Acute and Chronic Pain Management

Can be:

• Superficial: From skin, subcutaneous tissue, and mucous membranes. Usually well-localized, sharp, pricking, throbbing, or burning. Transmitted by A delta fibers.
• Somatic: From deep tissues such as muscle, tendon, joints, or bones. Constant, aching, throbbing, gnawing, less well-localized.
• Visceral: From affected organs. Deep, dull, dragging, squeezing, colicky, associated with sweating, blood pressure and pulse changes, nausea, and vomiting.

Pathophysiology of Pain

Pain is a complex phenomenon that involves a delicate interplay between various components of the nervous system. To understand it fully, we need to break down the different stages of pain processing, starting from the periphery and ending in the brain.

1. Peripheral Receptors:

   These are specialized nerve endings located throughout the body that detect potentially damaging stimuli. There are two main types of pain receptors:

   • Nociceptors: These respond to noxious stimuli like heat, cold, pressure, and chemicals. They can be further divided into:
     • A-delta fibers: Responsible for fast, sharp pain.
     • C-fibers: Responsible for slow, burning pain.
   • Mechanoreceptors: These respond to non-painful mechanical stimuli like touch, pressure, and vibration.
2. Neural Pathways:

   Once a nociceptor is activated, it sends an electrical signal along a sensory nerve fiber towards the spinal cord. The type of fiber determines the speed and quality of the pain signal:

   • A-delta fibers: Transmit signals quickly, resulting in the first sharp pain sensation.
   • C-fibers: Transmit signals slowly, contributing to the dull, burning pain sensation.
3. Spinal Cord Mechanisms & Long Tracts:

   The sensory nerve fibers carrying the pain signal enter the spinal cord through the dorsal root ganglia. Here, the signals are processed and modulated by various interneurons before being transmitted to the brain via ascending long tracts:

   • Spinothalamic tract: This tract transmits the sensory-discriminative aspects of pain, including location, intensity, and duration.
   • Spinoreticular tract: This tract transmits the emotional-motivational aspects of pain, including the unpleasantness and the urge to withdraw from the painful stimulus.
4. Brainstem, Thalamus, Cortex & Other Areas:

   The ascending tracts terminate in various brain regions, each playing a role in the perception of pain:

   • Brainstem: This region is involved in the initial processing of pain signals and the activation of descending pain control pathways.
   • Thalamus: This acts as a relay station, directing pain signals to the cortex for further processing.
   • Cortex: This is where the conscious perception of pain occurs. Different areas of the cortex are responsible for different aspects of pain, including sensory-discriminative (location and intensity), emotional-motivational (unpleasantness and suffering), and cognitive-evaluative (interpretation and meaning of pain).
5. Descending Pathways:

   The brain also sends signals back down the spinal cord via descending pathways to modulate pain perception. These pathways can inhibit pain signals at the level of the spinal cord, thereby reducing the intensity of pain perceived.

Mechanism of Pain Generation

Tissue damage results in the following:

1. Release of algogens (pain-causing substances).
2. The algogens bathe and stimulate/sensitize the nerve endings of small myelinated or unmyelinated fibers (nociceptors).
3. The nociceptors transmit the signal into the dorsal horn of the spinal cord (nociception).
4. The signal is then projected into specific areas of the brain.

Pain Mediators

Pain mediators activate and sensitize nociceptors. They include:

• Bradykinin
• Prostaglandins
• Histamine
• Serotonin
• Potassium
• Protons
• Cytokinin
• Neuropeptides, such as substance P.

Peripheral Nociceptors

Nociceptive afferents are widely distributed in the body (skin, muscle, joints, viscera, meninges) and comprise both medium-diameter lightly myelinated A-delta fibers and small-diameter, slow-conducting unmyelinated C-fibers.

The most numerous subclass of nociceptor is the C-fiber polymodal nociceptor, which responds to a broad range of physical (heat, cold, pressure) and chemical stimuli.

Peripheral Pain Fibres

• C Fibres: Small non-myelinated fibers from nociceptors in the skin and viscera, transmit pain due to thermal, mechanical, and chemical damage.
• Aδ Fibres: Small myelinated fibers respond to pin-prick and acupuncture; strong stimulation causes the sensation of pain.
• Aβ Fibres: Larger myelinated fibers carry impulses from mechanoreceptors which modulate pain sensation.

Central Projections of Pain Pathways

The spinothalamic pathway ascends from primary afferent terminals in laminae I and II, via connections in lamina V of the dorsal horn, to the thalamus and then to the somatosensory cortex.

This pathway provides information on the sensory-discriminative aspects of pain (i.e., the site and type of painful stimulus).

The spinoreticular (spinoparabrachial) and spinomesencephalic tracts project to the medulla and brainstem and are important for integrating nociceptive information with arousal, homeostatic and autonomic responses, as well as projecting to central areas mediating the emotional or affective component of pain.

Sensory Neuron Order in Pain Perception

First Order Neuron

The cell body of the first-order neuron lies in a dorsal root ganglion or a somatic afferent ganglion of cranial nerves.

Second Order Neuron

The cell body of the second-order neuron lies within the spinal cord or brain stem. Examples are dorsal column nuclei.

These cells usually decussate or terminate in the thalamus.

Third Order Neuron

The cell body of the third-order neuron, which lies in the thalamus, projects to the sensory cortex.

In the cortex, information is processed. They interpret location, quality, and intensity of various stimuli and make appropriate responses.

Sensory Pathways

Lemniscal/Dorsal Column: Carries touch, joint sensation, two-point discrimination, and vibratory senses from the receptors to the cortex.

Ventrolateral System: Relays impulses concerning nociceptive stimuli (pain, crude touch) or changes in skin temperature.

• Although commonly a cause of chronic symptoms, neuropathic pain can also present acutely following trauma and surgery.
• This pain can vary in severity and in nature.
• Can be associated with numbness or paraesthesia.
• Pain is often caused by oversensitization of nerves in the CNS.
• It can arise from peripheral neuropathy, neuralgia, nerve entrapment, and direct nerve trauma.
• Symptoms are reflected by the kind of nerve fibers affected.
• Character: often described as burning, pricking, stabbing, or a deep ache.
• Altered sensation: such as numbness, pins and needles, sensitivity to light touch, increased response to mild pain.

• Pain is an individual, multifactorial experience influenced, among other things, by culture, previous pain experience, belief, mood, and ability to cope.
• Pain may be an indicator of tissue damage but may also be experienced in the absence of an identifiable cause.
• The degree of disability experienced in relation to the experience of pain varies; similarly, there is individual variation in response to methods to alleviate pain.
• The contribution of psychosocial factors to the pain experience is important in acute.
• Preoperative anxiety has been shown to be associated with higher pain intensities in the first hour after a variety of different operations.

1. Assessment

• History:
  • Specific pain history
  • Relevant medical history
• Physical examination
• Psychological examination
• Relevant investigations
• Evaluation of associated functional impairment.

Must be undertaken at appropriately frequent intervals. Although not always possible in acute pain.

2. Treatment

• Analgesics/adjuvants
• Non-pharmacologic
• Interventional therapy
• Complementary therapy

Evaluate and record functional impact and side-effects of treatment at regular intervals.

Fundamentals of a Pain History

• Site of Pain
  1. Primary location: description ± body map diagram
  2. Radiation
• Circumstances associated with the pain onset, including details of trauma or surgical procedure
• Character of Pain
• Intensity of Pain
  1. At rest
  2. On movement
  3. Temporal factors
     • Duration
     • Current pain, during the last week, highest level
     • Continuous or intermittent
  4. Aggravating or relieving factor

Pain Measurement

Why do we need to measure pain?

1. Need to compare a single patient and a group of patients
2. To monitor the progress of individual patients.
3. To validate new treatments for research purposes.
4. To provide a means of assessing the efficacy of and response to analgesic.
5. Assigning a measure to the patient’s painful experience over time gives the patients some sense of control over his/her condition and has a positive effect on coping strategies.

Key Points about Pain Assessment

• Pain is a subjective experience.
• Can be perceived directly only by the sufferer.
• Observer-generated assessment is not reliable.
• Clinical standard for assessment is a self-report scale.

First step in the recognition and treatment of pain.

Should be assessed routinely alongside other vital signs, and intervention given and modified as clinical situation demands.

Should be assessed both at rest and during activity.

Clinical standard for assessment is a self-report scale (The Royal College of Surgeons and College of Anaesthetists 1990).

Single-Dimension Pain Instruments

• Rely on a single aspect of the pain experience, such as physical (intensity), functional, or behavioral.
• Simple and quick to administer.
• Good for bedside assessment.
• Methods vary from descriptive terms to visual analogue scales.
• Categorical scales have the advantage of being quick and simple and may be useful in the elderly or visually impaired patient and in some children. However, the limited number of choices in categorical compared with numerical scales may make it more difficult to detect differences between treatments.

1. Verbal Rating Scale
2. Numerical Rating Scale
3. Visual Analogue Scale
   • They are the most widely used pain rating scales.
   • Used both in clinical practice and research.
   • They are simple, minimally intrusive, effective, and easy to administer and score.

Verbal Rating Scale for Pain

Stratifies pain intensity according to levels of severity. It employs different word descriptions to rate the patient’s pain, e.g., no pain, mild pain, moderate pain, severe pain, worst possible pain. These words can be translated to any language. Numbers can be assigned to each of these words for recording purposes.

Scale	English	Yoruba
0	No pain	Kosi roara
1	Mild Pain	Irora die
2	Moderate Pain	Irora ti oninilara
3	Severe Pain	Irora ti oga
4	Excruciating Pain	Irora ti okoja ifarada

Verbal Numerical Rating Scales (VNRS)

Numerical Rating Scales (NRS) have both written and verbal forms. Patients rate their pain intensity on the scale of 0 to 10 where 0 represents ‘no pain’ and 10 represents ‘worst pain imaginable’. It is assumed that each number represents a proportional increase in pain severity.

Visual Analogue Scale (VAS)

This employs a 10 cm line rated from “no pain” at the left to “worst pain” possible on the right. It requires the patients to mark their pain on the continuum. The VAS “score” is the distance from the “no pain” point to the patient’s estimate. There should be no markings on, numbers, or words along the line, as these tend to influence the results.

VAS are the most commonly used scales for rating pain intensity in research, with the words ‘no pain’ at the left end and ‘worst pain imaginable’ at the right. Pictorial versions also exist. VAS can also be used to measure other aspects of the pain experience (e.g., affective components, patient satisfaction, side effects).

These scales have the advantage of being simple and quick to use, allow for a wide choice of ratings, and avoid imprecise descriptive terms. However, the scales require more concentration and coordination, need physical devices, are unsuitable for children under 5 years and may also be unsuitable in up to 26% of adult patients.

Pain Measurement in Children

• Because children have difficulty in communicating their pain, it can go unrecognized and untreated.
• Measurement is complicated by age and development of the child and his/her interaction with the parents.
• It is the child's behavior often, rather than their verbal report, which has to be interpreted to determine if they have pain.
• Infants with no verbal skills use non-specific measures of general distress like crying or motor withdrawal.
• Toddlers - these have begun to develop localizing and other signs which are more indicative of pain, such as rubbing, as well as more complex although less specific behaviors such as lip smacking, and aggressive behaviors.

Pain Measurement in Neonates, Infants, and Toddlers

• These have no verbal skills.
• It is the child's behavior often, rather than their verbal report, which has to be interpreted to determine if they have pain.
• Use non-specific measures of general distress like crying or motor withdrawal.

1. Objective Pain Scales
2. Clinical Observation Scoring

Clinical Observation e.g.	FINDING	SCORE
Cry	Not crying	0
	Crying	1
Posture	Relaxed	0
	Tensed	1
Expression	Relaxed or happy	1
	Distressed	1
Response	Respond when spoken to	0
	No Response	1

Score key:

• 0 = no pain
• 1 = slight pain
• 2 = moderate pain
• 3 = severe pain
• 4 = worst pain possible

Note: If patient is asleep, no further assessment is needed.

The Wong-Baker FACES Pain Scale

Designed for children 3 years of age and older, is useful in patients with whom communication may be difficult. The patient is asked to point to various facial expressions ranging from a smiling face (no pain) to an extremely unhappy one that expresses the worst possible pain.

Pain Assessment Tools in Children

Pain relief may be measured in the reverse direction with 0 representing ‘no relief’ to 10 representing ‘complete relief’.

Treatment of Acute Pain

Goals of Treatment:

1. Stop or alleviate pain
2. Prevent progression and aid healing
3. Restore normal lifestyle and improve quality of life

1. Pharmacologic
2. Non-pharmacologic
3. Psychological Intervention
4. Supportive Care

Sites of Intervention

1. The periphery where pain is initiated
2. The afferent neuron conveying pain signals
3. The dorsal horn cells and the CNS where pain signals are processed

Multimodal Analgesia

Methods of Treating Pain

Principles of Analgesic Use

• By the mouth
  • Oral route preferred
• By the clock:
  • At regular intervals
  • No place for ‘prn’ analgesia
  • Prescribe breakthrough dose
• By the ladder:
  • Stepwise progression
• For the individual

WHO 1986 Cancer Pain Relief

Choice of Analgesics for Acute Pain Management

• Multiple drug therapy is the cornerstone.
• Combine drugs with different mechanisms of action.
• No advantage to be gained in using more than one drug from a group.
• Consider cost, availability, safety, and ease of administration.

The Ideal Drug for Acute Pain

• Broad spectrum of indications
• Cost-effective
• Proven efficacy
• Flexible dosing
• Fast onset of action
• Safe in wide age groups

Analgesics

• Opioids (Morphine, Codeine, Tramadol)
• Non-opioids (Paracetamol, Diclofenac, Ibuprofen, Ketorolac)
• Adjuvants (Corticosteroids, Tricyclic antidepressants, Anticonvulsants, Benzodiazepines, Anticholinergics)

Local Anaesthetics

• Interrupt pain pathways by blocking axonal conduction.
• There are many straightforward L.A. techniques which can be used for acute pain management.
• Regional blocks include intrathecal and epidural.
• Local infiltration with long-acting L.A.
• Specific nerve blocks.
• Plexus blocks.

Non-Pharmacological Techniques

• Transcutaneous Electrical Nerve Stimulation
• Acupuncture
• Manual and Massage Therapies
• Heat and Cold Therapy
• Hypnosis
• Distraction
• Auricular Electrical Stimulation
• Therapeutic Touch Techniques

Psychological Interventions

• The role of psychological interventions in the management of acute pain is generally seen as adjunctive to somatic modalities.
• Evidence for the value of their contribution is strengthening.
• Preparatory information has been found to be effective in improving postoperative recovery and reducing pain reports, pain medication use, and length of hospital stay.

Preventive Analgesia

• The pain pathway is a tinderbox. Once in flames, it is difficult to put out.
• As the pain pathways become sensitized, the amount of medication needed to control patient pain increases.
• Intervening before the pain system becomes sensitized is an absolute necessity when your goal is optimal patient benefit.
• Pain management is most effective when instituted prior to the painful event.