Lecture 5: Pain

Question 1

What is pain?

Answer 1

An unpleasant sensory and emotional experience associated with actual or potential tissue damage.

Pain is whatever the experiencing person says it is.

Question 2

Is pain directly proportional to amount of tissue injury?

Answer 2

Not always

Question 3

Why is pain underrated?

Answer 3

It is highly subjective

Question 4

What does pain cause?

Answer 4

Amplifies the body’s stress response to traumatic injury (through SNS and glucocorticoids)

Causes endocrine and metabolic abnormalities

Impedes a patient’s recovery from trauma and surgery

Question 5

What is acute pain?

Answer 5

lasts less than 6 months, subsides once the healing process is accomplished.

Question 6

What is chronic pain?

Answer 6

involves complex processes and pathology.

Usually involves altered anatomy and neural pathways.

It is constant and prolonged, lasting longer than 6 months, and sometimes, for life.

Question 7

Why treat pain?

Answer 7

Tissue damage has the potential to elicit mechanisms that can create disabling, refractory, chronic situations that may prolong and even
outlast the period of healing.

If you don’t treat the initial pain, it may lead to chronic pain

Question 8

What is pain theory?

Answer 8

Severe, unrelieved acute pain results in abnormally enhanced physiological responses that lead to pronounced and progressively increasing pathophysiology

Increased pathophysiology -> increased morbidity and mortality

Question 9

Harmful effects of pain

Answer 9

Cardiovascular and respiratory systems are significantly affected

Adrenergic stimulation

Hypercoagulation

Increased heart rate, cardiac output and myocardial oxygen consumption

Decreased pulmonary vital capacity, alveolar ventilation, functional residual capacity

Arterial hypoxemia

Supression of immune functions -> wound infections and sepsis

Question 10

What happens to person’s social life during chronic pain syndrome

Answer 10

Pain becomes focus of life

Relationships become altered

Question 11

Causes of chronic pain syndrome

Answer 11

Can be the result of acute, unrelieved pain (multiple trauma, phantom limb pain after amputation, repeated back surgeries)

Sometimes set,s from near-muscular disorders (fibromyalgia, rheumatoid arthritis, multiple sclerosis)

Question 12

Pain pathways (receptors, stimulation, neurons, processes)

Answer 12

Specialized receptors = free nerve endings

Stimulation: Mechanical damage, extreme temperature, chemical irritation

2 types of neurons: A-delta and C

Four processes: transduction, transmission, modulation, perception

Question 13

Four processes to pain

Answer 13

Transduction: Local biochemical changes in nerve endings that generate a signal

Transmission: Movement of that signal from the site of pain to the spinal cord and brain

Perception: Synthesis and analysis in the brain

Modulation: Endogenous systems in place that can inhibit pain at any point along the pathway

Question 14

Which receptors send pain signals?

Answer 14

All receptors can

Question 15

What are nocireceptors?

Answer 15

Involved in transduction of pain

Free nerve endings

Capacity to distinguish between noxious and innocuous stimuli

Question 16

What happens when person is exposed to mechanical, thermal or chemical stimuli

Answer 16

Involved in transduction

Tissue damage occurs

Substances are released by the damaged tissue which facilitates the movement of pain impulse to the spinal cord.

Question 17

Substances released during transduction? What do they cause?

Answer 17

Released from traumatized tissue

Bradykinin

serotonin

substance P

histamine prostaglandin

Cell depolarization by sodium influx

Question 18

What drugs act on transduction process of pain?

Answer 18

Non-steroidal anti-inflammatories (ex: ibuprofen) - minimize the effects of substances released during transduction, especially prostaglandins.

Corticosteroids (ex: dexamethasone) - used for cancer pain, interferes with the production of prostaglandins.

Question 19

Transmission process of pain

Answer 19

Initial damage/stimulation -> nerve -> spinal cord -> brain stem -> thalamus -> central structures of brain -> pain is processed

Question 20

What is required to continue pain impulse from spinal cord to brain? What drugs targeted this step?

Answer 20

Transmission

Neurotransmitters

Opioids (narcotics) are analgesics, block release of neurotransmitters

Question 21

Two different types of peripheral that transmit pain signals from pain receptors to spinal cord

Answer 21

Transmission

A delta: “fast pain”, protective pain

C-fibers: “slow pain” nerve fibres, learning and behavioural modification

Question 22

Fast pain vs slow pain

Answer 22

See table

Question 23

Where does perception of pain occur?

Answer 23

Somatosensory cortex, cingulate cortex - sensory discrimination, emotional response (fear, anxiety, panic, subjective)

Reticular formation (increased arousal, emotional response, somatic and autonomic motor reflexes)

Question 24

Therapeutic strategies that target perception of pain

Answer 24

Behavioural strategies

Therapy

Brain can accommodate a
limited number of signals, so distraction, imagery and relaxation signals may get through the gate, leaving limited signals (such as pain) to be transmitted to the higher structures.

Question 25

How do higher vertebrates handle pain vs primitive vertebrates

Answer 25

Higher vertebrates: have anatomical components for perception of pain

Primitive vertebrates (Fish, reptiles, amphibians): avoidance or escape behaviour, poorly developed cerebral cortex

Question 26

Where does modulation process occur?

Answer 26

Descending tract (brain -> spinal cord)

Changing or inhibiting pain impulses

Question 27

What occurs during modulation

Answer 27

Descending fibres release substances (endogenous opioids or endorphins) which have capability of inhibiting transmission of pain

Question 28

Why are anti-depressants used to treat cancer pain?

Answer 28

Antidepressants interfere with reuptake of serotonin and norepinephrine, which increases their availability to inhibit noxious stimuli

Question 29

What activates descending pain modulation system?

Answer 29

STRESS!

fear

hunger

thirst

fatigue

prolonged motor activity

hypnosis

Question 30

Pain processes and possible medications

Answer 30

Perception: parenteral opioids, a2 agonists, general anaesthetics

Transmission: Local anaesthetics

Modulation: spinal opioids, a2 agonists, NMDA receptor antagonists, Ach esterases, NSAIDS, CCK antagonists, NO inhibitors, potassium channel openers

Transduction: NSAIDS, Antihistamines, Membrane stabilizing agents, local anesthetic cream, opioids, bradykinin and serotonin antagonists

See figure

Question 31

Categories of pain

Answer 31

Nociceptic: injury, trauma, infection

Neuropathic: damage or dysfunction of the peripheral or central nervous system

Visceral: Arising from internal organ (MI, appendicitis, bowel obstruction)

Question 32

Nociceptive vs neuropathic pain

Answer 32

See figure

Question 33

What does neuropathic pain feel like

Answer 33

Fire

Electricity

Typically in feet, legs and hands

Question 34

Types of neuropathic pain

Answer 34

Hyperalgesia: intense pain in response to mildly painful stimulus (pinprick)

Allodynia: pain in response to completely innocuous stimulus (touch)

Question 35

What can neuropathic pain be caused by?

Answer 35

injury (amputation and subsequent phantom limb pain)

scar tissue from surgery (back surgery high risk)

nerve entrapment (carpal tunnel)

damaged nerves (diabetic neuropathy)