Problem: Air embolisms frequently occur during neurosurgical operations. For detection of air embolisms, a re-usable doppler probe, integrated in a central venous line, is described. In an in-vitro test series the measuring sector as well as the function of a 8 MHz doppler probe are presented.
Method: The 8 MHz doppler probe is a 1.1 mm diameter cable, into the distal end of which a cylindrical doppler crystal from lead-circonate-titanate (PZT5) of 2 x 1.7 mm is integrated and connected with a doppler unit. The detection of micro bubbles with a volume of 0.4-5 microliters was effected in still liquid for simple measuring of the spatial characteristics of the probe as well as in flowing liquid for simulation of a blood circulation system.
Results: The doppler probe detected qualitatively and reproducibly all gas bubbles offered up to 4 cm around the tip of the probe.
Conclusion: A reliable detection of micro-bubbles in this test model is possible by means of a 8 Mhz doppler probe. Further animal and clinical studies are planned.
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