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PAIN The task of medicine is to preserve and
restore health and to relieve suffering.
Pain is an unpleasent sensation
Pain is universally understood as a signal of disease.
It is the most common symptom that brings a patient to a physician's attention.
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PAINPain is divided into acute & chronic
Acute pain last less than one month, after the injury that produces it is healed
Chronic pain last more than one month, after the injury that produce the pain is healed.
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PAIN Pain represents a “massive worldwide”
socio-economic impact
Pain is the main reason for medical consultation
Chronic pain treatment implies in US:
More than 2 million are incapacitated p/y
More than 100 million work days are lost p/y
The cost of medical, surgical, rehabilitation, especial devices is more than 70 billion dollars p/y.
Treatment of pain is one of the most remunerative business to drugs companies.
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PAIN The function of the pain sensory system is to:
Detect Localize Identify tissue-damaging processes.
Important diagnostic clues used to evaluate the response to treatment are:
Quality Time course Location of a patient's pain complaint Location of tenderness
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PAIN THE PAIN SENSORY SYSTEM
Pain is often described in terms of: Physical stabbing, burning, twisting, tearing, squeezing
Emotional reaction Terrifying, nauseating, sickening.
Pain has a duality characteristic
It is both a “sensation” and “emotion” Acute pain is associated with behavioral arousal and a
stress response with increased: Blood Pressure Heart rate Pupil diameter Plasma cortisol levels
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PAINTHE PAIN SENSORY SYSTEM
DEFINITIONS
Noxious stimuli is an internal or external stimuli that could elicit the activation of “pain receptors” , this could be:
Chemical Mechanical Thermal Polymodal
Nociception is the perception of signals evoked by activation of nociceptors at the C.N.S. To provide information of tissue damage
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PAINTHE PAIN SENSORY SYSTEM
DEFINITIONS Fast pain:
Is a short well localized sensation that is well matched to the noxious stimuli.
Starts & stops abruptly when stimuli is applied or removed.
Is strictly associated to the skin (Prick, sharp pain)
Transsmitted by A-Delta fibers
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PAINTHE PAIN SENSORY SYSTEM
DEFINITIONS Slow pain:
Is a throbbing, burning or aching sensation, is poorly localized & less especifically related to the stimuli.
The onset has a long latency following the application of the stimuli.
The pain continues for hours or days after removal of the stimuli.
Is associated to cutaneous and deep tissues.
Is transsmitted by C fibers
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PAIN
THE PAIN SENSORY SYSTEMDEFINITIONS
Nociceptors:
Specialized sensory receptors that provide information about tissular damage
Are “free nerve endings”, localized at the skin, underlying tissue and visceras
Nociceptors are the least differentiated of the sensory receptors, there are two types: Thermal or Mechanical & polymodal
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PAINTHE PAIN SENSORY SYSTEM
DEFINITIONS Nociceptors:
There are two types:
Thermal or mechanical, associated with fast, sharp pricking pain transmitted on small diameter, thinly myelinated A-Delta fibers) Release excitatory amino-acid-glutamate (Fast EPSP)
Polymodal nociceptors, activated by variety of high intensity mechanical & thermal stimuli, transmitted slowly on small unmyelinated C fibers, release excitatory aminoacid-glutamate and neuropeptides (Substance P = slow EPSP)
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Substances & effects on nociceptors
SUBSTANCES
Potassium Bradykinin
Substance P Serotonin Histamine Prostaglandins Leukotrienes
EFFECTS
Activation Activation &
sensitization Sensitization Activation Activation Sensitization Sensitization
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Substances & effects on nociceptors
SUBSTANCES
Bradykinin
Substance P
Histamine
EFFECTS
Most potent pain produced agent
Vasodilator & Release Histamine
Activates polymodal nociceptorswww.freelivedoctor.com
PAINDEFINITIONS
Hyperalgesia:
Is the lowering of the threshold level of the nociceptors, after noxius stimuli is applied and there is tissular damage.
There is increased sensation of pain with subsequent stimuli
Is divided into:
Primary: occurs at the site of tissue damage
Secondary: increased sensitivity at the surrounding undamaged tissue
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PAINDEFINITIONS
Primary hyperalgesia mechanism
Repetitive heating: reduces threshold of C & Alfa nociceptors
Repetitive mechanical stimuli: sensitize nearby nociceptors
Changes in synaptic efficacy of afferent fibers at spinal cord or C.N.S.
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PAINDEFINITIONS
Secondary hyperalgesia mechanism
Sensitization of nociceptors with diffuse collateral branches, one of which innervates the site of injury
Sensitization of central nociceptors as a result of sustained activation
Suggested CNS facilitation of incoming pain stimuli
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PAIN NOCICEPTOR-INDUCED INFLAMMATION
Released Substance P actions
Potent vasodilation
Degranulation of mast cells
Chemotaxis to leukocytes
Increase production and release of inflammatory mediators
Induces neurogenic formation
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PAIN Pain ascending pathways.
Nociceptor
Pain fibers: A-Delta fibers C Fiber
Spinal cord relays Lamina I & II (Substantia gelatinosa) Synapsis to spinal neurons
Spinal neurons receives convergence imputs from many primary afferents. Upper and lower spinal cord level (Important for “refered pain”)
Spinal neurons send axons to contralateral spinothalamic tract
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PAIN Pain ascending pathways.
Spinal cord relays send axons to contralateral spinothalamic tract
Spinothalamic tract axons connect to Thalamic neurons
Thalamic neurons projet to somatosensory cortex and cingulate gyrus and frontal lobe (Emotional responses)
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Substances & effects at the spinal cord
Substance Main location or source
Effects on pain
transmition
Glutamate A delta & C fibers
Excitatory
Substance P C fibers Excitatory
Opioids Substantia gelatinosa
Inhibition
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PAIN WHY THE DIFFERENT INDIVIDUAL RESPONSES
TO THE SAME NOXIOUS STIMULI OR TISSULAR DAMAGE??
Pain threshold is the same for everybody
The “Analgesia” system is involved in this individual response
It “modulates” (Increase or decrease) and sometimes suppress completely the transmition of the noxious stimuli
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PAIN ANALGESIA SYSTEM
SUPRASPINAL ANALGESIA SYSTEM
Periaqueductal Gray matter Opioids
Raphe magnus nucleus Serotonin
Nucleus Paragiantocellularis Nor-epinephrine
Send the Dorsolateral funiculus that end at the dorsal horn of the spinal cord
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PAIN SPINAL ANALGESIA SYSTEM
Dorsolateral funiculus;
Is a descending tract that end at the dorsal horn of the spinal cord inhibiting ascending spinothalamic projection neurons
Directly releases serotonin and nor-epinephrine
Indirectly through enkephalin interneurons in the dorsal horn
Local opioids Gate control theory Wide Dinamic Range Neurons
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PAIN Special considerations on pain
Refered pain: Is the pain that arises from nociceptors in
deep visceral structures, but is felt at sites on the body surface, sometimes remote areas
Examples: Myocardial infarction pain Esophageal diseases Gall bladder disease Apendicitis Gastric diseases
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PAIN Special considerations on pain
Deafferentation pain (Nerve elongation)
Limb phantom pain (Amputation)
Proposed mechanism: Loss of afferent input
plus Hyperactivity of dorsal neurons
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PAIN Special considerations on pain
Sympathetically maintained Pain “Causalgia”
Chronic pain after peripheral nerve injury, accompanied by swelling of the extremity, periarticular osteoporosis, and arthritic changes in the distal joints.
Pathophysiology is poorly understood
Rapid pain relief could be achived by blocking sympathetic nervous system
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PAIN TREATMENT
Peripheral analgesics
Acetaminophen
Aspirin
Non-steroidal Anti-inflammatory NSAIDs
COX 2 selective drugs (Rofecobix, celecobix)
Ketorolac
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PAIN TREATMENT
Central analgesics
Opioids: Orally Sublingual Transdermal Parenteral Intra-spinal
Chronic use of opioids
Patient controled analgesia (PCA)
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PAIN TREATMENT
Antidepresant drugs Tricyclic
Anticonvulsant Fenitoin Carbamazepine CBZ Gabapeptin
Antiarrhythmic Lidocaine Mexiletine
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