Ultrasound Destruction of Air Microemboli as a Novel Approach to Brain Protection in Cardiac Surgery

OBJECTIVE:

Evaluation of a novel approach to eliminate air microemboli from extracorporeal circulation via ultrasonic destruction.

DESIGN:

In vitro proof-of-concept study.

SETTING:

Research laboratory.

PARTICIPANTS:

None.

INTERVENTIONS:

None.

MEASUREMENTS AND MAIN RESULTS:

An
extracorporeal circulation device was filled with human blood
circulating at 3 L/min. Air bubbles were injected into the system. For
bubble destruction, the blood in the tubing system was repeatedly
insonated for 3 minutes using a therapeutic 60-kHz device, with
variation of intensity and duty cycle settings, ranging from 0.2 W/cm²
to 1.0 W/cm² and from duty cycle 60% to continuous wave (CW). Number and
diameter of air microemboli were counted upstream and downstream of the
ultrasound device by a 2-channel microemboli Doppler detector. For
safety assessment, circulating blood was insonated continuously for 2
hours at 0.8 W/cm² CW and compared with circulation without insonation;
and standard blood parameters were analyzed. Without treatment, 1,313 to
1,580 emboli were detected upstream, diameter ranging between 10 and
130 μm. Ultrasound treatment eliminated up to 87% of all detected
bubbles in cw application (p<0.01) and showed comparable effects at intensities from 0.4 W/cm² to 1.0 W/cm² cw. Bubbles sized>15 μm
almost were eliminated completely (p<0.001). Pulsed wave application rendered inferior results (p>0.05). No relevant changes of blood
parameters were observed compared with control circulation.

CONCLUSIONS:

Ultrasound
destruction of air emboli is a very efficient method to reduce number
and size of emboli. Within the limits of safety assessment, the authors
could not detect relevant side effects on standard blood parameters.