Pain Physiology, Assessment & Treatment PDF

PAIN PHYSIOLOGY, ASSESSMENT & TREATMENT VETC 2011 Veterinary Nursing 2 LAURA COUCH RVT, MSc, One Health (GradCert) BSc  REFERENCES FOR TODAY’S CONTENT: CHAPTER 9 , PAGES 110+ SMALL ANIMAL EMERGENCY AND CRITICAL CARE FOR VETERINARY TECHNICI...

PAIN PHYSIOLOGY, ASSESSMENT & TREATMENT VETC 2011 Veterinary Nursing 2 LAURA COUCH RVT, MSc, One Health (GradCert) BSc  REFERENCES FOR TODAY’S CONTENT: CHAPTER 9 , PAGES 110+ SMALL ANIMAL EMERGENCY AND CRITICAL CARE FOR VETERINARY TECHNICIANS ANDREA BAT TAGLIA , ANDREA STEELE & FELINE GRIMACE SCALE LINKS & COLORADO PAIN SCORES LINKS LEARNING OBJECTIVES LESSON 9.1: PAIN ASSESSMENT AND TREATMENT 1.Define pain. 2.Introduce different options for pain management. 3.Provide information on how to determine if a patient is painful. 4.Discuss how to calculate and administer a constant rate infusion. Sadly animals can not tell us they are painful We must recognize any changes from their normal behaviour/expressions, signs of stress, body position or tension signs, and physiologic responses When in doubt give them the benefit of the doubt, it often doesn’t hurt to treat for pain  “AN UNPLEASANT SENSORY AND EMOTIONAL EXPERIENCE ASSOCIATED WITH ACTUAL OR POTENTIAL TISSUE DEFINITIO DAMAGE OR DESCRIBED IN TERMS OF N OF SUCH DAMAGE. THE INABILITY TO COMMUNICATE IN NO WAY NEGATES PAIN THE POSSIBILITY THAT AN INDIVIDUAL *one of many IS EXPERIENCING PAIN AND IS IN NEED OF APPROPRIATE PAIN RELIEVING TREATMENT.” -INTERNATIONAL ASSOC. FOR THE STUDY OF PAIN  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 3  Physiology of Pain Nociceptors: Pain receptors in nervous system Pain has a physiologic explanation Acute pain: Severe, sudden onset that overwhelms endogenous analgesic mechanisms Chronic pain: Prolonged and persistent; body becomes habituated to nervous NOCICEPTIO PHYSIOLOGI PATHOLOGI N C C  Normal response to a noxious stimulus, producing protective behavioral responses to potential or actual PHYSIOLOGIC tissue damage PAIN “Ouch” pain Little or no tissue injury *can prevent pathologic pain Also called adaptive pain 9  The type of pain we usually think about, pathologic pain is PATHOLOGIC caused by damage PAIN or disease to the body  Tissue injury  Acute or chronic Copyright © 2017 by Elsevier, Inc. All rights reserved. 10  Classification based on mechanism  Inflammatory, neuropathic, PATHOLOGIC cancer, idiopathic PAIN CAN BE CLASSIFIED Classification based on origin IN DIFFERENT  Visceral or somatic: WAYS superficial or deep Classification based on severity of pain  None, mild, moderate, severe 11 Somatic pain = originates from damage Origin of types of pain to bone, joint, muscle, or definitions skin; well localized Visceral pain = originates from internal organs – stretching or twisting of viscera, mesenteries, and ligaments; poorly localized Neuropathic pain = originates from injury to the peripheral or central nervous system (ex. nerve transection or compression) Origin of types of pain. Inflammatory pain = originates from definitions tissue damage (ex. sx, trauma, ischemia, OA, laminitis, infection) Referred pain = originates from one part of the body but perceived as  Allodynia = Pain evoked by a stimulus that does not normally OTHER cause pain PATHOLOGIC Hyperalgesia = An increased or PAIN exaggerated response to a (EACH A stimulus that is normally painful DISEASE IN (heightened sense of pain) ITSELF )  Windup = Summation of painful stimulation in the spinal cord, constant nociceptive input from peripheries, leads to …. secondary hyperalgesia, & PATHOLOGIC allodynia PAIN (EACH A aka‘Central DISEASE IN nervous system hypersensitivity’ ITSELF ) - from unmanaged pain, or acute severe pain -removes the Mg++ block on NMDA receptors  Detection by the nervous system for the potential for, or actual tissue injury NOCICEPTION :. Neural process of PAIN noxious transmission  Nociception can protect animal/us from a painful or noxious stimuli 17  Nociception is when nerves are stimulated to send info about tissue damage to the brain Nociceptors are the pain-sensing nerve cells in skin, joints, muscles.. NOCICEPTION Pain is the subjective experience of VS PAIN tissue damage. Awareness of the pain. Nociception doesn’t always = pain E.g., Under Anesthesia animals may experience nociception from surgical stimulus (e.g., increase HR, or BP) but they would not experience the pain 18 NOCICEPTION THE PAIN PATHWAY TRANSDUCTIO TRANSMISSIO MODULATION PERCEPTION N N NOCICEPTION : THE PAIN PATHWA Y 20 NOCICEPTION: THE PAIN PATHWAY Step 1 Step 2 Step 3 Step 4 Transduction Transmission Modulation Perception Peripheral Sensory Nociceptive Conscious pain impulses/sig input is recognition receptors nal taken modified at at the activated from the spinal cerebral by a peripheral cord cortex stimulus nerve & Impulses Impulses are Transformati transmitted are either transmitted on of stimuli to spinal amplified or to the brain into sensory cord suppressed where they electrical - spinal cord are signals pathway processed (action and potentials) recognized 21 NOCICEPTION: THE PAIN PATHWAY  Each step has different (CONT’D) receptors  Drugs can be selected that will target specific receptors and block a specific step – so cool right?! 22 ANALGESIA GOAL Reduce pain by interrupting nociception at one or multiple levels (transduction, transmission, modulation, perception)   The use of more than one drug to control pain  Targeting two or more of the receptors MULTIMODAL THERAPY  Covers multiple receptors and mechanisms of action  Reduces dose of individual drugs and anesthetic agent 25  GABA Heat/Cold Stretching, compression  A. Acetaminophen and codeine  Oral treatment for moderate to severe pain in dogs B. Fentanyl and meloxicam  Administered at the same time to cats to provide analgesia until the fentanyl patch EXAMPLES OF takes effect MULTIMODAL THERAPY C. Morphine and injectable NSAID (meloxicam or carprofen)  Morphine Lidocaine Ketamine (MLK)  Administered in IV fluids during surgery, decreases amount of inhalant anesthetic needed, & appropriate for moderate- severe pain – dogs only 26  Analgesia is needed at every stage of hospitalization and treatment PHARMACOLOGI  Preanesthetic period C ANALGESIC  Surgical period THERAPY  Immediately postoperative period  Remainder of hospital stay  At home 27  Choice of drug depends on: PHARMACOLOGI C ANALGESIC Severity & type of THERAPY pain (CONT’D) Patient’s general condition Route of delivery Copyright © 2017 by Elsevier, Inc. All rights reserved. 28 SIGNS OF PAIN IN ANIMALS Pain elicits a stress response Stress-related pain results in “fight-or-flight- or-freeze” physiological response 29  BEHAVIORAL RESPONSES TO PAIN THAT YOU WILL SEE!  Vary depending on species, age, breed, and temperament  Young patients less tolerant  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  Aggression 30 GENERALIZED EVIDENCE OF PAIN (OWNERS DO NOT ALWAYS CORRELATE THESE WITH PAIN)  Decreased appetite  Decreased sleeping time  Changes in posture  Changes in gait &/or level of activity  Reluctance to lie down or constantly shifting position  Decreased grooming  Poor body condition 31...GENERALIZED EVIDENCE OF PAIN (OWNERS DO NOT ALWAYS CORRELATE THESE WITH PAIN)  Vocalization  Whine, growl, whimper, groan, snarl, bite, hiss, grunt, or purr  Emergence delirium  Immediate postoperative vocalization  Changes in facial expressions, appearance, and attitude Copyright © 2017 by Elsevier, Inc. All rights reserved. 32  PAIN BEHAVIOURS CANINE VS FELINE  Hiding, social Lameness withdrawal Praying position  Decreased appetite Head Tilt  anorexia Guarding  Decreased grooming  Excessive Licking Behaviour changes  Lameness Aggression  Reluctance to jump Withdrawal  Missing the litter box Antisocial  Squinting eyes Lethargic  Lowered Ears  Aggression  Equine Pain Ruminant Pain Behaviours Behaviours  Bruxism (teeth grinding), Lameness Standing at back of stall hypersalivation  Abnormal facial expression Decreased social interaction or  Decreased appetite and interest in surroundings Decreased appetite BO rumination Pain face – “low ears, angled NU  Decreased milk production  Isolation from herd eye with intense stare, dilated S  Vocalization, grunting nostrils and tension of the muzzle” Vet Anaesth Analg. 2015 Jan;42(1):103-14. An equine pain face. Gleerup KB1, Forkman B, Lindegaard C, Andersen PH. Colic Sweating, rolling, flank- watching or biting, pawing,   Commonly described signs/indicators of PAIN pain in veterinary patients  Increased heart rate WHAT DOES IT  Increased respiratory rate LOOK LIKE?  Increased blood pressure  Increased temperature  Vocalization  Inability to rest or sleep  Trembling  Inappetence  Changes in normal posture/movement  Chewing or licking at painful site 35  Anesthetized animals can process nociception pain (but are not consciously aware to experience the pain)  Pain is not prevented or stopped with general anesthesia PAIN IN Signs of pain seen under GA – KNOW THESE ANESTHETIZ  Increased HR ED  Increased RR – sudden increase common (tachypnea or ANIMALS “huffing”)  Difficulty maintaining an appropriate plane o Gets light, Movement, Trembling  Requires higher than MAC to stay at appropriate plane (1or2)  Increased blood pressure 36  PAIN Things to consider IN  When was the last analgesia SEDATED OR given ANESTHETIZE  Was it adequate? D  Age of animal & co-morbidities ANIMALS  Severity of pain  Surgery & duration 37   It is important to be able to distinguish between pain and anxiety because both can cause tachycardia, hypertension, and changes in posture. Removing the patient from its kennel or taking it out for a short PAIN walk may alleviate some anxiety. If an VS outside area is available, it is often ANXIETY advantageous to assess the patient outdoors to see if it is more relaxed out of the hospital environment. - Pain Recognition and Management in Critical Care Patients: https://todaysveterinarynurse.com/emergency-medicine -critical-care/pain-recognition-and-management-in-critic al-care-patients/ 38  CONSEQUENCES OF UNTREATED PAIN Sympathetic stimulation (e.g., from pain) can lead to vasoconstriction, increased cardiac work, increased HR, & oxygen consumption, and:  Immune system suppression  Inflammation & delayed wound healing  Anesthetic risk & increased anesthesia doses  Patient suffering  Catabolism & wasting from neuroendocrine 39  …….CONSEQUENCES OF UNTREATED PAIN STRESS RESPONSE mediated by sympathetic NS, release of hormones (ACTH, cortisol, vasopressin, growth hormone, decreased insulin) & neurotransmitters (epinephrine, norepi) Cardiovascular - tachycardia, hypertension, arrhythmias Respiratory - atelectasis, hyperventilation or hypoventilation, hypoxia GI - delayed gastric emptying, nausea, ileus BO Renal - oliguria and urinary retention S NU Hematologic – hypercoagulability, thrombosis risk Psychological – anxiety, fear, fatigue, suffering 40 Patient Pain Assessment Your Check List for assessing pain (in this order)  Observe the patient for behaviors associated with pain, such as anxious expression, facial expressions, restlessness, panting, and reluctance to move/change position.  Obtain the patient’s heart rate, blood pressure, and respiratory rate.  Palpate the patient to identify signs of painful areas (with assistance to keep you safe, if 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 Copyright © 2017 by Elsevier, Inc. All rights reserved. 42 Numerical rating system with descriptions of criteria for each score  Psychological and behavioural  Response to palpation  Body tension H TT P S : / / V E T M E D B I O S C I. C O LO S TAT E. E D U / V T H / S E RV I C E S / A N E S T H E S I A / A N I M A L- PA I N - S C A L E S / Recommendation made to “reassess analgesic plan” at scores 2-4 (give COLORADO PAIN analgesics or change plan) SCORE LINK FOR CANINE, FELINE, EQUINE CHARTS Note that animals are not evaluated if they are sleeping A sleeping animal, at least transiently, is not feeling pain Sleep is important for recovery and healing Let the patient sleep! Evaluate once 44 they are awake COLORADO PAIN SCORE LINK FOR CANINE, FELINE, EQUINE CHARTS H TT P S : / / V E T M E D B I O S C I. C O LO S TAT E. E D U / V T H / S E RV I C E S / A N E S T H E S I A / A N I M A L- P AIN-SCALES/ 45 COLORADO PAIN SCORE LINK FOR CANINE, FELINE, EQUINE CHARTS H TT P S : / / V E T M E D B I O S C I. C O LO S TAT E. E D U / V T H / S E RV I C E S / A N E S T H E S I A / A N I M A L- P AIN-SCALES/ 46 Pain assessment in cats | Feline Grimace Scale LINK 47  BO EQUINE: Post abdominal surgery S NU pain assessment scale (PASPAS) EQUINE PAIN o Physiological SCALE – o Postural ABDOMINAL o Interactive HTTPS://PUBMED.NCBI.NLM.NIH. GOV/20627635/ o Response to food o Colic behaviour o Stimulation of muscles o Palpation of incision Vet J. 2011 May;188(2):178-83. Clinical application and reliability of a post abdominal surgery pain assessment scale (PASPAS) in horses. Graubner C, Gerber V, Doherr M, Spadavecchia C. 48  BO EQUINE pain scale – orthopaedic S NU  Composite orthopaedic pain scale  Physiologic  Response to treatment EQUINE PAIN SCALE –  Behaviour ORTHOPEDIC  Appearance, posture, head HTTPS://PUBMED.NCBI.NLM.NIH. movement GOV/18061637/  Kicking, pawing  Sweating Res Vet Sci. 2008 Oct;85(2):294-306. Development of a composite orthopaedic pain scale in horses. Bussières G1, Jacques C, Lainay O, Beauchamp G, Leblond A, Cadoré JL, Desmaizières LM, Cuvelliez SG, Troncy E. 49 WHEN AND HOW SHOULD PAIN BE TREATED?  Severe acute pain can have deleterious physiologic effects  Pain should always be treated to inhibit deleterious effects  Always in best interest of patient to alleviate pain  Expected changes in heart rate, respiration, BP, and mentation should be understood before initiating treatment  RECALL: CRI REFERENCES: MCCURNIN’S CLINICAL TEXTBOOK FOR VT & NURSES, 10TH ED. JOANNA BASSERT CHAPTER 28 PHARMACOLOGY/PHARMACY PAGES 899-900 CONSTANT RATE INFUSION SMALL ANIMAL ECC FOR VT, 4TH ED. BATTAGLIA & STEELE CHAPTER 9 _PAIN ASSESSMENT & TREATMENT PAGES 114-116 CONSTANT RATE INFUSION RIs in bags when Rx dosage is mg/kg/h Determine bag duration in hours (how long the bag will last) Hours = Fluid bag Volume divided by Fluid Rate 1 Set this number aside to use later (step 4) Set up equation: Assess units, check that units match concentration, & align units by doing the necessary conversions if not 2 Aim is to find mg to add to bag at the fluid rate provided Replace hash (/) marks with multiplication sign mg x Kg x hr 3 Enter all known information & solve to find out the mg per bag = #mg x #kg x #hr = mg to add to bag (bag used in step 1 4 calc) Determine drug volume, and add it to the bag Desired mg divided by [concentration mg/mL] = #mL to add to bag 5 #mg ÷ #mg/mL = mL to add into the bag  1. E.g., 0.01mg/kg/hr hydromorphone [10mg/mL] Determine bag duration in hours into 250mL bag @ 15mL/hr Hours = Fluid bag Volume divided by Fluid Rate for a 20kg dog 250mL bag divided 15mL/hr fluid rate (bag duration) 1 = 250mL/15mL/hr = 16.67 hours 1 Set this number aside to use later (step 4) Set up equation: Assess units, check that units 0.01mg/kg/hr *Rx units match Drug match [Conc] – not need to convert, Rx time is Aim is to find mg to add to bag at the fluid rate same as fluid rate, no need to convert 2 2 provided anything Replace hash (/) marks with multiplication sign mg x Kg x hr 3 mg x Kg x hr 3 Enter known information & solve 0.01mg x 20kg x 16.67 hr = #mg x #kg x #hr = mg to add to bag =3.33 mg required in bag 4 4 Determine drug volume, and add it to 3.33mg divided by [drug the bag concentration 10mg/mL] Desired mg divided by [concentration =3.33mg/10mg/mL = 0.33mL drug 5 mg/mL] = #mL to add to bag 5 #mg ÷ #mg/mL = mL to add into the bag into bag 0.33mL of hydromorphone [10mg/mL] into 250mL bag @ rate of 15mL/hr will provide 0.01mg/kg/hr  2.E.g., 2mcg/kg/hr of Fentanyl [50mcg/mL] Determine bag duration in hours into 500mL bag @ Hours = Fluid bag Volume divided by62mL/hr, 33kg dog 500mL bag divided 62mL/hr fluid rate Fluid Rate = 500mL / 62mL/hr = 8.06 hours (bag 1 Set this number aside to use later (step 1 duration) 4) 2 mcg/kg/hr *Rx units match Drug Set up equation: Assess units, check that units match [Conc] – not need to convert, Rx time is Aim is to find mg to add to bag at the fluid rate same as fluid rate, no need to convert 2 2 provided anything Replace hash (/) marks with multiplication sign mcg x Kg x hr 3 mg x Kg x hr 3 2mcg x 33kg x 8.06 hr Enter known information & solve = 531.96 mcg fentanyl required in = #mg x #kg x #hr = mg to add to bag 4 bag 4 Determine drug volume, and add it to 531.96 mcg divided by [drug the bag concentration 50mcg/mL] Desired mg divided by [concentration =531.96mcg/50mcg/mL = 10.64mL 5 mg/mL] = #mL to add to bag 5 #mg ÷ #mg/mL = mL to add into the bag drug into bag 10.64mL of Fentanyl [50mcg/mL] into 500mL bag @ rate of 62mL/hr will provide 33kg patient CRIs in bags when Rx dosage is mcg/kg/min & drug Determine concentration: mg/mL bag duration in hours (how long the bag will last) Hours = Fluid bag Volume divided by Fluid Rate 1 Set this number aside to use later (step 4) Solve for minutes: number of hours (from Step 1) x 60min/hr 2 = bag duration in hours x 60min/hr = minutes in bag Replace hash (/) marks with multiplication sign 3 mcg x Kg x min Enter all known information & solve to find out the mcg to add to bag 4 Set up equation: Assess units, check that Rx units match concentration Convert, convert mcg to mg: mcg divided by 1000 = mg 4 Aim is to find mg or mcg to add to bag at the fluid rate provided b Determine drug volume and add it to bag Convert % to mg/mL 5 Desired mg divided÷ by [concentration mg/mL] = #mL to add to bag  3.E.g., 50mcg/kg/min of Lidocaine 2% into Determine bag duration in hours 1L bag @ 65mL/hr, 30kg dog 1L = 1000mL Hours = Fluid bag Volume divided by Fluid Hours in bag = 1000mL bag ÷ 65mL/hr rate 1 Rate 1 =15.38 hrs Set this number aside to use later (step 4) Solve for minutes: number of hours (from Step 1) x 60min/hr 15.38 hrs x 60min/hr = bag duration in hours x 60min/hr = = 922.80 minutes in bag 2 2 minutes in bag Replace hash (/) marks with multiplication sign Replace hash (/) marks with multiplication sign mcg x Kg x min mcg x Kg x min 3 3 Enter all known information & solve to find out the 50mcg x 30kg x 922.80 minutes 4 mcg to add to bag = 1 384 200 mcg to add to bag 4 Set up equation: Assess units, check that Rx units match concentration Convert mcg to mg: mcg divided by 1000 = 1 384 200 mcg to mg: 1 384 200mcg ÷ 1000 mg = 1384.2 mg to place into bag 4b 4b Aim is to find mg or mcg to add to bag at the fluid rate provided Determine drug volume and add it to bag Drug concentration in 2%  convert to mg: 2% = Desired mg divided÷ by [concentration mg/mL] = 2g/100mL = 2000mg/100mL = 20mg/mL 5 #mL to bag 5 1384.2mg ÷ 20mg/mL = 69.21 mL to add to bag 69.21 mL of Lidocaine 2% (20mg/mL)] into 1L bag @ rate of 65mL/hr will provide 30kg dog Remember to remove the same volume of fluid from the bag prior to adding the medication!! e.g. if you have to add 3.33mL medication to the bag/burette you must remove that same amount from the bag as to not dilute your proportions! Remember to also make your CRI or dilution before priming your line so that you don’t have to prime your line again! Using new bags will also provide more accuracy to volume inside bag if not using a burette CRIs, what a pain! Effective Postoperati ve Analgesia 60  Nonpharmacologic Interventions Differentiate between physical pain and other types of stress Provide comfort Assess emotional needs Distract as needed Reassess patient’s comfort after addressing patient’s physical and emotional needs  ANALGESICS: NON- PHARMACOLOGICAL  Good nursing care  cleanliness, padding, bandaging  Acupuncture  Laser  Physical therapy  Massage  Cold/ice compress or circulating ice water  SUMMARY OF AAHA PAIN MANAGEMENT STANDARDS McCurnin Pg 986 Box 30.2 Pain assessment for every patient, regardless of presenting complaint Assessment recorded in the medical record Use of preemptive pain management Appropriate pain management for anticipated level and duration Pain management for ALL surgical procedures Reassessment for pain throughout procedures Medical and chronic pain also treated Written protocols Teaching clients to recognize pain in their pets https://images.app.goo.gl/XrhdBw6GvXraWRbN8  - EACH PATIENT IS AN INDIVIDUAL AND MAY REQUIRE MORE ANALGESIA THAN YOU WOULD EXPECT - MANY PATIENTS HIDE PAIN WELL, CONSIDER THE PROCEDURE AND TREAT ACCORDINGLY REMEMBE - OPIOIDS ARE EASILY REVERSIBLE R IF YOU DON’T LIKE THE EFFECT YOU GET - IT’S EASIER TO BACK OFF ON PAIN CONTROL IN A COMFORTABLE PATIENT THAN PLAY CATCH-UP IN A PAINFUL PATIENT  CAREFUL MONITORING OF CARDIOVASCULAR STATUS AND MENTATION IS VITAL TO ACHIEVING GOOD PAIN MANAGEMENT WITHOUT DETRIMENTAL SIDE EFFECTS Monitorin SUPPORTIVE CARE IS INTEGRAL TO PAIN g Drug MANAGEMENT Effects MONITOR COMPLICATIONS AND SIDE EFFECTS OF TREATMENT MUST ELIMINATE PAIN AND STRESS WHEREVER POSSIBLE; TREAT ADVERSE CONSEQUENCES AS NEEDED   Dysphoria is a state of uncontrolled and unpleasant thoughts and feelings DYSPHORIA  Brought on by drugs VS ANXIETY  Anxiety is a feeling of worry, nervousness, or unease  Treatment of dysphoria is drug reversal, sedation, or time if within reason. 66 ANALGESICS – EXTRA – PHARM 2 PREVIEW OPIOIDS NSAIDS LOCALS ALPHA2- NMDA AGONISTS GABAPENTIN ADRENERGIC AGONISTS ANALGESICS: OPIOIDS  Mainstay treatment for perioperative pain or modsevere pain  Highly effective, minimal and manageable side-effects  Generally inexpensive  Titratable  Act on opioid receptors in the body: mu, kappa, delta  Receptors located peripherally (transduction), dorsal horn of spinal cord (modulation), and brain (perception) ANALGESICS: OPIOIDS  Mu agonists = morphine, hydromorphone, oxymorphone, fentanyl, methadone (+ NMDA antagonist properties), meperidine  Fully attaches/activates mu opiod receptors (aka full or pure mu)  Most potent analgesia,  Partial agonists = buprenorphine & butorphanol  Mu partial agonist, kappa antagonist= buprenorphine  Partial agonist --> some but less analgesia than pure agonists  Very high affinity for mu receptor, long duration and difficult to reverse  Mu antagonist, kappa agonist = butorphanol  Kappa = mild analgesia, mild-moderate sedation  Least potent analgesia ANALGESICS: NSAIDS  Analgesic act centrally &peripherally  Modulation & tranduction  Anti-inflammatory: inhibition of mediators of inflammation, free radical scavenger, membrane stabilization, inhibits leukocyte accumulation  Inhibit both COX-1 and COX-2 enzymes (convert arachidonic acid to prostaglandins)  Anti-pyretic  Caution in patients w/ GI, renal, or hepatic disease  Ideal patient should be well hydrated, normotensive, young-middle age, with normal renal function  Longer acting then opioids but less potent, cheaper, & okay to send home ANALGESICS: LOCAL ANESTHETICS  Local blocks – usually injected  Block Na-gated channels in nerve fibers, preventing propagation of action potential  May act on transduction or transmission depending on location and route of administration  Extremely effective analgesia, however, generally short acting  May increase duration of action by administering epidurally, through a wound soaker catheter, or catheter placed adjacent to a peripheral nerve TOPICAL ANALGESIA  Applying topical analgesia to surface skin or mucosa can reduce pain associated with minor procedures  Wound suturing  Venipuncture  Arterial puncture  Nasal cannulization  Twenty to thirty minutes of direct contact time is needed to ensure effectiveness  ANALGESICS: ALPHA 2 AGONISTS  Decrease release of NE peripherally, spinal cord, brain (modulation and perception)  Agonist at both α-1 and α-2 receptors  Individual drugs have different affinities α-1 vs. α-2 receptors  Xylazine least selective, dexmedetomidine most selective  Provide potent analgesia in horses, less in other species  Used as adjunct analgesics as a single dose or CRI with opioids, ketamine, lidocaine, etc.  Can be included in epidural ANALGESICS: NMDA ANTAGONISTS  NMDA receptors are located in spinal cord  Glutamate binds to NMDA receptors and facilitates pain transmission  Therefore, blocking these receptors inhibits the transmission of pain at the level of the spinal cord (modulation)  Helps decrease central sensitization  E.g. Ketamine  Dissociative agent ANALGESICS: GABAPENTIN  Analgesic adjunct  MOA (mechanism of action) not completely understood  Used primarily for neuropathic and chronic pain (modulation)  Helps prevent central sensitization if given preemptively (before surgery)  Sedative properties, esp in cats