Continuous detection of microemboli during cardiopulmonary bypass in animals and man

A device that continuously and accurately detects solid and gaseous microemboli (75-100 muM) during cardiopulmonary bypass is described. A continuous ultrasonic standingwave field was generated between two parallel piezoelectric crystals. Extremely high sensitivity to small changes in ultrasonic attenuation was achieved with a transmission oscillator ultrasonic spectrometer (TOUS). The device was relatively insensitive to variations in flow rate, gradual temperature changes, hematocrit, protein content, and pressure. The system was tested with 100, 200, and 300 muM microspheres. Animal perfusions demonstrated high initial counts that were markedly reduced by an arterial line filter. Furthermore, high cardiotomy suction rates, use of nitrogen, and physical disturbances of the oxygenator increased the microemboli rate. Of 30 clinical perfusions, 15 had complete data for analysis. There was a statistically significant difference (P less than 0.01) in the total number of microemboli between the first 10 minutes (4398 +/- 1132) versus the second 10 minutes of perfusion (2739 +/- 1195). It is concluded that an accurate device that continuously measures the number of microemboli may provide data that will lead to significant improvements in the quality of extracorporeal circulation in the future.