US Patent 7445592 Cannulae having reduced flow resistance

A percutaneous cannula is provided for the exchange of blood within a patient's vasculature. The cannula includes a main cannula portion and a tip portion. The main cannula portion comprises a proximal portion, a distal portion, a first lumen, and a second lumen extending through the proximal portion. The tip portion extends from the main cannula portion to a distal end of the cannula. The tip portion comprises a discharge opening and a redirecting member. The redirecting member is configured to direct blood flow being discharged through the discharge opening proximally along the cannula. At least one of the first and second lumens is configured to reduce the effect of flow resistance therein.