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Pain ??An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.(The International Association for the Study of Pain)Involved: Transduction: Change of noxious stimulus to electrical modalities

Transmision: along sensory nerve fiber A and C Modulation: Complex processing in substantia gelatinosa. Interaction between excitatory or inhibitory neurotransmitterPerception: in central somatosensory cortex

CLINICAL PAINInflammatory responsesurgery, cancer & chronic painPeripheral nerve injurysurgical section, invasion, traumaPeripheral SensitisationCentral sensitisationMetabolic & endocrine changes An affective component

Categorized1) acute pain, which is primarily due to nociceptionSomatic painVisceral pain2) chronic pain, which may be due to nociception but in which psychological and behavioral factors often play a major role (1-6 month)

TREATMENT OF PAIN GOALS OF THERAPYDecrease the frequency and / or severity of the painGeneral sense of feeling betterIncreased level of activityReturn to workDecreased health care utilizationElimination or reduction in medication usageCopyright 2003 American Society of Anesthesiologists. All rights reserved

PathophysiologyPain arises when nociceptors become sufficiently stimulated/damaged (i.e. by strength and/or duration of exposure)or when visceral nociceptors are sufficiently deformed/damaged to generate humoral and/or cellular responses.Parallel ascending pathways detect the affective (unpleasantness) and sensory (discriminative) components to convey to the CNS the information about damage in the tissue served. Resultant activation of descending pathways leads to modulation/inhibition of the nociceptive input.

Pathophysiologystimulation also produces altered gene expression in the spinal cord & brainleaving behind a physical memory of nociception & pain.In the periphery, immune cells activated by neural & humoral events respond by releasing cytokines, as well as endogenous opioids.

Term Allodynia: Perception of an ordinarily nonnoxious stimulus as painAnalgesia: Absence of pain perceptionAnesthesia: Absence of all sensationAnesthesia dolorosa:Pain in an area that lacks sensationDysesthesia: Unpleasant or abnormal sensation with or without a stimulus Hypalgesia (hypoalgesia):Diminished response to noxious stimulation (eg, pinprick)

Hyperalgesia: Increased response to noxious stimulationHyperesthesia:Increased response to mild stimulationHyperpathia:Presence of hyperesthesia, allodynia, and hyperalgesia usually associated with overreaction, and persistence of the sensation after the stimulusHypesthesia (hypoesthesia): Reduced cutaneous sensation (eg, light touch, pressure, or temperature)

Neuralgia:Pain in the distribution of a nerve or a group of nervesParesthesia:Abnormal sensation perceived without an apparent stimulusRadiculopathy:Functional abnormality of one or more nerve roots

Chemical Mediators of PainNeurotransmitter Receptor1 Effect on Nociception

Substance PNK1Excitatory

Calcitonin gene-related peptideExcitatory

GlutamateNMDA, AMPA, kainite, quisqualateExcitatory

AspartateNMDA, AMPA, kainite, quisqualateExcitatory

Adenosine triphosphate (ATP)P1, P2Excitatory

SomatostatinInhibitory

AcetylcholineMuscarinicInhibitory

EnkephalinsInhibitory

-Endorphin Inhibitory

Norepinephrine2Inhibitory

AdenosineA1Inhibitory

Serotonin5-HT1 (5-HT3)Inhibitory

-Aminobutyric acid (GABA)A, BInhibitory

GlycineInhibitory

1NMDA, N-methyl-D-aspartate; AMPA, 2-(aminomethyl)phenylacetic acid; 5-HT, 5-hydroxytryptamine.

Systemic Responses to Acute PainEfferent limb is mediated by the sympathetic nervous and endocrine system cathecolamine release:Cardiovascular effectsRespiratory effectsGastrointestinal and urinary effectsEndocrine effects cathecolamine, cortisol, glucagon increaseImmune effects: depress the reticuloendothelial system

ManagementPain measurement: Visual analog scale (VAS)McGill pain questionnaire (MPQ)Perioperatif Preemptif therapyBalanced analgesiaNeural blockadePharmacologic intervention:COX inhibitor,Opioids, Antidepresant, anticonvulsant, neuroleptic, corticosteroid, local anestheticsPost surgery rehabilitation

Multimodal analgesia

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