Vacuum assist: angel or demon CON.
Vacuum-assisted venous drainage (VAVD) to enhance venous return during cardiopulmonary bypass (CPB) was described as early as 1958 but was not widely used until the late 1990s. VAVD was initially used to facilitate the use of smaller cannulas with ministernotomy but was increasingly used to allow reduction in CPB circuit size while maintaining CPB flow rates. This innovation was made without planned consideration to CPB circuit design, most critically that of the venous reservoir. Clinical reports of prime reduction facilitated by VAVD in both adult and pediatric CPB were associated with reduced nadir hematocrit and rates of transfusion that encouraged the proliferation of VAVD in CPB. Concomitantly, investigators have reported both in vitro and in vivo significantly increased arterial emboli associated with the use of VAVD, mostly related to accelerated venous air entrainment. In vitro studies continue to confirm this association and likely underestimate the resulting embolic load as a result of flawed study design. While the evidence for VAVD is equivocal, our understanding of the clinical impact of gaseous microemboli in CPB is similarly limited, most likely confined to blood-brain barrier disruption. It is only after two decades that CPB component design is receiving serious attention in terms of air handling. The ethics of innovation in the field of CPB warrant careful consideration. The application of VAVD is not without consequence.
Green Lane Cardiothoracic Unit, Auckland City Hospital, Auckland, New Zealand. timw@adhb.govt.nz
Timothy W
TW
Willcox
D000328:Adult; D002315:Cardiopulmonary Bypass / Q000009:adverse effects* / Q000295:instrumentation*; D004322:Drainage; D004618:Embolism, Air / Q000209:etiology* / Q000517:prevention & control*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D010477:Perfusion / Q000009:adverse effects* / Q000295:instrumentation*; D013396:Suction / Q000009:adverse effects / Q000295:instrumentation; D013673:Technology Assessment, Biomedical; D014680:Veins