Exploring the Potential of Fish Skin Grafts in DFUs

Hi, I'm Dr. Lee Rogers. I am the Chief of Podiatry at the University of Texas Health Science Center in San Antonio, and I'm helping to lead this discussion on the appropriate use of fish skin in the diabetic foot.

Fish skin grafts are appropriate in a couple of scenarios in the diabetic foot. First we have our surgical limb salvage approach, and then we have our clinical healing approach. Let me talk about the surgical limb salvage approach where you have somebody in the operating room, you do a wide debridement, we always like to do a very wide excision and take out an entire ulcer, whether it's infected or even just chronic, so we almost look at it like cancer. This is an ulcer, got to get a very wide margin around it, then we leave healthy tissue behind.

Now when we do that we'll use fish skin to cover deeper structures. We'll put negative pressure directly over, with the foam, directly over the graft, and that's because we want to granulate that tissue. We want to get all that area covered, and that's a bridging therapy. That's what I tell people. It's not meant to bring you all the way to closure. This is meant to get you the next step. My first and most important concern is how I cover this bone or this tendon or get this deep wound shallow. What I'm trying to do is take a complex wound and make it simple, so I'm simplifying this process, right. This goes hand in hand with all the other stuff you need to do before this, the infection and the vascular and the managing the pressure, but specifically about fish skin, we're taking a complex wound and we're making it simple.

Now let's say we made this wound simple. It's level, it's granular, it's level with the surrounding skin. What do we do at this point? Well, we can either do autologous skin, we can take skin from the patient's thigh and we can put it on their foot, mesh it, put it down there, and do a skin graft. Works great, especially in really large wounds when it would take a long time to heal by secondary intention, even accelerated secondary intention, which is what we would use with the whole category of CTPs, cellular and tissue based products. Fish skin falls into that category of cellular and tissue based products. It is actually a really close analog to human skin, surprisingly. Although it had scales, it doesn't have scales when you're using it clinically, but if you look at it under electron microscopy, it is very closely analogous to human skin.

Now the other benefit of fish skin is that the only fish skin that's FDA approved for use in the United States comes from a cold water fish from... Icelandic cod. That fish lives at one degree above freezing, and there's never been a virus that has been transferred from a cold water fish to a human, so the FDA does not require those grafts to be virally inactivated, which means you don't have to use radiation or harsh chemicals on those grafts. They're intact fish skin and the collagen bonds are still there. We didn't disrupt a lot of these proteins. It also contains omega-3 fatty acids, which are a natural anti-inflammatory. We all know wounds sometimes get stuck in this inflammatory phase of healing, so it has a lot of benefits to be used in that clinical setting in the outpatient arena to help to close wounds.

Now often in limb salvage in the OR I'm doing just one to get me to my bridging therapy, but when you're using it in the clinical setting you're on a sequential treatment there. You're doing debridements every week, you're doing a graft and you're watching this wound close by accelerated secondary intention.

Probably the biggest technique in using fish skin that I would tell people is you got to have... it's a very thick piece of tissue and it's very durable, and that's useful for implantation sometimes, but it may not always be useful when you're covering tissue that's exudating, and you can get that exudate that gets trapped in between the tissue and the wound bed, so where some people will take a scalpel and try to fenestrate the graft, you can do that.

It's often even really tough to do that. I'll take it and I'll fold in half and I'll use scissors and I'll cut into it just to create fenestrations. I used to mesh it with a mesher when I was in the operating room but it's so thick and leathery that it would ruin our meshers sometimes, even for the skin, so we order now pre-meshed versions of the fish skin because it's got those holes in it. You allow the exudate to come out and the graft can really incorporate a lot better, so I think thinking in advance about the exudate and how to manage that, how to get that through the graft, that's a pearl that I would pass along.

Really, clinicians today can improve their practice with fish skin by thinking about these two areas in which it could be used, either surgically in the operating room for almost a single application to just promote that granulation tissue, cover those deeper structures, or when you have all of that done, you've simplified that wound and now you need to just get it to heal by secondary intention, you can use this graft in the clinic with sequential applications.

In our experience, it's around three applications, although I know some of the research studies show that it can be up to six applications of the graft weekly in order to get total healing, and that's honestly, that's really dependent upon the size of the wound because these wounds are healing. They're healing by secondary intention so the margins are still coming in. They're just healing faster because you're putting this scaffold on top of it, and I think the omega-3 fatty acids helping to reduce the inflammation are making a big impact.