The document discusses pain management and analgesia. It outlines the consequences of untreated pain such as wasting, immune suppression, and increased risk of complications. It then covers the physiology of pain, types of pain responses, signs of pain, behavioral responses, and methods of pain assessment. Finally, it discusses various pharmacological agents for perioperative pain management including opioids, NSAIDs, local anesthetics, and other drugs, outlining their mechanisms of action, uses, and potential adverse effects.

1. Pain Management
and Analgesia
Review

2. Consequences of Untreated Pain
 Catabolic state, may lead to wasting
 Immune suppression
 Inflammation
 Increased anesthetic risk
 Higher inhalant requirement
 Patient suffering

3. Physiology of Pain/Types of Pain
 Nociception- Detection by nervous system of
potential for or actual occurrence of tissue injury
 Pain pathway
 Physiologic pain- Minimal or no tissue injury
 Protective sensation of pain
 Pathologic pain- Pain that occurs after tissue injury
 Acute or chronic
 Classification
 Mechanism: inflammation, neuropathic, cancer, idiopathic
 Origin: visceral, somatic
 Severity: none, mild, moderate, or severe

5. Pain Response
 Mediators- Substances released with peripheral
tissue trauma
 Attract inflammatory cells
 Increase sensitivity of peripheral pain receptors
 Primary hyperalgesia – Peripheral
hypersensitivity
 Painful area close to the site of tissue injury
 Central nervous system hypersensitivity/“wind
up” - Hyperexcitable central neurons that are
sensitive to low-intensity peripheral stimuli
 NMDA receptor activation

6. Physiologic Signs of Pain
 Cardiovascular
 Hypertension
 Tachycardia/tachyarrhythmia
 Peripheral vasoconstriction (pale
MM)
 Respiratory
 Tachypnea
 Shallow breathing
 Exaggerated abdominal
breathing
 Panting (dogs)
 Open mouth breathing (cats)
 Ophthalmic
 Mydriasis http://www.bellevueanimalhospital.com/services.html

7. Behavioral Responses to Pain
 Varies with signalment,
temperament
 Changes in gait, activity level
 Lameness, stiffness, reluctance to move
 Exercise intolerance/decreased performance
 Vocalization
 Whining, growling, groaning, purring in SA
 Groaning, grunting, biting, kicking (LA)
 Facial expressions, appearance,
attitude
 Bruxism (LA)
 Poor grooming habits
 Hiding

8. Pain Assessment
 NO pain
 MILD pain
 MODERATE pain
 SEVERE pain
 Review pages 211-212 of Lerche and
1048-1050 of McCurnin on assessing
pain.

9. Perioperative Pain Management
 Preemptive analgesia and multimodal therapy are KEY to
successful perioperative analgesia
 Pain medication usually administered preemptively as part
of pre-medication
 Pharmacological agents for analgesia
 Opioids
 Nonsteroidal antiinflammatory drugs (NSAIDs)
 Local anesthetics
 Alpha2-agonists
 Ketamine
 Amantadine
 Corticosteroids
 Tramadol
 Gabapentin
 Tranquilizers

10. Opioids- Controlled Class
 Can be used for moderate to severe pain
 Can be given IV, CRI, IM, SC, PO, or via
transdermal patch
 Morphine
 Oxymorphone
 Hydromorohone
 Methadone (also NMDA receptor antagonist)
 Meperidine
 Fentanyl
 Buprenorphine
 Butorphanol
 (Nalbuphine – NOT controlled; reversal agent)

11. Opiods Mechanism
 Opioid receptors in brain and spinal dorsal horn cells
 Opioid receptors
 Mu1, Mu2, Kappa, Delta
 Modulate the pain and its perception

12. Opioid Classes
 Pure agonists
 Antagonists
 Partial agonists
 Mixed agonists-antagonists

13. Use of Opioids
 Injectable premedications in combination with
tranquilizer
 Neuroleptanalgesia (higher doses)
 Postoperative pain control with or without other agents
 Short duration of effect, potential for adverse effects
 IV infusion for constant, unremitting pain
 Intraarticular use (elbow, stifle surgery)
 8-12 hours of postoperative analgesia
 Epidural use (after induction, before surgery)
 6-24 hours of analgesia – can prolong with epidural catheter
 Transdermal use (fentanyl) – apply at least 6-12 hours before
procedure
 3-5 days of analgesia

14. Pure Agonists
 Produce a maximal response
 Pure mu agonist is best analgesia
 Impossible to separate analgesia from respiratory
depression
 e.g., morphine, fentanyl, meperidine, hydromophone,
oxymorphone

15. Partial Agonists
 Produce a submaximal response
 Dose-response curve
 less steep
 ceiling effect
 bell shaped
 Co-administration of partial + pure Agonists
antagonize the agonist
 Much less analgesia but less respiratory
depression
 Tendency to cause dysphoria so less abused
 e.g., buprenorphine, nalbuphine, diprenorphine

16. Antagonists
 Competitively reverse (antagonize) agonists
 Low (or no) intrinsic activity
 e.g., naloxone, nalmefene, naltrexone

17. Mixed Agonists-Antagonists
 Divergent activities on different receptors
 Agonist at one receptor (e.g., kappa + delta)
 Antagonist at another (e.g., mu);
 e.g., pentazocine, butorphanol

18. NSAIDs
 Analgesics for somatic (musculoskeletal) pain +/-
visceral pain
 Potent anti-inflammatory properties
 Some are antipyretic
 Work by inactivating cyclooxygenase (COX), an
enzyme needed for prostaglandin production
 Prostaglandins are a group of extremely potent chemicals
responsible for pain and inflammation as well as
“housekeeping” functions
 COX-1 and COX-2 isoenzymes
 COX-2 selective or specific NSAIDs less likely to cause GI
ulceration
 Effects on isoenzymes determine potency and severity/type of
adverse effects

19. NSAIDs
 Significant variation in duration of effect between
species
 Prolonged aspirin half-life (38 hours) in cat due to decreased
glucuronyl transferase levels
 Significant variation in NSAID toxicity between species
 Acetaminophen extremely toxic to cats
 Adverse effects
 Gastrointestinal problems – vomiting, ulceration
 Renal toxicity
 Dehydrated, hypotensive patients
 How do we screen for renal insufficiency?
 Impaired platelet function  prolonged bleeding times
 Liver damage (idiosyncratic reaction to carprofen in Labradors)

20. Contraindications for NSAIDs
 Presence of renal or hepatic dysfunction
 Coagulopathies
 GI disorders
 Shock
 Hypotension/hypovolemia
 Hypoalbuminemia
 Pregnancy
 Corticosteroids