The effectiveness of low-prime cardiopulmonary bypass circuits at removing gaseous emboli

During extracorporeal circulation, the patient's blood is siphoned into the extracorporeal circuit (ECC) by gravity or may be assisted kinetically or by vacuum. In all instances, negative pressure is generated in the venous line, which can cause entrainment of air into the ECC at the cannulation site. The typical ECC uses a venous reservoir, membrane oxygenator, and arterial line filter, which together aid in removal of air that has entered the venous line and minimize the transmission of gaseous microemboli to the patient. Recently, several manufacturers have introduced low prime ECCs with component configurations that differ from conventional ECCs, including the omission of a venous reservoir. These configuration changes may change the ability of the circuit to handle air and therefore their ability to minimize gaseous microemboli. The purpose of this study was to test the ability of new low prime ECCs to remove air introduced into the venous line and minimize gaseous microemboli from entering the patient's circulation. Using a model of CPB, air was introduced into the venous line of a low prime ECC and a conventional CPB circuit. The detection of the gaseous microemboli produced was monitored distal to the oxygenator by an ultrasonic emboli detector to determine if venous air was able to traverse the ECC at varying rates of air introduction and blood flow. Data was collected using data acquisition software loaded on a personal computer. Gaseous microemboli levels detected in the arterial line of the low prime ECC were 8 to 10 times higher than the microemboli levels detected in the conventional ECC at all blood flow rates. Every effort should be made to minimize and prevent air from being entrained in the venous line of a low prime CPB circuit to minimize the risk of arterial gaseous microemboli generation.