PRINCIPLES OF PAIN MANAGEMENT & ANALGESIA

1. PRINCIPLES OF PAIN MANAGEMENT & ANALGESIA “thERE IS NO COMING TO CONSCIOUSNESS WITHOUT PAIN.” -CARL JUNG

2. PRINCIPLES OF PAIN & ANALGESIA • WHAT IS PAIN? • An unpleasant sensory or emotional experience associated with actual or potential tissue damage • Pain results when nerve cells in the skin or deep tissues, called nociceptors, detect a noxious stimulus • Somatic pain arises from the skin, soft tissues, muscles, bones, or joints • Easily localized through stabbing, throbbing, or aching • Visceral pain arises from internal organs • not easily localized and is characterized by cramping or burning • Referred pain term used to describe the pain that is felt in a body part other than where the actual pain stimulus is coming from • Hyperesthesia is increased sensitivity to a stimulus • Neuropathic pain arises from direct damage to peripheral nerves or the spinal cord. • May be shooting, sharp, or tingling

3. PRINCIPLES OF PAIN & ANALGESIA • WHAT IS PAIN? cont’d • Pain can also be classified according to onset and duration • Acute pain has an abrupt onset and a relatively short duration of action. *Effectively treated with analgesic drugs • Chronic pain has a slow onset, and duration of several months to years. *May be unresponsive to drug therapy

4. PRINCIPLES OF PAIN & ANALGESIA • MONITORING SIGNS OF PAIN • Consider how we as humans display pain vs. how our animal patients display pain. Write some ways you can monitor for pain in animals.

5. PRINCIPLES OF PAIN & ANALGESIA WHAT ABOUT OUR ANIMAL PATIENTS AND/OR OUR JOBS COULD MAKE MONITORING FOR PAIN DIFFICULT?

6. PRINCIPLES OF PAIN & ANALGESIA • MYTHS ABOUT PAIN IN ANIMALS • Consider how some people without medical backgrounds may view the animal’s response to pain

7. PRINCIPLES OF PAIN & ANALGESIA • CONSEQUENCES OF UNTREATED PAIN • Consider the long term effects of untreated pain

8. PRINCIPLES OF PAIN & ANALGESIA • WHAT IS ANALGESIA? • Analgesia is the absence of the awareness of pain, achieved through the use of drugs or other modes of therapy. It applies to the relief of pain without the loss of consciousness. • WHAT ARE THE GOALS FOR PAIN CONTROL? • Control pain at every stage of treatment • to administer analgesics before the patient has an awareness of pain. This is known as preemptive analgesia. • To prevent windup, an event caused by a buildup of chemical mediators that intensify the pain response

9. PRINCIPLES OF PAIN & ANALGESIA • METHODS OF PAIN CONTROL WITHOUT MEDS • Endorphins are endogenous compounds produced by the pituitary gland and the hypothalamus that bind to opioidreceptors during situations of trauma or stress. They resemble opiates in their ability to provide pain relief and a feeling of well-being. “natural pain reliever” • Nursing care: • Other therapies to control pain:

10. THE PHYSIOLOGY OF PAIN

11. PRINCIPLES OF PAIN & ANALGESIA • METHODS OF PAIN CONTROL USING MEDS • OPIOIDS • NSAIDS • LOCAL ANESTHETICS • OTHERS: alpha-2 agonists,ketamine

12. METHODS OF PAIN CONTROL USING MEDS OPIOIDS

13. OPIOIDS • MODE OF ACTION: • Acts on 4 different receptors in the brain and spinal cord • Mu • Kappa • Sigma • Delta • An opioid agent may act as an agonist (stimulating agent) or antagonist (blocking agent) at each receptor • Some opioid agents are considered mixed agonist/antagonists in that they block one type of receptor and stimulate another or partial agonists in that they only partially stimulate opioid receptors • Binding to these receptors can result in a number of effects: • ANALGESIA • Respiratory depression • bradycardia • Sedation • Dysphoria • And others,…

14. OPIOIDS • REVERSIBILITY • One major advantage of opioids is their reversibility with pure antagonists such as NALOXONE, which is the most effective • Naloxone competitively binds to opioid receptors • It is also possible to use a mixed agonist/antagonist such as BUTORPHANOL to reverse the effects of the pure agonists

15. OPIOIDS • MORPHINE: a FULL AGONIST (stimulates all 4 receptors) • Great for moderate to severe pain • Produces significant sedation • Significant cardiovascular & respiratory effects • SIDE EFFECT/CAUTIONS: • Can cause excitement in cats (use lower doses) • Often results in VOMITING • Give slowly IV otherwise severe histamine release can lead to hypotension and pruritis • Other FULL AGONISTS include oxymorphone, hydromorphone, and fentanyl

16. OPIOIDS • FENTANYL: a FULL AGONIST (stimulates all 4 receptors) • the injectable has a rapid onset of action and short duration of action. Onset of action: 2 min; duration of effect: 20-30 min • commonly used as a transdermal skin patch • Fentanyl is slowly absorbed through the skin and may take 4-12 hrs in cats, and 12-24 hrs in dogs to reach therapeutic levels • See pg 230 in your book, Procedure 7-1 for instructions on placing a fentanyl patch.

17. OPIOIDS • BUPRENORPHINE: partial agonist (aka bupi, buprenex) • Delayed onset of action, (40 min IM) but longer duration of action than other opiods – up to 12 hours • Best used for mild to moderate pain • The injectable product is effectively given to cats transmucosally (applied to the gingiva, under the tongue, in cheek pouch) • Can be used to reverse the effects of pure agonists, while maintaining some analgesic effect. Not as effective as naloxone • THIS DRUG IS PART OF THE VTI PROTOCOL FOR DOGS & CATS*

18. OPIOIDS • BUTORPHANOL: mixed agonist/antagonist (aka torb, torbugesic) • Best used for mild to moderate pain; and can also be used as a cough suppressant • Can be used to reverse the effects of pure agonists. Not as effective as naloxone • Commonly combined with a sedative such as dexmedetomidine or acepromazine • MIXING AN OPIOID & SEDATIVE IS KNOWN AS NEUROLEPTANALGESIA

19. OPIOIDS • TRAMADOL: a non-opiate drug that has activity at the mu receptor • Oral tablets • Useful post-operative pain med in dogs and cats • Not currently controlled

20. METHODS OF PAIN CONTROL USING MEDS NSAIDS

21. NSAIDS • MECHANISM OF ACTION: • Inhibits the synthesis of prostaglandins by blocking the enzyme cyclooxygenase ( aka COX-1 & COX-2) • COX-1 leads to the production of beneficial prostaglandins • COX -2 leads to the production of harmful prostaglandins that are present during tissue damage and inflammation.

22. NSAIDS • BENEFITS OF NSAIDS: • No strict record keeping • Little abuse potential • Effective when given orally • No sedative, cardiovascular, or respiratory effects • Antipyretic effects • SIDE EFFECTS/CAUTIONS: • GI upset/GI ulcers due to inhibition of prostacyclin • DO NOT USE CONCURRENTLY w/ STEROIDS • renal toxicity due to inhibition of PGE2 • hepatic toxicity • Inhibits platelet aggregation due to blockage of thromboxane

23. NSAIDS • RIMADYL (carprofen) • Approved for use in DOGS ONLY! • Oral(chewable tablets) and injectable forms available • Less likely to cause side effects mentioned previously due to its COX-2 selectivity • Common uses: • Post-operative pain relief • Pain relief from osteoarthritis and other musculoskeletal injuries • PART OF THE CANINE POST-OP PAIN CONTROL PROTOCOL AT VTI

24. NSAIDS • METACAM (meloxicam) • Approved for use in dogs and cats • COX-2 selective • Oral and injectable formulations available • PART OF FELINE POST-OP PAIN CONTROL PROTOCOL AT VTI

25. METHODS OF PAIN CONTROL USING MEDS LOCAL ANESTHETICS

26. LOCAL ANESTHETICS • WHAT IS LOCAL ANESTHESIA/ANALGESIA? • The use of a chemical agent on sensory neurons to produce a disruption of nerve impulse transmission, leading to temporary loss of sensation

27. LOCAL ANESTHETICS • CHARACTERISTICS OF LOCAL ANESTHETICS • Exert their effects on neurons in the peripheral nervous system and spinal cord that control pain, heat, cold, & pressure • Relatively few effects of the cardiovascular and respiratory systems • Exert their effects in the area closest to the site of injection • Not normally transferred across the placenta • Safe for c-sections

28. LOCAL ANESTHETICS • ROUTES OF ADMINISTRATION • TOPICAL: must penetrate the epidermis to reach the dermis where the peripheral nerves are located • Sprayed on intact skin for superficial procedures such as skin biopsies (ex: ethyl chloride) • Creams can also be applied to desensitize skin for superficial minor procedures (ex: lidocaine/prilocaine) • Splash blocks refer to the use of sprays or anesthetic soaked gauze sponges on open wounds or surgical sites • Applied through a chest tube in patients having thoracic surgery • Should be done when patient is awake • Absorbed through the mucous membranes (larynx, eye, urethra) • Short duration of action and less pain relief when compared to other routes of administration of local anesthetics

29. LOCAL ANESTHETICS • ROUTES OF ADMINISTRATION: • INFILTRATION(injection): • Local anesthetic can be injected subcutaneously, intradermally, or between muscle planes • Ideally the site of injection is clipped and cleaned • Small needle (23-25 gauge) used to prevent tissue damage • Test efficacy by pricking the site with a needle • Do not inject into infected or inflamed tissues • Some local anesthetic drugs are combined with epinephrine • Epinephrine causes vasoconstriction which decreases rate of absorption and prolonging effect • It also decreases the amount of drug entering the circulation, decreasing chances of toxicity. • CAUTION AROUND AN INCISION OR ON EXTREMITIES AND WITH PATIENTS WITH CV ABNORMALITIES

30. LOCAL ANESTHETICS • ROUTES OF ADMINISTRATION • NERVE BLOCKS: Injection of a local anesthetic in the proximity of a specific nerve to desensitize a specific anatomic location. Location of target nerve must be known and palpated if possible. • Lameness exams in horses • Cornual blocks for dehorning cattle • Dental blocks in dogs and cats • Infiltration of nerves during amputation of a limb • Declawing cats • May take 15-20 minutes for absorption • Nerve blocks include line blocks and ring blocks

31. Cornual blocks for dehorning cattle THIS NERVE BLOCK IS ALSO A RING BLOCK

32. Dental blocks for tooth extractions Maxillary Nerve block via The infraorbital foramen

33. NERVE BLOCKS Nerve blocks help pinpoint areas of pain Paravertebral block THESE ARE EXAMPLES OF LINE BLOCKS

34. NERVE BLOCKS THIS NERVE BLOCK IS ALSO A RING BLOCK

35. LOCAL ANESTHETICS • ROUTES OF ADMINISTRATION • NERVE BLOCKS • LINE BLOCKS: continuous line of local anesthetics placed SQ in an area served by numerous small nerves • The needle is inserted along the line of infiltration and the anesthetic is injected as the needle is withdrawn • If placed encircling an anatomic part, it is called a RING BLOCK • INTRAARTICULAR: injecting local anesthetics directly into a joint usually after surgery of the joint, immediately after closure of the joint capsule

36. LOCAL ANESTHETICS • ROUTES OF ADMINISTRATION • EPIDURAL: blockage of sensory and motor nerves in the rear, abdomen, pelvis, tail, hind limbs, and perineum • Anesthetist must be familiar with the anatomy of the terminal spinal cord and lumbosacral vertebrae Epidural space Dura mater arachnoid Subarachnoid space w/CSF Pia mater Spinal cord

37. LOCAL ANESTHETICS EPIDURALS http://www.youtube.com/watch?v=zmwvMHZG_5g

38. SIDE EFFECTS OF LOCAL ANESTHETICS • Allergy • Rash or hives in the area • Systemic toxicity • Sedation, nausea, restlessness, hyperexcitability, seizures, respiratory suppression, coma • Infection (esp. w/epidurals) • Cranial infiltration of an epidural may cause serious toxicity, respiratory suppression • death

39. METHODS OF PAIN CONTROL USING MEDS OTHERS: ALPHA-2 AGONISTS KETAMINE

40. ALPHA-2 AGONISTS • ALPHA-2 AGONISTS (ex: dexdomitor, xylazine) • Short duration of action (~90 minutes) • Also causes profound sedation, bradycardia • Commonly combined with butorphanol • Reversible • KETAMINE • Good effect for skin and SQ pain • Duration of action is short 30min

41. METHODS OF PAIN CONTROL • Combining drugs from different categories (multi-modal therapy, balanced analgesia) is more beneficial than using high doses of one medication. • Pain is alleviated via different pathways