Updated: Mar 11, 2019
If you’re working through the technical elements of radial access for oncologic embolization, be sure to check out this in-depth ‘how to’ guide. Interventional radiologist Dr. Jason Iannuccilli covers patient selection, equipment, and step-by-step instructions to minimize complications and maximize technical success.
The BackTable Brief
When getting started with radial access, the ideal patient tends to be a younger male with suitable radial artery diameter, common radial artery anatomy, and very little plaque buildup.
To check if a radial approach is suitable for your patient, use ultrasound to confirm that the radial artery diameter is larger than two millimeters and doesn’t contain a radial loop or extreme tortuosity that might make the procedure difficult. In addition, a Barbeau test can be used to see how well the ulnar artery is perfusing the superficial palmar arch.
When preparing the radial access site, use topical anesthetic, such as lidocaine cream, rather than injecting via needle to lower the risk of spasm. Dr. Jason Iannuccilli recommends accessing with 20-gauge needle, a 018 wire, and a Terumo Glidesheath Slender
After access is gained, a medicinal cocktail of verapamil, nitro, and heparin can reduce the risk of peri-sheath thrombosis and stimulate vasodilation
Swapping out your catheter mid-procedure is likely to cause spasm in the radial artery. Plan the shape of your guide catheter accordingly and be sure that the inner lumen diameter is appropriate for delivery. Dr. Jason Iannuccilli recommends using a guide catheter with a large, hydrophilic inner diameter, such as the Surefire Launcher catheter.
Learn more about the unique advantages of radial access in our previous article.
Disclaimer: The opinions expressed by the participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
Patient Selection For Radial Access
Jason, I know you said everybody has a different way of doing this, but would you mind walking us through your approach to radial access when you're doing IO procedures?
Sure, absolutely. So obviously there are a bunch of technical aspects. Patient selection is key. And like I said, when you're first starting out you want to try to find the ideal patient that's going to have a suitable radial artery diameter, unlikely to have any plaque built up in the artery or any sort of unforeseen anatomic consideration as much as possible. It tends to be younger males that are the ideal candidates, particularly those that don't have all those risk factors. But since our patient population is pretty heavily weighted in the HCC realm, in IO we do get a lot of comorbid illness. So what we found is that as we have started going with this practice, even patients that we felt were not going to be candidates turned out to be good candidates.
And we can talk about some of the data toward the end of this discussion as far as the relative risk of vascular injury based on some of the pre-procedure testing stuff that we do. But what we found is that it's not as strict as what you initially think when you're starting. You don't have to be - I hate to say it - as careful as you really want to be in the beginning. There's a lot of leeway there and it's relatively rare that you're going to end up with a significant complication that's going to cause the patient long-term harm.
But in general, when we're talking about the technical aspects we always start off with an ultrasound to the forearm while the patient is in recovery. We'll check to make sure that the radial artery is sufficient diameter. I would set the threshold at two millimeters for a minimum diameter just based on the sheath size that we're putting in there, which we'll talk about. But in general there's also data to support that the complication rates are higher when the radial artery diameter is less than two millimeters. So we measure the artery, we do an ultrasound, we kind of follow the vessel up the forearm, make sure that we can't see any sort of radial loop or extreme tortuosity that might make it a difficult procedure. Even if you see a radial loop there are ways to overcome it, but again, it may sway you toward using a femoral access if it's a complete loop, for example.
So once we do the anatomic assessment with ultrasound we usually - you don't have to but we do - assess the completeness of the palmar arch by doing a Barbeau test. So the Barbeau test, I'm sure you guys are familiar with it, but it's basically an Allen's test used with a pulse oximeter that we place on either the thumb or the index finger or the hand. We compress the radial artery and observe the pulse ox's waveform. In general, the degree of depression of that waveform is going to tell you how well the ulnar artery is perfusing that superficial palmar arch. And there are various types of waveforms just based on the change. Type A or a type B is preferred. We have done a couple type Cs and haven't had any major issues with that yet but I would say that it's just a handful of patients that we run that risk with.
So that's sort of the overall assessment. If you've got a Barbeau type A or type B and the radial artery is two millimeters and the ultrasound at least to the forearm looks pretty good I'd say it's a go. And then we prep the patient up and bring him into the room.
Radial Artery Access
Once we do the access there's a big debate about how you anesthetize the access site. To inject lidocaine through a needle you usually are running the risk of inciting spasm in the radial artery. And I would say that from a technical standpoint, spasm is the one thing that could ruin your case, so anything you can do to minimize that chance of it occurring is going to bode well for more favorable outcome, at least in terms of the access site. So some people are using lidocaine cream on the skin and I believe there actually have been some studies that have shown that the rate of spasm in the artery is much lower when you're using the topical anesthetic. So if you have access to that I would recommend using it. In addition, there are some people that are putting nitropaste up on the forearm over the radial artery to try to even incite more vasodilation than what might be seen with the preliminary ultrasound at the beginning of the assessment.
So once we have the patient prepped, ready to go, we will put the local anesthetic on the skin. You're assessing with a ... It's more or less a 20 gauge needle 018 system. I use ultrasound for the access, I like the direct visualization. I'm not doing a through and through wall puncture. It's a single wall puncture directly visualizing the tip of the needle the entire time. Once you're in you get good return, you're threading your 018 wire, and the sheaths that we use are the Terumo glide sheaths.
The Slender sheaths in particular are designed such that the wall of the sheath is thinner than a standard access sheath that you would use, say, from a femoral approach. By doing that, by thinning out that wall what they've done is they have decreased the outer sheath size by about one French while maintaining the inner lumen diameter. So we're essentially using a five French sheath with a smaller outer diameter than what we would be seeing with a five French sheath in the groin. So with a two millimeter radial artery, that still allows for some blood flow around the sheath. The sheath's design, it's an 018 so it slips with a nice taper over that 018 wire. And I think that's key because what you don't want to do, in fact the thing you want to avoid at all costs with radial artery access is swapping out catheter sheaths. That's certainly going to send your artery into spasm. So it's nice that they have designed a sheath that inserts over an 018 system so it's a single, smooth insertion. It's also hydrophilic on the outside so that facilitates the access as well.
Reducing the Risk of Peri-sheath Thrombosis in Radial Access
Once we get into the system and we've got good blood return through the sheath, we'll then put in a medicinal cocktail that is designed to reduce the risk of peri-sheath thrombosis and also stimulate some vasodilation. We use 2.5 milligrams of verapamil, 200 mics of nitro, and 5,000 units of heparin. We use a full dose heparin instead of the low-dose 3,000 units. There is some data to show that radial artery occlusion rates are a lot lower if you're using the full-dose heparin. So 5,000 units of heparin, 200 mics of nitro, 2.5 of verapamil, and then we hemodilute that. We will draw up in a 20 to 30 cc syringe, from the sheath, the patient's own blood to dilute the medication and then slowly administer that back through the sheath over the course of about two minutes. That's mainly to prevent that burning sensation that the verapamil can cause, that can incite some spasm, it can cause some anxiety in the patient who at this point is probably just crossing over that threshold into conscious sedation.
Once you've got the cocktail in you're kind of good to go at that point. I will mention that there is some data out there that instead of giving the nitroglycerin through the sheath some practices are using sublingual nitro. And they've shown that they can increase the radial diameter size by about 0.5 millimeters without a deleterious effect on blood pressure by giving it sublingual. It's an interesting point, we don't do that, but it's something that others have adopted in practice.
Catheter Selection for Radial Access
So again, your cocktail is in, you're ready to go, sheath is in. Now it's a matter of just picking your guide catheter. And as I mentioned before, this is actually a pretty critical decision. You want to know ahead of time the shape that you want to use. You want to make sure your inner luminal diameter is appropriate. Because once you have a guide catheter in and you're down in the aorta there's no way you're going to be able to swap this thing out for a different one without causing spasm in that artery. I've tried it, it's never worked out for me. So I would just say that as a point of fair warning that you want to give it some thought as far as the guide catheter is concerned.
I think guide catheters for us have been a little bit of a process of trial and error. We first started out when we were doing this using the Terumo catheters because we had the support of the rep there and we sort of just purchased all the stuff as a packaged deal. The Sarah, the Jacky catheters, they've got a great shape, they definitely move well, they respond well to torque. What we found was the problem with those catheters the inner lumen was not hydrophilic and it was actually just about at the threshold of what you would expect the inner lumen of a five French catheter to be. So if we were doing treatments where we wanted to use an antireflux catheter like the Surefire device we found that in passing that device through the catheter it would move well until it got to the tip and then it would sort of get bound up. And maybe one out of three times it would pass through and you were able to do the treatment and the other two times it would bind up on the fabric of the antireflux umbrella and just sort of destroy the Surefire catheter. So that was no good and that's also when we learned that you can't swap out catheters without causing a lot of spasm in the radial artery.
So just to re-emphasize this process of introducing radial artery access in our practice was not exactly smooth-sailing the whole way but the idea is that you learn from the mistakes of others, and when you're implementing in your own practice, we've got some knowledge that we can add to the database to help you do it well.
The Launcher catheter is one that we kind of found with the help of Surefire because we were looking for a catheter that had slightly larger inner lumen diameter with a roughly equivalent outer diameter. So these Launcher catheters are known for their larger inner lumen. We talked before about getting good injection rates for diagnostic mappings and stuff, these catheters are actually fantastic for that. I mean you can get seven cc per second injections through them without any problem whatsoever. So you're certainly going to be able to do whatever you need to do from a flow rate standpoint and from a pressure standpoint with that catheter.
 A Technical Guide Describing the Use of Transradial Access Technique for Endovascular Interventions: https://www.techvir.com/article/S1089-2516(15)00022-0/fulltext
 Transradial Versus Transfemoral Arterial Access in Liver Cancer Embolization: Randomized Trial to Assess Patient Satisfaction: https://www.jvir.org/article/S1051-0443(17)30828-X/fulltext
Dr. Jason Iannuccilli is a practicing interventional radiologist with Rhode Island Medical Imaging.
Dr. Chris Beck is a practicing interventional radiologist with Regional Radiology Group in New Orleans.
Dr. Michael Barraza is a practicing interventional radiologist with Radiology Alliance in Nashville.
Cite this podcast:
BackTable, LLC (Producer). (2018, April 4). Ep 26 – Radial vs. Femoral Access in IO Procedures [Audio podcast]. Retrieved from https://www.backtable.com/podcasts
The Materials available on the BackTable Blog are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients.
The podcast referenced in this article was sponsored by Surefire Medical.