Pain Management

Objectives Minimize severity of post surgical pain.

Improve the animals ability to cope with that pain.

Decrease suffering & hasten return to normal function.

Definition

An unpleasant sensory or emotional experience associated with actual or

potential tissue damage or is described in terms of such damage-

(IASP)

Pain

Classification of PainClassification of Pain

Acute painAcute pain

Chronic painChronic pain

Tumour painTumour pain

Neuropathic painNeuropathic pain

PathophysiologyPathophysiology

Nociceptor – unencapsulated peripheral Nociceptor – unencapsulated peripheral termini of primary afferent neurons. A termini of primary afferent neurons. A receptor preferentially sensitive to a receptor preferentially sensitive to a noxious stimulus or to a stimulus that will noxious stimulus or to a stimulus that will become noxious if prolonged.become noxious if prolonged.

Each nociceptor has a detection threshold potential which must be exceeded before an impulse travels from the peripheral receptor site to the CNS.

Nociception

Physiological process which involves transduction, transmission, modulation and perception of the noxious stimuli.

Pain is the subjective interpretation of nociceptive input.

Types of nociceptorsTypes of nociceptors High threshold mechanoceptors (HTM)- AdeltaHigh threshold mechanoceptors (HTM)- Adelta Low threshold mechanothermal (LTM) Low threshold mechanothermal (LTM)

receptors associated with A- beta nerve fibers.receptors associated with A- beta nerve fibers. Myleinated mechanothermal (MMT)- A delta Myleinated mechanothermal (MMT)- A delta

heat nociceptors.heat nociceptors. C-Polymodal receptors (CPM) associated with C C-Polymodal receptors (CPM) associated with C

nerve fibers.nerve fibers.

Different types of stimuli

Chemical stimuli

Exogenous

Endogenous

Thermal

Mechanical

Different types of nerve fibers concerned with the impulse transfer

A- delta nerve fibers“Fast fibers”

First acute, fast, sharp pain associate with injury.

Receptive area is very discrete

Help to localize the pain to the site of stimulus. Eg HTM, MMT.C- nerve fibersSlow fibers

Second, dull, aching, burning, throbbing pain associated with injury.

Their receptive area is large.

They limit the localization of the site of stimulus to general body areas.

A- beta nerve fibersLower stimulation threshold than A- delta & C fibers

Transmit innocuous tactile sensations such as vibration, tickling, tingling etc.,.

Close the gate

Stimulating A beta nerve fibers seems to diminish A- delta & C nerve fiber nociceptor input.

A- delta or C nerve fibers carry nerve impulse from the periphery to the dorsal or ventral spinal root and then to the dorsal horn of the spinal cord after nociceptor threshold has been reached.

Different Types of pain and their conductionSomatic PainBoth A- delta & C fibers.

Discretely localizable.

Visceral painC fibers only.

Poorly localized.

Broad stimulation of visceral nerve endings by ischemia, smooth muscle spasm of hollow organs or ducts, or distention of viscera and ligaments.

Parietal surfaces of thorax and abdomen and retroperitoneal organs are richly supplied by A- delta and C fibers.

Pain tolerance Greatest level of pain that a subject will tolerate. Varies widely among both individual and species.

Hyperalgesia

Occurs when a nociceptor is stimulated and then respond to subsequent noxious stimuli more vigorously and at a low pain detection threshold.

1. Primary hyperalgesia

2. Secondary hyperalgesia

Central sensitization

An activity dependant increase in the excitability of the spinal neurons.

Hypersensitisation of post synaptic ascending spinal neurons.

Magnitude and duration of response to the subsequent noxious stimuli will increase.

Clinically significant-post operative analgesia.

Pain Pathway

The first order neuron originates in the periphery and projects to the spinal cord.

The second order neuron ascends the spinal cord.

The third order neuron projects into the brain.

SPINAL CORD SPINAL CORD STRUCTURESTRUCTURE

Nociceptive Afferent NervesNociceptive Afferent Nerves

• A-delta – laminae I,II,V,X.A-delta – laminae I,II,V,X.

• C-fiber – laminae I,II,V.C-fiber – laminae I,II,V.

• C-fiber mediating visceral C-fiber mediating visceral nociception – laminae I,V.nociception – laminae I,V.

Neurotransmitters involved – Neurotransmitters involved – Glutamate, Aspartate, Somatostatin, Glutamate, Aspartate, Somatostatin, vasoactive intestinal peptide, vasoactive intestinal peptide, cholecystokinin, angiotensin II, cholecystokinin, angiotensin II, dynorphin, enkephalin etc..dynorphin, enkephalin etc..

Dorsal Horn CellsDorsal Horn Cells

Nociceptive Specific cells (NS) are in Nociceptive Specific cells (NS) are in high concentration in lamina I & V – high concentration in lamina I & V – receive excitatory input from HTM,MMT receive excitatory input from HTM,MMT and CPM.and CPM.

Some NS cells receiving input only from Some NS cells receiving input only from HTMs.HTMs.

Wide Dynamic Range (WDR) neurons in Wide Dynamic Range (WDR) neurons in lamina V – Receive convergent input.lamina V – Receive convergent input.

Glutamate and Aspartate are the major Glutamate and Aspartate are the major excitatory neurotransmitters of CNS.excitatory neurotransmitters of CNS.

Ascending PathwaysAscending PathwaysBundles of nerve fibers whose cell bodies are Bundles of nerve fibers whose cell bodies are

located in the gray matter of spinal cord or located in the gray matter of spinal cord or brain stem and terminate by synapsing with brain stem and terminate by synapsing with cells in the brain, usually in the reticular cells in the brain, usually in the reticular formation or in the thalamus.formation or in the thalamus.

Also known as Also known as relay or transmitterrelay or transmitter cells. cells.

Divided into Lateral and Medial groups.Divided into Lateral and Medial groups.

• Lateral group- (a) Neospinothalamic tract, (b) Lateral group- (a) Neospinothalamic tract, (b) spinocervical tract, (c) dorsal column spinocervical tract, (c) dorsal column postsynaptic tract.postsynaptic tract.

• Medial group- (a) paleospinothalamic tract, (b) Medial group- (a) paleospinothalamic tract, (b) spinoreticular tract, (c) spinomesencephalic spinoreticular tract, (c) spinomesencephalic tract, (d) Propriospinal system.tract, (d) Propriospinal system.

NeospinothalamicNeospinothalamic

tracttract

Descending SystemDescending System

Each structure below the brain that projects to the cortex Each structure below the brain that projects to the cortex receives descending fibres from the cortex that can receives descending fibres from the cortex that can influence transmission in the thalamus, reticular influence transmission in the thalamus, reticular formation, trigeminal system and spinal cord.formation, trigeminal system and spinal cord.

Four tiered Four tiered

(a)(a) Cortical & diencephalic systems.Cortical & diencephalic systems.

(b)(b) Mesencephalic periaqueductal grey matter (PAG) & Mesencephalic periaqueductal grey matter (PAG) & periventricular grey matter (PVG)- rich in enkephalins periventricular grey matter (PVG)- rich in enkephalins and opiate receptors.and opiate receptors.

(c)(c) Parts of rostroventral medulla- the nucleus raphe Parts of rostroventral medulla- the nucleus raphe magnus (NRM).magnus (NRM).

(d)(d) The spinal and medullary dorsal horn.The spinal and medullary dorsal horn.

These axons are prominently seratonergic terminating on These axons are prominently seratonergic terminating on cells in the laminae I,II & V and selectively inhibit cells in the laminae I,II & V and selectively inhibit nociceptive neurons and interneurons.nociceptive neurons and interneurons.

Descending anlagesic Descending anlagesic systemsystem

Assessment and recognition Assessment and recognition of painof pain

Most important step.Most important step. Absence of verbal communicationAbsence of verbal communication Inconsistent interpretation.Inconsistent interpretation. Key source- Interpretation of Key source- Interpretation of

behaviouralbehavioural and physiologic and physiologic responses.responses.

Latest - Power Spectral Latest - Power Spectral Encephalogram analysis.Encephalogram analysis.

Physiologic Signs of painPhysiologic Signs of pain

Result of catecholamine release and Result of catecholamine release and activation of the sympathetic nervous system.activation of the sympathetic nervous system.

Systemic ChangesSystemic Changes Cardiovascular system - heart rate & BP.Cardiovascular system - heart rate & BP. Pulmonary sys - resp. rate, shallow Pulmonary sys - resp. rate, shallow

breathing.breathing. Musculoskeletal sys - tense muscles, M. Musculoskeletal sys - tense muscles, M.

tremors.tremors. Immune sys - resistance, stress leukogram.Immune sys - resistance, stress leukogram. Neuroendocrine sys - catabolism, anabolism.Neuroendocrine sys - catabolism, anabolism. Digestive sys - Inappetence, vomiting, Digestive sys - Inappetence, vomiting,

diarrhoea.diarrhoea.

Behavioural responseBehavioural response VocalizationVocalization Facial expressionFacial expression Body postureBody posture ActivityActivity Attitude Attitude AppetiteAppetite Urinary and bowel habitsUrinary and bowel habits GroomingGrooming Guarding and self-mutilation Guarding and self-mutilation

Degree of PainDegree of Pain

Mild pain.Mild pain.

Moderate pain.Moderate pain. It is the common degree of pain that is It is the common degree of pain that is

treated.treated.

Severe painSevere pain• it is intolerableit is intolerable• unprovoked vocalizationunprovoked vocalization• chance of self mutilationchance of self mutilation

Pain ManagementPain Management

Why pain management ?Why pain management ? Feel betterFeel better Physiologic changes that accompany Physiologic changes that accompany

painpain Should be able to eliminate pathologic Should be able to eliminate pathologic

painpain Pain free sleepPain free sleep

12 – 24 hr post operative pain management 12 – 24 hr post operative pain management is important.is important.

Non pharmacologic Non pharmacologic approach approach

1.1. Keep patient clean & dry.Keep patient clean & dry.

2.2. Keep the patient warm.Keep the patient warm.

3.3. Room with moderate temperature and Room with moderate temperature and humidity.humidity.

4.4. Well padded place to sleep.Well padded place to sleep.

5.5. Patients surrounding should be pleasant & Patients surrounding should be pleasant & quiet.quiet.

6.6. Human contactHuman contact

7.7. Acupressure, acupuncture, massage, Acupressure, acupuncture, massage, manipulation stimulate A-beta nerve fibers.manipulation stimulate A-beta nerve fibers.

Non pharmacologic Non pharmacologic approachapproach

CryotherapyCryotherapy ThermotherapyThermotherapy ActinotherapyActinotherapy Ultrasound therapyUltrasound therapy Low Level Laser Therapy (LLLT)Low Level Laser Therapy (LLLT) Transcutaneous Electrical Neuro-Transcutaneous Electrical Neuro-

stimulation (TENS)stimulation (TENS)

ContinuedContinued

Pharmacologic approachPharmacologic approach

Preemptive approachPreemptive approach Balanced approachBalanced approach

1.1. Multiple drugs for maximal effects – Multiple drugs for maximal effects – Customized Multimodal Therapy.Customized Multimodal Therapy.

2.2. Multiple site.Multiple site. Local Anaesthetics, NSAIDs, Opioids Local Anaesthetics, NSAIDs, Opioids

– alone or in combination.– alone or in combination. Phenothiazine tranquilizers, Phenothiazine tranquilizers,

Benzodiazepine tranquilizers & Benzodiazepine tranquilizers & αα2 2 agonists.agonists.

TransductionTransduction

Noxious Noxious StimulusStimulus

TransmissionTransmission

ModulationModulation

PerceptionPerception

LAs, NSAIDsLAs, NSAIDs

LAsLAs

Opiods, Opiods, αα2-2-agonistsagonists

General General Anaesthetics, Anaesthetics, Opiods, Opiods, αα2-2-agonistsagonists

Local AnaestheticsLocal Anaesthetics

Used in perioperative and postoperative Used in perioperative and postoperative pain.pain.

ApplicationApplication• Infiltration of surgical siteInfiltration of surgical site• Direct nerve blocksDirect nerve blocks• Regional InfiltrationRegional Infiltration• Intra-articular infiltrationIntra-articular infiltration• EpiduralsEpidurals

Mainly used – Lidocaine & Bupivacaine.Mainly used – Lidocaine & Bupivacaine.

Nonsteroidal Nonsteroidal antiinflammatory antiinflammatory drugs(NSAIDs)drugs(NSAIDs)

Inhibition of prostaglandin synthesis by Inhibition of prostaglandin synthesis by inhibiting cyclooxygenase enzyme (COX).inhibiting cyclooxygenase enzyme (COX).

NSAIDs vary in their ability to inhibit COX 1 NSAIDs vary in their ability to inhibit COX 1 & 2& 2

COX 2 inhibition will provide enhanced COX 2 inhibition will provide enhanced analgesia.analgesia.

Eg. Ketoprofen, Meloxicam, Flunixin Eg. Ketoprofen, Meloxicam, Flunixin meglumine.meglumine.

OpioidsOpioids

Bind at specific receptor sites in brain and Bind at specific receptor sites in brain and spinal cord by mimicking the actions of spinal cord by mimicking the actions of endogenous peptides modulating pain endogenous peptides modulating pain recognition.recognition.

Interfere with calcium influx.Interfere with calcium influx. Opioid agonists include morphine, Opioid agonists include morphine,

hydromorphine, codeine, meperidine, hydromorphine, codeine, meperidine, fentanyl, carfentanil, etorphine and fentanyl, carfentanil, etorphine and methadone. methadone.

Fentanyl patches are used recently in animals.Fentanyl patches are used recently in animals.

Principles of Postoperative Principles of Postoperative pain managementpain management

Prevent or limit painPrevent or limit pain Use analgesics pre-emptively to control Use analgesics pre-emptively to control

pain.pain. Do not wait until behavioural changes Do not wait until behavioural changes

are observed.are observed. Do not ignore patient behaviour.Do not ignore patient behaviour. Never as a method of restraint.Never as a method of restraint. Do not stop analgesic therapy abruptly.Do not stop analgesic therapy abruptly. Try to provide a calm environment.Try to provide a calm environment.

Thank You….Thank You….