4. TRANSDUCTION
• Mechanical, chemical and thermal energy are converted into electrical
energy/impulses by specialized nerve endings called “nociceptors”.
• NOCICEPTORS
• Free nerve endings of primary afferent fibers.
• Have high stimulus thresholds for activation.
5. TRANSMISSION
Occurs along 2 different types of afferent nerve fibers:
A-DELTA FIBERS
• Large diameter
• Myelinated
• Rapid impulse conduction (6-30 m/sec)
• Stimulates immediate reaction
6. C FIBERS
• Small diameter
• Unmyelinated
• Slow conduction
• (0.5 – 2 m/sec)
• Reinforces the immediate response that is signaled by a-delta
fibers.
Spinothalamic tract
• Most important tract in transmission of nociceptive information.
Spinoreticular tract
Spinohypothalamic tract
7. MODULATION
• SIGNAL PROCESSING
• Spinal cord
• Dorsal horn
• Endogenous systems
Tissue trauma
Signal enters dorsal horn
Reflex activity
exits ventral
horn
To higher
levels of
CNS
CROSS SECTION OF THE SPINAL CORD
8. PERCEPTION
• RECEIVING AND INTERPRETATION
• Successful transduction, transmission, &
modulation of a painful stimulus.
Modulation
Perception
9. TYPES OF PAIN
PERIPHERAL PAIN
Visceral
• abdominal or thoracic organs
• poorly localized
• referred
Somatic
superficial
• skin
deep
• tendons, joints, muscle, periosteum
10. PHYSIOLOGICAL PAIN
• It is a protective mechanism and causes avoidance.
• Little to no tissue injury.
• Pain stops once the stimulus is removed.
PATHOLOGICAL PAIN
• It results from tissue injury and causes inflammation ,
nerve damage etc.
• Persists after the stimulus is received.
11. NEUROPATHIC PAIN
• Damage to peripheral nerves or spinal cord.
• Often difficult to treat appropriately.
12. ACUTE PAIN
• Arises from soft tissue trauma or inflammation.
• Plays a biologically adaptive role by facilitating tissue repair.
CHRONIC PAIN
• Pain that persists beyond the expected time frame for a given
disease, process or injury.
• May be associated with ongoing inflammation.
• May be autonomous with no temporal relation to the inciting
cause.
13. ADAPTIVE PAIN
• Normal response.
• Protects from further injury.
• Inflammation is a large component.
MALADAPTIVE PAIN
• Abnormal response.
• Stimulus is gone but pain persists.
15. COMMON BEHAVIORAL RESPONSES TO PAIN
• Dogs arepack animals, theyshareemotions with pack members to receive
support.
Whine, whimper
Arched or abnormal posture
Guarding of injured tissue
Restlessness
Behavior change
Increased heart rate and blood pressure
Hypersalivation
Appetite reduction
Dilated pupils
Altered voiding behavior
16. Cats aremore solitary animals, they aregenerally more stoic thandogs; showing pain
highlights a cats vulnerability.
Over grooming
Hiding
Squinting
Guarding injured tissue
Desperate attempts to flee
Reduced grooming
Appetite reduction
Pupil dilation
Salivation
Restlessness
Increased heart rate and blood pressure
17. STRESS RESPONSE MARKERS/PAIN ASSESSMENT
Heart rate
Respiratory rate
Blood pressure
Posture
Attitude
Food and water intake
Patterns of defecation, urination
Change in activity levels
Natural behaviors – inquisitive,
grooming
Provoked behavior
Aggression
Gait-/Posture
Vocalization
Appearance of stereotypical
behaviors
18. ACTIONS OF ANALGESICS ON PAIN
PROCESSES
TRANSDUCTION:
• Can be blocked by local anesthetics by injection either at the site of
injury/incision or intravenously.
• Can be decreased by use of NSAIDs which decrease the production of
prostaglandins at the site of injury.
TRANSMISSION:
• Can be prevented by local anesthetics by injection along peripheral nerves,
at nerve plexus, or in the epidural or subarachnoid spaces.
MODULATION:
• Can be augmented by injection of local anesthetics or alpha2-adrenergic
agonists; gabapentin may also effect modulation.
PERCEPTION:
• Altered by use of general anesthetics or systemic injection of opioids and/or
alpha2-agonists.
19. GENERAL APPROACHES TO PAIN
MANAGEMENT
o PRE-EMPTIVE ANALGESIA: Giving analgesics prior to the noxious stimulus
(surgery)
• By blocking or inhibiting the nociceptive process before it begins,
hypersensitivity is prevented.
• May decrease the amount of anesthesia and post-operative analgesia
needed.
o MULTIMODAL OR “BALANCED” ANALGESIA: Using a combination of analgesics
which will impact more than one portion of the nociceptive process.
• for example: buprenorphine and meloxicam pre-surgically, lidocaine block
used prior to incision, and bupivicaine splash prior to closing incision
20. ANALGESICS
DIVIDED INTO FIVE MAIN CLASSES BASED ON MODE OF ACTION
• OPIOIDS
• NON-STEROIDAL ANTI-INFLAMMATORY DRUGS
• LOCAL ANESTHETICS
• ALPHA2-ADRENOCEPTOR AGONISTS
• MISCELLANEOUS DRUGS
22. OPIOID CLASSIFICATION
AGONISTS
• Stimulate receptor activity
• MU agonists
• most common group of opioid agonists used
• include morphine, meperidine, oxymorphone,
hydromorphone, fentanyl, carfentanil
AGONISTS-ANTAGONISTS
• Stimulate activity at some receptors and antagonize others
• Butorphanol – kappa agonist, mu antagonist
23. • PARTIAL AGONISTS
• Bind to receptor but only produce a partial effect
• Buprenorphine – partial mu agonist, kappa antagonist
• ANTAGONISTS
• Primary activity is mu receptor antagonism
• Naloxone
• Naltrexone
• Nalmefene
• Diprenorphine
26. GOOD
GREAT ANALGESIA
VARIABLE MUSCLE RELAXATION
SEDATION
BAD
RESPIRATORY DEPRESSION
GI EFFECTS
• vomiting
• defecation followed by
constipation
EXCITEMENT
DEPRESSION OF THE COUGH
CENTER
OPIOID EFFECTS
27. OPIOID SPECIES SPECIFIC EFFECTS
Excitement in cats (dose related).
Panting in dogs – resets thermostat.
29. TRAMADOL
• Synthetic opioid agonist which also inhibits serotonin and norepiniphrine
re-uptake in the spinal cord.
• The main metabolite has moderate opioid activity.
KETAMINE
• NMDA antagonist.
• Used as a cri during surgery at sub-anesthetic doses, it reduces mac and
can help prevent hypersensitivity
• More effective treating somatic pain than visceral pain
• Can be administered via epidural injection
GABAPENTIN
• Analogue of naturally occurring neurotransmitter GABA.
• Believed to increase production of GABA.
• part of endogenous inhibition of nociception
• Used to treat nerve pain.
31. • NSAIDS are weak organic acids with anti-inflammatory, analgesic,
and antipyretic properties.
• Inhibit prostaglandin production by inhibiting cox enzymes.
• Are either non-selective (inhibits both cox iso-enzymes) or
selective for cox-2.
• Non-selective NSAIDS have more serious side effects (gastric
ulceration and renal toxicity).
• Decreased renal blood flow during anesthesia makes kidneys more
susceptible to toxic effects.
• Cyclooxygenase inhibition decreased thromboxane decreases
platelet adhesion/clumpingdecreases clot formation and
thromboemboli.
33. PHENYLBUTAZONE
COX1 AND 2 INHIBITOR
VERY POTENT
COMMONLY USED IN HORSES
NOT RECOMMENDED IN DOGS
• GI SIDE EFFECTS COMMON
• NEVER IN CATS!
34. ASPIRIN
• COX1 AND 2 INHIBITOR
• VERY SHORT HALF-LIFE IN HORSES
• COMMONLY USED IN DOGS
• BUFFERED ONLY
• WITH FOOD
• USE WITH CAUTION IN CATS
• CAN’T METABOLIZE WELL
• HALF-LIFE 38 HOURS
• DOSED EVERY 48-72 HOURS
35. 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
36. FLUNIXIN MEGLUMINE
• BANAMINE® (COX1 AND COX2)
• INJECTABLE
• HORSES
• COLIC
• GOOD ANALGESIA
• DOGS
• GI SIDE EFFECTS COMMON, SEVERE
37. 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
42. Stimulation of the alpha2 – adrenoceptors result in sedation,
muscle relaxation, and analgesia.
Two alpha-2 agonists (xylazine, medetomidine) and 2 antagonists
(yohimbine, atipamezole) are approved for use in small animals in
canada.
Another alpha-2 agonist, romifidine, is approved for use in
horses, but not in dogs and cats.
44. • LOCAL INFILTRATION OF SURGICAL SITE
• INTRAVENOUS REGIONAL ANESTHESIA
• INTRA-ARTICULAR INJECTION
• NERVE BLOCKS
• EPIDURAL
• TOPICAL ON SKIN/ EYE/ LARYNX
The “-caine” family: Lidocaine, bupivicaine, mepivicaine,
proparicaine, tetracaine, etc.
45. EPIDURALS
• Administered alone or in combination with other
analgesics.
• If combined, smaller doses can be used, decreasing
risks of adverse effects.
• Can cause motor deficits at higher doses.
47. CAPSAICIN
• This medication is used to treat minor aches and pains
of the muscles/joints (e.g., arthritis, backache, sprains).
capsaicin works by decreasing a certain natural
substance in the body (substance p) that helps pass pain
signals to the brain.
49. 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.
