Does CO 2 flushing of the empty CPB circuit decrease the number of gaseous emboli in the prime?

Abstract

Twenty (20) CPB-circuits were randomized to a CO₂ group or a control group. In the CO ₂ group, each circuit was flushed with CO₂ (10L/min) at the top of the venous reservoir for 5 minutes, after which priming fluid was added without interruption of the CO₂ inflow. Control group circuits were not flushed and contained air. A perfusionist, blinded to the study, started the pump (5L/min), ventilated the oxygenator (3L O₂/min), and knocked on the oxygenator 20 times during the first and 14^th minutes. Arterial line microemboli counts were registered with a Doppler for 15 minutes. In both groups, the median number of microemboli was highest during the first minute, 380.5 (288.75/422.25, 25^th/75^th percentile) counts in the control group versus 264.5 (171.75/422.25) counts in the CO ₂ group (p=0.01). Throughout the experiment, the median microembolic count minute by minute in the CO₂ group remained lower (p≤ 0 .004) than in the control group. Knocking on the reservoir (14^th minute) increased the microemboli counts in both groups (p<0.01). The median values during the 15^th minute were 15.5 and 0.5 in the control and the CO₂ groups, respectively, which were 9% (15.5/173) and 0.5% (0.5/87), respectively, of the values registered after 14 minutes. In conclusion, CO ₂ flushing of the empty circuit decreases the number of gaseous emboli in the prime compared with a conventional circuit that contains air before being primed with fluid. Knocking of the oxygenator releases gaseous emboli and the duration of re-circulating the circuit with prime influences the number of microemboli.