Download Equine Pain

Equine Pain
INAG 120 – Equine Health
Management
October 10, 2011
What is Pain?
• Human pain:
An unpleasant sensory and emotional experience
associated with actual or potential tissue
damage or described in terms of such damage
(IASP - International Association for the Study of
Pain, 1979)
What is Pain in Animals?
• An aversive sensory experience that
elicits protective motor actions, results
in learned avoidance and may modify
species specific traits of
behavior, including
social behavior
Or…
• Animal pain is an aversive, sensory experience
representing awareness by the animal of damage or
threat to the integrity of its tissues (note that there might
not be any damage). It changes the animal’s
physiology and behavior to reduce or avoid the
damage, to reduce the likelihood of its recurrence and to
promote recovery.
• Non-functional (non-useful) pain occurs when the
intensity or duration of the experience is not appropriate
for damage sustained (especially if none exists) and
when physiological and behavioral responses are
unsuccessful in alleviating it
Pain Classification: Sites of Origin
• Somatic pain
• Visceral pain
• Neuropathic pain
• Referred pain
Pain Classification: Duration
• Acute
• Chronic
• Chronic inflammatory
• Chronic neuropathic
Type of Pain
• Acute Pain
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Sudden onset
Short duration
Variable severity
Identifiable cause
Focal to injury site
Acts as symptom or
warning
– Equine Acute Pain?
• Chronic Pain
– Pathologic/diseased
state
– Unrelenting
– May have no
identifiable cause
– May spread beyond
original site of injury
– May serve no
biological function
– Equine Chronic Pain?
Production of Pain
• Pain is in the brain…
• Peripheral mechanisms
– Skin, muscle, bone and other tissues have
multiple nerve endings
– These nerve endings, when stimulated send a
signal to the brain through the nervous
system
• Takes from 0.001 – 1 second to be recognized
Tissue Stimulation
• Noxious
– Stimulation that makes the horse aware of stimulation
that could or already has done damage
• Non-noxious
– Used by the horse to make it aware of the state of its
body and of its immediate environment (i.e. touch)
• Travel along thick, myelinated nerves and rarely produce
pain unless the fibers are sensitized such as by inflammation
Abnormal Pain Response
• Allodynia
– Not known/reported in horses
• Hyperalgesia
– Primary (peripheral tissue)
• Conversion of arachidonic acid to prostaglandins can be
significantly reduced:
– COX-1 is inhibited by drugs such as Aspirin
– COX-2 is inhibited by drugs such as Celecoxib and Rofecoxib
• COX-2 inhibitors generally have fewer unwanted effects.
– Secondary (occurs in surrounding uninjured tissue)
• Contributes to development and maintenance of chronic pain
Substance P
• Substance P
– Neruopeptide (short chain of amino acids)
produced by nociceptors and used to activate
neurons in the spinal cord.
– Can also be used for local inflammatory
responses (i.e., a scratch) without going
through spinal cord.
Inflammatory Responses
• Increased blood flow  REDNESS
• Increased blood flow  WARMTH
• Swelling as fluid leaks out of blood vessels
Injury  Pain Sensation
• Nociception
– Transduction, transmission, and spinal cord
modulation
• Perception
– Perceiving the unpleasant experience
• Cognition
– Behavioral response
• How can the sensation of pain be
lessened?
Pain Assessment
1. Assessment of pain in your horse is a value
judgment relying on measurement of
physiological and behavioral changes (indices)
2. Use a wide range of indices
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Training improves usage
Know the species, breed and individual animal well
Know when to seek advice from those with more
expertise (including owners or typical caretakers)
Pain Assessment
3. Experienced judge says horse is not in
pain? Acceptable
– HOWEVER: If judge not available  take
appropriate action to treat pain
– Better safe than sorry…
4. Leave your emotions at the stall door
(pasture gate, etc.).
Objective Assessment of Pain
• Measurements of physiological, biochemical and
behavioral responses:
– Threshold testing
– Behavioral response to a visual or auditory stimulus
• Physiological responses
– Changes in heart and respiration rate, blood pressure and stress
hormone values (cortisol)
• Biochemical changes
– blood glucose, acute phase proteins and muscle enzymes
• Behavioral responses
– precise measurements of the occurrence of well-defined
activities and postures
Physiological Responses to Pain
• Dilatation of the pupils and/or wide opening of
the eyelids
• Changes in blood pressure and heart rate
• Increased respiration rate and/or depth
• Pilo-erection (goose bumps)
• Changes in skin and body temperature
• Increased muscle tone
• Sweating
• Increased defecation and urination
Biochemical Pain Responses
• Changes in blood or cerebrospinal fluid
levels of certain chemicals
– Neurotransmitters, enzymes, other hormones
– Changes in things such as lactate levels in
blood are not specific indicators of pain
– Damaged tissues release enzymes into blood
– Values don’t necessarily reflect level of pain
Behavior
• Responses that allow
the animal to reduce
or avoid the pain
recurrence
– Involves emotional
experience and
learning
• Reflex responses
– Licking, biting
attacking or running
away
• Minimization of pain
and assist healing
• Response designed
to stop another
animal (or person)
from causing pain
• Failure to act normally
Behavior - Posture
• Normal Postures:
– Horses spend less
than 3% of the day
lying down
– If not in pain or ill,
normal horse will get
up when approached
– When lying, horses lie
in sternal (ventral)
posture
– May also lie laterally
(flat out)
Behavior - Posture
• Abnormal Postures:
– Lying in lateral posture
– Lying ventrally with hind
legs extended
– Normal sternal position but
trembling
– Standing or walking
abnormally
– Statue standing
• sustained standing still
• trembling, stretching, a
hunched back, a tucked in
tail and tucked up
abdomen
Behavior – Changes in Gait
• Later lecture on lameness…
Behavior - Activity
• What level/type of activity are they involved in?
• Examples:
– Pain in the mouth  “quidding”
– Pain in the head  headshaking or twitching ears
– Pain in the tail  tail rubbing
• Incidence of these activities increases with
increasing pain severity
• Can alter animal’s placement in herd hierarchy
Behavior - Activity
• Chronic Pain
– Same activities shown but usually at lower
incidence
– More difficult to detect than acute pain
– “Ain’t doin’ right…” “Something just isn’t
right…”
Behavior – Facial Expression
• Horses communicate primarily using
SIGHT (i.e., posture)
• Some horses perform
flehmen behavior in
response to pain
Behavior - Vocalization
• Grunting
• Groaning
• Squealing
• Not all that common in horses unless
severe pain
Behavior – Mental State
• Adjectives:
– Dull, depressed,
unresponsive,
unaware, sleepy,
apprehensive,
anxious, timid, bright,
alert, aware, excitable,
hypersensitive and
aggressive
• Play may be
decreased
• Decreased ability to
learn new tasks
• Inability to perform
learned tasks
Subjective Assessment of Pain
• Verbal descriptions:
– In humans: mild, moderate, severe,
excessive, excruciating, localized, sharp, dull,
burning
– Horses?
Systematic Assessment
• Details of animal
• Clinical history of the problem
• Clinical exam (vet)
• Physiological responses to pain
• Biochemical responses to pain (vet)
• Behavioral responses to pain