Venous air in the bypass circuit: A source of arterial line emboli exacerbated by vacuum-assisted drainage

Background. Arterial emboli cause neurocognitive deficits in cardiac surgic al patients. Carotid artery emboli, detected ultrasonically, have been obse rved after venous air entrainment into the cardiopulmonary bypass circuit. We investigated in vitro the extent to which venous air affected emboli det ected in the arterial line downstream from a 40-mu m filter. Methods. Using salvaged clinical cardiopulmonary bypass circuits, fixed vol umes of air were introduced into the venous return line at unrestricted rat es and at fixed rates using gravity venous drainage and vacuum-assisted ven ous drainage. Emboli counts were recorded distal to the arterial line filte r using a 2-MHz pulsed-wave Doppler monitor. Emboli counts were similarly r ecorded after the introduction of carbon dioxide into the venous return lin e instead of air. Results. The number of emboli rose with increasing volumes of entrained ven ous air (p < 0.001), and there was an almost tenfold increase with vacuum-a ssisted venous drainage (p < 0.0001) compared with gravity venous drainage. Venous air was entrained at a significantly faster rate under vacuum-assis ted venous drainage (p < 0.0001). When the entrainment rate of venous air w as fixed, the difference in emboli numbers recorded for gravity and assiste d venous drainage was not significant. There was a significant reduction in arterial line emboli when carbon dioxide rather than air was entrained und er both vacuum-assisted and gravity drainage (p < 0.001). Conclusions. Entrained venous air during cardiopulmonary bypass is a potent ial hazard, particularly during vacuum-assisted venous drainage. Every effo rt should be made to avoid venous air entrainment. (C) 1999 by The Society of Thoracic Surgeons.