Pain the most common symptom that brings patients to see a physician, nearly always manifests a pathologic process. Any treatment plan must be directed at the underlying process as well as at controlling pain. Pantients are generally referred for pain management by primary care practitioners or spesialists once a diagnosis has been made and treatment of any underlying process has been initiated. Notable exceptions are pantients with chronic pain in which the cause remains obscure after preliminary in investigations serious and life threatening illnesses should, however, have been excluded. The term pain management in a general sense aplies to the entire discipline of anesthesiology, but its modern usage is restricted to management of pain outside the operating room. This type of practice may be broadly divided into acute and chronic pain management. The former primarily deals with patiens recovering from surgery or with acute medical conditions in a hospital set ting, while the latter includes diverse groups of patients in the outpatient setting. Unfortunately, this distinction artifisial because considerable overlap exists, a good example is the cancer patient who frequently requires short and long term pain management, both in and out of the hospital.The practice of pain management is not just limited to anesthesiologists but other practitioners that include physicians ( such as internists, onkologists and neurologists) and non physicians ( physichologists, chiropractors, acupuncturists and hypnotists) . Clearly the most effectiv approach is multidisciplinary, where the patient is evaluated by one physician ( the case manager) who conducts the initial evaluation and formulates a trearment plan. And where the sevices and resources of other specialists are readily available. Moreover, the case manager and the various consultants meet regularly in formal case conferences to discuss patients. Single specialty pain clinics tend to be either syndrome or modality oriented. The former spesialize in chronic back pain, headache and temporomandibular joint dysfungtion, while the latter offer nerve block, acupuncture, hypnosis and biofeedback.Anesthesiologists trained in pain management are in a unique position to coordinate multi dischiplinary pain management centers because of broad training in dealing with a wide diversity of patients from surgical, obstetric, pediatric an medical subspecilties, as well as expertise in clinical pharmacology an applied neuroanatomy, including the use of periphereal and central nerve blocks.DEFINITIONS & CLASIFICATION OF PAINLike other conscious sensations, normal pain perception is dependent on specialized neurons that functions as receptors, detecthing the stimulus and then transducing and conducting it into the central nervous system. Sensation is often described as either protopathic ( noxious) or epicritic ( non noxious) . epicritic sensation ( light touch, pressure, proprioception and temperature discriminatoin) is characterized by low threshold receptors and generally conducted by large myelinated nerve fibers ( table 18-1). In contrast protopathic sensation ( pain) is subserved by high threshold receptors and conducted by smaller , lightly myelinated (A*) and unmyelinated (C) nerve fibers.What is pain?Pain is not just a sensory modality but an experience. The international assosiation for the study of pain defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage , or described in terms of such damage. This defenition recognizes the interplay between the objective, emotional and psychological components. The response to pain can be highly variable between individuals as well in the same individual at differents times.The term nociception, which is derives from noci ( latin for harm or injury), is used only to describe the neural response to traumatic or noxiuos stimuli. All nociception produces pain, but not all pain results from nociception. Many patients experience pain in the absense of noxious stimuli. It is therefore clinically useful to devide pain into one of two categories , (1) acute pain, which is primarily due to nociception and (2) chronic pain, which may be due to nociception but in which psychological and behavioral factors often play a major role. Table 18-2 lists terms frequently used in describing pain.TABLE 18-1. Clasification of nerve fibersFiber TypeSensory ClassificationModality ServedDiameterConductions (m/s)

AaMotor12-2070-120

AaType laProprioception12-2070-120

AaType lbProprioception12-3070-120

ABType llTouch pressure proprioception5-1230-70

AyMotor ( muscle spindle)3-615-30

A*Type lllPain cold temperature touch2-512-30

BTypr lvPregenglion autonomic fiber33-14

C dorsal rootPain warm and cold temperature touch0,4-1,20,5-2

C Sympathetic0,3-1,30,7-2,3

A.Acute PainAcute pain can be defined as that which is caused by noxious stimulation due to injury, a disease process, or abnormal function of muscle or visera. This type of pain is typically assosiated with a neuroendocrine stress that is propotional to intersity. Teleologically , acute pain serves to detect, localize and limit tissue damage, consequently, it is frequently referred to as nociceptive pain. Its most common forms include posttraumatic, postoperative and obstetrical pain, as well as that associated with acute medical illnesses such as myocardial infarction, pancreatitis andrenal calculi. Most forms of acute pain are self limited or resolve with treatment in a few day oe weeks. When the pain fails to resolve because of either abnormal healing or inadequate treatment, the pain becomes chronic ( below) . three types of acute pain : superfisial, deep somatic and viseral, are differentiated based on origin and features.1. Superficial This type of acute pain is due to nociceptive input arising from skin, subcutaneous tissues and mucouse membranes. It is characteristically well localized and described as a sharp, pricking throbbing or burning sensation.2.Deep somaticDeep somatic pain arises from muscles, tendons, joints or bones. It usually has dull, aching quality and is less well localized. An additional feature is that both the intensity and duration of the stimulus affect the degree of localization. For example, pain following brief minor trauma to the elbow joint is localized to the elbow, but severe or sustained traumaoften causes pain in the whole arm.3. VisceralThis third form of acute painis due to a disease process or abnormal fuction of an internal organ or its covering ( eg, parietal pleura, pericardium or peritoneum ). Four subtypes are described: (1)true localized viseral pain, (2) localized parietal pain (3) referred viseral pain and (4) referred parietal pain. True viseral pain is dull, diffuse and usually midline. It is frequently assosiated with either abnormal sympathetic or parasympathetic activity causing nause, vomiting, sweating and changes in blood pressure and heart rate. Parietal pain is typically sharp and often described as a stabbing sensation that is either localized to the area around the organ or referred to adistant site ( table (18-3). The phenomenon of visceral or parietal pain referred to cutaneous areas result from pattern of embryologic development and migration of tissues, and the convergence of visceral and somatic afferent input into the central nervous system ( below) .Thus , pain assosiated with disease processes involving the peritonium or pleura over the central diapragm is frequently referred to the neck and shoulder, whereas disease affecting the parietal surfaces of theperipheral diaphragm is referred to the chest or upper abdominal wall.B.CHRONIC PAINChronic pain is defined as that which persists beyond the usual course of an acute disease or after a reasonable time for healing to occur this period varies between 1 to 6 months in most definitions. Chronic pain may result from periphereal nociception, or periphereal or central nervous system sysfunction. A distinguishing feature is that psychological mechanisms or environmental factors frequently play a major role. Patients with chronic pain often have an attenuated or absent neuroendocrine stress response, and have prominent sleep and affective ( mood ) disturbances.The most common forms of chronic pain include those associated with musculoskeletal disorders, chronic viseral disorders, lesions of peripheral nerves, nerve roots, or dorsal root ganglia ( including causalgia, phantom limb pain and postherpetic neuralgia), lesions of the central nervous system ( stroke, spinal cord injury and multipel sclerosis) and cancers invading the nervous system. Some clinicians use the term chronic benign pain when pain does not result from cancer. This is to be discouraged, because pain is never benign from the patients point of view, regardless of it cause.Chronic pain assosiated with peripheral or central nervous system dysfunction is usually spontaneous, has a burning quality and is associated with hyperpathia. This type of pain is frequently referred to as neuropathic. When also assosiated with loss of sensory inpu into the central nervous system, it is termed deafferentaton pain.TTTTable 18-2 Terms used in pain managementTERMDESCRIPTIONS

AllodyniaPerception of an ordinarily nonnoxious stimulus as pain

AnalgesiaAbsense of pain perception

AnesthesiaAbsense of all sensation

Anesthesia dolorosaPain in an area that lacks sensation

DysesthesiaUnpleasant or abnormal sensation with or wthout a stimulus

Hypalgesia( Hypoalgesia)Diminished response to noxioux stimulation ( eg, pin prick )

HyperalgesiaIncreased response to noxious stimulation

HyperesthesiaIncreased response to mild stimulation

HyperpatiaPresece of hyperestesia, allodyna and hyperalgesia usually associated with overreaction and persistance of the sensation after the stimulus

Hypestesia( Hypoestesia)Reduced cutaneous sensation ( og, light touch, pressure, or temperature)

NeuralgiaPain in the distribution of s nerve or s group of nerves

ParesthesiaAbnormal sensation perceived with out an apperent stimulus

RadiculophatyFunctional abnormality of one or more nerve roots