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

_______________, detect a noxious stimulus

2 types of sensory neurons that detect and transmit pain _________________(large, myelinated)

Transmit sharp, discrete pain signals that allow the patient to localize the source of pain.

transmits somatic pain _________________(small, nonmyelinated)

Transmit dull, aching, throbbing pain that cannot be easily localized

transmits somatic & visceral pain (visceral pain is only transmitted by C fibers)


THE PAIN PATHWAY _________________: transformation of noxious thermal,

chemical, or mechanical stimuli into electrical signals called action potentials by A-delta & C fibers

_________________: these sensory impulses are then conducted to the spinal cord

_________________: in the spinal cord where the A-delta & C fibers terminate, the impulses can be altered by other neurons, which either amplify or suppress them.

_________________: the impulses are transmitted to the brain, where they are processed and recognized.

THE PHYSIOLOGY OF PAIN


WHAT IS PAIN? __________ arises from the skin, soft tissues,

muscles, bones, or jointsEasily localized through stabbing, throbbing,

or aching ___________arises from internal organs

not easily localized and is characterized by cramping or burning

____________term used to describe the pain that is felt in a body part other than where the actual pain stimulus is coming from


WHAT IS PAIN? ______________ is increased sensitivity to a stimulus _______________arises from direct damage to peripheral

nerves or the spinal cord. May be shooting, sharp, or tingling

_____________or stump pain is sensation or pain arising from the missing body part

Pain can also be classified according to onset and duration ________ pain has an abrupt onset and a relatively short

duration of action. *Effectively treated with analgesic drugs

________ pain has a slow onset, and duration of several months to years. *May be unresponsive to drug therapy


MYTHS ABOUT PAIN IN ANIMALS Consider how some people without medical

backgrounds may view the animal’s response to pain


THE 5 FREEDOMS OF ACCEPTABLE ANIMAL WELFARE Freedom from hunger Freedom from physical and thermal discomfort Freedom from pain, injury, & disease Freedom to express normal behavior Freedom from fear and distress


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


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.

3 TYPES OF BEHAVIORS ASSOICIATED W/PAIN IN ANIMALS


PAIN ASSESSMENT The measurement of pain is important to:

Pain scales Based on observer’s assessment of patient’s

spontaneous behaviors, and behaviors on handling, interaction, and manipulation, & maybe physiologic parameters.

Pain scores should be reassessed regularly and preferably by the same person to minimize observer variation.


PAIN ASSESSMENT TOOLS: Simple descriptive scale


PAIN ASSESSMENT TOOLS: Numeric rating scales


PAIN ASSESSMENT TOOLS: Visual analogue scale

PAIN ASSESSMENT TOOLS: Comprehensive scales


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


PHYSIOLOGICAL SIGNS OF PAIN


WHAT IS 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 ____________________. Decreases the analgesic requirements Decreases CNS sensitization

To prevent __________ an event caused by a buildup of chemical mediators that intensify the pain response


METHODS OF PAIN CONTROL WITHOUT MEDS _______________ 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:


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

OPIOIDS

METHODS OF PAIN CONTROL USING MEDS

OPIOIDS

MODE OF ACTION: Acts on 4 different receptors in the brain and spinal cord

_______ _______ _______ Sigma(only cause hallucination, euphoria/dysphoria) An opioid agent may act as an _______ (stimulating agent) or __________

(blocking agent) at each receptor Some opioid agents are considered _________________________in that they

block one type of receptor and stimulate another or _______________in that they only partially stimulate some opioid receptors

Binding to these receptors can result in a number of effects: ANALGESIA Respiratory depression Sedation Dysphoria And others,…

OPIOIDS

REVERSIBILITY One major advantage of opioids is their reversibility

with pure antagonists such as ______________, which is the most effective

Naloxone competitively binds to opioid receptors It is also possible to use a mixed agonist/antagonist such

as BUTORPHANOL or a partial agonist such as BUPRENORPHINE to reverse the effects of the pure agonists

CONTROLLED

OPIOIDS

MORPHINE: a FULL AGONIST (stimulates all 4 receptors) Great for moderate to severe pain Produces significant sedation cardiovascular & respiratory depression

SIDE EFFECT/CAUTIONS: Can cause excitement in cats (use lower doses) Often results in ______________ due to its effects on the CRTZ Give slowly IV otherwise severe __________________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 _____________ 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 of the mu receptor(aka bupi, buprenex) Delayed onset of action, (40 min IM) but longer

duration of action than other opioids – ___________

Best used for mild to moderate pain The injectable product is effectively given to cats

_____________________ (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(kappa,sigma)/antagonist (mu)(aka torb, torbugesic) Best used for mild to moderate pain;

and is commonly used as a ________________

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 _____________________

OPIOIDS

TRAMADOL: a non-opiate drug that has agonist 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) ______ leads to the

production of beneficial prostaglandins

________ 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 __________

DO NOT USE CONCURRENTLY w/ ___________ ______ toxicity due to inhibition of PGE2 hepatic toxicity Inhibits platelet aggregation due to blockage of

______________

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

OTHERS:ALPHA-2 AGONISTS

KETAMINE


ALPHA-2 AGONISTS & KETAMINE

ALPHA-2 AGONISTS (ex: dexdomitor, xylazine) Short duration of action (~90 minutes) Also causes profound sedation, bradycardia Commonly combined with butorphanol Reversible (analgesic effects are reversed as well)

KETAMINE Works by antagonizing ____________receptors in the spinal

cord Blocking NMDA receptors prevents central sensitization &

windup Effective for _________analgesia, but limited visceral

analgesia Duration of action is short 30min

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 _________ 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 ________ blocks and ______ 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

_________________: 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 ____________: 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

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

NEUROMUSCULAR BLOCKING AGENTS

MECHANICAL VENTILATION

SPECIAL TECHNIQUES


Aka muscle-paralyzing agents

These agents act by interrupting normal transmission of impulses from motor neurons to the muscle synapse Site of action: ________

_______________, where acetylcholine is released by the neurons to attach to muscle end plates.


Two ways for these agents to disrupt the nervous transmission _________________ agents – cause a single surge of activity at the

neuromuscular junction, followed by a refractory period. (Ex: succinylcholine) Animals may show spontaneous muscle twitching followed by

paralysis Reversal agents are not effective

_________________ agents- block the receptors and the end plate. (ex: pancuronium, atracurium) No initial surge of activity at the neuromuscular junction, no

spontaneous muscle movements. These agents can be reversed with neostigmine or

edrophonium

Not commonly used in vet med, but can be useful in the following situations.


Neuromuscular blocking agents allow relaxation of voluntary muscles only. Skeletal muscles are affected in a predictable order 1st- __________________ 2nd- __________________ Last- __________________

ADMINISTRATION Normally given slowly IV Onset of action: 2 minutes Duration: 10-30 minutes

Animals on these drugs will require manual or mechanical ventilation

ADVERSE EFFECTS Hypothermia Respiratory failure Cardiac arrhythmias


Patient’s breathing is controlled by a ________ rather than _____________________ The ventilator automatically compresses a bellows, which

forces oxygen and anesthetic gas into the patient’s airways The bellows is compressed at a specified rate and a

specified volumeUSES: not normally used in healthy anesthetized

patients, but can be helpful in:



Depending on the type of ventilator, the anesthetist can deliver gases according to a pressure cycle, a volume cycle, or a time cycle. ________ cycle – supplies air until the pressure reaches

a preset level. This is generally 12 cm to 20 cm. ________ cycle – supplies air according to a set

inspiratory time. This is generally 1 to 1.5 seconds. I:E ratio is 1:2 to 1:3

__________cycle – delivers a preset tidal volume regardless of the pressure required. This is generally 10-15 mL/kg


RISKS OF CONTROLLED VENTILATION Excessive airway pressure may rupture alveoli Cardiac output may be decreased if positive pressure

is maintained throughout inspiration and expiration If ventilation rate is too high, excessive carbon dioxide

may be exhaled leading to respiratory alkalosis Controlled ventilation is generally more efficient at

delivering anesthetic gas which may lead to exacerbation of side effects such as hypotension and CNS depression.

Anesthetist may be tempted to relax on the monitoring

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PRINCIPLES OF PAIN MANAGEMENT & ANALGESIA