PRINCIPLES OF PAIN MANAGEMENT & ANALGESIA

“THERE IS NO COMING TO CONSCIOUSNESS WITHOUT PAIN.”

-CARL JUNG

PRINCIPLES OF PAIN MANAGEMENT & ANALGESIA

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


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


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.


WHAT ABOUT OUR ANIMAL PATIENTS AND/OR OUR JOBS COULD MAKE MONITORING FOR PAIN DIFFICULT?


MYTHS ABOUT PAIN IN ANIMALS Consider how some people without medical

backgrounds may view the animal’s response to pain


CONSEQUENCES OF UNTREATED PAIN Consider the long term effects of untreated pain


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


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 well-being. “natural pain reliever”

Nursing care:

Other therapies to control pain:

THE PHYSIOLOGY OF PAIN


METHODS OF PAIN CONTROL USING MEDS OPIOIDS NSAIDS LOCAL ANESTHETICS OTHERS: alpha-2 agonists, ketamine

OPIOIDS

METHODS OF PAIN CONTROL USING MEDS

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 12-24 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

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

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 BLOCKIS ALSO A RING BLOCK

Dental blocks for tooth extractions

Maxillary Nerve block viaThe infraorbital foramen

NERVE BLOCKS

Paravertebral block

Nerve blocks help pinpoint areas of pain

THESE ARE EXAMPLES OF LINEBLOCKS

NERVE BLOCKS

THIS NERVEBLOCK 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

Spinal cord

Pia materSubarachnoid space w/CSF

arachnoidDura mater

Epidural space

LOCAL ANESTHETICS

EPIDURALS

http://www.youtube.com/watch?v=zmwvMHZG_5g



SIDE EFFECTS OF LOCAL ANESTHETICS

Allergy Rash or hives in the area

Systemic toxicity Sedation, nausea, restlessness, hyperexcitability,

seizures, respiratory suppression, comaInfection (esp. w/epidurals)Cranial infiltration of an epidural may cause

serious toxicity, respiratory suppressiondeath

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 (multi-modal therapy, balanced analgesia) is more beneficial than using high doses of one medication.

Pain is alleviated via different pathways

PRINCIPLES OF PAIN MANAGEMENT & ANALGESIA

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