Laboratory testing of femoral venous cannulae: effect of size, position and negative pressure on flow

Femoral venous cannulae (17-28 French) were tested to compare flows obtaine d by their placement in a simulated inferior vena cava (IVC) or right atriu m (RA) and by varying drainage pressures using gravity siphon drainage or a centrifugal pump in the venous line. The circuit consisted of conventional tubing and equipment including a segment of thin-walled latex tubing to si mulate the IVC connected to a flexible reservoir to simulate the RA. The te st fluid was a 40% glycerin solution. Flow was measured at height different ials of 30-60 cm (cannula-to-inlet of hard-shell venous reser/oiri and with a -10 to -80 mmHg negative pressure created by the centrifugal pump. A rol ler pump returned the test fluid to a flexible bag to maintain a filling pr essure of 0-1 mmHg. Flow increased modestly with an increasing height diffe rential. When negative pressure was applied with the centrifugal pump, flow increased 10% and 18% (IVC and RA positions, respectively) compared to gra vity siphon drainage conditions. There also was a tendency for flow to plat eau or cease when the centrifugal pump was used at higher levels of negativ e pressure or when larger cannulae were used. We conclude: (1) position of smaller cannulae in the RA yield better flows than when the cannulae are la rger and placed in the IVC; (2) smaller-sized cannulae are capable of achie ving higher flows when the centrifugal pump is used; (3) cannulae must be p roperly positioned to achieve maximum flow; (4) the centrifugal pump will a ugment Glow, but should be regulated to avoid extreme negative pressures; a nd (5) cannula design has no demonstrable effect on flow.