Pain Management

March

Pain is a complex subjective sensation and experience. With advancements in pain medicine, the definition, evaluation, and diagnostic approaches to pain continue to evolve.

Definition

In 2020, the International Association for the Study of Pain (IASP) revised the definition of "pain" to: "Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage."

Evaluation

Currently, there are no objective markers for measuring pain. The assessment of pain primarily relies on indirect methods. Key aspects of pain evaluation include the location, duration, nature, intensity, triggering and relieving factors, accompanying symptoms, psychological state, quality of life, and functional impact. Assessing the intensity of pain is fundamental to effectively diagnosing and managing pain. Various scales are available to measure pain intensity, and the choice of scale should consider the patient’s cognitive level, consciousness state, educational background, and cultural and linguistic factors. Below are some commonly used unidimensional pain intensity scales in clinical practice:

Numerical Rating Scale (NRS)

The NRS consists of 11 numbers ranging from 0 to 10, where higher numbers indicate greater pain intensity. Patients select a number that best represents their level of pain. Typically, 0 denotes no pain, 1–3 represents mild pain, 4–6 indicates moderate pain, and 7–10 corresponds to severe pain. This method requires patients to have the ability to understand abstract scales and is suitable for individuals with a certain level of education.

Verbal Rating Scale (VRS)

This scale involves healthcare providers categorizing pain into five levels: 1—mild pain; 2—discomforting pain; 3—distressing pain; 4—severe pain; and 5—excruciating pain. Patients choose the level that best reflects their pain. The method requires patients to have a basic understanding of language and can be affected by factors such as education, dialect, and culture.

Visual Analogue Scale (VAS)

The VAS features a 100-mm straight line, where one end (0 mm) represents "no pain at all," and the other end (100 mm) represents "the most intense pain imaginable." Patients mark a point on the line corresponding to their pain intensity, with higher scores reflecting higher levels of pain. This method is precise, simple, and widely used in both clinical and research settings, but it requires patients to have some degree of abstract thinking ability.

Revised Wong-Baker Faces Pain Scale (FPS-R)

This scale asks patients to rate their pain from 0 (no pain) to 10 (worst pain) while providing six facial expressions (smiling, sad, distressed, crying, etc.) corresponding to different levels of pain. Patients select the face or scale that best matches their pain intensity. This method is particularly useful for children, elderly individuals, those with low educational levels, or patients who have difficulty expressing themselves.

Diagnosis

Pain can manifest as both a symptom of a disease and a disease in itself. Before initiating treatment, efforts should be made to clarify the diagnosis or establish a preliminary diagnosis. The diagnostic process generally follows these steps:

History Taking

A targeted inquiry is conducted based on the chief complaint.

Physical Examination

Focused physical examination is performed based on the chief complaint and medical history.

Laboratory Tests

Necessary laboratory tests, imaging studies, and other relevant diagnostic evaluations are conducted.

Block Testing

Diagnostic block testing is performed when indicated.

March

Pathophysiology of Pain

The pathophysiology of pain is highly complex, involving intricate interactions between the periphery, spinal cord, and brain.

Pain Transmission Pathways

The classical pain transmission pathway (ascending pain pathway for the trunk and limbs) begins when nociceptive stimuli act on peripheral nociceptors. Pain signals are transmitted along nerve fibers and initially undergo preliminary processing in the dorsal root ganglion. Subsequently, the signals continue along afferent fibers and terminate at the dorsal horn of the corresponding spinal cord segment, where further integration of pain information occurs. Fibers then cross to the contralateral side to form the spinothalamic tract, which ascends to the thalamus. Finally, projections are sent to the corresponding regions of the cerebral cortex. Pain is analyzed and processed in broad areas of the brain, including the reticular formation, limbic system, frontal lobe, parietal lobe, and temporal lobe, where it generates emotional responses and reflexive or conscious motor reactions.

Pathophysiology

Based on pathophysiological mechanisms, pain can be categorized into nociceptive pain, neuropathic pain, and nociplastic pain.

Nociceptive Pain

This type of pain primarily results from structural tissue damage and occurs when nociceptive stimuli act on peripheral tissues. It is caused by inflammatory mediators stimulating nerve endings, peripheral nerves, or nerve roots. Known inflammatory mediators include substances such as substance P, calcitonin gene-related peptide (CGRP), glutamate, and adenosine triphosphate (ATP).

Neuropathic Pain

Neuropathic pain arises from damage or disease affecting the somatosensory nervous system. It involves multiple mechanisms such as peripheral sensitization, central sensitization, ion channel changes, and reduced functionality of the descending inhibitory system.

Peripheral Sensitization

This refers to an increased sensitivity of nociceptive neurons to incoming signals. Following peripheral nerve injury, damaged cells and inflammatory cells release various chemical substances, such as norepinephrine, bradykinin, histamine, prostaglandins, potassium ions, cytokines, serotonin, and neuropeptides. These mediators sensitize nociceptors and amplify incoming neural signals.

Central Sensitization

This describes pathological changes where the excitability of pain-related neurons in the spinal cord or above is abnormally elevated, or synaptic transmission is enhanced. These alterations include increased spontaneous neural firing, expanded receptive fields, lowered thresholds for external stimuli, and amplified responses to suprathreshold stimuli. These changes enhance the transmission of pain signals. Clinically, central sensitization can manifest as spontaneous pain, allodynia, or hyperalgesia.

Ion Channel Changes

Abnormalities in various ion channels, including calcium, sodium, and potassium channels, contribute to neuropathic pain. Studies on calcium channels have demonstrated that the expression of the α2-δ subunits in calcium channels within the spinal dorsal horn increases following nerve injury. This abnormal activation of calcium channels leads to increased calcium ion influx, which promotes the release of excitatory neurotransmitters and causes excessive neuronal excitability, resulting in hyperalgesia and allodynia.

Reduced Function of the Descending Inhibitory System

Peripheral nociceptive signals that reach the central nervous system can activate inhibitory neurons to dampen pain responses. In neuropathic pain patients, dysfunction of these neurons leads to a diminished inhibitory system, allowing excitatory activity to dominate. Consequently, the patients experience pain, anxiety, and sleep disturbances.

Nociplastic Pain

This term was introduced by the international pain research community to describe a third type of pain. Mechanistically, it differs from nociceptive pain caused by tissue injury and neuropathic pain resulting from somatosensory nerve damage. Nociplastic pain arises from enhanced pain and sensory processing and altered pain modulation within the central nervous system.

March

Treatment and Management of Acute Pain

Acute pain typically lasts for less than three months and is often associated with trauma, surgery, inflammation, or certain disease states. Among these, postoperative pain is the most common and clinically essential type of acute pain encountered in surgical practice. If inadequately controlled, postoperative pain can, in some cases, progress to chronic pain. The primary goals of postoperative pain management include: (1) optimal pain relief; (2) minimal adverse effects; (3) rapid recovery of physical and psychological functions; and (4) the highest possible comfort and satisfaction levels.

Principles and Methods of Postoperative Analgesia

Principles of Postoperative Analgesia

The sources of postoperative pain primarily include improperly managed intraoperative pain, residual incision pain, visceral pain, inflammatory pain, and neuropathic pain. Appropriate analgesic methods and medications should be selected based on the specific origins of the pain. For example:

Incisional pain can be effectively managed using epidural anesthesia, peripheral nerve blocks, or local infiltration, primarily with local anesthetics.

Visceral pain may be controlled with opioid administration or epidural anesthesia.

Inflammatory pain can be treated with nonsteroidal anti-inflammatory drugs (NSAIDs).

Methods of Postoperative Analgesia

Systemic Administration

This includes oral, intravenous, and intramuscular administration. Oral administration is mainly suited for patients experiencing mild to moderate pain, who are awake and have good postoperative gastrointestinal function. Intravenous administration provides rapid onset and is commonly used for short procedures or as part of a multimodal analgesia regimen. Continuous intravenous administration is often applied for postoperative analgesia in intensive care unit (ICU) patients. Intramuscular injection, although a traditional method, is rarely used in postoperative pain management due to large fluctuations in blood drug levels, which can result in incomplete or excessive analgesia.

Neuraxial Anesthesia

Neuraxial anesthesia includes subarachnoid anesthesia and epidural anesthesia (including caudal anesthesia). This method is mainly used for postoperative pain relief in thoracic, abdominal, and lower limb procedures. Its main advantage lies in minimal impact on respiratory and circulatory functions. However, complications such as incomplete or excessive blockade, lower extremity weakness, hypotension, or epidural hematoma may occur.

Peripheral Nerve Block

Blocking peripheral nerves can interrupt the transmission of pain signals. This method may be used independently for surgical incision analgesia within the innervation zone or in combination with other analgesic methods.

Local Infiltration

This technique is often used at surgical incisions to reduce the need for postoperative analgesics or as part of a multimodal analgesia regimen.

Postoperative Analgesic Drugs

Opioids

Commonly used for moderate to severe postoperative pain, opioids exert their analgesic effects by binding to opioid receptors in the central and peripheral nervous systems. Representing drugs include morphine, fentanyl, and sufentanil. Opioids are a cornerstone of postoperative pain management. However, due to their dose- and receptor-dependent adverse effects, multimodal analgesia regimens are often employed to reduce opioid dosing requirements.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

NSAIDs are frequently used for mild to moderate pain or as part of a multimodal analgesia regimen for severe pain. These drugs exert antipyretic, analgesic, anti-inflammatory, and anti-rheumatic effects by inhibiting cyclooxygenase (COX) and prostaglandin synthesis. Based on their mechanisms of action, NSAIDs are categorized into nonselective and COX-2 selective agents:

Nonselective NSAIDs, such as ibuprofen, ketorolac, and flurbiprofen axetil, provide effective pain relief but are associated with gastrointestinal damage and platelet function inhibition.
COX-2 selective NSAIDs, including etoricoxib and celecoxib, present with fewer adverse effects related to gastrointestinal damage and platelet function inhibition.
Local Anesthetics:

Local anesthetics are commonly used in neuraxial blockade, peripheral nerve block, and local infiltration. Representative drugs include bupivacaine and ropivacaine.

Other Analgesic Medications

Dexmedetomidine, a highly selective α₂-adrenergic receptor agonist, provides sedation, analgesia, anti-inflammatory, sympatholytic, and anxiolytic effects. It demonstrates good synergistic effects when combined with other sedative and analgesic medications and is commonly used in multimodal postoperative analgesia. However, dexmedetomidine has a risk of causing respiratory depression or bradycardia. Its use should be avoided or approached cautiously in patients with bradycardia or cardiac conduction block.

Postoperative Analgesia Protocol

To achieve optimal analgesic efficacy with minimal adverse effects and to enhance the prevention and management of postoperative analgesia risks, it is essential to optimize pain management protocols.

Multimodal Analgesia

Multimodal analgesia involves combining drugs and techniques with different mechanisms of action, using various routes of administration, and targeting different sites, phases, and mechanisms of pain. This approach produces a synergistic analgesic effect and is the most commonly utilized analgesia management strategy during the perioperative period.

Individualized Analgesia

Individual differences in pain perception and response to analgesic medications necessitate tailoring pain management plans. Factors such as the patient's condition, surgical site, extent of trauma, pain characteristics, and social background should be considered comprehensively. Regular evaluation of analgesic efficacy is necessary to allow timely adjustments to the pain management plan.

Standardized Analgesia

Establishment of an Acute Pain Service (APS) team, comprising multidisciplinary members such as anesthesiologists, surgeons, nurses, and pharmacists, is vital. The team systematically documents patient pain scores, pain locations, and characteristics, as well as analgesic procedures, their efficacy, and any adverse reactions.

Postoperative Analgesia Complications and Prevention

Postoperative analgesia can provide effective pain relief but often leads to some adverse reactions that may negatively affect a patient’s recovery. Early recognition and management are critical.

Common Complications and Preventive Measures

Nausea and Vomiting

Refer to related sections in the anesthesia chapters for detailed management strategies.

Respiratory Depression

Opioids can reduce respiratory rate and tidal volume, potentially causing hypoventilation, CO₂ retention, and even hypoxemia. Preventive and management measures include:

Routine monitoring of respiratory rate, level of consciousness, and oxygen saturation (SpO₂).
Maintaining a clear airway, suctioning oral secretions, providing oxygen via a mask, and offering assisted positive pressure ventilation if needed. An oropharyngeal airway may be placed for patients experiencing tongue base obstruction.
Discontinuation of narcotic analgesics and reduction or cessation of patient-controlled analgesia pumps.
Respiratory depression caused by opioid overdose can be reversed with naloxone administration.

Hypotension and Bradycardia

Narcotic analgesics can suppress sympathetic nervous activity, resulting in decreased heart rate and blood pressure. Preventive and management measures include:

Enhanced monitoring of vital signs, with close observation of blood pressure, heart rate, lip color, and extremity temperature.
General measures such as oxygen supplementation and elevating the lower extremities.
Administration of vasopressors such as ephedrine or norepinephrine if necessary.
Evaluation of the level of anesthesia and analgesic pump settings, with intermittent discontinuation of the analgesic pump if needed. Resumption of its use may follow once blood pressure stabilizes.

Urinary Retention

Causes of urinary retention include suppression of the micturition reflex by general or neuraxial anesthesia, reduced bladder and sphincter muscle tone due to narcotic analgesics, psychological factors, wound pain, and unfamiliarity with bed urination. Preventive and management measures include:

Strengthened nursing care, including patient education, warm compresses, and massage.
For patients who remain unresponsive to these measures, urinary catheterization can facilitate bladder emptying.

Gastric Retention, Abdominal Distension, and Constipation

Narcotic analgesics can inhibit bowel motility, and postoperative factors such as abdominal surgery, general anesthesia, anticholinergic medication use, and prolonged bed rest further contribute to these complications. Preventive and management measures include:

Encouraging early mobilization, both in and out of bed.
Strengthening nursing care, including observation of flatus, defecation, and bowel sound status.
Application of supportive care such as warm compresses, massage, and patient education.
Administration of laxatives, enemas, gastrointestinal decompression, or acupuncture may be considered when necessary.

March

Diagnosis and Treatment of Chronic Pain

Scope of Diagnosis and Treatment for Chronic Pain

Chronic pain refers to pain that persists for more than three months. This type of pain continues to exist even after normal tissue healing has occurred, and it is generally considered to have no biological value. The scope of diagnosis and treatment for chronic pain includes the following seven categories:

Chronic Primary Pain: Pain in one or more regions of the body that persists for over three months and cannot be explained by other pain conditions.
Cancer Pain: Pain arising from the tumor itself as well as pain caused by anti-tumor treatments.
Chronic Post-Traumatic Pain: Pain that persists for more than three months following an injury or surgery, excluding pain caused by infections or pre-existing diseases.
Chronic Neuropathic Pain: Pain resulting from damage to sensory nerves, commonly seen in conditions such as trigeminal neuralgia, postherpetic neuralgia, painful diabetic neuropathy, and central pain syndromes.
Chronic Headache and Orofacial Pain: Pain originating from the head or the oral and facial regions, commonly including conditions such as primary headaches, glossopharyngeal neuralgia, and trigeminal neuralgia.
Chronic Visceral Pain: Pain originating from visceral organs, with mechanisms that are not fully understood, primarily caused by dysfunction of the visceral organs.
Chronic Musculoskeletal Pain: Pain arising from the skeleton, muscles, joints, or connective tissues, commonly including conditions such as myofascial pain, tenosynovitis, frozen shoulder, lumbar strain, osteoarthritis, and intervertebral disc herniation.

Common Methods for Treating Chronic Pain

Pharmacological Treatment

Pharmacological treatment serves as the most fundamental and commonly employed method for managing chronic pain.

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

NSAIDs are used to relieve mild chronic pain or in combination with opioids for moderate to severe pain. They are commonly applied for chronic pain conditions such as musculoskeletal soft tissue pain, osteoarthritic pain, headaches, or cancer pain. During treatment, excessive use of NSAIDs should be avoided, and combining multiple NSAIDs is not recommended. Long-term high-dose application is not advised, and they are contraindicated in patients with a history of peptic ulcers, renal insufficiency, bleeding tendencies, or coronary artery bypass graft surgery. Acetaminophen carries a risk of liver damage, which needs to be considered in chronic pain management.

Opioid Analgesics

Opioids are effective for nearly all types of pain and are widely employed for cancer-related pain as well as a second-line treatment for chronic non-cancer pain. Opioid receptor agonists are typically recommended, with representative drugs including morphine, oxycodone, and hydromorphone. Oral administration is preferred for long-term use. Common side effects include constipation, nausea, vomiting, drowsiness, itching, dizziness, urinary retention, delirium, cognitive impairment, and respiratory depression. Monitoring for adverse effects is essential during usage.

Antineuropathic Drugs

These drugs are mainly used for the treatment of neuropathic pain, such as postherpetic neuralgia, painful diabetic neuropathy, and phantom limb pain. Common medications in this category include gabapentin, pregabalin, and tramadol.

Antidepressants

Antidepressants can significantly alleviate certain pain symptoms, possessing both antidepressant properties and independent analgesic effects. Commonly used agents include duloxetine, amitriptyline, doxepin, fluoxetine, and paroxetine.

Glucocorticoids

Glucocorticoids exhibit anti-inflammatory and immunosuppressive properties and are applicable to various forms of pain. However, their clinical use requires strict adherence to indications due to the potential for side effects. In addition to systemic administration, local administration is an option, such as intra-articular injections, injections at soft tissue pain points, nerve root (or trunk) injection, or epidural injection. Commonly used drugs include compound betamethasone and dexamethasone.

Local Anesthetics

Local anesthetics are primarily used for nerve blocks in chronic pain treatment. Commonly used drugs include lidocaine, bupivacaine, and ropivacaine.

Minimally Invasive Interventional Pain Management

Minimally invasive interventional pain management involves using imaging techniques (such as ultrasound, X-ray, CT, etc.) to guide the delivery of medications or instruments to diseased tissues or areas around nerves. Through chemical and physical methods, this approach treats pain with minimal trauma and maximum convenience.

Nerve Block

This technique involves injecting medications around nerves to temporarily or permanently block pain conduction pathways and interrupt vicious cycles through mechanisms such as anti-inflammation, improved local circulation, and protein denaturation. Commonly used drugs include local anesthetics, glucocorticoids, ozone, and neurolytic agents (e.g., absolute ethanol). Common methods include peripheral nerve blocks, nerve plexus (trunk, ganglion) blocks, and spinal canal blocks.

Radiofrequency Ablation

This technique utilizes specialized equipment and needles to deliver high-frequency radio waves to local tissues, achieving nerve modulation or cutting to treat pain-related conditions. Its targets include peripheral nerves, nerve ganglia, intervertebral discs, joints, and soft tissues. It is widely used to treat various refractory pain conditions, such as cervical and lumbar disc herniation, osteoarticular diseases, and postherpetic neuralgia.

Low-Temperature Plasma Technology

Low-temperature plasma technology breaks molecular bonds in the treatment area by generating plasma, converting long-chain molecular collagen and its analogs (e.g., in intervertebral discs) into liquid or gaseous states that are eventually absorbed. It is primarily used to treat discogenic neck, shoulder, lumbar, and back pain.

Percutaneous Spinal Endoscopic Technique

As a form of minimally invasive spinal surgery, this technique involves placing an endoscope in the affected area via a working channel, allowing operations to be performed under direct visualization in a continuous water environment to relieve neural compression. It is widely applied in the treatment of degenerative conditions, infections, and tumors affecting the cervical, thoracic, and lumbar spine.

Neuromodulation Techniques

Neuromodulation involves altering the function of the central, peripheral, or autonomic nervous systems through electrical stimulation or the administration of medications to alleviate symptoms and improve quality of life. This includes nerve electrical stimulation and intrathecal drug delivery system implantation.

Nerve Electrical Stimulation

This technique involves implanting electrodes near the epidural space or peripheral nerves through puncture or open surgery. Electrical pulses stimulate the spinal cord dorsal columns, spinal nerves, or peripheral nerves to modulate the nervous system and alleviate pain. Depending on the stimulation site, it is categorized into spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS). It is used for conditions such as postherpetic neuralgia, painful diabetic neuropathy, post-lumbar surgery pain syndrome, complex regional pain syndrome, pain following spinal cord injury, peripheral nerve injury pain, and pain caused by peripheral vascular diseases.

Intrathecal Drug Delivery System (IDDS) Implantation

This technique uses an infusion pump implanted within the patient's body to deliver medications to the subarachnoid space, acting on specific spinal cord locations to block the transmission of pain signals to the cerebral cortex. In addition to cancer pain, this approach is used for managing various forms of refractory pain.

Other Therapies

Given the complex mechanisms underlying pain, diverse therapeutic methodologies are available in addition to the aforementioned approaches. These include physical therapies (e.g., electrotherapy, phototherapy, ultrasound therapy), traditional Chinese medicine (e.g., acupuncture, acupotomy, herbal medicine), and psychological treatments.

Cancer Pain

Definition

Cancer pain (commonly referred to as cancer-related pain) is pain resulting from the tumor itself or caused by anti-cancer treatments.

Etiology

The mechanisms of cancer pain are complex and can generally be classified into three categories:

Tumor-Related Pain: Pain caused by direct tumor invasion or compression of local tissues, as well as pain resulting from bone, soft tissue, or nerve involvement by metastatic lesions.
Anti-Cancer Treatment-Related Pain: Pain resulting from surgeries, other invasive procedures, radiation therapy, physical therapies, and pharmacological treatments used in cancer management.
Non-Tumor-Related Pain: Pain originating from other underlying conditions, complications, or psychosocial factors unrelated to the tumor itself.

Treatment Principles

A comprehensive treatment approach is employed, tailored to the patient's condition and general health status. Effective, early, and continuous pain control is emphasized through appropriate pain management methods, alongside the prevention and management of adverse drug reactions. The aim is to mitigate the physical and psychological burden of pain and its treatments, ultimately improving the patient's quality of life.

Treatment Methods

Treatment methods consist of etiological treatment, pharmacological treatment, and non-pharmacological treatment.

Etiological Treatment

The primary cause of cancer pain typically stems from the tumor itself or complications. Addressing this requires targeted anti-tumor therapies, including surgery, radiotherapy, chemotherapy, molecular targeted therapy, immunotherapy, and traditional Chinese medicine treatments, all of which have the potential to alleviate cancer pain.

Pharmacological Treatment

Opioid analgesics serve as the cornerstone of cancer pain management, with additional adjuvant analgesics including nonsteroidal anti-inflammatory drugs (NSAIDs) and neuropathic pain medications. Their use adheres to the World Health Organization (WHO) three-step analgesic ladder principles: “stepwise prescribing, oral administration, time-scheduled dosing, individualized treatment, and attention to specific details.” Analgesics are selected rationally, with doses and dosing frequencies adjusted based on individual needs, and efforts are made to prevent and manage adverse events. The goal is to achieve optimal pain relief with minimal side effects.

Non-Pharmacological Treatment

This category encompasses minimally invasive interventional pain management, acupuncture, transcutaneous acupoint electrical stimulation, as well as social and psychological support therapies. Combining minimally invasive interventional pain treatments with pharmacological therapies when appropriate can enhance analgesic outcomes.

Comprehensive Pain Management

Comprehensive pain management includes both acute and chronic pain care, with the multidisciplinary approach to pain management serving as a key indicator of the effectiveness of such comprehensive strategies.

Acute Pain Management

Acute pain management is generally led by the anesthesiology department, involving collaboration with other departments related to acute pain conditions. It includes the management of pain in outpatient and inpatient settings after the definitive diagnosis of acute conditions (e.g., various acute abdominal disorders, trauma), perioperative pain management, and pain control during interventional procedures (e.g., painless gastrointestinal endoscopy, painless fiberoptic bronchoscopy).

Chronic Pain Diagnosis and Treatment

Chronic pain diagnosis and treatment is typically spearheaded by the pain medicine department, with contributions from other relevant specialties. It encompasses the diagnosis and management of conditions such as neuropathic pain, cancer-related pain, and chronic bone and joint pain.