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

Abstract

Femoral venous cannulae (17-28 French) were tested to compare flows obtained by their placement in a simulated inferior vena cava (IVC) or right atrium (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 simulate the IVC connected to a flexible reservoir to simulate the RA. The test fluid was a 40% glycerin solution. Flow was measured at height differentials of 30-60 cm (cannula-to-inlet of hard-shell venous reservoir) and with a -10 to -80 mmHg negative pressure created by the centrifugal pump. A roller pump returned the test fluid to a flexible bag to maintain a filling pressure of 0-1 mmHg. Flow increased modestly with an increasing height differential. When negative pressure was applied with the centrifugal pump, flow increased 10% and 18% (IVC and RA positions, respectively) compared to gravity siphon drainage conditions. There also was a tendency for flow to plateau or cease when the centrifugal pump was used at higher levels of negative 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 larger and placed in the IVC; (2) smaller-sized cannulae are capable of achieving higher flows when the centrifugal pump is used; (3) cannulae must be properly positioned to achieve maximum flow; (4) the centrifugal pump will augment flow, but should be regulated to avoid extreme negative pressures; and (5) cannula design has no demonstrable effect on flow.

Evaluation of different paediatric venous cannulae using gravity drainage and VAVD: an in vitro study

“…3 As a consequence of the small vascular structures, an optimal venous return is mandatory for a bloodless surgical field. In general, the resistance of cannulae is low in babies because of the relatively large cannula/vein ratio compared to adults.…”

“…Our pressure ± flow results support previous findings showing no correlation between filling pressure and maximum flow when the cannula is placed in an open reservoir. 3 However, with the cannula placed in the model, filling pressure and cannula size do influence flow rates.…”

“…This has been shown to compromise flow. 3 Based on the pressure flow characteristics in the open reservoir, one probably would have chosen a 14-French cannula, whereas the 12-French cannula performed almost as well in our experimental model. The 13.2-French cannula did not improve return compared to the 12-and 14-Fr cannulae.…”

“…This might prevent severe`fluttering' of the walls of the IVC around the end of the venous cannula. 3,9 The helix design resulted in excellent flow rate, most probably related to its large open area for flow.…”

“…This can be achieved by using active vacuum augmentation of the venous return, which allows the user to place the oxygenator closer to the patient. 2 Vacuum-assisted venous drainage has gained renewed interest since the start of minimally invasive cardiac procedures, 3,4 and for reduction of priming volume in paediatric circuits. 5 ± 8 Veins are compliance vessels and will collapse at negative pressures between ¡5 and ¡10 mmHg.…”