**2. Concept of pain**

An accurate understanding and definition of pain and related terms is fundamental to effective pain recognition, quantification, and mitigation. Pain is generally a difficult term to define. This is because pain is seen as a subjective experience with variable effects on patients [14] and as a complex phenomenon with sensory cognitive and emotional components [15]. Pain was defined by the International Association for the Study of Pain Subcommittee on Taxonomy as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage" [16]. However, this definition was recently refined. Thus, the most recent definition of pain by the International Association for the Study of Pain Subcommittee on Taxonomy described pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage [17]. To the author's understanding, pain is a subjective expression of neural impulses induced by a stimulus with a capacity to potentially damage tissues of the body. In other words, pain is the reaction of the body to a potentially noxious or noxious stimulus and threatens the normal homeostasis if unrelieved.

#### **2.1 The pain pathway**

Essentially, the pain pathway comprises of four major steps, including transduction, transmission, projection, and perception, all working together to achieve the awareness or sensation of pain as shown in **Figure 1**. Pain begins with the stimulation of specialized nerve endings (nociceptors) by chemical, mechanical, or thermal insult in a process termed transduction, followed by the transmission of these signals to the spinal cord (dorsal horn) via afferent peripheral sensory nerves. The afferent peripheral sensory nerves are composed of two major types, the myelinated A delta and unmyelinated C fibers, whose cell bodies reside in the spinal cord. The myelinated A delta fibers are known to be localized and fast conducting, while the unmyelinated C fibers conduct slowly but are more diffuse. The resulting peripheral nerve impulses are either amplified or suppressed in a process called modulation. Following modulation, these signals are further projected through numerous pathways to the brain centers for processing into pain [18]. The perception and localization of pain are thought to occur at the level of the thalamus and in the sensory cortex, respectively. In theory, pain refers to a centralized experience resulting from nociception in the peripheral nerves [19]. The pain pathway is essentially complex and striking in the sense that there exist several junctures for intrinsic and extrinsic factors to control the nature, amplitude, location, and duration of original sensory signal [18]. As a result, pain memory is influenced by many factors including the intensity of painful events, environment, expectation of pain, and behavioral pattern of the patient [20]. The nervous system is known to be neuroplastic [20] or neuro-pliable. This denotes the change or adaptation of the biochemical and physiological functions of the nervous system in response to a stimulus [20]. The implication of this phenomenon is that response exhibited by the nervous system can be modified by an external or internal stimulus. The disadvantage of this action of the nervous system is that it could complicate the diagnosis and alleviation of pain [18]. Thus, pain is a complex neurophysiological process which can be modulated, amplified, and interrupted.

#### **2.2 Classification of pain**

There is no one unified classification of pain. Rather, there is heterogeneity in the reports classifying pain in the literature. According to Gaynor and Muir [20], it is classified based on disease such as arthritis, pancreatitis, or cancer pain; anatomy

**47**

**Figure 1.**

*Why Effective Pain Management Remains a Challenge DOI: http://dx.doi.org/10.5772/intechopen.93612*

such as bladder, pancreatic, back, or orthopedic pain; location as in superficial, visceral, or deep pain; duration including transient, acute, or chronic pain; intensity such as mild, moderate, or severe pain; and finally, based on the response to manipulation. Pain was also classified according to the duration into acute and chronic pain [21–23] and by origin into nociceptive, pathologic, and neuropathic pain [21, 20]. Acute and chronic pain appear to be the most widely studied by researchers. Fox [24] defined acute pain as "a symptom of disease" which lasts for less than 3 months. Acute pain is said to result from injury to the body which may be selflimiting and disappears with healing [20]. Ideally, acute pain refers to pain of short duration, while chronic pain denotes pain of long duration. In practice, however, there is no clear-cut distinction between the end of acute pain and the commencement of chronic pain. It is indeed difficult to pinpoint when an acute phase of pain

*A flowchart showing the pathway of pain from the point of tissue insult to perception of pain.*

*Why Effective Pain Management Remains a Challenge DOI: http://dx.doi.org/10.5772/intechopen.93612*

*Pain Management - Practices, Novel Therapies and Bioactives*

An accurate understanding and definition of pain and related terms is fundamental to effective pain recognition, quantification, and mitigation. Pain is generally a difficult term to define. This is because pain is seen as a subjective experience with variable effects on patients [14] and as a complex phenomenon with sensory cognitive and emotional components [15]. Pain was defined by the International Association for the Study of Pain Subcommittee on Taxonomy as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage" [16]. However, this definition was recently refined. Thus, the most recent definition of pain by the International Association for the Study of Pain Subcommittee on Taxonomy described pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage [17]. To the author's understanding, pain is a subjective expression of neural impulses induced by a stimulus with a capacity to potentially damage tissues of the body. In other words, pain is the reaction of the body to a potentially noxious or

noxious stimulus and threatens the normal homeostasis if unrelieved.

Essentially, the pain pathway comprises of four major steps, including transduction, transmission, projection, and perception, all working together to achieve the awareness or sensation of pain as shown in **Figure 1**. Pain begins with the stimulation of specialized nerve endings (nociceptors) by chemical, mechanical, or thermal insult in a process termed transduction, followed by the transmission of these signals to the spinal cord (dorsal horn) via afferent peripheral sensory nerves. The afferent peripheral sensory nerves are composed of two major types, the myelinated A delta and unmyelinated C fibers, whose cell bodies reside in the spinal cord. The myelinated A delta fibers are known to be localized and fast conducting, while the unmyelinated C fibers conduct slowly but are more diffuse. The resulting peripheral nerve impulses are either amplified or suppressed in a process called modulation. Following modulation, these signals are further projected through numerous pathways to the brain centers for processing into pain [18]. The perception and localization of pain are thought to occur at the level of the thalamus and in the sensory cortex, respectively. In theory, pain refers to a centralized experience resulting from nociception in the peripheral nerves [19]. The pain pathway is essentially complex and striking in the sense that there exist several junctures for intrinsic and extrinsic factors to control the nature, amplitude, location, and duration of original sensory signal [18]. As a result, pain memory is influenced by many factors including the intensity of painful events, environment, expectation of pain, and behavioral pattern of the patient [20]. The nervous system is known to be neuroplastic [20] or neuro-pliable. This denotes the change or adaptation of the biochemical and physiological functions of the nervous system in response to a stimulus [20]. The implication of this phenomenon is that response exhibited by the nervous system can be modified by an external or internal stimulus. The disadvantage of this action of the nervous system is that it could complicate the diagnosis and alleviation of pain [18]. Thus, pain is a complex neurophysiological process which can be modulated, amplified, and interrupted.

There is no one unified classification of pain. Rather, there is heterogeneity in the reports classifying pain in the literature. According to Gaynor and Muir [20], it is classified based on disease such as arthritis, pancreatitis, or cancer pain; anatomy

**2. Concept of pain**

**2.1 The pain pathway**

**46**

**2.2 Classification of pain**

#### **Figure 1.**

*A flowchart showing the pathway of pain from the point of tissue insult to perception of pain.*

such as bladder, pancreatic, back, or orthopedic pain; location as in superficial, visceral, or deep pain; duration including transient, acute, or chronic pain; intensity such as mild, moderate, or severe pain; and finally, based on the response to manipulation. Pain was also classified according to the duration into acute and chronic pain [21–23] and by origin into nociceptive, pathologic, and neuropathic pain [21, 20].

Acute and chronic pain appear to be the most widely studied by researchers. Fox [24] defined acute pain as "a symptom of disease" which lasts for less than 3 months. Acute pain is said to result from injury to the body which may be selflimiting and disappears with healing [20]. Ideally, acute pain refers to pain of short duration, while chronic pain denotes pain of long duration. In practice, however, there is no clear-cut distinction between the end of acute pain and the commencement of chronic pain. It is indeed difficult to pinpoint when an acute phase of pain

transcends into a chronic phase. This does not mean that every acute pain phase will gradually become chronic. However, in the absence of effective pain intervention and inability to self-limit acute pain, it is expected to assume this course.

#### **2.3 Pain management**

Pain is managed using pharmacological and non-pharmacological means. Pharmacological agents used in the management of pain include opioids, nonsteroidal anti-inflammatory drugs, steroidal anti-inflammatory drugs, and local anesthetics [25]. Additionally, tranquilizers, corticosteroids, tricyclic antidepressants and antiepileptic medications (topical capsaicin, mexiletine, and N-methyl-d-aspartate receptor antagonists), serotonin norepinephrine reuptake inhibitors, calcium channel α2-δ ligands, topicals, anticonvulsants, and transdermal substances are included in the pain management regimen as adjuvants to analgesics depending on the type and severity of pain [26–29]. Nonpharmacological management of pain involves the use of suitable housing, bed rest, gentle handling and manipulation (massage, osteopathic and chiropractic), meditative movements (such as Tai Chi and yoga), and diets [30, 31]. Much recent strategies for non-pharmacological pain management were classified into sensory (massage, positioning, acupuncture, hot and cold treatment, progressive muscle relaxation, and transcutaneous electrical nerve stimulation), psychological interventions, and others including music, belief, and spirituality [31, 32]. These non-pharmacological means are thought to play a huge role in relieving postsurgical pain.
