ECC Sources of Gaseous Microemboli

___________ _ We have tried to locate sources of gaseous microemboli during the ECC using a newly developed ultrasonic detector. The detector was calibrated with filters of known pore size and the recorder setting was kept constant at all times. We studied, at the oxygenator, the effect of low and high fill volume, refilling with or without air into the cardiotomy line, mechanical disturbance, rewarming and high p02. Arterial line filters were examined for their capacity to retain microemboli. All bubble oxygenators tested released microemboli, especially at low fill volume when operated at high blood flows. Any mechanical interference (shock) either to the oxygenator or the filter will cause massive release of microemboli. This was also seen during fast rewarming of the blood, fast refilling of the oxygenator and high p02. Slow rewarming of the blood as well as slow refilling of the oxygenator, even with air in the cardiotomy line, did not cause any excessive microemboli. All filters tested retained microemboli to a great extent. Membrane oxygenators demonstrated no measurable microbubble formation at normal flows or with mechanical interference (shock) to the unit. Microemboli detection during ECC has helped to trace various sources of gaseous microemboli which could be avoided using better perfusion techniques. Arterial line filters do reduce the amount and the size of gaseous microemboli during ECC. Introduction ___________ _ Microemboli are a major source of complications during extracorporeal circulation (ECC) and death can result if massive air embolism occurs. Many authors, using different devices, have attempted to detect microbubbles with variable success 1 37 . The purpose of our study was to further identify sources of microemboli using a newly developed miDirect communications to: D. Demierre, Chirurgische Klinik A, Forschungsabteilung FL 42, Universitatsspital Zurich. Ramistrasse 100, CH-8091 Zurich. Switzerland 20 The Journal of Extra-Corporeal Technology crobubble detector and, with this knowledge. improve our current ECC techniques. A comparison between the various brand named components was not intended. Material and Methods _______ _ Detector-A prototype transmission ultrasonic microbubble detector' was used for our study. The transducer, attached to a special connector (ID 3/8" or 112"), sends a 2 MHz ultrasonic beam across the entire cross-section of the arterial line. The resulting signal is detected by the receiver and amplified. Artifacts produced by changes in flow or pressure are removed by electronic filtration. Detector "Calibration"-Our "calibration" circuit is shown in Fig. 1. The circuit was primed with lactated Ringer's solution and debubbled. The bypass line around the 40 micron filter" as well as the inlet side of the 25 micron filter were clamped and circulation at 4 1/min. initiated for 3 hours. Air was injected through a 25 G needle using a peristaltic infusion pump. A purge line was connected to the reservoir to drain excess air from the filter. The recorder" was calibrated in such a Figure 1: "Calibration" circuit a Stiickert Instrument, Munchen (FRG) b Pall Biomedical, Glen Cove, NY 11542 c Shiley. Inc. Irvine, CA 92174 d Gould, Inc., Brush Div. Cleveland, OH 44114 Volume 17. Number I, 1985 BubbleGenerator without Filter 4 1/min. with 40,u Filter -·· I +-----·-~+-L--~­ ·-··--,.--.--..-.-+ ··---~ -~--~ .... ;_,. __ +