Pain Management

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Pain Management
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Why Treat Pain?

• Animals feel pain just like us
• Unethical not to address pain
• Animal owner and public concerns
• Many anesthetics have no analgesic effect
• Which do?
• Pain results in poor anesthetic recovery

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MYTHS
Anesthetics mask symptoms Patient will harm
itself if theres no pain Pain is difficult to
assess
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The Truth!

• Pain is BAD
• Decreased cardiovascular function
• Decresed appetite
• Slows wound healing
• Decreased immune function
• Greater chance of infection
• Increased fear and anxiety

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Use of Analgesics in Practice

• Overall poor
• 13-26 dog and cat spay/neuters receive
  analgesics
• 50-70 of non-neutering soft tissue surgery
• gt80 orthopedic surgery and severe trauma
• Why not better?
• DEA / theft concerns
• Older vets not trained that way
• Older drugs dangerous
• Animals are stoic

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Pain Perception

• Pain sensor? nerve fiber?spinal cord?brain
• Neurotransmittersgtgt
• Somatic ( superficial ) pain
• Visceral ( internal organ ) pain
• Bone pain

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Classification of Pain

• Intensity (scale of 1-10)
• Acute, sharp, sudden, short
• Surgical pain
• Responds well to drug tx
• Chronic, dull, prolonged
• Cancer or arthritis
• Doesnt always respond well to tx
• Referred (from somewhere else)
• Hyperesthesia (increased sensitivity)
• Neuropathic (Nerve damage)
• Poorly responsive

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Degree and Type of Pain Depend On

• The procedure
• The animal
• Pain is an individual experience
• Tailor analgesic protocol to the patient
• Analgesic administration
• Timing
• Dosage

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Preemptive Analgesia

• If the body doesnt sense the pain during the
  procedure, the pain will be easier to deal with
  post-operatively
• A patient in surgical anesthesia is not aware of
  pain, but the body is still responding?
  sensitizes the nervous system

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Preemptive Analgesia Results In

• Marked decrease in amount of analgesic medication
  needed post-operatively
• Increased patient comfort

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Balanced Anesthesia

• Several anesthetic drugs are combined into
  anesthetic protocol
• Include analgesic
• Synergism
• Smaller dosages needed
• Decreased potential for side effects

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Monitoring Signs of Pain
Facial Expression Vocalization Body
Posture Abnormal Gait Decreased Activity
Level Attitude Appetite Grooming Urination/Defecat
ion Habits
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Methods of Pain Control

• Non-pharmacological methods
• Endorphins The bodys natural painkillers
• Good nursing care
• Comfortable bedding
• Clean and dry
• Easy access to bathroom, food, water
• TLC
• Rotate recumbency
• Allow time to sleep

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Non-pharmacological Methods

• Apply cold to site (acute- 1st 24 hours)
• Decreases inflammation
• Numbs
• Apply heat to site (chronic)
• Massage
• Acupuncture/acupressure
• Complementary methods
• Herbs, laser, magnetic, chiropractic

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Pharmacologic Methods

• Opioids
• ?2 agonists
• Steroids
• NSAIDS
• Local anesthetics
• Chondroprotective drugs

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Opioids
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Opiate Receptors
MOA? 4 types of receptors mu kappa
sigma delta Should we be wondering why
fraternities/sororities name themselves after
receptors of pain??
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OpioidsBackbone of Analgesia

• Pure Agonists
• Morphine, oxymorphone, meperidine, hydromorphone,
  fentanyl
• Partial agonists, mixed agonist-antagonists
• Buprenorphine
• Butorphanol
• Pure Antagonists (reversal of agonists)
• Naloxone
• ABUSE POTENTIAL

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Opioid Administration

• Systemic IV, SQ, IM, CRI
• Intra-articular injection
• Local injection
• Epidural injection
• Transdermal fentanyl patch

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Opioid Effects

• GOOD
• Great analgesia
• Variable muscle relaxation
• Sedation
• BAD
• Respiratory depression
• GI effects
• Vomiting
• Defecation followed by constipation

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Opioids (other effects)

• Excitement
• Panting
• Vocalization
• Noise sensitivity
• Depression of the cough center
• Advantage for?

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Fentanyl Patch

• Lag time
• apply 6-12 hours prior to surgery in cats,
• 12-24 hours in dogs
• Lasts about 3 days (up to 6 in cats)
• Variation in absorption rate
• Dose of patch (in micrograms/hr)
• Avoid heat sources
• Excessive amounts can cause ataxia, sedation in
  dogs, excitement, disorientation, wide-eyed stare
  in cats
• Remove patch, can reverse

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Fentanyl Patch

• Applied to dorsal neck or shoulders, lateral
  thorax
• Clip hair, clean skin with water only
• Do not cut patch
• Can remove just part of backing if small animal
• Apply patch, hold firmly 2 minutes
• Bandage

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Opioid Partial Agonists

• Buprenorphine
• Buprenex
• 4-8 hour duration

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Opioid Mixed Agonist-Antagonist

• Butorphanol
• (Torbutrol, Torbugesic)
• For mild to moderate pain
• Duration 1 to 4 hours IM, SQ
• Less abuse potential than agonists

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Opioid Antagonists

• Naloxone
• Used to reverse opiates/opioids
• Remember Reverses analgesia too!
• May not last as long as the agonist
• Relapse renarcotization
• Partial reversal with butorphanol possible

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Alpha-2 Agoniststhiazines
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Alpha-2 Agonists

• MOA?
• Examples
• Xylazine (Rompun)
• Medetomidine (Domitor)

Engages receptors in CNS gtgt decrease
norepinephrine
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Xylazine Good Things

• Moderate analgesia
• Potent sedative effect
• Good muscle relaxation

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Xylazine Bad Things

• Bradycardia due to stimulation of the vagus
  nerve?heart block
• Profound cardiac disturbances!
• Sensitizes the heart to catecholamines?Arrhythmias
  
• Decreased cardiac output
• Hypotension (BP decreases by 1/4-1/3)

1 ?
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Xylazine More Bad Things

• Vomiting (sometimes used as emetic)

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Xylazine Reversal?

• Yohimbine is reversal agent
• Mixed Alpha- antagonist (blocker)
• Trade name Yobine

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Medetomidine
Common name?

• DOMITOR
• More specific to CNS alpha-2 receptors
• Alpha-2 so has reversal agent
• (Antisedan)

Name?
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Steroids corticosteroids,glucocoticoids

• Examples
• Prednisone Prednisolone
• Dexamethasone
• Betamethasone
• Solu-Delta-Cortef
• Solu-Medrol
• Decrease pain
• by decreasing inflammation

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Steroids MOA inhibit phospholipase
A2gtgtgt inhibits prostoglandin/leukotrienes
Steroids inhibit here
Phospholipase A2
COX-2
COX-1
NSAIDS inhibit here
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Side Effects and Toxicity

• Iatrogenic hyperadrenocorticism
• Cushings Dz
• Polyphagia
• PU/PD
• Glaucoma and cataracts
• Gastric ulceration
• Delayed wound healing
• Immunosuppression

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More !

• Insulin resistance
• Hepatopathy
• CNS restlessness, seizure activity
• Infection

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Non-Steroidal Anti-inflammatory Drugs ( NSAIDS )

• Aspirin
• Carprofen - Rimadyl
• Etodolac - Etogesic
• Ketoprofen - Ketofen
• Phenylbutazone Bute
• Flunixin - Banamine
• (Acetaminophen - Tylenol )

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NSAIDS

• Most have effective somatic (superficial)
  analgesic effect
• Some have good visceral analgesic effect also
• All take 30-60 minutes to take effect, even if
  injected
• All have antiinflammatory properties
• Reduce fevers

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NSAIDS

• MOA cyclooxygenase inhibitors gtgt prostaglandin
  inhibitors
• Many side effects are due to good prostaglandin
  inhibition (COX 1)
• GI upset/ ulceration
• Renal toxicity
• Impaired platelet function

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NSAIDS MOA inhibit cyclooxygenasegtgtgt inhibits
prostoglandin/thromboxane
Steroids inhibit here
Phospholipase A2
COX-2
COX-1
NSAIDS inhibit here
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NSAIDS - Metabolism

• Metabolized by the liver
• Variation in metabolism between species
• Aspirin half-life 12 hours in dogs, 1 hour in
  horses, 38 hours in cats
• Many NSAIDS toxic to cats due to inability to
  metabolize them
• Acetaminophen is toxic in dogs AND cats!

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NSAIDS Inhibit Production of Protective GI
Prostaglandins

• Erosion/ulceration of GI tract
• Stomach upset
• Inappetance
• Vomiting
• Diarrhea
• Melena ?

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Prostaglandins in the Kidneys

• Cause dilation of renal vasculature, allowing
  perfusion despite decreased blood pressure due to
• Shock
• Dehydration
• Blood loss
• Anesthesia
• Inhibition of prostaglandin production can cause
  kidney cell death due to lack of perfusion
• Only an issue if decreased BP

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NSAIDS

• Cyclooxygenase inhibition? decreased thromboxane?
  decreases platelet adhesion/clumping?decreases
  clot formation and thromboemboli

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TYPES of NSAIDs
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Phenylbutazone

• COX1 and 2 Inhibitor
• Very Potent
• Commonly used in horses
• Not recommended in dogs
• GI side effects common
• NEVER IN CATS!

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Aspirin

• COX1 and 2 Inhibitor
• Very short half-life in horses
• Commonly used in dogs
• Buffered only
• With food
• Use with caution in cats
• Cant metabolize well
• Half-life 38 hours
• Dosed every 48-72 hours

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Neither Ibuprofen Nor Naproxen Is Recommended for
Use in Cats
Ibuprofen Advil COX1 COX2
Inhibitors Officially not recommended in dogs.
most do OK if used like aspirin
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Ketoprofen

• Ketofen (COX1 and COX2)
• Licensed in horses
• Approved for use in dogs and cats in Canada,
  Europe
• Good analgesia, potent antipyretic
• Injectable
• Limit use
• Blood clotting

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Flunixin meglumine

• Banamine (COX1 and COX2)
• Injectable
• Horses
• Colic
• Good analgesia
• Dogs
• GI side effects common, severe

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Carprofen

• Rimadyl
• COX-2 inhibitor spares good prostaglandins
• Fewer side effects
• DOGS ONLY
• Black labs
• 0.06 of all dogs develop hepatic problems (rare)
• BID Dosing

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Etodolac

• Etogesic
• COX 1 and 2 Inhibition
• Once daily administration
• DOGS ONLY

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Derramax

• Use in dogs
• COX 2 Specific
• SID dosing

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Metacam Meloxicam

• COX-2 Specific
• Use in dogs and cats
• Liquid
• Well tolerated

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NSAID Precautions

• Use only 1 NSAID at a time
• Never combine NSAIDS with glucocorticoids
• Gastric Ulceration
• Taper to lowest effective dose
• Change to alternative NSAID if poor response

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NSAID Contraindications

• Renal of hepatic dysfunction
• Decreased circulating blood volume
• Coagulopathies
• GI disease
• Pregnancy

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Local Anesthetics
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Local Anesthetics

• The -caine family Lidocaine, bupivicaine,
  mepivicaine, proparicaine, tetracaine, etc.
• MOA Block nerve impulses by blocking Na
  channels in nerve membranes

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Local Anesthetics

• Local infiltration of surgical site
• Intravenous regional anesthesia
• Intra-articular injection
• Nerve blocks
• Epidural
• Topical on skin/ eye/ larynx
• http//www.cvm.okstate.edu/courses/vmed5412/Lect23
  .asp

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Commonly Used With Neuroleptanalgesic
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Capsaicin

• Hot peppers
• Excites then fatigues nerve transmission?local
  analgesia
• Also get endorphin release

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St. Johnswort

• Arthritic pain
• Hypericin
• Stimulates neural inhibitory pathways? analgesia

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Chondroprotective Agents

• Nutraceuticals
• Chondroitin sulfate
• Glucosamine
• Hyaluronic acid
• Building blocks for cartilage and synovial fluid

Examples (oral) Synovi, Glycoflex (injectable)
Adequan Can be mixed with many other ingredients
(MSM, Creatine) to enhance effects.
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Antibiotic Analogyto understand pain control

• Antibiotics prescribed based on clinical signs,
  not always based on culture and sensitivity
• Rely on return to normal function to confirm
  diagnosis
• If doesnt help, add to or change drug protocol
• May need a loading dose
• May need a combination of drugs

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Questions??