Study of Accidental Decannulation of an Air Lock in Valve-type, Semi-closed, Extracorporeal Circulation

Abstract

At facilities where the number of cases of cardiopulmonary bypass (CPB) is less than 100 per year, which accounts for 60% of the cardiac surgery facilities in Japan, it is difficult to acquire and maintain the operation technique of CPB by the open circuit. Therefore, a valve-type semi-closed extracorporeal circulation (VACC) system was devised. In the VACC, which is a closed circuit like ECMO (extracorporeal membrane oxygenation), the volume control reservoir (VR) is connected to the venous circuit via a check valve as a safety valve. The safety valve opens and closes depending on the pressure gradient between the VR which is under negative pressure and the venous circuit. As a result, the VACC can be switched between an open circuit and a closed circuit. For the purpose of improving safety in the case of air entering the venous circuit, which is the weakness of the closed circuit, water experiments to simulate an accidental venous decannulation were conducted. In the VACC, like the open circuit, when one of the two venous cannulas was decannulated, an air lock occurred. That is a phenomenon in which venous drainage and air movement are stagnant due to being obstructed by the siphon effect of a mass of air in the venous circuit. The safety valve was open when an air lock occurred, and it was easy for it to occur when the negative pressure was weaker. If a venous cannula is decannulated, the negative pressure in the venous circuit will be augmented, and then the pressure in the venous circuit will be limited to the pressure in the VR. Therefore, the suction power of a mass of air is reduced, and air movement is stagnant. As a result, an air lock occurs. When using a closed circuit, venous decannulation causes a large amount of air entering. On the other hand, the VACC can control air behavior in the venous circuit by adjusting the pressure in the VR;for example, by opening the VR to atmospheric pressure.