Measures to prevent microembolization in cardiac surgery and during angiography with special reference to carbon dioxide

Abstract: Background: Cardiovascular interventions including open heart surgery using cardiopulmonary bypass (CPB) and coronary angiography may introduce air and particulate arterial embolism that may lead to tissue lesions of the brain and other organs. Aims: To assess: if CO2-insufflation of an empty CPB circuit decreases number of gaseous emboli in the prime compared with a conventional CPB circuit, which holds air before fluid priming (Study I); the efficacy of a new mini-diffuser device for CO2 de-airing in a minimally invasive open cardiothoracic wound cavity model and in patients undergoing minimally invasive open aortic valve surgery (Study II); if an extra separate venous reservoir abolishes CO2-insufflation induced hypercapnia and retains sweep gas flow of the oxygenator constant during open heart surgery (Study III); if there is a difference in the incidence of cerebral microemboli when using either the femoral or the radial approach during coronary angiography (Study IV). Methods: Study I-II were experimental. Study I: Number of gaseous microemboli in the arterial line were counted after randomization to insufflation with CO2-gas or not prior to priming in 20 CPB-circuits. Study II: Air displacement efficacy of a mini-diffuser and of an open-ended tube was measured during CO2-insufflation in a minimally invasive open cardiothoracic wound cavity model and in patients undergoing minimally invasive open aortic valve surgery. Study III: A separate reservoir was used during CPB in addition to a standard venous reservoir. The separate reservoir received drained blood and CO2-gas continuously via a suction drain (1 L/min) and handheld suction devices from the surgical wound. CO2-gas was insufflated via a gas-diffuser in the open wound at 10 L/min. In a crossover design for each patient, gas and blood were either uninterruptedly drained from the separate to the standard venous reservoir or not. PaCO2 was determined after tuning of sweep-gas flow as necessary and following steady state of PaCO2 with an online monitor. Study IV: We randomized 51 patients to either right femoral or right radial arterial approach and documented with transcranial Doppler the number of particulate microemboli circulating through the middle cerebral arteries. Results: Study I. Throughout the experiment, the median microembolic count per minute in the CO2 group stayed lower than in the control group (p≤0.004). Study II. The air content was <1% and 10-75% in the open wound model during CO2 inflow of 2–10 L/min with the mini diffuser and the open-ended tube, respectively. In 6 patients air content in the open surgical wound stayed <1% during CO2 flows of 5 and 8 L/min via the mini-diffuser. Study III. Median PaCO2 did not vary between setups (5.41; 5.29-5.57, interquartile range [IQR] vs. 5.41; 5.24-5.58, p=0.92), while sweep-gas flow (L/min) was lower (2.58; 2.50-3.16 vs. 4.42; 4.00-5.40, p=0.002) when CO2-gas was not drained from the separate to the standard reservoir. Study IV. The median (range) number of particulate emboli was significantly higher with radial 10 (1–120) than with femoral 6 (1–19) approach. Also, with the radial approach more particulate microemboli circulated through the right sided middle cerebral artery compared with the femoral approach. Conclusions: CO2-insufflation of an empty CPB circuit reduces the number of gaseous emboli in the prime compared with conventional CPB circuit priming (Study I); CO2 deairing with the mini-diffuser was effective in a minimally invasive open cardiothoracic wound cavity model and in patients (Study II); A separate venous reservoir, with a clamped connecting tube to the standard venous reservoir for evacuation of gas and blood from the open surgical wound, prevents CO2-insufflation induced hypercapnia in open heart surgery, keeping PaCO2 and sweep gas flow constant (Study III); When performing coronary angiography, the radial access produces a higher number of particulate cerebral microemboli than the femoral alternative (Study IV). This approach is hence advocated in this aspect.