7. Analgesia


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  • Some diseases or surgeries may result in more than one type of pain.
  • Multimodal therapy involves using several analgesic drugs, each with a different mechanism of action. This results in lower doses of each drug used, which will decrease adverse side effects and improve safety.
  • Rate pain as absent, mild, moderate, or severe. Not suitable for chronic pain or subtle changes in pain level.
  • Assigns point values to physiologic parameters, locomotor activity, and behavior. Each category is subdivided into different descriptors, which in turn are awarded different points. All points are added together and the higher the total, the more painful the animal. Are frequently customized for specific types of pain.
  • Consists of a ruler in which the left end of the line is no pain and the right end of the line is the worst pain imaginable for a specific disease or surgical procedure. An ‘X’ is placed on the ruler corresponding to the level of pain the assessor feels the animal is experiencing.
  • These are customized assessment forms that combine different types of pain assessment tools.
  • If analgesics are administered as part of the anesthetic premedication they should provide or enhance sedation. Drugs that do this are opioids, alpha 2 -adrenoceptor agonists, and ketamine.
  • Morphine administered IV must be given slowly to prevent release of histamine that can result in a fall in blood pressure, flushing, and pruritus. IM injection will give a longer duration of action but may be painful to the patient. SC injections are less painful but have a longer onset of action. Most side effects from morphine are seldom a significant problem in patients in pain treated with an analgesic dose.
  • Rapid IV administration to cats may cause excitement. Rarely used in large animals because of cost and lack of information regarding efficacy. Not commonly used in small animals because of cost.
  • Rarely used in large animals because of lack of information about efficacy or adverse side effects.
  • Butorphanol can be used in dogs, cats, horses, and ruminants.
  • Administering opioids by alternative routes constitutes “off label” use and the owner’s consent should be obtained prior to administration.
  • Epidural injections should not be administered to patients with septicemia, local infections in the lumbosacral space, bleeding disorders, spinal trauma, or neurologic disease of the spinal cord. Epidural injections are difficult in obese patients. Epidural hematomas and abscesses may form as a result of an improper or unsterile technique.
  • Don’t use butorphanol or buprenorphine in combination with fentanyl because they may partially block the opioid receptors, reducing the analgesic effect of fentanyl.
  • Because of the danger of accidental human exposure, some veterinary practices use the patch only on hospitalized patients. If an animal is sent home with the patch on, the patch may be swallowed by a child. Clients should be well-educated if a patient is discharged with a patch.
  • Some are antipyretic. Administered orally as a tablet or liquid; some are now available for injection.
  • The duration of effect varies with species (e.g., from 1 hour [horse] to 38 hours [cat]). Toxicity varies with species (e.g., acetaminophen is toxic to cats; ibuprofen is toxic to dogs and cats).
  • Acetaminophen in cats: a 325-mg capsule can cause acute hepatotoxicosis within 4 hours.
  • The effectiveness of some of these therapies has not been demonstrated in controlled studies.
  • 7. Analgesia

    1. 1. Controlling Pain Analgesia Chapter 7
    2. 2. Physiology of Pain <ul><li>Nociception: detection by the nervous system for the potential for, or actual tissue injury </li></ul><ul><ul><li>Protects animal from painful or noxious stimuli </li></ul></ul><ul><li>Physiologic pain </li></ul><ul><ul><li>Ouch pain </li></ul></ul><ul><ul><li>Little or no tissue injury </li></ul></ul><ul><li>Pathologic pain </li></ul><ul><ul><li>Follows tissue injury </li></ul></ul><ul><ul><li>Acute or chronic </li></ul></ul>
    3. 3. Pathologic Pain <ul><li>Classification based on mechanism </li></ul><ul><ul><li>Inflammatory, neuropathic, cancer, idiopathic </li></ul></ul><ul><li>Classification based on origin </li></ul><ul><ul><li>Visceral or somatic: superficial or deep </li></ul></ul><ul><li>Classification based on severity of pain </li></ul><ul><ul><li>None, mild, moderate, severe </li></ul></ul>
    4. 4. Nociception: The Pain Pathway <ul><li>Step 1: transduction </li></ul><ul><ul><li>Transformation of stimuli into sensory electrical signals (action potentials) </li></ul></ul><ul><li>Step 2: transmission </li></ul><ul><ul><li>Sensory impulses conducted to spinal cord </li></ul></ul><ul><li>Step 3: modulation </li></ul><ul><ul><li>Impulses are either amplified or suppressed </li></ul></ul><ul><li>Step 4: perception </li></ul><ul><ul><li>Impulses are transmitted to the brain where they are processed and recognized </li></ul></ul>
    5. 5. Nociception: The Pain Pathway (Cont’d) <ul><li>Each step has different receptors </li></ul><ul><li>Drugs can be selected that will target specific receptors and block a specific step </li></ul><ul><ul><li>Multimodal therapy: targeting two or more of the receptors </li></ul></ul>
    6. 6. Consequences of Untreated Pain <ul><li>Catabolism and wasting </li></ul><ul><li>Immune system suppression </li></ul><ul><li>Inflammation and delayed wound healing </li></ul><ul><li>Anesthetic risk and increased anesthesia doses </li></ul><ul><li>Patient suffering </li></ul>
    7. 7. Primary Hyperalgesia <ul><li>Peripheral hypersensitivity </li></ul><ul><li>Results from tissue damage and constant stimulation of nerves </li></ul><ul><li>Area close to the site of tissue injury becomes painful when stimulated with non-noxious stimuli </li></ul>
    8. 8. Secondary Hyperalgesia <ul><li>Central nervous system hypersensitivity or windup </li></ul><ul><li>Area of hypersensitivity is further away from the site of tissue injury </li></ul><ul><li>Results from constant stimulation of spinal cord neurons </li></ul><ul><li>Neurons become hyperexcitable and sensitive </li></ul>
    9. 9. Physiologic Changes Caused by Pain <ul><li>Neuroendocrine changes: can result in a catabolic state and wasting </li></ul><ul><ul><li>ACTH release </li></ul></ul><ul><ul><li>Elevated cortisol, norepinephrine, and epinephrine </li></ul></ul><ul><ul><li>Decreased insulin </li></ul></ul><ul><li>Sympathetic stimulation: can result in cardiac arrhythmias </li></ul><ul><ul><li>Vasoconstriction </li></ul></ul><ul><ul><li>Increased myocardial work </li></ul></ul><ul><ul><li>Increased myocardial oxygen consumption </li></ul></ul>
    10. 10. Signs of Pain in Animals <ul><li>Pain elicits a stress response </li></ul><ul><li>Stress-related pain results in “fight-or-flight” physiological response </li></ul><ul><li>Avoid anthropomorphosis </li></ul>
    11. 11. Preemptive Analgesia <ul><li>Administration of pain medication before the pain occurs </li></ul><ul><li>Commonly involves adding analgesic to premedication prior to anesthesia </li></ul><ul><li>Reduces overall requirement for analgesia and duration of administration </li></ul><ul><li>Prevents windup </li></ul>
    12. 12. Behavioral Responses to Pain <ul><li>Vary depending on species, age, breed, and temperament </li></ul><ul><ul><li>Young patients less tolerant </li></ul></ul><ul><ul><li>Cattle very stoic </li></ul></ul><ul><ul><li>Large dog breeds more stoic than small toy breeds </li></ul></ul><ul><ul><li>Cats hide; dogs seek owner comfort; herd animals separate themselves </li></ul></ul><ul><li>Vary depending on nature, duration, and severity of pain </li></ul><ul><li>Vary on the presence or absence of humans </li></ul>
    13. 13. Physical Evidence of Pain <ul><li>Changes in gait and level of activity </li></ul><ul><ul><li>Evidence of arthritic pain </li></ul></ul><ul><li>Reluctance to lie down or constantly shifting position </li></ul><ul><ul><li>Evidence of thoracic or abdominal pain </li></ul></ul>
    14. 14. Physical Evidence of Pain (Cont’d) <ul><li>Vocalization </li></ul><ul><ul><li>Whine, growl, whimper, groan, snarl, bite, hiss, grunt, or purr </li></ul></ul><ul><ul><li>Emergence delirium </li></ul></ul><ul><ul><ul><li>Immediate postoperative vocalization </li></ul></ul></ul><ul><li>Changes in facial expressions, appearance, and attitude </li></ul>
    15. 15. Pain Assessment Tools <ul><li>Verbal rating scales </li></ul><ul><li>Simple descriptive scales </li></ul><ul><li>Numeric rating scales </li></ul><ul><li>Visual analogue scales </li></ul><ul><li>Comprehensive scales </li></ul>
    16. 16. Pain Assessment Tools: Verbal Rating Scales and Simple Descriptive Scales
    17. 17. Pain Assessment Tools: Numeric Rating Scales
    18. 18. Pain Assessment Tools: Visual Analogue Scales
    19. 19. Pain Assessment Tools: Comprehensive Scales
    20. 20. Assessing Response to Therapy <ul><li>Acute surgical pain vs. chronic pain </li></ul><ul><li>Hourly vs. monthly </li></ul><ul><li>With effective analgesia, pain-associated behaviors will recede </li></ul><ul><ul><li>Appetite, grooming, body position or posture, interaction with people </li></ul></ul><ul><li>With effective analgesia, pain assessment scores will decrease </li></ul>
    21. 21. Effective Postoperative Analgesia
    22. 22. Perioperative Pain Management <ul><li>Preemptive analgesia </li></ul><ul><ul><li>Begins in preoperative period with premedication </li></ul></ul><ul><ul><li>May be administered as part of anesthetic premedication </li></ul></ul><ul><ul><li>Transdermal fentanyl patch </li></ul></ul><ul><ul><li>NSAIDs primarily in large animals </li></ul></ul><ul><li>Multimodal therapy </li></ul><ul><ul><li>The use of more than one drug to control pain </li></ul></ul><ul><ul><li>Cover multiple receptors and mechanisms of action </li></ul></ul><ul><ul><li>Reduce dose of individual drugs and anesthetic agent </li></ul></ul>
    23. 23. Pharmacologic Analgesic Therapy <ul><li>Analgesia is needed at every stage of hospitalization and treatment </li></ul><ul><ul><li>Preanesthetic period </li></ul></ul><ul><ul><li>Surgical period </li></ul></ul><ul><ul><li>Immediately postoperative period </li></ul></ul><ul><ul><li>Remainder of hospital stay </li></ul></ul><ul><ul><li>At home </li></ul></ul>
    24. 24. Pharmacologic Analgesic Therapy (Cont’d) <ul><li>Choice of drug depends on: </li></ul><ul><ul><li>Severity and type of pain </li></ul></ul><ul><ul><li>Patient’s general condition </li></ul></ul><ul><ul><li>Route of delivery </li></ul></ul>
    25. 25. Using Opioids as Analgesics <ul><li>Vary in potency, duration, and adverse effects </li></ul><ul><li>Injectable premedication </li></ul><ul><ul><li>Often in combination with a tranquilizer (acepromazine or dexmedetomidine) </li></ul></ul><ul><ul><li>Diminish windup </li></ul></ul><ul><ul><li>Duration of action is 2-4 hours, so not good for postoperative pain </li></ul></ul><ul><li>Induce state of potent sedation </li></ul><ul><ul><li>Neuroleptanalgesia </li></ul></ul><ul><ul><li>Provides analgesia throughout surgery and for some time postoperatively </li></ul></ul>
    26. 26. Using Opioids as Analgesics (Cont’d) <ul><li>Postoperative analgesia </li></ul><ul><ul><li>Alone or in combination with other drugs </li></ul></ul><ul><li>Sedative and antianxiety drug </li></ul><ul><ul><li>Excitement in awake cats and horses </li></ul></ul><ul><li>Gastrointestinal effects </li></ul><ul><ul><li>Initial increased gastrointestinal activity: nausea, vomiting, defecation </li></ul></ul><ul><ul><li>Followed by a slow down in gastrointestinal activity: ileus, colic, constipation </li></ul></ul><ul><li>Metabolized in the liver </li></ul>
    27. 27. Opioid Agents: Morphine <ul><li>Schedule II drug (United States) and narcotic (Canada) </li></ul><ul><li>Used for moderate to severe visceral or somatic pain </li></ul><ul><ul><li>Preanesthetic and analgesic </li></ul></ul><ul><ul><li>Pure agonist with affinity for mu and kappa opioid receptors </li></ul></ul><ul><ul><li>May cause excitement or dysphoria in cats and horses </li></ul></ul><ul><ul><li>May cause restlessness in dogs and horses </li></ul></ul>
    28. 28. Opioid Agents: Morphine (Cont’d) <ul><li>Administered IV, IM, SC, intraarticular, epidural, or spinal injection </li></ul><ul><li>Adverse side effects </li></ul><ul><ul><li>Initial gastrointestinal stimulation in dogs and cats </li></ul></ul><ul><ul><li>Ileus and colic development in horses </li></ul></ul><ul><ul><li>Excitement, miosis (dogs), mydriasis (cats), hypothermia, hyperthermia (cats) </li></ul></ul><ul><ul><li>Bradycardia, panting, increased intraocular pressure, urinary retention </li></ul></ul><ul><ul><li>Physical addiction (humans) </li></ul></ul>
    29. 29. Opioid Agents: Oxymorphone <ul><li>Pure opioid agonist </li></ul><ul><li>Greater analgesic potency and sedative effect than morphine </li></ul><ul><li>Fewer side effects and longer duration of effect than morphine </li></ul><ul><li>Fewer tendencies to induce vomiting </li></ul><ul><li>Administered IV, IM, SC, or epidural </li></ul><ul><ul><li>May use concurrently with a tranquilizer </li></ul></ul><ul><li>Expensive Schedule II drug (United States) and narcotic (Canada) </li></ul>
    30. 30. Opioid Agents: Hydromorphone <ul><li>Opioid agonist </li></ul><ul><li>Less potency but similar duration of effect compared with oxymorphone </li></ul><ul><li>Administered IV, IM, SC to dogs and cats </li></ul><ul><ul><li>Used as a premedication alone or with a tranquilizer </li></ul></ul><ul><li>Less expensive than oxymorphone </li></ul><ul><li>Schedule II drug (United States) and narcotic (Canada) </li></ul>
    31. 31. Opioid Agents: Methadone <ul><li>Synthetic opioid </li></ul><ul><li>Characteristics similar to oxymorphone and hydromorphone </li></ul><ul><li>Least likely to cause vomiting in cats and dogs </li></ul><ul><li>Antagonist at the NMDA receptor </li></ul>
    32. 32. Opioid Agents: Fentanyl <ul><li>One of the most potent analgesics known </li></ul><ul><li>Rapid onset (2 minutes) and short duration of effect (20-30 minutes) when administered IV </li></ul><ul><li>Administered by continuous IV drip, transdermal patch, IM, SC, or epidural injection </li></ul><ul><ul><li>Used in combination with midazolam or diazepam drawn into separate syringes </li></ul></ul><ul><li>Schedule II drug (United States) and narcotic (Canada) </li></ul>
    33. 33. Opioid Agents: Meperidine/Pethidine <ul><ul><li>Pure opioid agonist with less potent analgesic properties and shorter duration of action </li></ul></ul><ul><ul><li>Administered by SC injection </li></ul></ul><ul><ul><li>Wide margin of safety </li></ul></ul><ul><ul><li>Used mostly as a preanesthetic in combination with atropine or acepromazine </li></ul></ul><ul><ul><li>When used with a tranquilizer, it provides effective neuroleptanalgesia in puppies </li></ul></ul><ul><ul><li>Used with injectable NSAIDs to provide analgesia before NSAIDs take effect </li></ul></ul><ul><ul><li>Schedule II drug (United States) and narcotic (Canada) </li></ul></ul>
    34. 34. Opioid Agents: Butorphanol <ul><li>Synthetic opioid with agonist and antagonist properties </li></ul><ul><ul><li>Stimulates kappa receptors and blocks mu receptors </li></ul></ul><ul><ul><li>Not as effective an analgesic as a pure agonist </li></ul></ul><ul><ul><li>Produces less sedation, dysphoria, and respiratory depression </li></ul></ul><ul><ul><li>Can be used to reverse the effects of morphine and fentanyl </li></ul></ul>
    35. 35. Opioid Agents: Butorphanol (Cont’d) <ul><li>Used as a preanesthetic, sedative, and postoperative visceral analgesic </li></ul><ul><li>Administered IV, IM, SC, or orally (as tablets for long-term analgesia) </li></ul><ul><ul><li>Constant rate infusion IV can prevent redosing </li></ul></ul><ul><li>Schedule IV drug (United States) and controlled drug (Canada) </li></ul>
    36. 36. Opioid Agents: Buprenorphine <ul><li>A partial mu agonist that produces some analgesia for mild to moderate pain </li></ul><ul><ul><li>Used to provide postoperative analgesia to dogs and cats </li></ul></ul><ul><ul><li>Can be used to reverse the effects of morphine and fentanyl </li></ul></ul><ul><li>Administered IV, IM, or epidural; orally to cats </li></ul><ul><li>Delayed onset of action and longer duration of analgesia </li></ul><ul><li>Used with a sedative it can prolong sleep times </li></ul><ul><li>Expensive Schedule V drug (United States) and unavailable in Canada </li></ul>
    37. 37. Opioid Agents: Nalbuphine <ul><li>Kappa agonist and mu antagonist with greater antagonist properties than butorphanol </li></ul><ul><ul><li>Weak analgesic and sedative </li></ul></ul><ul><ul><li>Used as a reversal agent for opioid agonists </li></ul></ul><ul><ul><li>Fewer adverse effects </li></ul></ul><ul><li>Not a controlled drug in the United States </li></ul>
    38. 38. Opioids as Postoperative Analgesics <ul><li>Administered IM or SC before animal regains consciousness </li></ul><ul><ul><li>Injections repeated as necessary </li></ul></ul><ul><ul><li>Alternative routes (IV, epidural, intraarticular, transdermal patch) minimize adverse effects </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>Short duration of action </li></ul></ul><ul><ul><li>Potential adverse reactions: respiratory depression, bradycardia, excitement, apprehension, hypersalivation, mydriasis, excessive sedation, panting, increased sensitivity to sound, urinary retention, gastrointestinal effects </li></ul></ul>
    39. 39. Opioids: Intravenous Infusion <ul><li>Morphine, fentanyl, oxymorphone, hydromorphone, methadone, butorphanol </li></ul><ul><li>Provides continuous analgesia for constant, unremitting pain </li></ul>
    40. 40. Opioids: Intravenous Infusion (Cont’d) <ul><li>Initial loading dose given to effect followed by same dose given over 4 hours through constant flow </li></ul><ul><ul><li>Drug may be added to a bag of fluids if an automated infusion pump is not available </li></ul></ul><ul><ul><li>Monitor patient frequently for adequate pain control, excessive sedation, or adverse effects </li></ul></ul><ul><ul><li>Adjust rate of administration according to patient response </li></ul></ul><ul><li>Morphine (for example) can administered with lidocaine or lidocaine/ketamine to control severe pain </li></ul>
    41. 41. Opioids: Intraarticular Injection <ul><li>Especially useful after elbow or stifle surgery </li></ul><ul><li>Morphine diluted in saline instilled into joint via catheter </li></ul><ul><ul><li>Immediately after joint closure </li></ul></ul><ul><ul><li>Can be combined with a local anesthetic (e.g., bupivacaine) </li></ul></ul><ul><ul><li>Provides 8-10 hours postoperative analgesia </li></ul></ul>
    42. 42. Opioids: Epidural Injection <ul><li>Instillation of opioid into epidural space at lumbosacral junction </li></ul><ul><ul><li>To provide analgesia to hind limbs, abdomen, caudal thorax, pelvis, tail </li></ul></ul><ul><ul><li>Morphine is the most commonly used drug </li></ul></ul><ul><ul><li>May be combined with an alpha 2 -agonist in large animals </li></ul></ul><ul><ul><li>Profound postoperative analgesia with long duration of action </li></ul></ul>
    43. 43. Opioids: Epidural Injection (Cont’d) <ul><li>Instillation of an opioid into the epidural space at the lumbosacral junction </li></ul><ul><ul><li>Administer after induction of anesthesia, but before surgical procedure begins </li></ul></ul><ul><ul><li>Onset of action: 20-60 minutes </li></ul></ul><ul><ul><li>Duration of action 6-24 hours </li></ul></ul><ul><ul><li>Must be supplemented with general anesthesia for surgical procedures </li></ul></ul><ul><ul><li>Reposition animals every 2-4 hours to prevent pulmonary atelectasis or prolonged pressure on superficial nerves </li></ul></ul>
    44. 44. Opioids: Transdermal Use <ul><li>Fentanyl transdermal patch </li></ul><ul><ul><li>Reservoir of fentanyl enclosed in plastic </li></ul></ul><ul><ul><li>Attached to clipped skin and left in place for several days </li></ul></ul><ul><ul><li>Comes in various sizes (25 mcg/hr; 50 mcg/hr; 75 mcg/hr; 100 mcg/hr) </li></ul></ul><ul><ul><li>Large animals may require more than one patch </li></ul></ul>
    45. 45. Opioids: Transdermal Use (Cont’d) <ul><li>Provide convenient, long-term opioid administration </li></ul><ul><ul><li>Similar to IM oxymorphone injection but longer duration of action </li></ul></ul><ul><ul><li>Delay of action from 4 to 12 hours (cats) or 12 to 24 hours (dogs) as drug is absorbed through the skin </li></ul></ul><ul><ul><li>Apply patch at least 6-12 hours prior to the start of surgery </li></ul></ul><ul><ul><li>Supplement with another opioid or NSAID if patch isn’t applied until after surgery </li></ul></ul>
    46. 46. Opioids: Fentanyl Patch <ul><li>Use: Provide analgesia for postoperative pain and pain associated with trauma, burns, cancer, and painful abdominal conditions </li></ul><ul><ul><li>Amount of drug absorbed through skin varies among animals </li></ul></ul><ul><ul><li>Monitor for breakthrough pain and supplement as necessary </li></ul></ul><ul><ul><li>Monitor for fentanyl overdose </li></ul></ul><ul><ul><ul><li>Ataxia and sedation (dogs) </li></ul></ul></ul><ul><ul><ul><li>Dysphoria and disorientation (cats) </li></ul></ul></ul><ul><ul><li>Remove patch if necessary </li></ul></ul>
    47. 47. Opioids: Fentanyl Patch (Cont’d) <ul><li>Heat may increase the amount of fentanyl absorbed </li></ul><ul><ul><li>Avoid using in animals with fevers </li></ul></ul><ul><ul><li>Avoid contact of patch with external sources of heat (e.g., hot water bottles) </li></ul></ul>
    48. 48. Nonsteroidal Antiinflammatory Drugs <ul><li>NSAIDs or nonsteroidal antiinflammatory analgesics (NSAAs) </li></ul><ul><ul><li>Acetylsalicylic acid (aspirin) Carprofen </li></ul></ul><ul><ul><li>Acetaminophen Etodolac </li></ul></ul><ul><ul><li>Meloxicam Tolfenamic acid </li></ul></ul><ul><ul><li>Ketoprofen Deracoxib </li></ul></ul><ul><ul><li>Firocoxib </li></ul></ul>
    49. 49. Nonsteroidal Antiinflammatory Drugs (Cont’d) <ul><li>Mechanism of action </li></ul><ul><ul><li>Efficacy: somatic and visceral pain (varies by drug) </li></ul></ul><ul><ul><li>Onset of action: 30-60 minutes </li></ul></ul><ul><ul><li>Duration of effect varies with species </li></ul></ul><ul><ul><li>Toxicity varies with species </li></ul></ul><ul><ul><li>Analgesic and antiinflammatory properties vary by drug </li></ul></ul><ul><ul><li>Inhibit prostaglandin synthesis by inactivating COX isoenzymes </li></ul></ul><ul><li>Metabolized in the liver; eliminated by the kidneys and the gastrointestinal tract </li></ul>
    50. 50. Adverse Effects of NSAIDs <ul><li>Prevent the production of beneficial prostaglandins along with the production of prostaglandins that mediate pain, inflammation, and fever </li></ul><ul><li>NSAIDs that inhibit the COX-2 enzyme but not the COX-1 enzyme produce the least adverse effects </li></ul><ul><li>The perfect NSAID is not available yet </li></ul>
    51. 51. Adverse Effects of NSAIDs (Cont’d) <ul><li>Adverse effects vary with drug, species, breed, and individual animals </li></ul><ul><ul><li>Stomach ulcers, vomiting, gastrointestinal bleeding, lack of appetite </li></ul></ul><ul><ul><li>Gastrointestinal ulceration leading to hemorrhage </li></ul></ul><ul><ul><li>Renal toxicity </li></ul></ul><ul><ul><li>Impaired platelet aggregation leading to prolonged bleeding time </li></ul></ul><ul><ul><li>Liver damage </li></ul></ul><ul><ul><li>Antagonist to several drugs prescribed for cardiac disease and hypertension </li></ul></ul>
    52. 52. Other Analgesic Agents <ul><li>Opioids and NSAIDs are the most commonly used analgesics </li></ul><ul><li>Local anesthetics, alpha 2 -adrenergic agonists, and ketamine are also used as analgesics in special circumstances </li></ul>
    53. 53. Local Anesthetics as Analgesics <ul><li>Used to prevent or treat postoperative pain </li></ul><ul><ul><li>Sprayed or injected at the site of injury or surgical site or infiltrated around a nerve supplying the affected area </li></ul></ul><ul><ul><li>Desensitize the entire region (epidural or IV infusion) </li></ul></ul>
    54. 54. Local Anesthetics as Analgesics (Cont’d) <ul><li>Advantages </li></ul><ul><ul><li>Complete anesthesia of affected area </li></ul></ul><ul><ul><li>Low toxicity </li></ul></ul><ul><ul><li>Rapid onset of action </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>Short duration of action </li></ul></ul><ul><ul><li>CNS and cardiac toxicity with repeated use </li></ul></ul>
    55. 55. Alpha 2 -Adrenoceptor Agonists as Analgesics <ul><li>Limited use in small animals </li></ul><ul><ul><li>Short duration of analgesic effect </li></ul></ul><ul><ul><li>Profound sedative effect </li></ul></ul><ul><ul><li>Adverse effects: respiratory depression, vomiting, bradycardia, heart block, hypotension </li></ul></ul><ul><ul><li>When used in low doses may potentiate opioid effects and increase quality of postoperative analgesia </li></ul></ul><ul><ul><li>Produce significant analgesia via the epidural route alone or with other agents </li></ul></ul>
    56. 56. Alpha 2 -Adrenoceptor Agonists as Analgesics (Cont’d) <ul><li>Used in horses to provide sedation, muscle relaxation, and analgesia </li></ul><ul><ul><li>Xylazine, detomidine, romifidine </li></ul></ul><ul><ul><li>Horses remain standing but may become ataxic </li></ul></ul><ul><ul><li>Analgesia okay for moderately to severely painful diseases or procedures </li></ul></ul><ul><ul><li>Adverse effects </li></ul></ul><ul><ul><ul><li>Cardiovascular effects, respiratory effects, GI effects </li></ul></ul></ul><ul><li>Reversal with alpha 2 -adrenoceptor antagonists will also reverse sedation and analgesia </li></ul>
    57. 57. Ketamine as an Analgesic <ul><li>Used as an adjunct to more potent analgesics (opioids, local anesthetics, alpha 2 -agonists) </li></ul><ul><ul><li>Doesn’t produce analgesia by itself </li></ul></ul><ul><ul><li>MLK (morphine, lidocaine, ketamine) provides intraoperative analgesia </li></ul></ul><ul><li>Blocks NMDA at the level of the spinal cord to prevent windup </li></ul><ul><li>Use a lower dose than the one used to induce anesthesia </li></ul>
    58. 58. Ketamine as an Analgesic (Cont’d) <ul><li>Adverse effects: dose-related effects rarely seen at analgesic levels </li></ul><ul><ul><li>Tachycardia </li></ul></ul><ul><ul><li>Hypertension </li></ul></ul><ul><ul><li>Seizures </li></ul></ul><ul><ul><li>Postoperative delirium </li></ul></ul><ul><ul><li>Increased intraocular and intracranial pressure </li></ul></ul><ul><ul><li>Salivation </li></ul></ul>
    59. 59. Corticosteroids as Analgesics <ul><li>Strong antiinflammatory properties </li></ul><ul><ul><li>Decrease prostaglandin activity such as NSAIDs </li></ul></ul><ul><ul><li>Don’t use concurrently with NSAIDs </li></ul></ul><ul><li>Adverse effects </li></ul><ul><ul><li>Ulcerogenic </li></ul></ul><ul><ul><li>Immunosuppression with long-term use </li></ul></ul><ul><ul><li>Hyperadrenocorticism </li></ul></ul>
    60. 60. Tramadol as an Analgesic <ul><li>Nonopiate drug with activity at the mu receptor </li></ul><ul><ul><li>Also inhibits reuptake of norepinephrine and serotonin </li></ul></ul><ul><li>Administered orally after patient has resumed eating </li></ul><ul><ul><li>A postoperative alternative to opiates </li></ul></ul><ul><ul><li>Can be administered at home </li></ul></ul><ul><li>Don’t use concurrently with other norepinephrine or serotonin reuptake inhibitors (e.g., amitriptyline) </li></ul>
    61. 61. Tranquilizers and Analgesia <ul><li>Tranquilizers are not considered analgesics </li></ul><ul><ul><li>May potentiate effects of opioids in anxious patients </li></ul></ul><ul><ul><li>Useful in calming the excitement sometimes seen in cats and horses following opioid administration </li></ul></ul><ul><ul><li>Cannot be substituted for opioids or other analgesic agents </li></ul></ul>
    62. 62. Multimodal Therapy <ul><li>Use of more than one type of analgesic to relieve pain </li></ul><ul><ul><li>Pain is produced by several mechanisms </li></ul></ul><ul><ul><li>Different drugs will target different mechanisms along the pain pathway </li></ul></ul>
    63. 63. Examples of Multimodal Therapy <ul><li>Acetaminophen and codeine </li></ul><ul><ul><li>Oral treatment for moderate to severe pain in dogs </li></ul></ul><ul><li>Fentanyl and meloxicam </li></ul><ul><ul><li>Administered at the same time to cats to provide analgesia until the fentanyl patch takes effect </li></ul></ul><ul><li>Morphine and injectable NSAID (meloxicam or carprofen) </li></ul><ul><ul><li>Administered at the end of surgery followed by oral NSAID for 3 days </li></ul></ul><ul><li>MLK </li></ul><ul><ul><li>Administered in IV fluids during surgery, decreases amount of inhalant anesthetic needed </li></ul></ul>
    64. 64. Home Analgesia <ul><li>Fentanyl patches </li></ul><ul><ul><li>Used sequentially for up to several months for chronic pain (dogs and cats) </li></ul></ul><ul><li>NSAIDs </li></ul><ul><ul><li>Long-term therapy of chronic painful conditions </li></ul></ul><ul><li>Oral morphine </li></ul><ul><ul><li>Sustained-release tablet administered BID to effect </li></ul></ul><ul><li>Tylenol with codeine (dogs) and butorphanol </li></ul><ul><ul><li>Tablet for mild-to-moderate pain </li></ul></ul><ul><li>Tramadol </li></ul>
    65. 65. Nursing Care <ul><li>Relieving patient discomfort will help pain control </li></ul><ul><ul><li>Keep patient and cage or stall clean and dry </li></ul></ul><ul><ul><li>Comfortable bedding/quiet surroundings </li></ul></ul><ul><ul><li>Opportunity to urinate and defecate </li></ul></ul><ul><ul><li>Comfortable position </li></ul></ul><ul><ul><ul><li>May have to turn every 2-3 hours </li></ul></ul></ul><ul><ul><li>Reduce anxiety with toy or blanket from home </li></ul></ul><ul><ul><li>Ophthalmic ointment in unconscious patients to prevent corneal drying </li></ul></ul><ul><ul><li>Comforting reassurance through touch and talking </li></ul></ul>
    66. 66. Nonpharmacologic Therapies <ul><li>Used in conjunction with or as an adjunct to pharmacological therapy </li></ul><ul><ul><li>Acupuncture </li></ul></ul><ul><ul><li>Transcutaneous electric nerve stimulation </li></ul></ul><ul><ul><li>Massage therapy </li></ul></ul><ul><ul><li>Apply cold (acute injuries) or heat (chronic injuries) </li></ul></ul><ul><ul><li>Physiotherapy </li></ul></ul><ul><ul><li>Laser or magnetic therapy </li></ul></ul><ul><ul><li>Homeopathic or herbal remedies </li></ul></ul>