In vitro assessment of the vacuum-assisted venous drainage (VAVD) system: risks and benefits

The vacuum-assisted venous drainage (VAVD) technique has been introduced with the utilization of small-bore venous cannulae to facilitate minimally invasive cardiac surgery and it has found widespread use for traditional surgical approaches. Although this technique was devised to increase venous return, it may cause a reduction of blood flow through a negative pressure effect on the raceway tubing. In this study, the potential of this system to increase the venous drainage was evaluated in vitro together with the measurements of delivered blood flow. The VAVD has been tested in association with normal gravitational drainage or as a substitute for gravitational drainage. The flow was calculated by multiplying the pump rate by the stroke volume and it was simultaneously measured by a magnetic flowmeter. A steady state maximal flow was defined as the flow that could maintain a constant level of fluid in the graduated canister used to act as the patient. Based on our results, the VAVD can increase venous drainage by as much as 50% above baseline levels. However, delivered blood flow may be overestimated, particularly when negative pressure values > 60 mmHg are employed. A 100 mmHg negative pressure may produce an overestimate of blood flow as great as 54% of the measured flow.