PRINCIPLES OF PAIN
MANAGEMENT & ANALGESIA
“THERE IS NO COMING TO
CONSCIOUSNESS WITHOUT PAIN.”
-CARL JUNG
PRINCIPLES OF PAIN & ANALGESIA
 WHAT IS PAIN?

An unpleasant sensory or emotional experience associated with
actual or potential tissue damage
Pain results when nerve cells in the skin or deep tissues, called
nociceptors, detect a noxious stimulus
 Somatic pain arises from the skin, soft tissues, muscles, bones, or
joints
 Easily localized through stabbing, throbbing, or aching
 Visceral pain arises from internal organs
 not easily localized and is characterized by cramping or burning
 Referred pain term used to describe the pain that is felt in a body part
other than where the actual pain stimulus is coming from
 Hyperesthesia is increased sensitivity to a stimulus
 Neuropathic pain arises from direct damage to peripheral nerves or
the spinal cord.
 May be shooting, sharp, or tingling

PRINCIPLES OF PAIN & ANALGESIA
 WHAT IS PAIN? cont’d
 Pain can also be classified according to onset and duration

Acute pain has an abrupt onset and a relatively short duration of
action. *Effectively treated with analgesic drugs

Chronic pain has a slow onset, and duration of several months to
years. *May be unresponsive to drug therapy
PRINCIPLES OF PAIN & ANALGESIA
 MONITORING SIGNS OF PAIN
 Consider how we as humans display pain vs. how our animal
patients display pain. Write some ways you can monitor for
pain in animals.
PRINCIPLES OF PAIN & ANALGESIA
 WHAT ABOUT OUR ANIMAL PATIENTS AND/OR
OUR JOBS COULD MAKE MONITORING FOR
PAIN DIFFICULT?
PRINCIPLES OF PAIN & ANALGESIA
 MYTHS ABOUT PAIN IN ANIMALS
 Consider how some people without medical backgrounds may
view the animal’s response to pain
PRINCIPLES OF PAIN & ANALGESIA
 CONSEQUENCES OF UNTREATED PAIN
 Consider the long term effects of untreated pain
PRINCIPLES OF PAIN & ANALGESIA
 WHAT IS ANALGESIA?
 Analgesia is the absence of the awareness of pain, achieved
through the use of drugs or other modes of therapy. It applies
to the relief of pain without the loss of consciousness.
 WHAT ARE THE GOALS FOR PAIN CONTROL?
 Control pain at every stage of treatment
 to administer analgesics before the patient has an awareness of
pain. This is known as preemptive analgesia.
 To prevent windup, an event caused by a buildup of chemical
mediators that intensify the pain response
PRINCIPLES OF PAIN & ANALGESIA
 METHODS OF PAIN CONTROL WITHOUT MEDS
 Endorphins are endogenous compounds produced by the
pituitary gland and the hypothalamus that bind to opioid
receptors during situations of trauma or stress. They resemble
opiates in their ability to provide pain relief and a feeling of wellbeing. “natural pain reliever”
 Nursing care:

Other therapies to control pain:
THE PHYSIOLOGY OF PAIN
PRINCIPLES OF PAIN & ANALGESIA
 METHODS OF PAIN CONTROL USING MEDS
 OPIOIDS
 NSAIDS
 LOCAL ANESTHETICS
 OTHERS: alpha-2 agonists, ketamine
METHODS OF PAIN
CONTROL USING MEDS
OPIOIDS
OPIOIDS
 MODE OF ACTION:
 Acts on 4 different receptors in the brain and spinal cord






Mu
Kappa
Sigma
Delta
An opioid agent may act as an agonist (stimulating agent) or antagonist
(blocking agent) at each receptor
 Some opioid agents are considered mixed agonist/antagonists in that they
block one type of receptor and stimulate another or partial agonists in that
they only partially stimulate opioid receptors
Binding to these receptors can result in a number of effects:
 ANALGESIA
 Respiratory depression
 bradycardia
 Sedation
 Dysphoria
 And others,…
OPIOIDS
 REVERSIBILITY
 One major advantage of opioids is their reversibility with pure
antagonists such as NALOXONE, which is the most effective
 Naloxone competitively binds to opioid receptors

It is also possible to use a mixed agonist/antagonist such as
BUTORPHANOL to reverse the effects of the pure agonists
OPIOIDS
 MORPHINE: a FULL AGONIST (stimulates all 4
receptors)




Great for moderate to severe pain
Produces significant sedation
Significant cardiovascular & respiratory effects
SIDE EFFECT/CAUTIONS:
Can cause excitement in cats (use lower doses)
 Often results in VOMITING
 Give slowly IV otherwise severe histamine release can lead to
hypotension and pruritis

 Other FULL AGONISTS include oxymorphone,
hydromorphone, and fentanyl
OPIOIDS
 FENTANYL: a FULL AGONIST
(stimulates all 4 receptors)


the injectable has a rapid onset of action
and short duration of action. Onset of
action: 2 min; duration of effect: 20-30 min
commonly used as a transdermal skin patch
Fentanyl is slowly absorbed through the
skin and may take 4-12 hrs in cats, and 1224 hrs in dogs to reach therapeutic levels
 See pg 230 in your book, Procedure 7-1 for
instructions on placing a fentanyl patch.

OPIOIDS
 BUPRENORPHINE: partial
agonist (aka bupi, buprenex)





Delayed onset of action, (40 min IM) but longer
duration of action than other opiods – up to 12
hours
Best used for mild to moderate pain
The injectable product is effectively given to
cats transmucosally (applied to the gingiva,
under the tongue, in cheek pouch)
Can be used to reverse the effects of pure
agonists, while maintaining some analgesic
effect. Not as effective as naloxone
THIS DRUG IS PART OF THE VTI PROTOCOL
FOR DOGS & CATS*
OPIOIDS
 BUTORPHANOL: mixed
agonist/antagonist (aka torb,
torbugesic)




Best used for mild to moderate pain; and
can also be used as a cough suppressant
Can be used to reverse the effects of pure
agonists. Not as effective as naloxone
Commonly combined with a sedative such as
dexmedetomidine or acepromazine
MIXING AN OPIOID & SEDATIVE IS
KNOWN AS NEUROLEPTANALGESIA
OPIOIDS
 TRAMADOL: a non-opiate drug that has activity at
the mu receptor



Oral tablets
Useful post-operative pain med in dogs and cats
Not currently controlled
METHODS OF PAIN
CONTROL USING MEDS
NSAIDS
NSAIDS
 MECHANISM OF
ACTION:

Inhibits the synthesis of
prostaglandins by blocking
the enzyme cyclooxygenase
( aka COX-1 & COX-2)
COX-1 leads to the
production of beneficial
prostaglandins
 COX -2 leads to the
production of harmful
prostaglandins that are
present during tissue damage
and inflammation.

NSAIDS
 BENEFITS OF NSAIDS:
 No strict record keeping
 Little abuse potential
 Effective when given orally
 No sedative, cardiovascular, or respiratory effects
 Antipyretic effects
 SIDE EFFECTS/CAUTIONS:
 GI upset/GI ulcers due to inhibition of prostacyclin




DO NOT USE CONCURRENTLY w/ STEROIDS
renal toxicity due to inhibition of PGE2
hepatic toxicity
Inhibits platelet aggregation due to blockage of thromboxane
NSAIDS
 RIMADYL (carprofen)
 Approved for use in DOGS ONLY!
 Oral(chewable tablets) and injectable forms available
 Less likely to cause side effects mentioned previously due to its
COX-2 selectivity
 Common uses:
Post-operative pain relief
 Pain relief from osteoarthritis and other musculoskeletal injuries


PART OF THE CANINE POST-OP PAIN CONTROL
PROTOCOL AT VTI
NSAIDS
 METACAM (meloxicam)
 Approved for use in dogs and cats
 COX-2 selective
 Oral and injectable formulations available

PART OF FELINE POST-OP PAIN CONTROL PROTOCOL AT
VTI
METHODS OF PAIN
CONTROL USING MEDS
LOCAL
ANESTHETICS
LOCAL ANESTHETICS
 WHAT IS LOCAL
ANESTHESIA/ANALGESIA?

The use of a chemical agent on sensory neurons to produce a
disruption of nerve impulse transmission, leading to
temporary loss of sensation
LOCAL ANESTHETICS
 CHARACTERISTICS OF LOCAL
ANESTHETICS




Exert their effects on neurons in the peripheral nervous system
and spinal cord that control pain, heat, cold, & pressure
Relatively few effects of the cardiovascular and respiratory
systems
Exert their effects in the area closest to the site of injection
Not normally transferred across the placenta

Safe for c-sections
LOCAL ANESTHETICS
 ROUTES OF ADMINISTRATION
 TOPICAL: must penetrate the epidermis to reach the dermis
where the peripheral nerves are located
Sprayed on intact skin for superficial procedures such as skin
biopsies (ex: ethyl chloride)
 Creams can also be applied to desensitize skin for superficial
minor procedures (ex: lidocaine/prilocaine)
 Splash blocks refer to the use of sprays or anesthetic soaked gauze
sponges on open wounds or surgical sites
 Applied through a chest tube in patients having thoracic surgery
 Should be done when patient is awake
 Absorbed through the mucous membranes (larynx, eye, urethra)
 Short duration of action and less pain relief when compared to
other routes of administration of local anesthetics

LOCAL ANESTHETICS
 ROUTES OF ADMINISTRATION:
 INFILTRATION(injection):
Local anesthetic can be injected subcutaneously, intradermally, or
between muscle planes
 Ideally the site of injection is clipped and cleaned
 Small needle (23-25 gauge) used to prevent tissue damage
 Test efficacy by pricking the site with a needle
 Do not inject into infected or inflamed tissues


Some local anesthetic drugs are combined with epinephrine
Epinephrine causes vasoconstriction which decreases rate of
absorption and prolonging effect
 It also decreases the amount of drug entering the circulation,
decreasing chances of toxicity.
 CAUTION AROUND AN INCISION OR ON EXTREMITIES AND
WITH PATIENTS WITH CV ABNORMALITIES

LOCAL ANESTHETICS
 ROUTES OF ADMINISTRATION
 NERVE BLOCKS: Injection of a local anesthetic in the
proximity of a specific nerve to desensitize a specific anatomic
location. Location of target nerve must be known and palpated
if possible.
Lameness exams in horses
 Cornual blocks for dehorning cattle
 Dental blocks in dogs and cats
 Infiltration of nerves during amputation of a limb
 Declawing cats



May take 15-20 minutes for absorption
Nerve blocks include line blocks and ring blocks
Cornual blocks for dehorning cattle
THIS NERVE BLOCK
IS ALSO A RING BLOCK
Dental blocks for tooth extractions
Maxillary Nerve block via
The infraorbital foramen
NERVE BLOCKS
Nerve blocks help pinpoint areas of pain
Paravertebral block
THESE ARE EXAMPLES OF LINE
BLOCKS
NERVE BLOCKS
THIS NERVE
BLOCK IS ALSO
A RING BLOCK
LOCAL ANESTHETICS
 ROUTES OF ADMINISTRATION
 NERVE BLOCKS


LINE BLOCKS: continuous line of local anesthetics placed SQ in
an area served by numerous small nerves
 The needle is inserted along the line of infiltration and the
anesthetic is injected as the needle is withdrawn
 If placed encircling an anatomic part, it is called a RING
BLOCK
INTRAARTICULAR: injecting local anesthetics directly into
a joint usually after surgery of the joint, immediately after
closure of the joint capsule
LOCAL ANESTHETICS
 ROUTES OF ADMINISTRATION
 EPIDURAL: blockage of sensory and motor nerves in the
rear, abdomen, pelvis, tail, hind limbs, and perineum

Anesthetist must be familiar with the anatomy of the terminal
spinal cord and lumbosacral vertebrae
Epidural space
Dura mater
arachnoid
Subarachnoid space w/CSF
Pia mater
Spinal cord
LOCAL ANESTHETICS
 EPIDURALS
http://www.youtube.com/watch?v=zmwv
MHZG_5g
SIDE EFFECTS OF LOCAL ANESTHETICS
 Allergy
 Rash or hives in the area
 Systemic toxicity
 Sedation, nausea, restlessness, hyperexcitability, seizures,
respiratory suppression, coma
 Infection (esp. w/epidurals)
 Cranial infiltration of an epidural may cause serious
toxicity, respiratory suppression
 death
METHODS OF PAIN
CONTROL USING MEDS
OTHERS:
ALPHA-2 AGONISTS
KETAMINE
ALPHA-2 AGONISTS
 ALPHA-2 AGONISTS (ex: dexdomitor, xylazine)
 Short duration of action (~90 minutes)
 Also causes profound sedation, bradycardia
 Commonly combined with butorphanol
 Reversible
 KETAMINE
 Good effect for skin and SQ pain
 Duration of action is short 30min
METHODS OF PAIN CONTROL
Combining drugs from different categories (multimodal therapy, balanced analgesia) is more
beneficial than using high doses of one medication.
Pain is alleviated via different pathways