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Analgesia in Shelter Medicine: How to Recognize and Manage Pain in our Patients
Dr. Fran Rotondo B.Sc., D.V.M.
Defining Pain in Animals
“…an aversive sensory and emotional experience representing an awareness by the animal of damage or threat to the integrity of its tissues. It changes the animal’s physiology and behaviour to reduce or avoid the damage, to reduce the likelihood of recurrence and to promote recovery” Non-functional (non-useful) pain occurs ‘‘when the intensity or duration of the experience is not appropriate for damage sustained (especially if none exists) and when physiological and behavioural responses are unsuccessful in alleviating it’’. (Molony, V. and Kent, J.E. Assessment of acute pain in farm animals using behavioral and physiological measurements. Journal of Animal Science. 1997;75:266–272.) Physiology of Pain
 2 types of axons: A ∂ Fibres (fast and myelinated); C Fibres (slow and unmyelinated)  Persistent nociception causes signal recruitment and amplification locally and at the level of the spinal cord; this is the ‘wind up’ phenomenon. Categories of Pain:
 Inflammatory: response to tissue damage  Tissue or nerve damage (including surgical pain)  Inflammation (e.g. pancreatitis; osteoarthritis)  Inappropriately managed adaptive pain Pathologic Pain:
 clinical pain; ongoing discomfort and abnormal sensitivity are features of the patient’s o Inflammatory pain (involving somatic or visceral structures) o Neuropathic pain (involving lesions of the nervous system) o Spontaneous pain: dull, burning or stabbing pain: causalgia o Exaggerated pain: in response to a noxious stimulus: hyperalgesia o Allodynia: pain produced by a stimulus which is not normally noxious  Distinction between: Recently occurring (acute) vs. Long lasting (chronic) Chronic Pain:
 May be the result of sustained noxious input e.g. ongoing inflammation  May be autonomous, with no temporal relationship to the inciting cause  May manifest itself spontaneously, or it may be provoked by various external stimuli; response is typically exaggerated in duration or amplitude, or both  More than 200 clinical syndromes have been classified as chronic pain  Among the most relevant to the veterinary practitioner:  Maladaptive; offers no useful biologic function or survival advantage Objective measures of pain by observation and recording of:
1. Behavioural responses
a. Body Posture b. Attitude/Interaction with caregiver c. Behavior with no caregiver presence d. Presence/Absence of normal things like: eating/drinking; rising to urinate/defecate; moving around cage with comfort; sleeping/dreaming e. Behavior directed at the painful site by licking or chewing f. Responses elicited from movement or manipulation of painful site 2. Physiological responses
a. Heart rate and blood pressure b. Respiratory rate, and particularly character, are generally more sensitive indicators than heart rate; Comparison to pre-operative baseline and/or the trend of RR or HR is also more sensitive 3. Neuroendocrine (cortisol, b-endorphin, catecholamines, etc.)
4. Biochemical markers
5. Locomotor responses
6. Quantitative sensory testing (QST) methods
 Decreased interaction with family and other pets  Elevations in heart rate; breathing; temperature; blood pressure Variations exist within: Species; Breed; Sex; Age; Environmental influences Surgical Pain leads to Varying degrees depending on procedure: Abdominal; Superficial soft-tissue; Orthopedic Don’t forget the “not-so-obvious” vs. obvious causes of pain in animals:  Manual stool evacuation and enemas in constipated patients  Ocular disorders (corneal ulcers, glaucoma) Ohio State University Pain Scoring Chart:
(A ss es s a ft e r R /O n ee d to v oid a nd c ag e S C OR E 0-9
A w a ke , s ee ks w ill ing ly or A sle e p M ay b e n orm a l/ Gu ar d ed bu t v olun ta ry, M od erat e , v oc al izi n g, fo cu se d o n inj u ry M ay b e a bn or ma l/ U nw illi n g to la y d ow n, S ev er e , v oc al izi n g, th ra shi n g A bn orm a l/ Un w illi n g un le ss force d HO SP ITA L
B E HAV IO R SCOR E (1-5)
S ep ar a ti o n An xi e ty , C on stan t vo ca li z in g C al m , A ffe c ti o na te , n o v oc al izi n g C ag e A nx ie ty , C on st a nt vo ca li z in g in C al m i f a lo n e, A gi tat ion if hum an pres e nt Multimodal Analgesia
Aim to impact the pain amplification response in as many places as possible: o NSAIDs e.g. e.g. Firocoxib (Previcox); Meloxicam (Metacam); Carprofen (Rimadyl); Deracoxib (Deramaxx); Ketoprofen (Anafen) o Local anesthetics (blocks, systemic, incisional, catheter) e.g. Lidocaine; o Opioids (systemic/epidural) e.g. Morphine; Hydromorphone; Oxymorphone; o Alpha-2 agonists (epidural) e.g. Medetomidine; Dexmedetomidine ; Xylazine o NMDA Antagonists (systemic) e.g. Ketamine; Dextromethorphan Tramadol: centrally-acting synthetic analgesic; mu-opioid receptor agonist Glucocorticoids: e.g. prednisolone, dexamethasone Gabapentin: GABA (gamma-aminobutyric acid neurotransmitter); mechanism of action as analgesic not entirely known

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