Ouch! That Hurts Multimodal Pain Management

Ouch! That Hurts!

By Robert Sullivan, VMD

Multimodal Pain Management

“He’s just getting old and slowing down, he’s not in pain.” Too often I hear these sentiments expressed from clients. I feel that pain management is all-too-often overlooked in our patients. As I work mostly with dogs and cats, I will concentrate on their needs, but we must transpose our knowledge of pain to all species. Learning how to recognize—even anticipate—pain in our patients, how pain is transmitted, and where we can block or attenuate it with a multimodal approach will help our pets live better.

First, pain management isn’t all about medication. There are many strategies that may help. For acute injury such as postsurgery pain, cold therapy applied immediately for 10 to 15 minutes will decrease pain and inflammation. In chronic pain management, a heat pack for 10 to 15 minutes can decrease pain by increasing blood flow to the area. Avoid burns from either option by placing a dry towel between the skin and heat/cold source. Deep-tissue warming can be facilitated with massage, photobiomodulation (laser) therapy, or therapeutic ultrasound. Acupuncture has been shown to decrease pain by either blocking or freeing pain channels. Trigger point (myofascial) therapy uses needles, direct pressure, or focused laser to ease nerve spasm and thus allow tense muscles to relax. Transepidermal nerve stimulation (TENS) can aid in pain management through rapid polarization and depolarization of nerve endings. Last, pulsed electromagnetic field (PEMF) therapy using mats or devices such as the Assisi loop have helped some patients.

Before we get to treating pain, we have to recognize pain in our pets. There are numerous pain management questionnaires available for download that can be of use. We have found the Canine Brief Pain Inventory useful for dog owners. Developed at Penn, it quantitates, for you and the owner, the severity of a pet’s pain. It will help the owner to recognize that their pet IS in pain. All of our middle-age and older patient owners get a copy before an exam.

I learned something about cats a number of years ago. Dogs and people may be from earth, but cats are from the Andromeda galaxy. Cats are not small dogs, whether it be their anatomy, physiology, or behavior, so their pain assessment and management has had to evolve from a different direction. One assessment was developed by the University of Montreal and Zoetis. The Feline Grimace Scale is one way to measure pain in cats, either acute or chronic.

Pain is defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage,” by the International Association for the Study of Pain, 2020. Inflammation is the body’s response to injury, and inflammation is actively required to promote healing. The problem lies in the plasma and cellular-derived mediators associated with inflammation. These mediators, which promote vasodilation, migration, and activation of pro-inflammatory cells and phagocytosis of damaged cells, are also responsible for the perception of pain. The antiinflammatories we use are directed at blocking the mediators most commonly responsible for pain such as bradykinins, prostaglandins, interleukins, leukotrienes, and tissue necrosis factor. The production of prostaglandins (PG) is inhibited by various pharmaceuticals that work on various levels of the PG pathway starting with aspirin, which works on cyclooxygenase 1 (COX-1). Unfortunately, inhibiting COX-1 also decreases the production of protective mucus in the stomach leading to ulcers. Newer medications blocked further down the PG pathway, decreasing, but not eliminating, side effects, including COX-2, PGE2, and COX-3 inhibition.

Aside from anti-inflammatories to mitigate pain, it helps to look at the steps in the pain pathway to determine other pharmaceuticals to block pain. Pain is triggered by nociceptors, which transform the stimulus into an action potential, electrical signal using sodium channels to transmit or transduce the stimulus to the spine. Transduction can be decreased by local anesthetics such as using a line block of lidocaine along your spay incision or an intratesticular lidocaine injection prior to castration. No transduction of pain signal, no pain perception.

Transmission of pain is the signal reaching the spine and traveling to the brain. Drugs that can block this signal include α-2 agonists such as using dexmedetomidine with anesthesia or local anesthesia, such as epidural nerve blocks with lidocaine.

Along the way, the pain signal can be modulated along the spine, either inhibited or enhanced. Enhancement can occur from either circulating cytokines from inflammation or from previous chronic

pain stimulus. Referred to as “wind-up” pain, nerve endings that have had continuous stimulation are sensitive to further stimulation down the road and a simple muscle spasm may ramp up to crippling pain. NSAIDS will help decrease the circling cytokines, but N-methyl-D-aspartate (NMDA) antagonists such as ketamine and amantadine will aid in desensitizing the nerve ends.

Perception of pain is the brain recognizing the stimulus and saying “OW!” Removal of pain perception is accomplished during surgery through anesthesia. Once anesthesia is removed, the perception component of pain needs to be addressed via opioids or benzodiazepines.

Other adjunct treatments for pain have been used to aid in blocking the projection of pain along the pathway. Tricyclic antidepressants, such as amitriptyline, block the reuptake of serotonin and noradrenaline. NMDA antagonists can again decrease the projection of pain and the calcium-channel modulators gabapentin and pregabalin are invaluable in a multimodal management routine.

Newer modalities are available. Owing to the macrophage’s innate role in inflammation within the synovium, SynovetinOA has been developed to provide a year’s worth of pain management in joints with osteoarthritis. A small amount of SN117 is injected intra-articularly, and the macrophages ingest the isotope and die. Other macrophages ingest the dead macrophage and so on. The isotope is present for 6 months and it takes 6 months for inflammation to build up again.

Nerve growth factor (NGF) has been shown to be an important component of osteoarthritis pain and inflammation. A monoclonal antibody has been developed to block NGF and is currently available in Europe.

By learning how to recognize pain in our patients and combining physical modalities with a knowledge of the pain pathway and how to attenuate pain transmission at each stage, we can help our pets heal with minimal pain.

About the Author: Robert Sullivan, VMD, graduated from the University of Pennsylvania School of Veterinary Medicine in 1996, then moved to and started working in Montrose, PA. In 2005, he started Southtown Veterinary Hospital, and eight years later, built the current facility, which includes rehab. In 2014, Dr. Bob completed certification in Canine Rehabilitation at the University of Tennessee. He also has special interests in internal medicine, general and orthopedic surgery, and lately, pain management.

Dr. Bob is married to Rebecca and they have two wonderful children, Alannah and Lee John. Over the years, his pets have included ferrets, fish, horses, and rodents. Currently, the Sullivans have a 12-year-old rescue dog, Hank, a Chesapeake Bay Retriever who spends most days with Dr. Bob at the office. They also have four cats: two pairs of orange siblings, Pumpkin and Blizzard, and Trick and Treat that were orphaned at 5 days old, bottle fed, and cared for by the family. When not in the office, Dr. Bob is tending to his flock of chickens, his beehives, or his garden.

Small Animal Pain Assessment

Pain Management Associations

International Association of Veterinary Pain Management

ivapm.org

Veterinary Anesthesia and Analgesia Support Group

vasq.org

American College of Veterinary Anesthesia and Analgesia

acvaa.org

Canine Pain Assessment

Canine Brief Pain Inventory scoring - bit.ly/3oHiMhO Glasgow Composite Measure Pain Scale - bit.ly/3gKxwYN Helsinki Chronic Pain Index - bit.ly/3HONJbu Colorado State University Canine Acute Pain Scale -

bit.ly/3BmwGey

Feline Pain Assessment

Feline Grimace Scale - felinegrimacescale.com Colorado State University Feline Acute Pain Scale -

bit.ly/3swkYcY

Feline Musculoskeletal Pain Index -

bit.ly/3GNtCJa

The Pain Pathway and Useful Medications

Transduction

Local anesthetics Opioids NSAIDS Corticosteroids

Projection

NMDA antagonists Tricyclic anti-depressants Calcium-channel modulators

Transmission

Local anesthetics α-2 agonists

Modulation

Local anesthetics Opioids α-2 agonists NMDA antagonists NSAIDS

Perception

Anesthetics Opioids α-2 agonists Benzodiazepines