15: Pathophysiology of Pain

Question 1

What is pain in animals?

Answer 1

Aversive sensory and emotional experience which represents an awareness by the animal of damage or threat of damage to integrity of tissues.

Question 2

What is nociception?

Answer 2

Physiologic neural processes for encoding pain –> transduction, conduction –> CNS processing;

Process that leads to the perception of pain

Question 3

What is adaptive pain?

Answer 3

“Normal” pain, occurs when injury stimulus is applied to body/tissues;

Intensity/duration proportional to stimulus

Question 4

What is maladaptive pain?

Answer 4

Pain uncoupled from noxious stimulus or healing tissues;

Dysfunctional, results from abnormal functioning of the nervous system;

Abnormal sensory processing;

Persistent or recurrent, pain as disease

Question 5

What is acute pain?

Answer 5

Follows bodily injury, disappears with healing, self-limiting

Question 6

What is chronic pain?

Answer 6

Outlasts original injury, expected healing time, or a specified time (3-6 months)

Question 7

Why treat pain?

Answer 7

As veterinarians we have an ethical and moral responsibility to prevent and relieve animal suffering, and consider the patient’s well being

Question 8

What are 7 negative physiologic sequela of pain and stress?

Answer 8

1. Decreased pulm function
2. CV = Increased HR, BP –> increased myocardial work
3. Decreased immune function
4. Increased stress hormones
5. Coagulation = increased plt adhesion, decreased fibrinolysis
6. GI & GU = increased sphincter tone, decreased muscle tone
7. Immobility, inappetence, insomnia

Question 9

What is somatic pain?

Answer 9

Originates from damage to bones, joints, muscles, or skin;

Described as localized, constant, sharp

Question 10

What is visceral pain?

Answer 10

Arises from stretching, distention, or inflammation of viscera;

Described as deep, aching, without good localization

Question 11

What is neuropathic pain?

Answer 11

Originates from injury or involvement of the PNS or CNS;

Described as burning or shooting

+/- neurological deficits

Question 12

What are the steps to nociception/pain?

Answer 12

1. Transduction
2. Transmission
3. Modulation
4. Projection
5. Perception

Question 13

Where are transduction nociceptors present?

Answer 13

Skin, muscle, viscera

Question 14

Most transduction nociceptors are _____, some are _____.

Answer 14

polymodal, silent

Question 15

Transduction nociceptors transform mechanical, thermal, and chemical stimuli into _____.

Answer 15

action potentials

Question 16

What is the MOA of transduction?

Answer 16

Injurious stimulus activates nociceptor cell membrane –> ion channels open –> influx of Na, Ca –> action potential

Question 17

What is transmission?

Answer 17

Action potential is transmitted to cell body in DRG –> to dorsal horn of spinal cord

Question 18

What does transmission utilize?

Answer 18

Aδ nociceptor axon fibers that are myelinated and C nociceptor axon fibers that are unmyelinated

Question 19

What pain is transmitted by Aδ nociceptors?

Answer 19

Sharp, pricking “first pain”

Question 20

What pain is transmitted by C nociceptors?

Answer 20

Slow onset, “second pain”; burning, aching

Question 21

What is modulation?

Answer 21

Synapse with neurons in dorsal horn of spinal cord grey matter;

Impulses are amplified or suppressed;

Glutamate = excitatory, Substance P, Glycine, GABA = inhibitory

Question 22

What is projection?

Answer 22

Nociceptive information conveyed to brain by nerve tracts (spinothalamic and spinocervicothalamic)

Question 23

What is perception?

Answer 23

Integration, processing, and recognition of sensory info occurring in multiple areas of the brain

Question 24

What system is part of perception?

Answer 24

Reticular Activating System;

Integration of sensory experience;

Mediates motor, autonomic, endocrine response

Question 25

What is the periaqueductal gray area?

Answer 25

Part of perception that transfers info to thalamus/hypothalamus;

Relay for descending facilitative/inhibitory modulation

Question 26

What is the purpose of the thalamus?

Answer 26

Transfers information to cerebral cortex/limbic system

Question 27

What is peripheral sensitization?

Answer 27

Tissue damage releases chemical mediators –> recruit inflammatory cells –> “sensitizing soup” –> decreases excitation threshold, activates silent nociceptors –> increases nociceptive output to spinal cord

Question 28

What is central sensitization?

Answer 28

Frequent, severe, prolonged action of nociceptors –> increased excitatory ntms (glut, substance P) in dorsal horn –> activates NMDA, NK, AMPA receptors –> increased signal molecules, gene expression, neuroplasticity –> chronic pain

Question 29

What are benefits of multi-modal pain management?

Answer 29

Variety of drugs affects different receptors and levels of pain pathway, increased efficacy/decreased dose of each drug, decreased side effects

Question 30

Why should analgesia not be “as needed”?

Answer 30

Patient should not have to “prove” pain for analgesics

Question 31

Anesthetics are _____ in sleeping patients. Why?

Answer 31

withheld;

Sleeping/resting comfortably indicates adequate pain control

Question 32

What are the risks to a patient that is unarousable?

Answer 32

Gastro-esophageal regurgitation, aspiration pneumonia, hypoventilation, hypoxemia