Carbon dioxide de-airing in cardiac surgery

Abstract

Background: The risks connected with the presence of air microemboli in open-heart surgery, have recently been emphasized by reports that their number is correlated with the degree of postoperative neuropsychological disorder. Insufflation of carbon dioxide (C02) into the chest wound is used in open-heart surgery to de-air the heart and great vessels. A new insufflation device, a gas-diffuser, was compared with traditional devices for de-airing in an experimental wound model. Finally, to assess the clinical value Of C02 insufflation into the cardiothoracic wound, the effect of such insufflation on the incidence and behavior of microemboli in the heart and ascending aorta was studied under the conditions of a randomized clinical trial.

Methods: In a cardiothoracic wound model, a full-size torso, the degree of air displacement achieved by the gas-diffuser, was compared with that of a 2.5 mm. open-ended tube, a 6.35 mm open-ended tube, a multiperforated catheter, and a gauze sponge, respectively, during steady state. The influence of suction, varying C02 flow rates, an open pleural cavity, exposure to fluids and the position of the device were also evaluated. De-airing was assessed by measuring the remaining air content at the right atrium. In the trial, twenty (20) patients undergoing single valve surgery were randomly divided into two groups. Ten patients were insufflated with C02 via a gas-diffuser and ten were not. Microemboli were ascertained by intraoperative transesophageal echocardiography (TEE) from release of the aortic crossdamp until 20 minutes after end of cardiopulmonary bypass (CPB).

Results: During steady state, the gas-diffuser produced efficient air displacement in the wound cavity model at C02 flows of >=5 I/Min (<0.65% remaining air), while the 2.5mm and 6.35mm open-ended tube were much less efficient with >=82% and >19.5% remaining air, respectively, at 2.5-10 I/min C02 flows (p<0.001). When using the gas-diffuser, an open pleural cavity prolonged the time needed to obtain a high degree of air displacement in the wound cavity (p=0.001). With suction of 10 I/min the median air content was still low (<0.50%) at a simultaneous C02 flow of 10 I/min. Conversely, suction of 25 I/min caused a marked increase in air content both at a C02 flow of 5 and 10 I/min (p<0.001). When exposed to fluid, the gauze sponge and the multi-perforated catheter immediately became inefficient (70% and 96% air, respectively), whereas the gasdiffuser remained efficient (0.4% air). The two patient groups did not differ in clinical parameters. The median number of microemboli registered during the whole study period was 161 in the C02 group versus 723 in the control-group (p<0.001). Corresponding numbers for the left atrium were 69 versus 340 (p<0.001), left ventricle 68 versus 254 (p<0.001), ascending aorta 56 versus 185 (p<0.001). In the C02 group the median number of detectable microemboli after CPB fell to zero 7 minutes after CPB versus 19 minutes in the control group (p<0.001).

Conclusion: The most efficient de-airing (<1% remaining air) in a cardiothoracic wound model was provided by a gas-diffuser at a C02 flow of 10 I/min. For efficient de-airing, C02 has to be delivered from within the wound cavity. Additional suction impaired air displacement with the gas-diffuser only when suction exceeded C02 inflow. The gasdiffuser remained efficient after exposure to fluid, while both the gauze sponge and the multi-perforated catheter lost their function when they got wet. Insufflation Of C02 into the thoracic wound markedly decreases the incidence of microemboli during valve surgery.