Pathophysiology and Assessment of Pain Flashcards
what is pain?
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
describe the 5 steps in the pain pathway
- transduction: converts energy from one form to another
-many different receptors (nociceptors) involved - transmission: the electrical signal is transmitted via afferent neurons
-travels from periphery to spinal cord trough along nerve fibers - modulation: peripheral, spinal, supraspinal
- projection: electrical signal moves from the spinal cord to the supraspinal structures
- perception: the electrical signal is now processed in the cerebral cortex = pain!
describe nociceptors, involved in the transduction step of the pain pathway
-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
define peripheral sensitization
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
describe the types of nerve fibers involved in pain
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
where is the pain signal transmitted in the spinal cord? what is the substantia gelatinosa?
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
describe peripheral, spinal, and supraspinal modulation
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
define central sensitization
- repeated impulse activity of C fibers
- the A-delta and C fibers release a variety of neurotransmitters in the dorsal horn of the spinal cord
- this causes hyperalgesia, allodynia, and spontaneous pain
- inappropriate activation of the normally quiescent N-methyl-D aspartate (NMDA) receptors
- 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
describe recognition of pain in animals
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
identify common behavioral signs of pain in dogs and cats (and horses)
describe physiological indicators of pain
- heart rate
- respiratory rate
- blood pressure
- cortisol concentration
- good stoic subjects
all can be affected by other factors! (anxiety, drugs)
describe the glasgow composite measure pain scale-short form for dogs
- the maximum score for the 6 categories is 24, or 20 if mobility is impossible to assess
- recommended analgesic intervention levels is 6/24 or 5/20 (if mobility impossible to assess)
-can treat if lower if seem ouchy
describe the feline grimace scale
- 10 point scale
- 5 action unites (AU)
-ear position
-orbital tightening
-muzzle tension
-whiskers change
-head position - each AU:
0 = absent
1 = moderate or unsure if present
2 = obvious appearance - analgesia if score is greater than or equal to 4/10
describe the equine grimace scale
- 12 point scale
- 6 facial action units (FAU)
-ear position
-orbital tightening
-tension above eyes
-strained chewing muscles
-mouth strained and pronounced chin
-strained nostrils - each FAU
0 = absent
1 = moderately present
2= obvious appearance
treat around 4-5
