Ask the Clinical Instructor: A Q&A Column for Those New to the Cath Lab

“When I was first taught how to do angiograms, I was told that you never want to leave blood in the sidearm of the sheath. I was to aspirate to make sure there was no clot and then flush with sterile heparinized saline. Now, we are composing a protocol in our facility, and we are unsure if we should be aspirating 10 ml of blood prior to removing sheath. I know that I aspirated one sheath sidearm on a patient who had waited about 20 minutes for her sheath to be removed and there was a huge clot that was aspirated. But from all the other procedures we have from other facilities, there is no mention of aspiration of blood prior to removal. What is the correct procedure?”
— via Cath Lab Digest

The way you were first taught was correct. Let’s walk through this.

The routine use of heparin for heart catheterizations is still something that is a physician’s preference, and no specific data or study indicates heparin to be administered or NOT administered for these cases (see our June 2009 article at https://www.cathlabdigest.com/articles/ Ask-Clinical-Instructor-A-QA-column-those-new-cath-lab-25, or https://tinyurl.com/sheathflushing). For this article, we will assume that you are referencing a diagnostic-only heart cath, and one in which a therapeutic dose of heparin HAS NOT been given.

It doesn’t take very long for small clots to develop in areas where blood flow is either slow or non-existent. In this case, any blood left in the sheath would not move, and therefore be susceptible to quick clotting. One way to learn this for yourself is to put it to work in your lab. Before removing a sheath, withdraw 10ccs of blood and gently squirt it into a gauze pad. You will likely see small clots, with those clots becoming larger as time goes by.

Of course, if you use heparinized saline flush, the time that it would take for this to occur would be longer, since the heparin left in the sheath would have some effect on preventing clots within the sheath (Figure 1).

According to most of the cardiac catheterization books (Kern, Grossman, etc.), sheaths should be flushed after initial insertion before inserting a wire/catheter, after each catheter exchange, after extended “idle” times, and before removal. The “flushing” should include withdrawing at least 5 ccs of blood and discarding it. Then, flushing with a new syringe of flush should occur.

This would help ensure that clots or foreign objects (i.e., air, fat tissue, etc.) are not injected into the arterial system. To answer the question that was asked, yes, sheaths should be aspirated to remove clots before being removed. The concept is the same as why there should be a small “squirt” of blood before applying compression — in order to allow any thrombi remaining in the puncture track to escape. Also, over-zealous compression while the sheath is being removed can cause the sheath itself to be slightly compressed. Any thrombi left in the sheath could be “milked” out of the sheath into the artery.

For the purpose of sheath removal, at the time of removal, 10 ccs of blood removed from the sheath should occur. The sheath would not have to be flushed with saline, but could just be removed at that time. I have also seen where opening the stopcock and allowing the blood to escape into gauze or towel through the sheath for a few beats is used. It would accomplish the same thing as withdrawing blood from a syringe.

Of course, this concept should be used for either arterial or venous sheaths. On the venous sheaths, the blood would have to be manually removed, since there isn’t enough pressure to allow aggressive bleed-back.

Sheath management should not be taken lightly, as thrombotic complications can certainly occur.

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