Thursday, October 23, 2003

It was filter day at Big Hospital as my partner and I changed out four (two apiece) of the removable caval filters I talked about in this post. It amazes me that it takes less time to replace the filters than it takes to place them primarily. Why?, you may ask. Well....
When you place a caval filter, you ideally want to place it below the renal veins (although you can place it above the renal veins if need be). You assure this by performing a venogram prior to placing the filter. The conventional Greenfield filter is placed through a 14-french sheath (about 5mm). You can get a good cavagram with hand-injecion with a sheath that large. Since the newer filters are placed with a 6-french (2mm) it is difficult to get a good image without a power injector. You have to find the renals by selective imaging of them (or get the wire to go in, much easier on the left). This can take some time.
When they are replaced, the first thing you do is find it with the c-arm, lock the flouro machine, and mark the position on the screen. The filter is removed with a snare through a 9-french sheath, and the 6 french sheath is passed throught the left-in-place 9-french sheath. Since the position of the old filter is marked on the screen, I don't have to spend a lot of time hunting the renal veins. Pull the sheath and hold pressure for a few minutes. Done in twelve minutes. See you in four weeks.
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