Of Clot, Tofu, and Cheese

The process of clotting is something vascular surgeons take for granted, but patients may have a hard time understanding what a clot is because in most people’s experience, it is rare for someone to see enough blood to form clot. How many patients or even health care providers have seen a tube or a basin of blood clot? So how do we describe clot to patients? I think the solution lies in food.

Most people who know me will say that I propose food as the answer for most things but hear me out. In describing clot, food is particularly salient. Clot is protein made insoluble, and there are many foods that have similar properties. Tofu, jello, and cheese and their making can give context where the word “clot” cannot.

All are made by taking a solution of protein and allowing them to form clumps that cause them to fall out of solution. It may require an acid, as in the case of tofu and cheese, but mere time and cooling may be sufficient as in the case of jello. And like these, clot may take on a soft crumbly quality when it is fresh clot, to a tenacious formed clump when given enough time. The difference is like silken or soft tofu and firm tofu. Or fresh ricotta cheese before it has time to set in its mold and the firmer cheese you get after weeks of curing.
With enough time, you get a hard substance that you can slice with a knife, like a dry cheddar or Parmesan. That is how I think of clot. It can be soft and formless like early jello before it is ready to eat. Or it can be hard and formed like mature dry cheese. The softer it is, the easier it is to dissolve or suck out via gadget or catheter, but there is a time factor to this softness -thing of your jello setting and hardening in your fridge. The harder the thrombus is, the less likely it is you can remove it with catheters and more likely you will have success with an operation as in the first picture. The harder stuff in fact crumbles well like a parmesan cheese and is harder to remove.

There are several things to draw from this with regard to devices designed to retrieve clot. Clot can occlude catheters as much as they can occlude arteries. Clot retrieval depends on net output of fresh clot that deforms well and flows well but fails in the hardened brittle clot that is well organized and adherent. Retrieving these crusty dried clot matter may be impossible for a device that depends on clot deformability or a maximum particle size, and these clots are the ones that are more partial to crumbling and embolizing. All devices must accept the fact that the unclogging is done in a flowing circulatory system where items swept downstream have the consequence of killing tissues whose arteries are blocked by emboli. There is always embolism with minimally invasive approaches. These devices make sense for hard to access circuits like the brain, but make far less sense in circuits like the extremities where surgical control is relatively low risk and results in reversal of blood flow -like in TCAR. Each of these devices can cost several thousand dollars. The fact is, operations can be faster and safer because embolism can be controlled and a wider range of clots, and larger amounts of it, can be removed at a lower cost. The first picture shows the results of a popliteal cut down and tibial thrombectomy where inflow was first restored in the below knee popliteal artery, and clot retrieved from each of the three tibial vessels (misleadingly, the tibial thrombus is all lined up), and a simultaneous 4 compartment fasciotomy performed, all under 90 minutes with no use of contrast. Unfortunately, open thrombectomy is a bit of a lost art in that many of the maneuvers and steps required to revascularize a limb successfully with no preoperative imaging requires experience. A younger patient with an arrthymia related embolism and normal soft arteries is approached far differently from an older person with atherosclerosis and diabetes, where open thrombectomy is better suited for the first, and catheter based approaches better for the latter.

Diagnostic and Therapeutic

The open surgical exploration of the extremity arteries is fast becoming a lost art along with the physical examination. In the setting of acute limb ischemia, the first decision in my mind is: was this an embolism? The presence of arrrhythmias, cardiac shunts, and aneurysms may suggest this, the next question is did this patient have a prodrome of limb ischemia related symptoms and history of atherosclerosis. The fact is, you have about 4-6 hours to return blood flow before irreversible neuromuscular damage sets in, maybe less if important collaterals are lost. Choice of procedure then devolves to choices about the most expedient methods for returning blood flow to the extremity, and between endovascular procedures and open surgery, it is rarely possible to manage significant clot burden with endovascular methods without adding the burden of procedural time. These considerations are balanced by patient risk. If the patient cannot tolerate general anesthesia, it is still possible to operate under local anesthesia. Otherwise, one is faced with choices like stenting across clot or common femoral artery. The algorithm is simple -ensure inflow, thrombectomize outflow, check for backbleeding, restore flow, check flow, repeat as necessary downstream. Fasciotomy as needed and close the skin if you can.

Endovascular options deal with the basic physics of trying to pull clot of varying consistency through a small lumen over a long length while not pushing emboli. The needs are simple -a low profile, cheap, over the wire solution for evacuating clot without embolizing nor injuring the patient on a 100cm and 150cm length catheter. Cost wise, open surgery always beats any endovascular option if wound complications of open surgical exposure are avoided. Both methods can’t cover themselves if open fasciotomy wounds keep the patient in the hospital for weeks. The fact is, we already have this magic system in the catheters that we already have on the wall, albeit, they don’t work particularly well if you are dealing with Parmesan, but none of the systems do. I recently declotted a graft fistula with just 6F sheaths, a regular #3 Fogarty ballon, 6mg of tissue plasminogen activator, and was able to salvage the blood and return to the patient.

Conclusion

Vascular surgeons should have as many words for clot as Eskimos purportedly do for snow. There is no one solution to a problem, but all the tools must be available to the vascular surgeon. Ironically, only the simplest are needed most of the time.