[Prevention of gas microemboli during cardiac surgery. Numerical control of cardiac cavity purging by an ultrasonic detector]. / Prévention des micro-embolies gazeuses en chirurgie cardiaque. Contrôle numérique du débullage des cavités cardiaques par détecteur à ultra-sons.

ABSTRACT

Despite all precautions taken by cardiac surgeons to eliminate air remaining in the cardiac cavities and pulmonary veins at the end of cardiopulmonary bypass, many micro bubbles probably remain and pass into the systemic circulation with a risk of deteriorations of cerebral or myocardial function. Over the last four years we have used ultrasound to try to prevent the risk of preoperative gas microemboli the machine is equipped with a detector (a quartz oscillator coupled to a piezoelectric transducer emitting a continuous beam of ultrasound at a frequency of 5 Mhz) which allows the following variables to be determined the time interval from the onset of detection, the total quantity of bubbles (arbitrary units) in the examined regions, the quantity of bubbles detected over a given time interval which can be adjusted from 15 to 120 seconds. The passage of bubbles is also indicated by light and sound alarms. The smallest diameter of bubbles which can be detected is about 10 mu. There are periaortic probes adaptable to the calibre of the ascending aorta, transcutaneous probes for carotid artery detection and a left ventricular probe. In a preliminary series of 74 valve replacements in adults, this apparatus was used immediately after terminating cardiopulmonary bypass after we had thought that the cardiac cavities had been satisfactorily purged of air, and whilst active aspiration was continued in the ascending aorta distal to the periaortic probe the total quantity of bubbles detected varied from less than 50 to more than 2000 AU, over a variable period of time which may exceed 20 min after termination of cardiopulmonary bypass. The total quantity of bubbles recorded after mitral valve (582 +/- 154 AU) or combined mitral and aortic valve replacement (685 +/- 167 AU) was generally greater than after isolated aortic valve replacement (335 +/- 126 AU). Therefore, after cardiopulmonary bypass, and despite all efforts at purging the air, we showed that numbers of microbubbles were ejected into the ascending aorta for a variable period of time only some of them were eliminated by active aspiration through a trocar placed distal to the periaortic probe. The right coronary ostium was poorly protected against microbubbles because of its anatomical situation (6 cases in this series). We therefore established a protocol for the use of this apparatus to aid the purging of the cardiac cavities and pulmonary veins before stopping cardiopulmonary bypass the manoeuvres, guided by the ultrasound probes, are performed before the left ventricle is allowed to eject blood into the ascending aorta.(ABSTRACT TRUNCATED AT 400 WORDS)