PAIN IN SURGERYPAIN IN SURGERY

MS Surgery – Part IMS Surgery – Part I

May 2008 May 2008

LECTURE PLANLECTURE PLAN

Definitions Definitions

Pain pathwaysPain pathways

Modifications – Current thinkingModifications – Current thinking

Pain controlPain control

PAINPAIN

Sherrington Sherrington : “ the physical adjunct of an: “ the physical adjunct of an

imperative protective reflex ”imperative protective reflex ”

MerskeyMerskey : “ Pain is an unpleasant sensory : “ Pain is an unpleasant sensory and and

emotional experience associated with actual emotional experience associated with actual or or

potential tissue damage or described in terms potential tissue damage or described in terms of of

such damage”such damage”

Acute PainAcute Pain

International Association for the Study of PainInternational Association for the Study of Pain

““An unpleasant sensory or emotional experienceAn unpleasant sensory or emotional experience

associated with actual or potential tissue associated with actual or potential tissue damage,damage,

or described in terms of such damage”or described in terms of such damage”

“ “ Pain is always subjective; & it is Pain is always subjective; & it is unquestionably aunquestionably a

sensation in a part of the body ”sensation in a part of the body ”

Acute pain ……Acute pain ……Survival valueSurvival value

Chronic pain ……Chronic pain ……No valueNo value

Pain PathwaysPain PathwaysPreviously – 3 componentsPreviously – 3 components

1. First order neurone1. First order neuroneperipheral receptor peripheral receptor …… ……

2. Second order neurone2. Second order neuronecrosses midline crosses midline spinothalamic tract spinothalamic tract

thalamusthalamus

3. Third order neurone3. Third order neuroneprojects to post-central gyrusprojects to post-central gyrus

Pain PathwaysPain PathwaysNowNow

1.1. Peripheral receptorsPeripheral receptors

2.2. Neural pathwaysNeural pathways

3.3. Spinal cord mechanisms & long tractsSpinal cord mechanisms & long tracts

4.4. Brain stem, thalamus, cortex & other Brain stem, thalamus, cortex & other

areasareas

5.5. Descending pathwaysDescending pathways

Pain ResponsePain Response

First painFirst pain

Second painSecond pain

NociceptorsNociceptors

Neurogenic Neurogenic InflammationInflammation

Nociceptors Nociceptors

silent nociceptorssilent nociceptors

silent antinociceptorssilent antinociceptors

Pain PerceptionPain Perception

thresholds constantthresholds constant

response and tolerance differresponse and tolerance differ

Neural PathwaysNeural Pathways

Spinal Cord PathwaysSpinal Cord Pathways

Initial connectionsInitial connections

Spinal PathwaysSpinal PathwaysInitial ConnectionsInitial ConnectionsImportant second order neuronesImportant second order neurones

1. Wide Dynamic Range (WDR) cell1. Wide Dynamic Range (WDR) cell

“ “ wind up ”wind up ”

2. Nociceptive specific neurones2. Nociceptive specific neurones

3. Complex neurones3. Complex neurones

Spinal PathwaysSpinal Pathways

LocalLocal

InterconnectiInterconnectionsons

GatingGating

Ascending PathwaysAscending Pathways

1.1. Spino-reticulo-diencephalic Spino-reticulo-diencephalic pathwaypathway

2.2. Spinothalamic tractSpinothalamic tract

Descending PathwaysDescending Pathways

OriginOrigin

CortexCortex

ThalamusThalamus

Brain stem – periaqueductal grey matterBrain stem – periaqueductal grey matter

Noxious stimuli

Response to PainResponse to Pain

Visceral PainVisceral Pain

Tonic muscular spasmTonic muscular spasm

Somatic painSomatic pain

Withdrawal of affected partWithdrawal of affected part

☼ ☼ Autonomic effectsAutonomic effects

Response to painResponse to pain

Fast & slow painFast & slow pain

Deep & superficial painDeep & superficial pain

Referred painReferred pain

C-fosC-fos

Proto oncogene that codes for protein Proto oncogene that codes for protein fos.fos.

Expressed in response to Expressed in response to painfulpainful peripheral peripheral

stimulistimuli

Molecular memory of painMolecular memory of pain

PAIN CONTROLPAIN CONTROL

PAIN CONTROLPAIN CONTROL

Primary analgesicsPrimary analgesics

opioids – opioids – receptors – sites, typesreceptors – sites, typesdrugsdrugsroutes of administrationroutes of administrationside effectsside effects

PAIN CONTROLPAIN CONTROL

Primary analgesicsPrimary analgesics

simple analgesics and NSAID’ssimple analgesics and NSAID’s

drugs – inhibit COX drugs – inhibit COX routes of administrationroutes of administrationcontraindicationscontraindications

COX 2 selective inhibitors – parecoxib, COX 2 selective inhibitors – parecoxib, valdecoxibvaldecoxib

PAIN CONTROLPAIN CONTROL

Primary analgesicsPrimary analgesics

Local anaestheticsLocal anaestheticsdrugsdrugsusesusestoxic effectstoxic effects

othersothers- Tramadol- Tramadol- clonidine- clonidine

PAIN CONTROLPAIN CONTROL

Secondary analgesicsSecondary analgesics

antidepressantsantidepressants

anticonvulsantsanticonvulsants

anxiolyticsanxiolytics

muscle relaxantsmuscle relaxants

Ca channel blockersCa channel blockers

steroidssteroids

PAIN CONTROLPAIN CONTROL

Interventional therapyInterventional therapy

TENS/acupunctureTENS/acupuncture

neurolytic agentsneurolytic agents

radiofrequency/heat treatmentradiofrequency/heat treatment

surgerysurgery

PAIN CONTROLPAIN CONTROL

Psychological treatmentPsychological treatment

psychological supportpsychological support

behavioural therapybehavioural therapy

PAIN CONTROLPAIN CONTROL

pre emptive analgesiapre emptive analgesia

Jan 1996Jan 1996

2. Discuss the physiological basis of 2. Discuss the physiological basis of the different methods of pain the different methods of pain control.control.

Thank youThank you