Introduction
Pain is an unpleasant experience with very high interindividual variations in terms of its perception. It is often a common reason to visit a physician. The management and taking care of a patient is not only challenging but also adds to increased healthcare costs, poor quality of life (QOL), and lost days of work. The proper assessment and treatment of pain with appropriate medical and surgical interventions alleviate patient’s suffering and improves the QOL.
Pain and Pain Physiology (AS8.1)
The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with or resembling that associated with, actual or potential tissue damage.”
The IASP emphasizes the complex nature of pain with its physical, emotional, and psychological components. The perception and interpretation of pain involve the transmission of painful stimuli from receptors to the cerebral cortex. The processing and transmission of pain can be understood through the following mechanisms:
Transduction: It is the conversion of painful stimuli into electrical energy. The electrical energy induces an action potential when it reaches a threshold value, and the resultant impulse is carried toward the central nervous system through nerve fibers.
Transmission: The sharp localized pain is carried by myelinated A-fibers, while the poorly localized, burning, and persistent pain is carried by unmyelinated C fibers. The pain impulse is transmitted from the periphery through the spinal cord, brain stem, and thalamus to the cortex.
Perception: The somatosensory cortex identifies the location and intensity of pain, and the perception may manifest as arousal and attention, somatic as well as autonomic reflexes, endocrine responses, and emotional changes.
Modulation: Modulation of pain involves changing or inhibiting pain impulses in the descending tract. The modulation can occur both at peripheral as well as central level. The neurotransmitters in pain modulation are:
Assessment of Pain (AS8.2)
The assessment of pain is quite challenging because of high interindividual variation for the same painful stimulus. However, the common methods of pain assessment include a number of the pain rating scales and questionnaire (Table 36.1).
Abbreviations: CHEOPS, Children’s Hospital of Eastern Ontario Pain Scale; CRIES, crying, requires SpO2 > 95%, increased vital signs, expression, sleeplessness; FLACC, face, leg, activity, cry, consolability; NRS, numeric rating scale; VAS, visual analog scale.
Acute Pain Management
Acute pain occurs because of noxious stimulation due to injury or a disease process or an abnormal function of muscle or viscera. Acute pain can occur after trauma, in the postoperative period, and in association with acute medical illnesses. The strategies for pain control include pharmacological and nonpharmacological options.
Pharmacological (AS8.3)
The goal is to maximize the positive effects and limit the side effects. The guiding principle is that balanced analgesia provides optimal pain relief. Multimodal analgesia is the preferred method of treating pain. It minimizes the adverse effects of using synergistic agents. The pharmacological methods include:
Nonsteroidal anti-inflammatory drugs (NSAIDs): These are important components of multimodal analgesia and reduce the dose of opioids.
Acetaminophen: Acetaminophen along with NSAIDs decrease the requirement of opioids.
Opioids: These are the mainstay for the management of postoperative pain. Opioids can be given through intravenous (IV), intramuscular (IM), and epidural routes.
Nonpharmacological
Keeping in mind the biopsychosocial model of pain, nonpharmacological measures are employed. Psychological support is an integral part of acute trauma management as well as the rehabilitation phase. Other techniques like transcutaneous electrical nerve stimulation (TENS), hypnosis, relaxation techniques, biofeedback, and acupuncture are also useful. Regional blocks play a pivotal role in the alleviation of pain in this ultrasound era. The common regional techniques are:
Chronic Pain Management
The chronic pain conditions have complex pathophysiology, with a varying incidence of 25 to 30%. The common clinical conditions associated with chronic pain are:
Low backache: The low backache is commonly encountered in clinical practice. It has a prevalence of 13.8 and an incidence of 31% in the general population. The proper evaluation in consultation with orthopedics is often warranted to rule out surgical causes of low backache. Red flag signs must be ruled out, which include:
Loss of control of the bowel or bladder.
Weakness or numbness in a leg or arm.
Saddle anesthesia (numbness of the anus, perineum, or genitals).
Treatment is initiated once the pain generator is identified after the examination. The medical management supplemented by physiotherapy is employed as standard care. The interventions may be required in case of failure of medical management. The commonly used interventions are:
Facet joint injection with steroids.
Percutaneous discectomy for a prolapsed disc.
Sacroiliac joint injection for sacroiliitis.
Neuropathic pain: Neuropathic pain can occur due to the dysfunction of peripheral as well as the central nervous system. The pathophysiology includes ectopic discharges, cross-excitation of nerves, collateral sprouting, and cerebral reorganization. The most common neuropathic pain conditions are:
In neuropathic pain, there is increased activity and decreased inhibition in the somatosensory system. Pharmacotherapy is based on modulation of these phenomena by reducing the spontaneous activity and transmitter release and enhancing the inhibitory mechanisms. Pharmacotherapy is the most important treatment modality (Table 36.2). Complete pain relief is exceptional; hence, some pain relief is a realistic goal, which needs to be explained to the patient. The practical goals are:
Cancer pain: Cancer pain syndromes can be divided into acute and chronic. Acute ones are usually a direct consequence of invasive diagnostic or therapeutic procedures, but they can less commonly be related to cancer itself. Chronic ones are more likely to be caused by the neoplastic process or antineoplastic therapy.
The local expansion and metastases to distant organs result in the increasing severity of cancer pain. Treatment should be in an integrated fashion and the approach includes:
The WHO ladder recommends nonopioid analgesics as possible options at all steps. Opioids are the mainstay of analgesic therapy and are stratified based on their ability to control pain. The dosing of opioids should be titrated based on the desired pain control and associated side effects. The cancer patients often report breakthrough pain in the background of optimized pain control for which immediate-release opioids are helpful.
Myofascial pain syndrome (MPS): MPS is characterized by local and referred pain and perceived as deep and aching in the presence of myofascial trigger points. It is distributed equally between men and women, with an overall prevalence of 40 to 70%. Myofascial pain (MP) causes a significant reduction in QOL and is a major cause of time lost from work. The treatment goals are:
Correction of perpetuating factors.
Trigger point inactivation: Either invasive or noninvasive methods.
The treatment methods are physiotherapy, transcutaneous electrical nerve stimulation, acupuncture, topical cooling of muscle, and trigger point injection with local anesthetics.
Fibromyalgia: Definition: “A common rheumatological syndrome characterized by chronic, diffuse musculoskeletal pain, and tenderness with a number of associated symptoms, among which sleep disturbances, fatigue, and affective dysfunction are particularly frequent.”
The diagnostic criteria for fibromyalgia are:
Widespread pain index (WPI) score > 7 and symptom severity (SS) scale score > 5 or WPI score of 3 to 6 and SS scale score > 9.
Symptoms present at a similar level for at least 3 months.
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