[Detection of air embolism by a re-usable Doppler probe integrated in a central venous line--application in-vivo]

Air embolism frequently occurs under neurosurgical operations performed in the sitting position. Recently we reported the idea of inserting a re-usable doppler probe into a blind-ending lumen of a central venous catheter (Schregel-Volk-Catheter, SVC). In vitro testing in a circulation model showed a high sensitivity: air bubbles as small as 0.5 microliter were reliably detected at a distance up to 4 cm from the tip of the SVC.

After approval by the local ethics committee pigs were anaesthetised and a cardiopulmonary bypass was connected. During the bypass period a 12 F SVC (Medex Medical, Germany) with one blind-ending lumen was positioned into the proximal vena cava cranialis or vena cava caudalis. An 8 MHz doppler probe (MTB Basler, Suisse) was introduced into the SVC and connected with the doppler device Multi-Dop T (DWL, Germany). Well defined air bubbles (3-6 microliter) were generated by a bubble generator and injected into the right femoral vein or the left vena jugularis interna.

All bubbles were reliably detected by the re-usable doppler probe. Embolic events can be documented, counted and quantified by the Multi-Dop T.

Using SVC's with a blind-ending lumen could improve and simplify the detection of air embolism. We see several advantages (e.g. sensitivity, costs) compared with established methods (precordial doppler, TEE) for detection of air embolism.