A new expandable venous cannula for minimal access heart surgery

During percutaneous cannulation, the diameter of the venous cannula is determined by the size of the access site. To limit this restriction, the Smart cannula (Cardiosmart Ltd., Fribourg, Switzerland) has been developed. Because its design allows self-expansion within the recipient vein, diameter restriction is limited to the access site.

In 6 calves (78 +/- 4.3 kg), the jugular vein and the carotid artery were cannulated through a cervicotomy. The Smart cannula was tested against three percutaneous cannulas with a diameter of 27, 25, and 21F, respectively. Stenotic percutaneous access to the vein was simulated by 1-cm wide tape encircling the vein that could be adjusted to a diameter of 27, 25, and 21F, respectively. The maximal flow rate, reached with stable reservoir level and a negative pressure of 44 mm Hg, was determined three times for each access size with the Smart cannula (one size fits all) and the corresponding percutaneous cannula successively.

For an access size of 27F, the flow of the Smart cannula was 5.7 +/- 0.4 L/min and that of the percutaneous cannula was 4.3 +/- 0.2 L/min (p < 0.0001); for 25F, flow rates were 5.6 +/- 0.5 and 3.9 +/- 0.2 L/min, respectively (p < 0.0001); and for 21F, the flow rates were 4.3 +/- 0.4 and 2.7 +/- 0.3 L/min, respectively (p < 0.0001). The percentage increase of flow for the 27, 25, and 21F sizes were 34% +/- 9%, 42% +/- 16%, and 53% +/- 18%, respectively (one-way analysis of variance, p = 0.014).

For the present set-up, the Smart cannula outperforms commercially available percutaneous cannulas. The smaller the size of the insertion site, we observed a higher gain of flow with the Smart cannula.