2.16.4 Confounders of Pain
There are a variety of other situations that can complicate the assessment and management of pain in animals.
Age: young, still‐growing patients have enormous “plasticity” in their CNS, and early painful experiences can elicit permanent alterations embedded in the CNS and can manifest as increased pain sensitivity later in life. Older patients are often beset by chronic inflammatory processes (OA, gingivitis, otitis, dermatitis) which can elicit a neuropathic component, and whose spinal cord is a “smoldering ember” of hypersensitization upon which a subsequent acutely painful event can cause greatly exaggerated pain.
Obesity: adipose tissue is the body's largest endocrine organ and secretes a witch’s brew of proinflammatory cytokines and mediators that circulate systemically and sensitize nociceptors. In humans, excess abdominal fat will double the risk for a chronic pain condition later in life [7].
Example 1: Ovariohysterectomy (OHE) in a 5‐month‐old mixed‐breed dog. Client administers trazodone at home prior to transport to hospital. Patient admitted with fear‐free and low‐stress handling techniques, premedicated with buprenorphine, midazolam intramuscularly (IM), and NSAID of choice orally (PO). Induction of anesthesia, placed on intravenous (IV) fluids, incisional block with bupivacaine. OHE proceeds with lidocaine mesovarium block. Patient discharged with three days of NSAID.
Example 2: Comminuted femoral fracture resulting in hindlimb amputation of 7‐year‐old cat. Client administers gabapentin and NSAID at home prior to transport to hospital. Patient admitted with fear‐free and low‐stress handling techniques, premedicated with combination of buprenorphine, dexmedetomidine, and ketamine IM. Induction of anesthesia, placed on IV fluids with ketamine constant rate infusion (CRI), epidural with bupivacaine via lumbosacral or sacral‐coccygeal approach. Post‐op administered long‐acting buprenorphine and discharged with NSAID and gabapentin PO.
Example 3: Cruciate repair surgery in a 6‐year‐old lab mix. Client administers NSAID and high‐dose gabapentin at home prior to transport to hospital. Patient admitted with fear‐free and low‐stress handling techniques, premedicated with hydromorphone and midazolam IM. Induction of anesthesia includes loading dose of ketamine IV, placed on IV fluids with ketamine CRI. Femoral and sciatic regional nerve block performed with bupivacaine, and IA hydromorphone. Patient prepped and surgery performed. Long‐acting (liposome‐encapsulated) bupivacaine infused into several layers of closure. Post‐op cold compression, continue ketamine ± opioid CRI for 4–6 hours. Patient discharged with NSAID, gabapentin PO, and physical rehabilitation instructions (or referral), to include therapeutic laser if available.
Example 4 : 12‐year‐old golden retriever with a BCS of 7/9 stiff in the mornings and after exercise; owner has to help up onto the couch. Physical exam reveals straight‐legged conformation and atrophy rear quarters, discomfort, physical examination, and radiographic signs consistent with hip dysplasia and advancing OA. Priority is to place patient on NSAID or PRA of choice and switched to an EPA‐rich diet formulation that also promotes weight loss to BCS of 6 and ultimately a lean 5. If owners agreeable, patient is also placed on polysulfated glycosaminoglycan, or alternatively, a high‐quality and reputable nutraceutical; exercise program implemented that includes vigorous walks and inclines but unrestricted activity is limited. If and when eventually deemed appropriate and available, choice (and/or combination of) pain‐modifying analgesic medication (e.g., amantadine, gabapentin) is prescribed as adjunct to the NSAID or PRA, IA biologic injections, and anti‐NGF mAb treatments are implemented. Acupuncture, therapeutic laser, pulsed electromagnetic field, myofascial trigger point, referral for aggressive physical rehabilitation, and other nonpharmacological modalities can be utilized at any time.
Underrecognized and undermanaged pain inflicts very real physiological and medical consequences, resulting in significant patient morbidity and in the extreme can contribute to mortality.
Through the process of peripheral and central hypersensitization (“wind‐up”), pain becomes maladaptive, exaggerated in scope, severity, character, duration, and field; a number of factors will place a patient at risk for maladaptive pain, including (but not limited to) nerve injury, severe trauma, chronic inflammation, heritable tendency.
Assessment of both acute postsurgical and chronic OA‐related pain is possible with validated CMIs.
Evidence‐based industry guidelines and consensus statements are available to direct veterinary clinicians to the highest, wisest, safest multimodal strategies for acute and chronic pain.
Veterinarians are advised to adopt the emerging trend of reducing, full mu agonist opioid usage, insofar as possible and still maintain patient comfort, in favor of buprenorphine and butorphanol along with multiple opioid‐sparing modalities and strategies.
2.16.5 Cautions
With an aggressive multimodal approach to peri‐perative pain management, anesthetic requirements may be significantly reduced; adjust induction doses and vaporizer settings accordingly.
Abbreviation
BCSBody condition score
References
1 1 Bonica, J.J. (1979). International for the study of pain: pain definition. The need of a taxonomy. Pain 6 (3): 247–248.
2 2 Tony Buffington, C.A., Westropp, J.L., and Chew, D.J. (2014). From FUS to Pandora syndrome: where are we, how did we get here, and where to now? J. Feline Med. Surg. 16 (5): 385–394.
3 3 Mathews, K., Kronen, P.W., Lascelles, D. et al. (2014). Guidelines for recognition, assessment and treatment of pain: WSAVA Global Pain Council. J. Small Anim. Pract. 55 (6): E10–E68.
4 4 Epstein, M., Rodan, I., Griffenhagen, G. et al. (2015). 2015 AAHA/AAFP pain management guidelines for dogs and cats. J. Am. Anim. Hosp. Assoc. 51 (2): 67–84.
5 5 Muir, W.W., Berry, J., Boothe, D.M., et al. (2018). Opioid‐Sparing Pain Therapy in Animals: Working Task Force. https://ivapm.org/wp‐content/uploads/2018/12/Op‐Sparring‐Task‐Force‐WP.pdf
6 6 Fan, T.M., de Lorimier, L.P., O'Dell‐Anderson, K. et al. (2007). Single‐agent pamidronate for palliative therapy of canine appendicular osteosarcoma bone pain. J. Vet. Intern. Med. 21 (3): 431–439.
7 7 Ray, L., Lipton, R.B., Zimmerman, M.E. et al. (2011). Mechanisms of association between obesity and chronic pain in the elderly. Pain 152 (1): 53–59.
Recommended Reading
1 Rodan, I., Sundahl, E., and Carney, H. (2011). AAFP and ISFM feline‐friendly handling guidelines. J. Feline Med. Surg. 13 (5): 364–375.et al., for the