Closed circuit cardiopulmonary bypass with centrifugal pump for open-heartsurgery: New trial for air removal

The purpose of this study is to examine the efficiency of venous air remova l with a new cardiopulmonary bypass (CPB) circuit design for conventional o pen-heart surgeries. A main concern with a closed circuit for open-heart su rgeries is air entrainment into the venous line. A venous filter was placed proximal to the centrifugal pump. The circuit proximal to the centrifugal pump was divided into two lines; one line was attached to the venous reserv oir outlet. By clamping the line to the reservoir, this circuit becomes clo sed. Negative pressure was applied to the purge line connected to the venou s reservoir for venous air removal. Micro bubbles were measured at two loca tions, both distal to the venous and arterial filters. When the injection r ate reached 100 ml/min, with the air-injection over 30 s, micro bubbles gre ater than 40 mu were observed at the outlet of venous filter. However, ther e was no micro bubble greater than 40 mu detected at the outlet of arterial filter. Although micro bubbles greater than 40 mu were not detected at the outlet of the arterial filter up to the injection rate of 300 ml/min, when the injection rate reached 400 ml/min, micro bubbles greater than 50 mu m were detected distal to the arterial filter. From this examination, we dete rmined that air entrained in the venous line up to approximately 300 ml/min is automatically removed by this method with the pressure-balanced conditi on. This pressure balance means that resistance of venous return, gravity s iphon, negative pressure by centrifugal pump, and negative pressure applied to the air-purge line of the filter are balanced; that is, the venous retu rn is sufficient, and the venous reservoir volume is kept stable. From this study we determined that this circuit design efficiently removes the entra ined air in the venous line.