Theories of Pain, Its Anatomy and Physiology, and How to Treat the Pain - Essay Example

? Pain Management Definition of Pain Pain is an experience that is common to all animals. It is the result of certain forms of stimulation and involves complex, multidimensional processes. The word pain has been utilized to explain many conditions. There are two types of pain: acute pain is generally any relatively short duration pain with known organic cause and chronic pain is deep, long-lasting, intractable pain (Holdcroft & Jaggar, 2005; Shorten et al., 2006). Cyclooxygenases Prostaglandin endoperoxide H synthase (commonly known as Cyclooxygenases) was purified in 1976 and cloned in 1988. This enzyme is the key catalytic protein in the synthesis of prostaglandins from arachidonic acid, resulting in pain and inflammation, and is subject to inhibition by non­steroidal anti-inflammatory drugs (NSAIDS). In 1991, several laboratories identified a second gene product with COX activity, now termed COX-2. It is clear now that both isoforms, COX-l and COX-2 are expressed in both peripheral tissues and several areas of the CNS (Prochazkova et al., 2006). Theories of Pain Gatchel, Polatin, and Kinney (1995) state that there are two prominent theories of pain: the traditional specificity theory of pain and the gate control theory of pain. The former, still widely taught, proposes that pain is a specific sensation and that the intensity of pain is proportional to the extent of tissue damage. This theory implies a fixed, straight-through transmission system from somatic pain receptors to a pain center in the brain (p.416). In 1965, Melzack and Wall proposed the gate control theory. This theory suggests that there are physiological and neural mechanisms in the body that can have an effect on the perception of the painful stimulus (Hawthorn & Redmond 2001). The theory postulates that there are two controls that affect the gate. One originates in the cortex and other brain locations and descends to the gate, while the other is peripherally located and ascends to the gate. In the former, inhibition is accomplished through central summation and input control. In the later, pain information conducting over C-fibers is modulated through pre-synaptic inhibition from incoming beta fibers in the substancia gelantosa. This gating mechanism depends on the relative quantity of information being received over the larger fibers versus the smaller fibers. In essence, the two peripheral impulses interfere with each other to alter pain perception. The gate control theory has received the most recognition in the field of pain research (Gatchel, Polatin, and Kinney 416). Anatomy & Physiology The complexities associated with the experience of pain are immense. Hall (1994) addresses those that deal with the physiological aspects by observing that medical science has not fully explained pain mechanisms. The specialization of receptors has been discovered. This refers to receptors being more sensitive to one stimulus than others. Hall (1994) continues with the identification of the receptor that is "incriminated" in the reception of pain, the unmyelinated or thinly myelinated nerve ending, an "unencapsulated" nerve ending. Hall describes the myelin sheath covering that encloses nerve fibers. The thickness of this sheath varies throughout the body, from none in the periphery, to very thick where nerves enter bones, and other parts of the body. The covering acts as insulation to keep stimuli from entering the nerve from regions other than those served by the nerve (p. 11). Hall (1994) goes on to describe the receptor as a "primitive unorganized nerve ending and often has a weed-like appearance. It has many branches and overlaps with other receptors to totally cover the area which it serves" (p. 11). The area that a particular nerve serves is called a dermatome, which may serve an area of skin, a muscle, or any organ of the body. Hall states, "It is important to realize that the strength of stimulus is a critical factor in the production of pain in this and other types of receptors" (p. 11). Thus, any stimulus can become painful if its intensity threshold is surpassed. Hall (1994) further explains that the intensity threshold is a noxious stimulus at which point the receptor is referred to as being nociceptive and tissue damage may result. It is at this point that the generation of the impulse of pain happens. Once generated, the impulse travels along afferent pain fibers. These fibers connect the various systems that are associated with the perception of stimuli. They are of different sizes and functions. Hall (1994) states that all nerve fibers are classified by their size and conduction rate: A - fibers are the largest in diameter and fastest conductors; B - fibers, are intermediate in diameter and conduction rate; and C - fibers are the smallest in diameter and have the slowest conduction rate. Only some nerve fibers are associated with the transmission of pain impulses (p. 11). Bennett (2000) like Hall (1994) states that all muscles, tendons, organs, (including the skin), and blood vessels are "innervated" by neurons that are "specialized" to receive stimuli that are generated by injury. These pain-sensing neurons are called "nociceptors," and they come in two general types. The C-fiber nociceptors are slow conducting. The A-delta nociceptors are more thinly myelinated and are faster conducting (p. 83). Neural fibers that carry information from the skin to the spinal column enter it through the dorsal roots (Hall, 1994, p. 11). Summarily, different types of nerve fibers serve different functions in the body. Those fibers form a network of interconnecting pathways that supply information to the brain. The primary fibers that are associated with the transmission of painful stimuli differ from those that serve other functions. Once the painful stimulus is generated, the nerve fiber transmits the impulse to the next fiber and so on until it enters the spinal column, and then proceeds to the brain. The experience of pain in the human brain appears to take place in the primary somatosensory cortex (Pinel, 1997). The area of the brain that Pinel (1997) is describing is located in the parietal regions near the central fissure; however, when attempting to find the exact location of pain perception in the brain, he points out: "The perception of pain is paradoxical in three respects: it's adaptiveness, it's lack of critical representation, and the fact that it can be suppressed by descending control" (p. 198). The lack of critical representation of which Pinel speaks is a testament to the elusiveness of our pain center. Descending control speaks to the gate control theory and the body's own ability to have influence on pain (p.198). Chemicals known as neurotransmitters are the link between neural fibers (Pinel, 1997). Pain Assessment Pain assessment is required for most clinical activities after surgery. An ideal test of pain assessment should be reasonably simple to administer and direct at a level that is easily understood. Moreover, such an instrument should fulfill the criteria of validity and sensitivity and possess reliable scaling properties. There are three broad categories of methods for pain assessment: single dimension measurement, multiple dimension measurement, and nonverbal measurement. Under each category, a pain measure is selected according to its clinical applicability. How to treat the pain WHO’s Pain Relief Ladder World health organization has constructed a three-step "ladder" for pain relief. According to this model, drugs should be administered in the following order: nonopioids (aspirin and paracetamol); then, as necessary, mild opioids (codeine); then strong opioids such as morphine, until the patient is free of pain (Hawthorn & Redmond, 2001: p. 148) Figure: The WHO analgesic ladder (Source: Hawthorn & Redmond, 2001: p. 148) Pharmacotherapy, benefits and risks Often it is uncontrolled pain that keeps a patient hospitalized several days following surgery. Treating patient pain is an important component of anesthesia practice. Postoperative pain has a number of adverse consequences. Severe pain can prevent a patient from progressing through the postoperative period. Upper abdominal and thoracic surgeries are associated with severe pain leading to restrictive lung defect and depressed diaphragmatic activity. The autonomic reflex response to pain results in gastro intestinal hypomotility leading to nausea, vomiting and ileus (Bardram et al, 1995). A pain free state also helps to mobilize the patients faster, increasing pulmonary toilet and reducing hospital stay. Anesthetists are important providers of intraoperative pain management through many aspects. Adverse effects of opioids and the advent of ambulatory surgery with rapid rehabilitation has led to a reappraisal of postoperative pain management and a shift away from reliance on powerful opioids as the sole postoperative analgesic. Due to this shift, the concept of multi-modal or balanced anesthesia has been established. This is when opioids are used in conjunction with non-opioid analgesics in order to control postoperative pain. Many different methods are used by anesthetists in their quest to achieve adequate analgesia. Patient controlled analgesia (PCA) allows the patient to self administer small doses of opioids as needed. This provides for a more individualized dosing according to that specific patient need. In order for the PCA to be used effectively, the patient must by able to understand the concept and retain instructions about how it works. It is typically dosed in a 1-2 mg bolus giving rapid onset of analgesia. Paracetamol (also known as Acetaminophen) has an important role in balanced analgesia. It inhibits the synthesis of prostaglandins in the central nervous system and peripherally blocks pain impulse generation (Donnelly et al., 2005). In adults the regular prescription of acetaminophen has significant opioid-sparing effects in postoperative patients. It is often prescribed in combination with codeine. Acetaminophen is well absorbed orally but can also be given rectally. For the most part, acetaminophen is used as an adjunct in postoperative pain management. Non Steroidal Anti-Inflammatory Drugs (NSAIDS) in combination with are generally considered to be inadequate as sole agents in the control of immediate postoperative pain. Although in conjunction with opioids they work synergistically and have a significant opioid sparing effect. NSAIDS exert their anti-inflammatory effects through the inhibition of Cyclooxygenases (COX) and hence reduce the production of inflammatory prostaglandins. NSAIDS do not produce any sedative or respiratory depressive side effects. These drugs are useful in the management of pain associated with minor procedures and ambulatory surgery. NSAIDS are contraindicated in patients with peptic ulcer disease, renal impairment, aspirin-induced asthma and coagulation defects. Currently, several classes of analgesics are in use to treat pain. They include traditional analgesics such as opiates and COX inhibitors and newly added classes of compounds originally discovered as antidepressants and anti epileptics. In moderate to severe pain, opioids are highly efficacious in relieving pain. However, acute use of opioids is associated with side effects such as respiratory depression and chronic use is associated with development of tolerance and dependence. Moreover, opioids are inconsistent in relieving symptoms of neuropathic pain (Eisenberg et al., 2006). In inflammatory pain conditions, COX- inhibitors are mainstay of therapy. COX inhibitors too are associated with wide ranging side effects that include development of gastrointestinal ulcers, increased risk for cardiovascular events and renal impairment (Mamdani et al., 2004). Multimodal Pain relief Management of post surgical pain can be dealt with in various ways. Multimodal pain relief programs assess and treat physical, psychosocial, medical, vocational, and social aspects of pain. There are a number of studies supporting the effectiveness of multimodal (also called multidimensional or multidisciplinary) programs of pain management. The findings of the study conducted by Dysvik et al. (2004) showed patients reporting that the program improved their mood, their capacity to cope with pain, and their interpersonal adjustment. Both the formal features of the program, such as education and physiotherapy, and the informal aspects of the program, such as social support from other participants, were perceived as contributing to their improvement. Benefits of Multimodal Pain relief program The management of chronic pain in patients has become so difficult that several skills and knowledge are necessary (IASP, 2004). People coping with pain need to have some sense of control over their lives. Oftentimes the pain will create concern, and the person may worry that the pain will never again be within tolerable limits. Multimodal pain relief program can improve the lives of those who deal with pain by simultaneously treating the psychological, social, environmental, and physical factors their patients face. Psychological treatments for pain management play an important role in reducing perceived pain and, therefore, reduce psychological factors of dealing with pain, like anxiety and depression. Individuals suffer emotionally, physically, financially, and personally; this means that all the possible resources for physical and psychological pain treatment must be joined at the same time with those from the medical side. Conclusion Pain is one of the leading reasons that people seek medical treatment. Many of those suffer from pain that persists even though medical procedures have been performed. Of the theories of pain, the gate control theory offers the best model for explaining the experience of pain. Though all individuals have similar physiological and chemical reactions to painful stimuli, pain is a subjective experience. It involves sociological and psycho logical dimensions. Medical treatments often do not take into consideration the multiple dimensions of pain. This leads to the inference that one might intervene on pain by using treatment techniques that operate within the systems that involve those dimensions. Work Cited Bardram, L. Funch-Jensen, P. Jensen, P. (1995). Recovery after Laparoscopic Colonic Surgery with Epidural Analgesia, Early Oral Nutrition and Mobilization. Lancet.;345: 763-764. Bennett, G. (2000). Update on the neurophysiology of pain transmission and modulation. Journal of Pain and Symptom Management. 19 (1) (Suppl.), S2-S6. Donnelly, AJ. Baughman, VL. Gonzales, JP. Tomsik, EA. (2005). Anesthesiology and Critical Care Handbook. 6th edition. Lexi-Comp Inc. Hudson, Ohio. Dysvik E; Vinsnes AG; Eikeland O (2004). The effectiveness of a multidisciplinary pain management programme managing chronic pain. International Journal of Nursing Practice, 2004; 10: 224–234 Eisenberg E, McNicol ED, Carr DB (2006) Efficacy of mu-opioid agonists in the treatment of evoked neuropathic pain: Systematic review of randomized controlled trials. European Journal of Pain. 10(8):667-76. (Information retrieved from abstract http://www.ncbi.nlm.nih.gov/pubmed/16337151) Gatchel. R. J., Polatin, P. B., & Kinney, R. K. (1995). Predicting outcome of chronic pain using clinical predictors of psychopathology: A prospective analysis. Health Psychology, 14 (5), 415-420. Hall, J. L. (1994). Anatomy of pain. In Tollison, R., Satterthwaite, & Tollison, J. W. (2nd ed.), Handbook of Pain Management. Baltimore: Williams & Wilkins. Hawthorn J, Redmond K, (2001) Pain – Causes and Management. Blackwell Science Holdcroft A & Jaggar S (2005) Core Topics in Pain. Cambridge University Press, Cambridge International Association for the Study of Pain. (2004). Desirable characteristics for pain management facilities. Retrieved from http:// www.iasp-pain.org James, MM. Heijke, SM. Gordon, PC. (1996). Intravenous Tramadol Versus Epidural Morphine for Post-thoracotomy Pain Relief. Anesthesia and Analgesia, 83:87-91. 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