures We videotaped the bubble phenomenon during two actual procedures in Dr. Larson's operating room: The first videotape was created on 2/24/04 with a standard VHS video camera. We acquired a high resolution digital video camera to videotape a second procedure on 3/31/04.

April 9, 2004BME 272/27312 Videotape Analysis Observations: There are many bubbles forming! Out of 4 minutes of footage, we recorded 15 bubble occurrences. Bubbles appear to be coming from within the catheter In 14 out of 15 cases, the bubbles appear under set conditions: 1.Saline is flowing forward into the catheter 2.The 3-way valve is opened and flow is reversed 3.Bubbles appear immediately and seem to be coming from within the catheter.

April 9, 2004BME 272/27313 Current & Future Work In a meeting with Dr. Larson, we laid out our final goals for the project, including: –Determining all possible sources of bubbles –Ruling out as many as possible through our observations, calculations, and experiments. –Taking the remaining possibilities and determining the likelihood of each theory. –Create a final analysis of the most likely cause. –Give suggestions for improving the situation. We have researched the following catheter clearing methods: –Wetting agents –Dynamic Bubble Traps (DBTs) –Degassing saline before injection (and heat?)

April 9, 2004BME 272/27314 Acknowledgements Dr. Ted Larson and staff Dr. Paul King Dr. Joan Walker Dr. Robert Roselli Dr. Todd Giorgio Dr. Cynthia Paschal Dr. Rick Haselton Dr. Bob Galloway Matt Lytle for his services as cameraman. We would like to thank the following professionals and experts for their input:

April 9, 2004BME 272/27315 Bibliography Catheter Flushing, Bubble Formation within Catheters, Dynamic Bubble Traps, Wetting Agents: Manufacturing Links for Tuohy-Borst Adaptors: Images for Catheter Insertion Procedure: Interventional Neuroradiology Links:

April 9, 2004BME 272/27316 Questions…? Visit our website at 5_06/5_06_06.html