Augmented venous drainage improves venous return during minimally invasive cardiac surgery. Two systems to augment drainage are common: in one, a centrifugal pump draws blood from the venous site and pumps it into a venous reservoir. In the other, suction is applied directly to a hard-shell venous reservoir. Both systems overcome the high resistance of the venous cannula when gravity alone is insufficient to provide adequate drainage. Both systems also have shortcomings: in the first approach, the centrifugal pump head can entrap large bubbles, reducing flow and requiring pump stoppage to remove them. Air from the venous line also can be broken up by the centrifugal pump into small bubbles that can pass through the pump head. The direct suction system in the second approach cannot use a closed-bag reservoir, and has the potential to introduce air into the arterial line. We have developed a new venous augmentation system for a closed venous reservoir that provides excellent suction control without the potential to introduce air into the arterial line. Our system replaces the centrifugal pump of the first approach with a roller pump controlled by the Better-Bladder, a new device with FDA 510(k) clearance for long-term pumping. The Better-Bladder is a length of medical tubing, processed to form a thin-walled, enlarged bladder that is sealed within a clear rigid housing. It acts as an in-line reservoir that provides compliance in the venous line and a noninvasive means to measure blood pressure at the pump inlet. The bladder housing can maintain a negative pressure set by the user that controls the degree of gravity drainage. Tests have shown that the Better-Bladder allows for safe, smooth pump control using a roller pump in the venous line.
A new venous bag has been developed, prototyped, and tested. The new bag has its inlet, outlet purge, and infusion tubes extending upward from the top of the bag, and are threaded through, bonded to, and sealed within a flat rigid top plate. This design allows the bag to be hung from its top plate by its tubes. It also allows the bag to be: 1) dropped into or removed from its holder, as is done with existing hard-shell reservoirs so that its weight pulls it into the holder without the need for eyelets and hooks and 2) placed closer to the floor so that gravity drainage is facilitated. The V-Bag (VB) is easily sealed within an accompanying rigid housing. Once sealed, vacuum applied to the housing is transmitted across the flexible walls of the bag to the venous blood. Thus, vacuum-assisted venous drainage (VAVD) is obtained as it is with a hard-shell reservoir, but without any contact of air with the blood. Bench tests, using a circuit that simulated the venous side of the cardiopulmonary bypass (CPB) circuit, showed that applying suction to the housing increased venous flow, and the fractional increase in flow was not a function of the venous cannula, but of the level of vacuum applied. In the gravity drainage mode, the bubble counts at the outlet of the V-Bag compared to two other bags were lower at any pumping condition. When used in the VAVD mode, bubble counts were two orders of magnitude lower than when using kinetically assisted venous drainage (KAVD) with a centrifugal pump. Results obtained with the VB suggest its clinical usefulness.
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