Exploring the new frontier in pain management

(Getty Images)Recently we have progressed light years in our management of pain in our patients. We are now acknowledging that it exists, recognizing its gravity, and doing what we can to prevent and treat it. But we can do better. Here's a look at the out-of-this-world options we have (or will have soon!) to choose from.

Did you know?

Sometimes, pain experts give pets that have chronic pain a pain vacation. In addition to being humane, by stopping the pain completely for awhile, it can be an attempt to try to "reset" the nerves to a nonpainful baseline.

Before we start our journey into the expanse of veterinary pain management, keep in mind that we have learned that managing pain in our patients requires a continuum of care. So from the very beginning, I cannot emphasize enough how important it is to watch for, evaluate and attempt to qualify pain being experienced by our veterinary patients. Standardization is important, so I highly recommend using a pain scale, such as the Colorado State University's pain scales for acute and chronic pain in dogs and cats:

• Canine acute pain scale: http://www.vasg.org/pdfs/CSU_Acute_Pain_Scale_Canine.pdf

• Canine brief pain inventory for chronic pain (link to download): http://www.vet.upenn.edu/research/clinical-trials/vcic/pennchart

• Feline acute pain scale: http://csuanimalcancercenter.org/assets/files/csu_acute_pain_scale_feline.pdf

• Feline chronic pain scale: http://carrboroplazavet.com/clients/15178/documents/feline_pain.pdf

In my practice, we evaluate and record pain scores for every patient at every visit. Whether that pet is in the clinic for vaccination or surgery, there is a space on the physical examination form for rating current pain status.

If dogs are from Earth, cats are from Venus?

Because of cats' behavioral and physiologic differences from other species, they can sometimes seem like alien creatures. As a result, effective pain management in cats has continued to be a bit of a black hole, or at least somewhat more of a challenge.

Behavioral differences have made pain evaluation difficult in cats. We are starting to commonly recognize the signs now, such as withdrawal, not jumping onto things, hunched posture and squinting. I think you should consider pain as a potential stand-alone cause of litter box habit changes as well.

Feline physiologic differences have ensured that the traditional nonsteroidal anti-inflammatory and opioid pain medications have not been used much in cats.

Did you know that pruritus receptors are a subset of nociceptors? Why does that matter? Well, for instance, can we then postulate that cats with hyperesthesia of the lumbosacral area may have back pain? Thus, I think amitriptyline is a frequently overlooked and underused drug for pain-and itchiness-in cats. It is a tricyclic antidepressant that we already use to treat feline idiopathic cystitis (FIC) and feline psychogenic alopecia, thinking that it is the behavioral action of the drug that it is helping. Maybe those cats with FIC or self-grooming alopecia of the caudoventral abdomen really have painful bladders.

Close encounters: Locoregional anesthesia

A few of the local anesthetic blocks that we use with surgery are line, ring, testicular and ovarian blocks. Regional blocking techniques, such as epidural anesthesia for cats with urethral blockages, are also very valuable to have in your pain toolkit.

Far-out fact! Local anesthetics have been found to have local anti-inflammatory, antibacterial, antifungal and antiviral effects?1,2

And did you know that when using intra-articular blocks, about the only drug you can use safely is mepivacaine?

To infinity and beyond: Anesthetic CRIs

There are several methods of administering constant-rate infusions (CRIs) of anesthetic agents, but it is beginning to look like this modality is really helpful for treating and preventing pain in the short and long run.

Subanesthetic-dosage CRIs of ketamine are used for any surgical procedure in our hospital. It helps prevent central sensitization to pain-and that is galactically important. For it to be effective, a bolus must given before the CRI and the CRI must be run during and after surgery. We usually continue to run it during anesthetic recovery until I am ready to take the catheter out, but it can be run longer for more painful surgeries and conditions.

Star-shaped obstacles: Glial cell-inhibiting drugs

More and more is being discovered about glial cells' role in the pain pathway. It turns out they are active, important and cranky little cells that are quite involved with acute and chronic pain and interference with opioid drug function. They enhance pain and prevent opioids from working. They also contribute to increased pain associated with repeat surgery.

Some glial cell-attenuating drugs are being developed for people to be given with opioids to prevent this hostile atmosphere in there.

Did you know? Scientists now think that if they can block the opioid receptor (TLR4) on glial cells, that it will stop the withdrawal signs and side effects of the opiates. Stellar!

Regenerative medicine: Straight outta sci-fi

Regenerative medicine includes using platelet-rich plasma (PRP) and stem cells. There are different systems for deriving the PRP from the patient's blood, and none have been found to be superior to the others. Similarly, at the moment, the debate in stem cell use is whether stem cells derived from adipose tissue or those derived from bone marrow are more effective. I think that regeneration of tendons and ligaments is probably the best use for them at this time.

Far-out fact: Pets treated with PRP can get more painful for the first few days after treatment? There is no consensus on whether to treat this pain or how to do so.

Coming to a solar system near you

A long-acting bupivacaine liposomal solution has been approved by the FDA and will be released this year. It is purported to have a duration of action of at least 72 hours. This could be ideal for things such as local and regional anesthetic blocks for dental procedures.

Are you ready to rocket your osteoarthritis pain control into orbit? Another new drug is on the horizon that I feel will revolutionize the treatment of osteoarthritis. This drug, grapiprant, is a selective antagonist of the EP4 prostaglandin receptor-the main one associated with osteoarthritis. You'll be hearing more about this drug, for sure.

Outside the system: Nonpharmacological modalities

You don't have to turn to drugs alone to control pain. Acupuncture has pain-relieving and drug-sparing effects. I use it in my practice extensively.

In addition, physical rehabilitation is the fastest growing part of veterinary medicine. Many physical rehabilitation modalities can easily be added to your practice, such as laser therapy, exercise therapy, massage therapy, hot and cold therapy and transcutaneous electrical nerve stimulation (TENS).

Two simple and easy modalities you can start with:

1. Have all your geriatric patients walk over Cavaletti poles or other raised obstacles placed a precise distance apart. You can construct them yourself or even just use pool noodles. The idea is to just get them flexing and extending all of their joints.

2. Train dogs to walk backward to build the hamstrings since the hamstrings support the knee.

References

1. Johnson SM, Saint John BE, Dine AP. Local anesthetics as antimicrobial agents: a review. Surg Infect (Larchmt) 2008;9:205-213.

2. Cassuto J, Sinclair R, Bonderovic M. Anti-inflammatory properties of local anesthetics and their present and potential clinical implications. Acta Anaesthesiol Scand 2006;50:265-282.

Janice Huntingford, DVM, DACVSMR, CVA, CVPP, CCRT, CAVCA, is president of Essex Animal Hospital in Essex, Ontario.