Infectious Diseases

The Dao of Regional Limb Perfusion

By Paul Basilio

Regional limb perfusion (RLP) is an excellent way to manage active infections, aid in wound healing and provide proper antimicrobial prophylaxis to the distal limb. For veterinarians who are unsure of proper RLP technique, however, the procedure can be an anxious affair.

Holly L. Stewart, VMD, PhD, DACVS (LA), assistant professor of large animal surgery at the University of Pennsylvania School of Veterinary Medicine, offered several quick tips to help equine practitioners find their zen with RLP during a presentation at the 70th Annual AAEP Convention in Orlando, Fla.

When to Do and When to Not Do
“I use [RLP] for antimicrobial prophylaxis after surgery, in horses with septic joints, and after I’ve performed any form of internal fixation,” she explained. “RLP is absolutely part of my plan for wounds as well, or if there’s a component of cellulitis present.”

Dr. Stewart also has started to use RLP in horses with osteomyelitis in some of her laminitis cases that remain painful despite appropriate management. If evidence of osteomyelitis is visible on radiographs or if the horse is having an acute-on-chronic episode and is obviously uncomfortable, she will reach for her butterfly catheter.

“I have been treating [osteomyelitis] with 3 days of regional limb perfusions. It’s a small number of cases, but I’ve had good success,” she said. “It’s a new thing for me, specifically to manage the osteomyelitis aspect of laminitis cases that remain painful despite appropriate management. I’ve been pleasantly surprised by the clinical response in a very small number of cases.”

RLP is typically not helpful with lacerations above the stifle or elbow, and over the axial skeleton regions, but it can be of use if there is also cellulitis present in the distal limb. Dr. Stewart mentioned several other caveats, particularly in patients that may require a referral.

“If you’re out in the field and you think that you might refer a case, then it’s important to consider that you are about to expose the animal to antibiotics,” she said. “It may be better to allow the referral practice to get a sample before doing a perfusion.”

In addition, she also recommended holding off on RLP if you have insufficient antibiotics on your truck. From an antimicrobial stewardship standpoint, she recommended against RLP in such a situation. “Refer the horse, or come back when you have sufficient supplies.”

Sedation for Meditation
A good sedation makes for a good regional limb perfusion experience, and Dr. Stewart said that she is not shy when mixing sedative cocktails for her patients. She typically chooses a “6, 6 and 6” cocktail that includes 6 to 8 mg each of detomidine, butorphanol and acepromazine.

“I’ll top that off with [125 to 200 mg] of xylazine when I need it,” she explained.

For draft horses, donkeys and Friesians, however, she cautioned that their response to sedation can be different from what’s expected from other equids, so sedation in those cases may require some tweaking.

Zen and the Art of Vein Maintenance
To avoid venous blowouts, Dr. Stewart recommended ensuring that the horse is properly sedated, that the surrounding environment is controlled, that all preparations are done in a timely manner, and that the venipuncture is accurate. After the horse is sedated and (hopefully) relatively still, it’s time to address the vein.

“The tools matter,” she said. “Use a 25-gauge butterfly catheter and a wide tourniquet.”

Dr. Stewart also places a strip of white tape over the tourniquet. By taking the catheter and looping the tubing and attaching it to the horse with that strip of tape, the needle is stabilized in case the horse moves.

“After that, make sure you have a nice flash in the catheter, then administer the drugs over the course of 2 to 3 minutes,” she said. “You really want them to stay still, so use a twitch if needed.”

She cautioned that not all drugs are created equally. Dr. Stewart typically uses a concentration-dependent antibiotic such as amikacin, but ideally the decision is informed by culture and sensitivity testing. She also estimates the RLP dose as one-third of the systemic dose, and repeats the procedure for 1 to 5 days, preferably at the same time of day.

The saphenous, cephalic and palmar/plantar digital veins are her usual targets, depending on where she intends to deliver the antibiotics. After the needle is removed, apply a bandage to the site. It’s also important to remember to remove the tourniquet before removing the bandage.

“You’ll only make that mistake once,” Dr. Stewart joked.

Topical diclofenac can assist in pain management over the perfusion site afterward. A small amount can also be dispensed in a plastic bag so that the owner can apply it the next day. MeV