Ultrasound destruction of air microemboli as a novel approach to brain protection in cardiac surgery

Abstract

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.

Keywords: CNS protection; air emboli; brain; cardiopulmonary bypass; complications; embolism; microemboli; stroke; ultrasound.