Management of pain in small animals

MANAGEMENT OF PAIN IN SMALL ANIMALS

PRESENTED BY ,

SWATHI KRISHNA 12 – BVP - 230

PAIN

• “UNPLEASANT SENSORY AND EMOTIONAL EXPERIENCE ASSOCIATED WITH ACTUAL OR POTENTIAL TISSUE DAMAGE”.

THE PAIN PATHWAY

Transduction

TransmissionModulation

Perception

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.

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

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

MODULATION

• SIGNAL PROCESSING

• Spinal cord

• Dorsal horn

• Endogenous systemsTissue trauma

Signal enters dorsal horn

Reflex activity

exits ventral horn

To higher levels of CNS

CROSS SECTION OF THE SPINAL CORD

PERCEPTION

• RECEIVING AND INTERPRETATION

• Successful transduction, transmission, & modulation of a painful stimulus.

Modulation

Perception

TYPES OF PAIN

PERIPHERAL PAIN

Visceral

• abdominal or thoracic organs

• poorly localized

• referred

Somatic

superficial

• skin

deep

• tendons, joints, muscle, periosteum

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.

NEUROPATHIC PAIN

• Damage to peripheral nerves or spinal cord.

• Often difficult to treat appropriately.

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.

ADAPTIVE PAIN

• Normal response.

• Protects from further injury.

• Inflammation is a large component.

MALADAPTIVE PAIN

• Abnormal response.

• Stimulus is gone but pain persists.

FACTORS AFFECTING PAIN

• STRESS

• ANXIETY

• WIND-UP

• CENTRAL SENSITIZATION

COMMON BEHAVIORAL RESPONSES TO PAIN

• Dogs are pack animals, they share emotions 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

Cats are more solitary animals, they are generally more stoic than dogs; 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

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

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.

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

ANALGESICS

DIVIDED INTO FIVE MAIN CLASSES BASED ON MODE OF ACTION

• OPIOIDS

• NON-STEROIDAL ANTI-INFLAMMATORY DRUGS

• LOCAL ANESTHETICS

• ALPHA2-ADRENOCEPTOR AGONISTS

• MISCELLANEOUS DRUGS

OPIOID ANALGESICS

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

• 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

OPIOID RECEPTOR PHARMACOLOGY

• CLASSIFICATION: 4 types μ, κ, ε, σ

MU

• supraspinal, spinal, peripheral and analgesia , respiratory depression ,

euphoria/sedation , physical dependence , bradycardia.

KAPPA

• spinal analgesia , sedation , respiratory depression.

SIGMA

• dysphoria/hallucinations , hypertonia , respiratory stimulation , tachycardia.

OPIOID ADMINISTRATION

• SYSTEMIC: IV, SQ, IM, CRI

• INTRA-ARTICULAR INJECTION

• LOCAL INJECTION

• EPIDURAL INJECTION

• TRANSDERMAL FENTANYL PATCH

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

OPIOID SPECIES SPECIFIC EFFECTS

Excitement in cats (dose related).

Panting in dogs – resets thermostat.

MISCELLANEOUS ANALGESICS

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.

NON-STEROIDAL ANTI-INFLAMMATORY DRUGS ( NSAIDS )

• 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.

TYPES OF NSAIDS

PHENYLBUTAZONE

COX1 AND 2 INHIBITOR

VERY POTENT

COMMONLY USED IN HORSES

NOT RECOMMENDED IN DOGS

• GI SIDE EFFECTS COMMON

• NEVER IN CATS!

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

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

FLUNIXIN MEGLUMINE

• BANAMINE® (COX1 AND COX2)

• INJECTABLE

• HORSES

• COLIC

• GOOD ANALGESIA

• DOGS

• GI SIDE EFFECTS COMMON, SEVERE

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

ETODOLAC

• ETOGESIC ®

• COX 1 AND 2 INHIBITION

• ONCE DAILY ADMINISTRATION

• DOGS ONLY

DERRAMAX

• USE IN DOGS

• COX 2 SPECIFIC

• SID DOSING

“METACAM” =MELOXICAM

• COX-2 SPECIFIC

• USE IN DOGS AND CATS

• LIQUID

• WELL TOLERATED

ALPHA2-ADRENERGIC AGONISTS

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.

LOCAL ANESTHETICS

• 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.

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.

MISCELLANEOUS AGENTS

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.

ST. JOHNSWORT

• Arthritic pain

• Stimulates neural inhibitory pathways analgesia

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.

THANK YOU……….