Chapter 8 Analgesia PDF

Chapter 8 Analgesia Anesthesia and Analgesia for Veterinary Technicians and Nurses, 6th ed. Thomas and Lerche Learning Objectives—Lesson 8.1 (1 of 2) 1. Define pain, nociception, physiologic pain, pathologic pain, inflammatory pain, neuropathi...

Chapter 8 Analgesia Anesthesia and Analgesia for Veterinary Technicians and Nurses, 6th ed. Thomas and Lerche Learning Objectives—Lesson 8.1 (1 of 2) 1. Define pain, nociception, physiologic pain, pathologic pain, inflammatory pain, neuropathic pain, idiopathic pain, visceral pain, somatic pain, preemptive analgesia, pain scale, and multimodal therapy. 2. List the main steps of the pain pathway. 3. List the benefits of multimodal analgesia. 4. List the consequences of untreated pain. 5. Explain how primary hyperalgesia (peripheral hypersensitivity) develops. 6. Explain how secondary hyperalgesia (central hypersensitivity) develops. Learning Objectives—Lesson 8.1 (2 of 2) 7. List common surgical and medical conditions that are considered to be painful. 8. Describe how to recognize and assess pain- associated behaviors in animals. 9. Compare and contrast major types of pain assessment tools and describe how to use each.  Nature of Pain  Complex phenomenon  An aversive sensory and emotional experience  Elicits protective motor actions  Results in leaned avoidance  May modify species-specific behavior traits  Physiology of Pain  Nociception: detection by the nervous system for the potential for, or actual tissue injury  Protects animal from painful or noxious stimuli  Physiologic pain (adaptive)  Ouch pain  Little or no tissue injury  Pathologic pain  Follows tissue injury  Acute or chronic  Pathologic Pain  Classification based on mechanism  Inflammatory, neuropathic, cancer, idiopathic  Classification based on origin  Visceral or somatic: superficial or deep  Classification based on severity of pain  None, mild, moderate, severe  Nociception: The Pain Pathway (1 of 2)  Step 1: Transduction  Transformation of stimuli into sensory electrical signals (action potentials)  Step 2: Transmission  Sensory impulses conducted to spinal cord  Step 3: Modulation  Impulses are either amplified or suppressed  Step 4: Perception  Impulses are transmitted to the brain where they are processed and recognized  Nociception: The Pain Pathway (2 of 2)  Each step has different receptors  Drugs can be selected that will target specific receptors and block a specific step  Multimodal therapy: targeting two or more of the receptors Consequences of Untreated Pain  Catabolism and wasting  Immune system suppression  Inflammation and delayed wound healing  Anesthetic risk and increased anesthesia doses  Patient suffering  Primary Hyperalgesia  Peripheral hypersensitivity  Results from tissue damage and constant stimulation of nerves  Area close to the site of tissue injury becomes painful when stimulated with non- noxious stimuli  Secondary Hyperalgesia  Central nervous system hypersensitivity or “windup”  Area of hypersensitivity is further away from the site of tissue injury  Results from constant stimulation of spinal cord neurons  Neurons become hyperexcitable and sensitive  Physiologic Changes Caused by Pain  Hypertension  Tachycardia, tacharrhythmia  Peripheral vasoconstriction (pale mucosae)  Tachypnea  Shallow breathing  Exaggerated abdominal component  Panting (dogs)  Open-mouthed breathing (cats)  Mydriasis  Signs of Pain in Animals  Pain elicits a stress response  Stress-related pain results in “fight-or-flight” physiological response  Preemptive Analgesia  Administration of pain medication before the pain occurs  Commonly involves adding analgesic to premedication before anesthesia  Reduces overall requirement for analgesia and duration of administration  Prevents windup  Behavioral Responses to Pain  Vary depending on species, age, breed, and temperament  Young patients less tolerant  Cattle very stoic  Large dog breeds more stoic than small toy breeds  Cats hide; dogs seek owner comfort; herd animals separate themselves  Vary depending on nature, duration, and severity of pain and presence of humans  Physical Evidence of Pain  Changes in gait and level of activity  Evidence of arthritic pain  Reluctance to lie down or constantly shifting position  Evidence of thoracic or abdominal pain  Vocalization  Changes in facial expressions, appearance, and attitude  Pain Assessment Tools  Simple descriptive scales  Visual analogue scales  Numeric rating scales  CSU Canine Acute Pain Scale and CSU Feline Acute Pain Scale  Categorical numeric rating scale  Validated  Feline Grimace Scale  Chronic Pain Assessment Assessing Response to Therapy  Acute surgical pain vs. chronic pain  Hourly vs. monthly  With effective analgesia, pain-associated behaviors will recede  Appetite, grooming, body position or posture, interaction with people  With effective analgesia, pain assessment scores will decrease Learning Objectives—Lesson 8.2 (1 of 2) 10. List the routes by which analgesic drugs are commonly administered. 11. List the uses for and adverse effects of opioid analgesics. 12. Explain the mechanism of action of nonsteroidal antiinflammatory drugs. 13. List the uses for and adverse effects of nonsteroidal antiinflammatory drugs. Learning Objectives—Lesson 8.2 (2 of 2) 14. Describe the uses for and procedure for application of fentanyl transdermal patch. 15. Define multimodal therapy and list two examples of multimodal therapy. 16. Describe nursing care that relieves discomfort in hospitalized patients. Perioperative Pain Management  Preemptive analgesia  Begins in preoperative period with premedication  May be administered as part of anesthetic premedication  Transdermal fentanyl patch  NSAIDs primarily in large animals  Multimodal therapy  The use of more than one drug to control pain  Cover multiple receptors and mechanisms of action  Reduce dose of individual drugs and anesthetic agent  Pharmacologic Analgesic Therapy  Analgesia is needed at every stage of hospitalization and treatment  Choice of drug depends on:  Severity and type of pain  Patient’s general condition  Route of delivery  Using Opioids as Analgesics (1 of 2)  Vary in potency, duration, and adverse effects  Injectable premedication  Often in combination with a tranquilizer (acepromazine or dexmedetomidine)  Diminish windup  Duration of action is 2 to 4 hours, so not good for postoperative pain  Induce state of potent sedation (neuroleptanalgesia) at higher doses  Provides analgesia throughout surgery and for some time afterward  Using Opioids as Analgesics (2 of 2)  Postoperative analgesia  Alone or in combination with other drugs  Sedative and antianxiety drug  Excitement in awake cats and horses  Gastrointestinal effects  Initial increased gastrointestinal activity: nausea, vomiting, defecation  Followed by a slow down in gastrointestinal activity: ileus, colic, constipation  Metabolized in the liver  Opioid Agents Used for Moderate to Severe Pain  Morphine  Hydromorphone  Methadone  Fentanyl  Buprenorphine  Butorphanol  Nalbuphine  Opioid Agents: Morphine (1 of 2)  Schedule II drug (United States) and narcotic (Canada)  Used for moderate to severe visceral or somatic pain  Preanesthetic and analgesic  Pure agonist with affinity for mu and kappa opioid receptors  May cause excitement or dysphoria in cats and horses  May cause restlessness in dogs and horses  Opioid Agents: Morphine (2 of 2)  Administered by intravenous, intramuscular, subcutaneous, intraarticular, epidural, or spinal injection  Adverse effects  Initial gastrointestinal stimulation in dogs and cats  Ileus and colic development in horses  Excitement, miosis (dogs), mydriasis (cats), hypothermia, hyperthermia (cats)  Bradycardia, panting, increased intraocular pressure, urinary retention  Physical addiction (humans)  Opioid Agents: Hydromorphone  Opioid agonist  Greater potency than morphine, but similar duration of effect  Administered via intravenous, intramuscular, subcutaneous routes to dogs and cats  Used as a premedication alone or with a tranquilizer  Schedule II drug (United States) and narcotic (Canada)  Opioid Agents: Methadone  Synthetic opioid  Characteristics similar to oxymorphone and hydromorphone  Least likely to cause vomiting in cats and dogs  Antagonist at the NMDA receptor  Opioid Agents: Fentanyl  Schedule II drug (United States) and narcotic (Canada)  One of the most potent analgesics known  Rapid onset (2 minutes) and short duration of effect (20 to 30 minutes) when administered via intravenous route  Administered by continuous intravenous drip, transdermal patch, intramuscular, subcutaneous, or epidural injection  Used in combination with midazolam or diazepam drawn into separate syringes  Opioid Agents: Buprenorphine  A partial mu agonist that produces some analgesia for mild to moderate pain  Used to provide postoperative analgesia to dogs and cats  Can be used to reverse the effects of morphine and fentanyl  Administered IV, IM, or epidural; orally to cats  Delayed onset of action and longer duration of analgesia  Used with a sedative it can prolong sleep times  Expensive Schedule III drug (United States)  Opioid Agents: Butorphanol  Synthetic opioid with agonist and antagonist properties  Used as a preanesthetic, sedative, and postoperative visceral analgesic  Administered via intravenous, intramuscular, subcutaneous, or oral routes (as tablets for long-term analgesia)  Schedule IV drug (United States) and controlled drug (Canada)  Opioid Agents: Nalbuphine  Kappa agonist and mu antagonist with greater antagonist properties than butorphanol  Weak analgesic and sedative  Used as a reversal agent for opioid agonists  Fewer adverse effects  Not a controlled drug in the United States  Opioids as Postoperative Analgesics  Administered via intramuscular or subcutaneous route before animal regains consciousness  Injections repeated as necessary  Alternative routes (intravenous, epidural, intraarticular, transdermal patch) minimize adverse effects  Disadvantages  Short duration of action  Potential adverse reactions: respiratory depression, bradycardia, excitement, apprehension, hypersalivation, mydriasis, excessive sedation, panting, increased sensitivity to sound, urinary retention, gastrointestinal effects  Opioids: Intravenous Infusion  Morphine, fentanyl, hydromorphone, methadone, butorphanol  Provides continuous analgesia for constant, unremitting pain  Initial loading dose given to effect followed by same dose given over 4 hours through constant flow  Morphine (for example) can be administered with lidocaine or lidocaine/ketamine to control severe pain  Opioids: Intraarticular Injection  Especially useful after elbow or stifle surgery  Morphine diluted in saline solution instilled into joint via a catheter  Immediately after joint closure  Can be combined with a local anesthetic (e.g., bupivacaine)  Provides 8 to 10 hours postoperative analgesia  Opioids: Epidural Injection  Instillation of an opioid into the epidural space at the lumbosacral junction  To provide analgesia to hind limbs, abdomen, caudal thorax, pelvis, tail  Morphine is the most commonly used drug  May be combined with an alpha2-agonist in large animals  Profound postoperative analgesia with long duration of action  Opioids: Transdermal Use  Fentanyl transdermal patch  Reservoir of fentanyl enclosed in plastic  Attached to clipped skin and left in place for several days  Large animals may require more than one patch  Provides convenient, long-term opioid administration  Similar to intramuscular morphine injection but longer duration of action  Nonsteroidal Antiinflammatory Drugs (NSAIDs)  NSAIDs or nonsteroidal antiinflammatory analgesics (NSAAs)  Mechanism of action  Onset of action: 30 to 60 minutes  Duration of effect varies with species  Toxicity varies with species  Analgesic and antiinflammatory properties vary by drug  Inhibit prostaglandin synthesis by inactivating COX isoenzymes  Metabolized in the liver; eliminated by the kidneys and the gastrointestinal tract  Adverse Effects of NSAIDs (1 of 2)  Prevent the production of beneficial prostaglandins along with the production of prostaglandins that mediate pain, inflammation, and fever  NSAIDs that inhibit the COX-2 enzyme but not the COX-1 enzyme produce the least adverse effects  The perfect NSAID is not available yet  Adverse Effects of NSAIDs (2 of 2)  Adverse effects vary with drug, species, breed, and individual animals  Stomach ulcers, vomiting, gastrointestinal bleeding, lack of appetite  Gastrointestinal ulceration leading to hemorrhage  Renal toxicity  Impaired platelet aggregation leading to prolonged bleeding time  Liver damage  Antagonist to several drugs prescribed for cardiac disease and hypertension Local Anesthetics as Analgesics  Used to prevent or treat postoperative pain  Advantages  Complete anesthesia of affected area  Low toxicity  Rapid onset of action  Disadvantages  Short duration of action  Central nervous system and cardiac toxicity with repeated use  Other Analgesic Agents: Alpha2-Adrenoceptor Agonists  Limited use in small animals  Adverse effects: respiratory depression, vomiting, bradycardia, heart block, hypotension  Used in horses to provide sedation, muscle relaxation, and analgesia  Xylazine, detomidine, romifidine  Horses remain standing but may become ataxic  Analgesia okay for moderately to severely painful diseases or procedures  Adverse effects: cardiovascular, respiratory, GI  Other Analgesic Agents: Ketamine  Used as an adjunct to more potent analgesics (opioids, local anesthetics, alpha2-agonists)  Doesn’t produce analgesia by itself  MLK (morphine, lidocaine, ketamine) provides intraoperative analgesia  Blocks NMDA at the level of the spinal cord to prevent windup  Use a lower dose than the one used to induce anesthesia  Other Analgesic Agents: Gabapentin  An anticonvulsant  Treats neuropathic pain and hypersensitivity  Similar in structure to GABA  Useful in dogs and cats for chronic pain unresponsive to NSAIDs  Few adverse effects, except drowsiness  Liquid form contains xylitol, toxic to dogs and cats  Other Analgesic Agents: Amantadine  A NMDA receptor antagonist  Useful for  Neuropathic pain and central hypersensitivity  Chronic pain of musculoskeletal disease  Side effects  Agitation  Gastrointestinal upset  Other Analgesic Agents: Corticosteroids  Strong antiinflammatory properties  Decrease prostaglandin activity such as NSAIDs  Don’t use concurrently with NSAIDs  Adverse effects  Ulcerogenic  Immunosuppression with long-term use  Hyperadrenocorticism  Use of more than one type of analgesic to relieve pain  Pain is produced by several mechanisms  Different drugs will target different mechanisms along the pain pathway  Other Analgesic Agents: Tramadol  Nonopiate drug with activity at the mu receptor  Administered orally after patient has resumed eating  A postoperative alternative to opiates  Can be administered at home  Don’t use concurrently with other norepinephrine or serotonin reuptake inhibitors (e.g., amitriptyline)  Other Analgesic Agents: Tranquilizers  Tranquilizers are not considered analgesics  May potentiate effects of opioids in anxious patients  Useful in calming the excitement sometimes seen in cats and horses following opioid administration  Cannot be substituted for opioids or other analgesic agents  Other Analgesic Adjuncts  Several drug classes used to treat pain  Antidepressants  Antianxiety  Bisphosphonates  Multimodal Therapy  Often useful to use more than one type of analgesic to relieve pain  Combination or balanced analgesia may be more successful Examples of Multimodal Therapy  Acetaminophen and codeine  Oral treatment for moderate to severe pain in dogs  Fentanyl and meloxicam  Administered at the same time to cats to provide analgesia until the fentanyl patch takes effect  Morphine and injectable NSAID (meloxicam or carprofen)  Administered at the end of surgery followed by oral NSAID for 3 days  MLK  Administered in IV fluids during surgery, decreases amount of inhalant anesthetic needed  Home Analgesia  Fentanyl patches  Used sequentially for up to several months for chronic pain (dogs and cats)  NSAIDs  Long-term therapy of chronic painful conditions  Oral morphine  Sustained-release tablet administered BID to effect  Tylenol with codeine (dogs) and butorphanol  Tablet for mild-to-moderate pain  Tramadol  Nursing Care  Relieving patient discomfort will help pain control  Keep patient and cage or stall clean and dry  Comfortable bedding/quiet surroundings  Opportunity to urinate and defecate  Comfortable position May have to turn every 2 to 3 hours  Reduce anxiety with toy or blanket from home  Ophthalmic ointment in unconscious patients to prevent corneal drying  Comforting reassurance through touch and talking  Nonpharmacologic Therapies  Used in conjunction with or as an adjunct to pharmacological therapy  Acupuncture  Transcutaneous electric nerve stimulation  Massage therapy  Apply cold (acute injuries) or heat (chronic injuries)  Physiotherapy  Laser or magnetic therapy  Homeopathic or herbal remedies