Pathophysiology and Assessment of Pain

Question 1

what is pain?

Answer 1

adaptive: contributes to survival by protecting the organism from injury or promoting healing when injury has occurred

maladaptive: an expression of the pathologic operation of the nervous system; pain as a disease

when acute = physiological pain
-protective function
-normal pain
-noxious stimulus activates peripheral nociceptors
-duration: 3-5 days (easy to prevent/treat)

when chronic: pathologic or pathophysiologic or clinical pain
-following the physiological pain or the injury resulting in a stimulus
-duration: >3 months (challenging to manage

Question 2

describe the 5 steps in the pain pathway

Answer 2

1. transduction: converts energy from one form to another
   -many different receptors (nociceptors) involved
2. transmission: the electrical signal is transmitted via afferent neurons
   -travels from periphery to spinal cord trough along nerve fibers
3. modulation: peripheral, spinal, supraspinal
4. projection: electrical signal moves from the spinal cord to the supraspinal structures
5. perception: the electrical signal is now processed in the cerebral cortex = pain!

Question 3

describe nociceptors, involved in the transduction step of the pain pathway

Answer 3

-mechanoreceptors
-thermoreceptors: heat via transient receptor potential vanilloid-1 (TRPV1) or capsacin receptors
-chemoreceptors

-the nociceptors are the terminal ends of the nerve fibers:
-A-delta fibers
-C fibers
-A-beta fibers: in pathologic pain (pressure sensors)

-transduce different stimuli into electrical impulse

Question 4

define peripheral sensitization

Answer 4

tissue damage causes release of inflammatory mediators (inflammatory soup)

so many of these inflammatory mediators, start vicious cycle bc they bind to receptors and recruit inflammatory cells

recruited cells are macrophages, leukocytes, neutrophils, platelets, mast cells; the recruited cells then release even more inflammatory mediators

inflammatory mediators will also decrease the nociceptor threshold
-responsible for hyperalgesia and allodynia

Question 5

describe the types of nerve fibers involved in pain

Answer 5

A-delta: (bigger and faster)
-1-5um diameter
-myelinated
-conduct impulses rapidly at a rate of 5-30m/sec
-conduction rate is correlated with the initial sensation of pain: sharp, localized, and transient

C fibers: (slower and thinner)
-small diameter (0.25-1.5um)
-unmyelinated with conduction velocity of only 0.5-2m.sec
-larger receptive fields compared to A-delta fibers
-poorly localized, gnawing sensation of second pain, which persists after termination of the noxious stimulus

Question 6

where is the pain signal transmitted in the spinal cord? what is the substantia gelatinosa?

Answer 6

pain is transmitted to the dorsal border of the spinal cord! (lamina 2-6)

substantia gelatinosa: an important area for pain in the spinal cord; lamina 2

Question 7

describe peripheral, spinal, and supraspinal modulation

Answer 7

peripheral: C fibers and different substances
-silent nociceptors, peripheral opioid receptors, nociceptor sensitizers (prostaglandin, leukotrienes, bradykinin). nociceptor activators

spinal modulation: different receptors and mediatory in the spinal cord
-decrease response to pain: opioid, serotoniergic, noradrenergic
-increase response to pain/windup/central modulation: glutamate, prostaglandins, substance P

supraspinal: descending pathways controlled by 3 main sources
-periaqueductal gray matter of midbrain
-medulla and pons of brainstem
-thalamocortical structures

Question 8

define central sensitization

Answer 8

1. repeated impulse activity of C fibers
2. the A-delta and C fibers release a variety of neurotransmitters in the dorsal horn of the spinal cord
3. this causes hyperalgesia, allodynia, and spontaneous pain
4. inappropriate activation of the normally quiescent N-methyl-D aspartate (NMDA) receptors
5. summary:
   -constant release of glutamate and activation of NMDA receptors causes increase of excitatory postsynaptic currents
   -downregulation of GABAergic and glycine receptor activity causes disinhibition of protein kinase interneurons
   -activation of microglia causes secretion of IL1, IL6, and TNF-alpha

Question 9

describe recognition of pain in animals

Answer 9

measures of general body function or productivity:
-food/water intake
-weight gain/loss
-reflect what is happening to the animal over time

physiologic measures

behavioral measures:
-pain specific: limping, head shaking, vocalization
-a decline in frequency of magnitude: decreased locomotion

assess/palpate the surgical area to determine if painful!! use some firm pressure that should not cause pain in normal tissue

Question 10

identify common behavioral signs of pain in dogs and cats (and horses)

Question 11

describe physiological indicators of pain

Answer 11

1. heart rate
2. respiratory rate
3. blood pressure
4. cortisol concentration
5. good stoic subjects

all can be affected by other factors! (anxiety, drugs)

Question 12

describe the glasgow composite measure pain scale-short form for dogs

Answer 12

1. the maximum score for the 6 categories is 24, or 20 if mobility is impossible to assess
2. recommended analgesic intervention levels is 6/24 or 5/20 (if mobility impossible to assess)
   -can treat if lower if seem ouchy

Question 13

describe the feline grimace scale

Answer 13

1. 10 point scale
2. 5 action unites (AU)
   -ear position
   -orbital tightening
   -muzzle tension
   -whiskers change
   -head position
3. each AU:
   0 = absent
   1 = moderate or unsure if present
   2 = obvious appearance
4. analgesia if score is greater than or equal to 4/10

Question 14

describe the equine grimace scale

Answer 14

1. 12 point scale
2. 6 facial action units (FAU)
   -ear position
   -orbital tightening
   -tension above eyes
   -strained chewing muscles
   -mouth strained and pronounced chin
   -strained nostrils
3. each FAU
   0 = absent
   1 = moderately present
   2= obvious appearance

treat around 4-5