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Week 6
Your Obligation
To recognize and alleviate animal pain Many years believed pain was good to
remind the animal to avoid movementFalse belief
Uncontrolled pain leads to prolonged recovery
You are the person in with the animal and need to be able to assess pain level
Definitions IASP- International Association for the Study
of Pain Pain- unpleasant sensory and emotional
experience associated with actual or potential tissue damage, or described in terms of such damage
Nociceptor- receptor that is preferentially sensitive to a noxious stimulus3 phases- Transduction, Transmission, Modulation
Analgesia- absence of pain in response to stimulation that would normally be painful
Cont. Hyperalgesia- increased response to a
stimulus that is normally painful Peripheral sensitization- reduction in activation
threshold of peripheral nociceptors due to exposure to a # of chemical substances that arise as a result of tissue damage
Central sensitization- changes in the receptive field properties of neurons located in the spinal cord
Wind-up- produced following repeated, low-frequency input from nociceptors
Peripheral nervous system Transmission of a noxious stimulation
involves activation of specialized receptors and peripheral nerves in damaged tissue
Degree of sensitivity is directly related to density of nociceptors in that tissue (skin, joint capsule, muscle, tendon, dental pulp)
Nociceptors convert the chemical, mechanical and thermal insult into nerve impulses
Central nervous system
Pathways involved are considerably more complex than those in the periphery
Spinothalamic tract- transmits pain impulses through the spinal cord and to the brain
Axons- nerve fibers that terminate in several areas of the thalamic area of the brain and brain stem
This allows body to perceive
the aspects of the pain:
location, nature, and intensity
Problems with evaluating pain Critical before appropriate analgesic therapy
can be initiated Watch for specific behavior patterns Autonomic nervous system activates “fight
or flight” response and releases epinephrine and norepinephrine
Results in ↑HR, BP, and RR and pupil dilation
Fight or flight not specific to pain
Signs of pain and distress ↑ HR. BP, RR, pupil dilation, vocalization, and arousal
Some may have ↓HR in response to pain Behavioral signs include restlessness, ↓ appetite, not
sleeping, unusual body position, resent handling Post-op pain response: biting, scratching, or licking Know typical behavioral patterns and physical
appearance of species and breeds
Environment and nursing care Environmental factors often affect
emotional component of pain perception Keep surroundings familiar and calm Recovery areas should be quiet and
located away from high traffic Interaction with humans can help relieve
stress and anxiety Schedule tx and monitoring for less
disturbances
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Frequency of Pain Evaluation Upon admission During immediate postoperative period Every 30 minutes through critical phase Every 4-6 hours throughout
hospitalization
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Pain Scale Describes observer’s subjective opinion Describes patient’s physiological signs Should be documented in medical record Colorado State University Acute Pain Scale
pages 862-863New pain scale for dogs and catsNumerical, pictorial, and descriptive assessments
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Pain is Bad
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Pain Management Standards
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Perception Fourth phase of pain pathway
(after transduction, transmission and modulation)
Occurs in the conscious brainIs the awareness that “I hurt”
Differentiates pain from nociceptionNociception occurs even in state of unconsciousness
Occurs as anesthesia wears off; occurs as consciousness returnsGood pain management should be initiated when
pain is anticipated
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Preemptive Analgesia
Best way to treat pain is to prevent it Benefits of preventive analgesia
Reduces postprocedure analgesia requirements
Minimizes detrimental effects of painImproves handling of patientsLowers sedation or anesthetic requirementsPrevents hypersensitization at spinal cord
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“Don’t Quit Until the Pain Quits” Postoperative analgesia
3-4 days for soft tissue procedures1 week for orthopedic procedures
Pain medications sent home with patient Taper medications carefully Additional analgesia if pain persists
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Analgesic Therapy
Requires knowledge of drugs Requires anticipation of pain levels
associated with various conditions Ultimate criteria: pain relief Analgesic plan for each patient
Maximize pain controlMaintain patient on analgesic planeReduce unwanted side effects
Analgesic drugs
2 main types:Nonnarcotic NSAIDsNarcotics
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Types of Opioids Efficiency determined from specific receptors in brain
and spinal columnMu receptors
○ Sedation, analgesia, respiratory depressionKappa receptors
○ Sedation, analgesiaSigma receptors
○ Thought to be responsible for adverse effects of opioid administration
○ Dysphoria, excitement, restlessness, anxietyDelta receptors
○ Analgesia and motor disfunction
Classified as agonists or antagonists
Opioids
Narcotics Pure agonist- exert effects by only
stimulating opioid receptors (morphine) Antagonists- bind at opioid receptors and
block response; reversal agents (naloxone) Mixed agonist/antagonist- act like agonists
as some receptors and antagonists at others (butorphanol)
Narcotic effects
Minimal cardiovascular effects Bradycardia Hypotension if stimulates release of
histamine Respiratory depression Possible sedation Metabolized by liver and excreted in
urine; watch in liver disease and neonates
Narcotic agonists Morphine
All other opioids compared to itDepresses respiratory and CNSGiven IV and IM routes, can be used as a pre-
med
FentanylSynthetic, 100x potency, short duration (30-45
min)Transdermal patch- variable uptake, apply to
cats 12-16 hrs before pain and dogs 24 hours before.
Narcotic agonists Hydromorphone
6-7x more potentSynthetic, 4-6 hr durationUsed more commonly than Oxy
Oxymorphone10-15x more potentSynthetic, 2-4 hr duration
EpiduralsMany of these and the local anesthetics can be
administered via epidural
Mixed agonist/antagonists Butorphanol (Torbutrol)
Synthetic, stronger agonist, weak antagonistUsed commonly as perioperative analgesiaUsed as antiemetic for chemo
Buprenorphine (Buprenex)300x potencyUsed for post-op pain transmucosalCan be absorbed through mm when given PO
Antagonists
NaloxoneAntagonizes all opiate receptorsLess effective for reversal of buprenorphine
NaltrexoneSimilar to Naloxone but longer acting and
administered orally
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Tramadol For moderate pain Synthetic drug Opioid-like analgesic effects Fewer side effects than with opioids Oral route of administration Suitable for long-term at-home management
Cancer patientsProblem osteoarthritis casesPostoperative prolonged pain
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NSAIDs Precautions for Patients Normal blood pressure Normal renal function Normal liver function No bleeding abnormalities No evidence or concern for gastric
ulceration No dosing of other NSAIDs,
corticosteroids, or aspirin
NSAIDs Nonsteroidal anti-inflammatory drugs Exert analgesic effects in the peripheral
tissues by blocking production of prostaglandins
Inflammation begins with local tissue injury Vasoactive substances produce pain, heat
and swelling NSAIDs control pain by inhibiting
cyclooxygenase, leads to production of prostaglandins
Salicylate analgesics
Aspirin Bismuth subsalicylate Effective in relieving pain associated with
peripheral inflammation: muscle and joint disease
Absorbed through GI tract, metabolized by liver, excreted by kidneys
Absorbed into synovial fluid, peritoneal fluid, milk, saliva, and placental membranes
Propionic acid derivatives Carprofen (______)
Inhibits COX2 but doesn’t totally aviod COX1
Used for musculoskeletal and acute pain
Deracoxib (______)More focused on COX2 compared to
RimadylUsed same as Rimadyl
Naproxen (Naxen)Nonselective and used for musculoskeletal
Propionic acid derivatives Ibuprofen
Nonselective, not as safe
Ketoprofen (Ketofen)Nonselective, used in large and small
animal
Etodolac (EtoGesic)Nonselective , used in large and small
animal
Fenamic acids Meclofenamic acid
Inhibits cyclooxygenase and blocks cell surface receptors from prostaglandins
Musculoskeletal painSide effects: V and D, GI ulceration
Flunixin MeglumineAnalgesic and antipyretic activityBlocks production of prostaglandinsUsed for DJD that is unresponsive to other
NSAIDsCan cause GI ulceration and bleeding
Oxicans
MeloxicamControl of pain and inflammation associated
with osteoarthritisTx in dogs and cats
Pyrazolone derivative
PhenylbutazoneAnalgesic, anti-inflammatory and antipyretic
propertiesTx in dogsPainful arthritis and skeletal muscle disease
Tx of GI ulceration
SucralfateMixes with mucous and forms a band aid
H2 blockersCimetidine (Tagamet), ranitidine(Zantac), famotadine (Pepcid)
Tranquilizers
Psychotropic drug Provide sedation and some muscle
relaxation and anxiolysis Tranquilizers provide no analgesia and
that it is inappropriate to use these drugs alone for postoperative pain control
Alpha2-Adrenergic agonists Xylazine
Binds to alpha2 receptors in CNS causing sedative and analgesic effects
Effects may be reversed with antagonists: yohimbine, atipamezole, tolazoline, or idazoxan
Can be used for analgesia in small animals however medetomidine works better
Others include: Domitor, Dexdomitor
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“Kitty Magic”
Most common use of α2-agonists in cats
General anesthetic for minor procedures Anesthetic before gas anesthetic for
more advanced procedures Components
An α2-agonist
An opioid (commonly buprenorphine)Ketamine
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MLK Combination
Administered as a CRI Infusion combination
Morphine ○ An opioid
Lidocaine ○ A local anesthetic
Ketamine ○ Provides optimal analgesia○ Prevents wind-up
Corticosteroids
Dampen the fire of inflammation but doesn’t eliminate the cause of it
Can cause impairment of wound healing and mask underlying diseases
Should not be used with NSAIDs due to ↑ risk of GI ulceration
Includes: cortisone, hydrocortisone, prednisone, prednisolone
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Local Anesthetics Mode of action: disrupt neural transmission Routes of administration
Topical Local infiltration Circumferential ring block Dental nerve block Intraarticular (joint space) Epidural nerve block Transdermal Intravenous
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Topical Route of Administration Application to skin or mucosa
Soaked gauze pads, creams, or jelliesApply 20-30 minutes direct contact timeDesensitization at application site
Reduces pain associated with minor proceduresWound suturing, venipuncture, arterial puncture,
nasal cannulization, and urinary catherization
Solutions usedLidocaine, bupivacaine, tetracaine, and/or
ephinephrine
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Circumferential Ring Block
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Dental Nerve Block
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Intraarticular Block
A local anesthetic Also effective in reducing joint pain
Use of morphine
Injection directly into joint space Smooth plane of anesthesia maintained
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Epidural Nerve Block
Analgesia to caudal half of body Sedative effects kept to a minimum Injection made at lumbosacral space
Opioids (morphine, fentanyl)And/or local anesthetics (lidocaine,
bupivacaine)
Epidural catheters for long-term administration
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Transdermal Anesthetics
Lidocaine transdermal patchWidely accepted in humansUse in veterinary medicine is being tested
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Intravenous Administration Manages variety of pain states
Visceral pain○ Pancreatitis○ Parvovirus
Extensive nerve damage○ Limb amputation
Effective administration by CRILidocaine as sole agentLidocaine in conjunction with other analgesics
Local Anesthetics All inhibit nerve conduction via sodium
channel blockade. Bupivacaine hydrochloride (Marcaine)
Inhibits nerve conductionStronger and longer acting than lidocaine
○ 15-20 minutes, lasts 6-8 hours.Commonly used for declaws and tooth extractions
Mepivacaine (Carbocaine-V)Shorter acting and not as potent as BupivacaineLonger acting but equal potency to lidocaine
Local Anesthetics
LidocaineAlso is an antiarrhythmic commonly used for
ventricular arrhythmiasUsed in horses for GI motility after ileusUsed as local block for small mass removals
or suturing skin wounds without anethesiaTakes effect in 3-5 minutes and is effective
for 60-90 minutes.“-caine” at the end of a word means it blocks
a nerve.
Tx of pain in dogs and cats 1st step- recognizing behavioral and
physiologic signs Good nursing care is critical Always watch for side effects of any
drugs being administered Know if pain is chronic or acute Know Hx of animal being treated
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Why Is Large Animal Pain Not Treated? 1- “Animals don’t feel pain” 2- “Animals don’t show pain” 3- “Limited number of analgesic drugs
available for farm animals” 4- “Owners or producers won’t pay for
analgesia”
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Pain in Large Animals
Strong tendency to hide pain until severe
Consequences of painDecreased food intakeWeight lossDecreased milk production
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Signs of Pain in Large Animals Stop eating Appear lethargic Stand with hunched back (ruminants) Stretch out in abnormal posture (horses) Grind teeth (horses) “Dog sit” (foals)
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Treating Pain in Large Animals NSAIDs
Therapeutic analgesic due to effect on inflammation Safe Easy to administer: IV, IM, SQ, PO, or transdermal Inexpensive Long lasting Should be paired with more potent short-acting drugs
Commonly used NSAIDs Phenylbutazone (“bute”) Flunixin meglumine (“Banamin”)
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Treating Pain in Large Animals Opioids
Primarily for acute medical or surgical painVaried responses from various receptorsMay cause excitement in farm animals; use in
conjunction with sedative.Administration by IV, IM, SQ, transdermal,
epidural, intraarticular, and CRI
Commonly used opioidsButorphanol is most commonMorphine, buprenorphine, fentanyl
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Treating Pain in Large Animals α2-agonists
Used more commonly in large animals, than smallWide variation in species’ response
○ Pigs most resistant and require high dosages for sedation
○ Horses next in sensitivity○ Cattle, sheep, and goats are most sensitive
Considered a sedative, but provide pain reliefOften combined with opioids for painful proceduresCommon α2-agonists:
○ Detomidine, Xylazine, Medetomidine
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Treating Pain in Large Animals Local anesthetic agents
Most effective of analgesic drugs Least expensive of analgesic drugsBlock transmission of painful impulsesAdministration by IV as a CRI
Commonly used anesthetic agentsLidocaine, bupivacaine
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Horse-specific Information Receive better analgesic treatment
Treated as “companion” animalsAre generally performance animalsBecome violent when in acute painDo not have absolute economic value
NSAIDs for chronic and acute pain Opioids used more commonly in horses
for intraoperative and postoperative pain and for medical pain
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Analgesia for Food-producing Animals
Cows, sheep, and goats are least likely large animals to receive analgesia because of narrow profit margin
Difficult to regulate analgesia when many procedures are done by producers and not by veterinarians
Strict regulations regarding use of many drugs in meat and milk-producing animals
Oral drugs slowly absorbed, or inactivated in rumen