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Cannula in Ex Vivo Perfusion

Some key facts about vascular cannulation, which cannot be cut in the organ perfusion experiment.

  • How should I place a tube and what thickness should it be in relation to the blood vessel?

  • Is it acceptable to use a needle?

  • How can you fix a cannula to a blood vessel??

In this article, I will explain the answer to some important questions about vascular cannulation,




table of contents


  1. Why do we need cannulation in the first place?

  2. What is a cannula?

  3. The basic concept of cannulation

  4. List of corresponding vessel diameters

  5. How to fix blood vessels and cannules

  6. Summary




1. Why do we need cannulation in the first place?



Organ perfusion experiments usually require an operation called cannulation, which involves inserting a tube into a blood vessel.


The reason for this is that the perfusion liquid is supplied to the organ through the blood vessel mimicking the living body.


This provides us with direct access to arteries and veins, enabling direct drug administration to organs and immediate perfusion analysis through a venous return analysis.



Click here for the "organ culture system" which can achieve the same perfusion performance as living organisms can, thanks to Ex-vivo

 

Organ culture system


It is possible to remove biological organs and perform independent analysis.

See the track record for a rat's small intestine and skeletal muscle.

Click here for details

 






2. What is cannula?




The word cannula is Latin and is a medical term.


According to Wikipedia,

A cannula (/ˈkænjʊlə/; from Latin "little reed"; plural cannulae or cannulas ) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples.

(Wikipedia English https://en.wikipedia.org/wiki/Cannula Accessed July 16, 2020)


So, apparently, it seems good to call the tube connecting the inside of the body and the outside a ‘cannula’.


Alongside vascular cannula, there are tracheal cannula, heart cannula, etc.




3. Is cannulation ≈ perfusion



From here, I will explain the necessary cannulations for Ex-vivo organ perfusion.

The animal's organs are first removed. They are then cannulated into the blood vessels. This enables perfusion to be successfully performed.

"Can the major organs be perfused?"

It is sometimes asked…


The answer is:


"If it can be removed and cannulated, it is likely to at least be possible."

"We have a successful track record in rat small intestines and femoral skeletal muscles"

Basically, it can be physically perfused as long as it is able to be removed. However, it is also true that the process of such an extraction and the cannulation required is not such an easy one to grasp.

In the proven rat small intestine, for 8-week-old SD rats, the arterial diameter was about 0.8mm and the vein diameter was about 0.9mm.


In the case of rat femoral skeletal muscle, for access to the rat femoral arterial vein, it is roughly the same diameter as that of the small intestine, but the artery is less than 0.7mm, and the vein less than 0.9mm.

In fact, using stereo or surgical microscopes (arterial cannula are a little thicker than the inner diameter of blood vessels), veins can be successfully cannulated by inserting a slightly thinner cannula.



4. Cannulation with a retaining needle


Can I look for an indwelling needle or tube that matches the diameter of the vessel and can I process it? (If you asked this, you are either a teacher who is doing it by yourself, or are quite an organ perfusion fanatic! )...


I believe that most of the people performing self-made organ perfusion use an indwelling needle in the process, then tie them with thread in order to easily access them. .


However, even surgeons are not so dexterous, and if I, as an engineer, attempted to do the same with an indwelling needle, it would almost always fail to come off.

Actually, I did try the process several times with an indwelling needle, but when I put the cannula in and tried tying it with the thread, it regularly came out of the blood vessel and the blood pressure then rose during perfusion. Perfusion often stopped (in fact, the culture solution is filled with full tongues in the device and leaks, or else the organ is dry by the morning.).


Without wanting to repeat myself, I thought that we had to do something about this situation and so my team and I proceeded with the development of a vascular connection tube.




5. Development of vascular connection tubes



"When inserting a tube into a blood vessel, it enters quickly, and after entering it is hard to remove and does not make a hole in the blood vessel."

The days of repeated trial and error on problems such as unreasonable challenges have begun.

The vascular connection tube took nearly two years to reach its final form.


It has been produced by incorporating a special material and enters a wet blood vessel. It is difficult for it to come loose, due to the retention and friction of its shape. With the moderate softness of the material, it is difficult to make holes in blood vessels. And because it is soft, it is difficult to come off when tied with a thread.


Furthermore, with up to 200 mmHg of blood pressure, it is now possible to cope with high blood pressure by adopting a special structure that does not leak in the tube structure.

Now, even as an engineer, I can perform cannulation without effectively. At least without making too many minor errors in the process.


I imagine that most of the people who are reading this article are researchers familiar with animal testing. If an engineer such as myself can perform a cannulation procedure, then you researchers should be able to do too!




6. Summary


This article was about the cannulation of one of the most important elements of Ex-vivo perfusion to the blood vessels.


To summarize:


  • If blood vessels can be cannulated and removed from the subject, a subsequent perfusion is likely possible.

  • It is possible that the apparatus being used in cannulation may come off with a retaining needle.

  • As a countermeasure, the production of the vascular connection tube was created, following a process of trial and error.


“How was it?” This is the most common question when starting organ perfusion

"How do you connect to blood vessels?" you may have also asked.


“Which organs can be perfused?" is another pertinent question.

I hope that the content in this article was able to answer such questions. If you still feel unsure, please get in touch!


Thank you for reading to the end.