1. Introduction.
2. Definition.
3. Pain Theories.
4. Pain reception, perception and response.
5. Factors affecting the pain experience.
Introduction
Pain is a universal phenomenon that has been described throughout history as a human affliction. Despite much work undertaken to study the nature of pain, experts still admit they do not understand it completely. It is a subjective experience and no objective test exists to measure it. In addition, no two persons experience pain in the same way, and no two painful events create identical responses or feeling in a person.
What is Pain?
"The normal, predicted physiological responses to an adverse chemical, thermal, or mechanical stimulus associated with surgery, trauma, or an acute illness".
It is whatever the person says it is and exists whenever they say it does.
There are two broad categories of pain
ü Acute.
ü Chronic.
Acute pain is that pain which is accompanied by anxiety on the part of the patient, who is distinctly worried about it what is going to happen? Does the pain be token something dreadful? What can be done about it? It tends to be of short duration and focal to the site of injury. It is usually associated with autonomic activity, such as tachycardia and diaphoresis, and is relatively brief and subsides with healing. Furthermore, acute pain functions as endogenous protective mechanism that signals the brain of the occurrence of real or potential tissue injury, thus prompting a protective response.
On the other hand, pain can persist beyond the point of tissue healing and develop into a chronic state which serves no biological function. Chronic pain usually lasts continuously or intermittently for 3 months or more. The psychological consequence of chronic pain is depression not anxiety as occur in acute pain.
Procedural pain can be defined as "the unpleasant sensory and emotional experience that arises from actual or potential tissue damage associated with diagnostic or treatment procedure". is an acute type of pain because it has an identifiable cause and time limited duration. Specifically, it is an inflammatory type of acute pain. When this type of pain is poorly managed, it can be a source of substantial physiological stress.
Pain theories
Many theorists tried to explain how pain can be produced, transmitted, and manifested. There is no consensus about which theories are most useful, existing theories provide guidance for clinical practice.
Affect theory: ( 1)
This theory dates back to Aristotle who considers pain as an emotion that colors all sensory events. Aristotle described as painful both listening to badly played music and bereavement. Sherrington (1900) proposed that affective tone is an attribute of all sensations; skin pain is an attribute of sensation. Titchener (1909) added the view that pain and unpleasantness were on a continuum.
Specificity theory: (2)
It is developed by Descartés in 1644. This theory is the first reflection of a physiologic basis for pain. It proposes that pain is a specific sensation that is proportional to the extent of tissue damage. The specificity theory proposes that the transmission of pain is through special fibers to specific pain centers in the brain via the spinal cord.
It proposes that a specific pain pathway carries the message from a pain receptor in the skin to a pain center in the brain. It assumes a direct relationship between stimulus intensity and perceived pain, even though the same stimulus may evoke different responses in different people or even in the same person under different circumstances. It assumes that only one brain structure responds to the pain impulses. It does not explain how sensation can progress from a pleasant to a painful feeling. It does not account for the psychological component of pain.
Goldscheider proposed that stimulus, intensity and central summation are the critical determinants of pain. Pain sensation becomes cumulative and the response increased as time increases. Goldscheider believed that the large cutaneous fibers comprise a specific touch system, whereas the smaller fibers converge on dorsal horn cells in the spinal cord that summate their input and transmit the pattern to the brain.
Summation theory:(3)
Livingstone (1943) proposed the involvement of the spinal cord and brain (central nervous system) mechanisms to account for summation. He hypothesized that there were self-exciting nerve loops, or "reverberating circuits", activated as a result of nerve damage that could explain how long duration pain could result from brief period of nerve stimulation.
Pattern theory:(4)
To deal with some of the specificity theory's limitations, researchers developed the pattern theory. According to this theory, pain impulses generated by receptors form a pattern or code that informs the central nervous system that pain is present. This theory explains why intense stimuli may produce pain on one occasion but not another. Weddell (1800) posited that virtually all nerve endings, then thought to be alike, responded to different types of stimulation with different patterns of impulses.
Sensory interaction theory:(5)
Noordenbos (1959) proposed an input control mechanism that, under normal circumstances, prevents central summation from occurring. When this mechanism is damaged, pathologic pain states result. An important part of this theory was the idea that there are two kinds of peripheral nerves involved: small-diameter nerves, which conduct the nerve impulses that are necessary for pain, and large diameter nerves, which inhibit these impulses. A greater number of active small-diameter nerves would increase summation and pain, whereas a preponderance of large-diameter nerve activity would inhibit pain.
Behaviorist theory:(6)
Lazarus (1977) stated "Nearly everyone will agree that the only way we can know anything about another person is through his behavior". It is through pain behaviors that pain is recognized and interpreted by clinicians. Behaviors may include verbal descriptors, splinting, increase in heart rate, limping, rubbing a body part, sweaty palms, grimacing, or other overt expressions. Behaviors have meaning both for the person demonstrate them and for the observer.
Gate control theory:-(7)
Puntillo (1990) advocates the "gate control theory" as a framework that supports non pharmacological methods of pain relief such as the use of relaxation and distraction to modulate pain at supraspinal sites including the brain stem and cerebral cortex. The gate control theory of pain introduced by Melzack and wall in 1965. They suggested that pain experience consists of three dimensions:
sensory-discriminative, motivational-affective, and cognitive central process. They introduced the idea that pain transmission through the spinal cord was modulated by a number of dynamic inhibitory and excitatory inputs.
As noted in Figure (2), impulses evoked by peripheral stimulation are transmitted to three systems: the cells in the substantia gelatinosa, the dorsal column fibers that project toward the brain, and the spinal cord transmission.
The theory proposes that the substantia gelatinosa in the spinal cord operates as the gate control system, modulating the transmission of nerve impulses from the peripheral cells to the transmission cells in the dorsal horn. Transmission cells in the spinal cord are believed to be excitatory, activating the central transmission of the sensory and emotional aspects of pain. The substantia gelatinosa is thought to modulate this central transmission by influencing the activation of T cells.
Small diameter myelinated and unmyelinated A-β and C fibers that carry pain inhibit modulation and activate T cells, thus "opening the gate" and allowing the transmission of pain. While large diameter A-β fibers from touch and pressure receptors project into the substantia gelatinosa cause inhibition of T cells, thus "closing the gate". Higher central nervous system processes can influence the gate control system by delivering inhibitory messages to the spinal cord. This opens up the possibility that psychological factors may play a major part in the perception of pain.
Understanding the physiologic dimension of pain requires knowledge of neural anatomy and physiology. The neural mechanism by which pain is perceived consists of four major steps:
(1) Transduction (2) Transmission
(3) Perception (4) Modulation.
1. Transduction
It is the conversion of a mechanical, thermal, or chemical stimulus into a neuronal action potential. It occurs at the level of the peripheral nerves, in particular the free nerve endings, or nociceptors. Noxious (tissue-damaging) stimuli (e.g., pressure), thermal damage (e.g., sunburn), mechanical damage (e.g., surgical incision), or chemical damage (toxic substances) cause the release of numerous chemicals into the area around the peripheral afferent noci-ceptor (PAN). Some of these chemicals (e.g., bradykinin, serotonin, histamine, potassium, and nor-epinephrine) activate or sensitize the PAN to excitation. If the PAN is activated or excited, it will fire an action potential to the spinal cord.
The pain action potential results from two sources:
(1) A release of the sensitizing and activating chemicals (nociceptive pain)
(2) Abnormal processing of stimuli by the nervous system (neuropathic pain both producing a change in the charge along the neuronal membrane. In other words, when the PAN terminal is transuded, the PAN membrane becomes depolarized, and sodium enters the cell. Potassium exits the cell, thereby generating an action potential. The action potential is then transmitted along the entire length of the neuron to cells in the spinal cord.
Therapies directed at altering either the PAN environment or sensitivity of the PAN are used to prevent the transduction and
initiation of an action potential. Decreasing the effects of chemicals released at the periphery is the basis of several pharmacologic approaches to pain relief. For example, non steroidal anti inflammatory drugs (NSAIDs), such as ibuprofen (Advil, Motrin) and naproxen (Naprosyn, Aleve), and corticosteroids, such as dexamethasone (Decadron), exert their analgesic effects by blocking pain-producing chemicals. NSAIDs block action of cyclooxygenase, and corticosteroids block the action of phospholipase, thereby interfering with the production of prostaglandins.
2. Transmission:
Is the movement of pain impulse from the site of Transduction to the brain.
Three segments are involved in nociceptive signal transmission:
(a) Transmission along the nociceptor fibers to the level of the spinal cord.
One nerve cell extends the entire distance from the periphery to the dorsal horn of the spinal cord with no synapse. Two types of peripheral nerve fibers are responsible for transmission of pain impulse from the site of transduction to the level of the spinal cord: A fibers (alpha, beta, and delta) and C fibers Drugs that stabilize the neuron membrane and inactivated Sodium channels disrupt the transmission of the action potential along the PAN axon. Some drugs, such as local anesthetics
(b) Dorsal born processing.
Dorsal horn processing. Once the nociceptive signal arrives In the central nervous system, it's processed within the Dorsal horn to the spinal cord . this processing include the release of the neurotransmitters which bind to receptors on nearby cell bodies and dendrites of cells which may be located elsewhere in the dorsal horn . The effect of the complex neurotransmittors release can facilitate or inhibit transmission of nociceptive stimuli . in this area exogenous and endogenous opioids also play an important role by binding to opioid receptors and blocking the release of neurotransmitters.
(c) Transmission to the thalamus and the cortex.
Transmission to the thalamus and the cortex. From the dorsal horn, nociceptive stimuli are communicated to the third-order neuron, primarily in the thalamus, and several other areas of the, brain. Fibers of dorsal horn projection cells enter the brain through several pathways to the thalamus and the cortex.
3. Perception:
Perception occurs when pain is recognized, defined , and responded by the individual experiencing the pain . in the brain , nociceptive input is perceived as pain , there is no single , precise location where the pain perception occurs
4. Modulation:
Modulation involves the activation of descending pathways that exert inhibitory or facilitators effects on the transmission of pain. Depending on the type and degree of modulation, the nociceptive stimuli may or may not be perceived as pain. Modulation of pain signal can occur at the level of the periphery, spinal cord, brainstem, and cerebral cortex.
Pain responses
1- Behavioral (voluntary) responses:-
· Moving away from painful stimuli
· Grimacing, moaning, and crying
· Restlessness
· Protecting the painful area and refusing to move
2- Physiologic (involuntary) responses:-
A-typical sympathetic responses when pain is moderate and superficial:
· increase blood pressure
· increase pulse and respiratory rate
· pupil dilatation
· muscle tension and rigidity
· pallor(peripheral vasoconstriction)
· increase adrenalin output
· increase blood glucose
b- typical Para-sympathetic responses when pain is severe and deep:
· nausea and vomiting
· fainting and unconsciousness
· decrease blood pressure
· decrease pulse rate
· rapid and irregular breathing
3- Affective (psychological) responses:
· withdrawal
· anxiety
· depression
· fear
· anger
· anorexia
· fatigue
· hopelessness
· powerlessness
Factors affecting pain response
1- physiological factors
· age
Age affects perception of pain. For example, a young child may think pain is the result of doing wrong. School age children are able to understand the cause of their pain and to describe the pain they are feeling.
· sex
Sex may have influence more than many factors on individual sensitivity to pain. Although the research literature reveals no sex differences in a individual sensitivity to pain. it was stated that males are expected to show less expression of pain than females
· cause and intensity of pain
-The cause of pain for a patient a factor that influences his or her response to pain. If the cause is known, it may help the client to respond to it positively. If the cause is unknown, more negative psychological factor such as fear and anxiety come into play.
2-intellectual factors
· past experience and meaning of pain
People who have experienced more pain than usual in there life time tend to anticipate more pain and to increase sensitivity to pain
3- Socio cultural factors
· Believes - attitudes and traditions
Cultural and race are critical factors in an individual's response to pain.
Also the child learns much about how to respond to pain and other experiences from the family. By showing approval and disapproval parents teach their children how to behave when pain. In one culture, the child's crying may be rewarded, in another culture the cessation of crying may be praise.
· Ethnicity and race
Racial groups differ in the way they react to pain. Blacks may react differently from whites. Davitz and davitz, 1980 reported in their study that southern blacks are more vocal in their reports of pain than northern blacks.
· Religion
· Occupation
· Socio economic status
· Family relationship
4- Psychological factors
Emotions as fear, anger, loneliness, isolation, stress and anxiety
Influence the perception of pain. For example individual who are
depressed are more likely to think about their pain and be more aware of it. Also, a highly anxious individual is more likely to have a heightened perception of pain, and a less anxious individual will tolerate pain more effectively.
5-behavioral factors
It may also provide an indirect measure from which the presence and intensity of pain may be inferred. Observable indicators of pain may include behavioral cues such as; non speech vocalizations, palliative behaviors such as guarding or rubbing the painful area, behaviors that are not typical for the individual such as excessive sleeping or swearing, locomotor activity, and changes in facial expression.
Pain is a subjective experience. In addition, no two persons experience pain in the same way, and no two painful events create identical responses or feeling in a person.
It is whatever the person says it is and exists whenever they say it does.
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