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Anesthesia - Pain

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sihirlifil's version from 2017-04-06 13:15

PHYSIOLOGY OF PAIN

Question Answer
Challenges in treating pain in animals?Difficulty recognizing
Lack of knowledge in appropriate use of analgesics
Fear of drug side effects
"Myths"
T/F: Nociception and pain are the same thingFALSE! Pain has a perception component in addition to sensory
Components of pain: Affective (emotional) = Neuroendocrine response
Behavioral response
Physiological response
Suffering
Fear
Anxiety
Components of pain: Sensory (discriminative) depend on... Source
Intensity
Quality
Duration
Components of pain: Cognitive (evaluative) = Interpretation
Rationalization
(Dont apply much to animals)
Pain classification: physiologic (nociceptive) vs. pathologic (clinical)?Physiologic: protective, essential for body integrity
Pahologic: inflammatory and neuropathic pain
Pain classification: Physiologic / Nociceptive characteristics?Physological protective system
Essential for body integrity
"Too hot, cold, sharp..."
Pain classification: Pathologic / Clinical characteristics?Inflammatory pain: assist in healing by discouraging physical contact or movement, adaptive but still needs to be reduced
Neuropathic: not protective, MALADAPTIVE, results from abnormal functioning of the nervous system. MUST BE TREATED!
What is a nociceptor?Specialized free nerve ending in tissue (peripheral or central) that transforms stimuli into action potentials
Where is the cell body of a nociceptor?Dorsal root ganglion
Nociceptors react to which noxious stimuli?Thermal
Mechanical
Chemical
Which nociceptors must be activated for pain sensation to occur?Aδ and C fibers
Aδ fibers: threshold? what type of receptor?Low/high mechano- and thermal
Aδ fibers: myelination?Myelinated- conduct impulses FAST! (5-25m/s)
Aδ fibers: duration of pain?Pain stops when stimulus ends
Aδ fibers: general characteristics?Fast, sharp, well-localized, "first pain"
C fibers: threshold? what type of receptor?High (activated by intense stimuli) polymodal (reacts to different stimuli)
C fibers: myelination?Unmyelinated- conduct impulses slowly (0.5 m/s)
C fibers: duration of pain?Pain can last beyond ending of stimulus
C fibers: general characteristics?Second or "slow" pain sensation
Which nociceptors are silent (sleeping)?Aδ and C
What are silent nociceptors activated by?Inflammation (not tissue damage!!!)
What kind of stimulation are silent nociceptors particularly sensitive to?Mechanical
T/F: Sleeping nociceptors are activated by inflammation and tissue damageFALSE! NOT activated by tissue damaging events!
What happens during transduction?Aδ & C fiber free nerve endings transform noxious stimulus to an action potential
What happens during transmission?Action potential is transmitted via afferent nerve axon to dorsal horn of SC (from periphery to CNS)
Happens quickly (Aδ) or slowly (C)
What happens during modulation?Amplification of ascending signal OR suppression of signal from descending inhibitory control
Where does modulation occur?Dorsal horn neurons of substantia gelatinosa of SC:
Laminae I & V (Aδ)
Lamina II (C)
Where does decussation occur?During modulation, decussation of 2nd order neurons
Projection neurons: in spinothalamic tract
What is the gate control theory?Non-painful stimulus 'closes the gate'
Aβ fibers (fast) can activate inhibitory interneurons in the dorsal horn --> decrease likelihood of projection neuron to fire -->noxious stimulus not transported to brain
Which neurons activate dorsal horn inhibitory neurons in the gate control theory?Aβ (fast, transmit touch sensation, NOT PAIN)
What happens during perception?Processing, integration and recognition of sensory input
Where does perception of pain occur?Multiple areas of the brain
Which areas of the brain are involved in perception of pain?Reticular activating system (brainstem): awareness of pain
Thalamus
Somatosensory complex: conciousness
Limbic system: emotions, behavior
What is allodynia?Pain response to non-painful stimuli
What is hyperalgesia?Over-reaction to pain stimuli (amplification, increased perception)
What is analgesia?Reduced pain response
What happens at the periphery when tissue damage / inflammation occurs?Chemical mediators released from damaged cells --> PERIPHERAL SENSITIZATION
What is peripheral sensitization?Result of changes in nociceptor terminal environment ("sensitizing soup")
What are the changes in nociceptor terminal environment (sensitizing soup)? Increased excitability of afferent fiber
Vasodilation
Recruitment of inflammatory cells
What does peripheral sensitization do to the nerve threshold? Firing frequency?Lowers threshold, increases frequency
Which nerves are peripheral sensitization related to?Aδ and C
What stage does peripheral sensitization happen?Transduction
Peripheral sensitization causes (3)Lowers threshold for activation of Aδ and C fibers
Activation of silent nociceptors
Amplifying of signal
Peripheral sensitization ultimately leads to:PRIMARY HYPERALGESIA at injury site & surrounding tissue
Central sensitization occurs due toChronic or excessive activation of primary afferent fibers in the SC
What stage does central sensitization happen?Modulation
What is the result of central sensitization?Increased excitability of dorsal horn neurons (decreases threshold)
What are the consequences of central sensitization?Higher synaptic response:
Higher response to low threshold stimuli
Larger receptive field
WIND-UP! (temporal summation, same input --> higher output)
More of the laminae in the dorsal horn become activated
Does wind-up happen in peripheral sensitization?NO!
Which drug is awesome for treating wind-up?Ketamine
Which nerve fibers are also recruited during central sensitization?Aβ (myelinated, low-threshold peripheral mechanoreceptors, transmit TOUCH sensation)
Central sensitization ultimately leads to:SECONDARY HYPERALGESIA in normal tissue around injury
ALLODYNIA
What is plasticity?Central nervous system moves to a new excitable state (change in processing)
Altered neuroprocessing, lack of correlation between injury and pain
Where does all perception of pain occur?BRAIN
2 examples of plasticityChronic pain
Neuropathic pain
What is chronic pain?Pain that lasts beyond an expected normal physiological response to the noxious insult (beyond period of tissue healing, persists despite low levels of pathology that are insufficient to explain the presence / extent of pain)
What is neuropathic pain?Pain due to a primary lesion or malfunction of the PNS or CNS
Example of neuropathic pain?Phantom limb (many nerves cut, strong peripheral and central sensitizaion reactions) (need local block)
Reasons for neuropathic pain:Peripheral & central sensitization
Altered expression, distribution & funtion of ion channels
Increased central excitation
Reduced spinal inhibition
Deregulated supraspinal control
Immune system involvement
memorize

PAIN ASSESSMENT

Question Answer
Pain can only be treated if it is?Recognized
How will behavior help you recognize pain?Normal behavior present or absent?
Abnormal behavior present?
Reasons it's difficult to recognize painSpecies-specific
Inter-individual variance
Disease-specific
Trying to quantify a complex physiologic and emotional process
What is special about animals of prey?Tend to be stoic- survival depends on behaving and appearing unremarkable, so show no outward signs
What are some physiologic parameters you can use to assess pain objectively? Limitations?HR/RR/ABP
Pupil size
Cortisol levels
β-endorphins
(These are unreliable and unspecific- could be related to many things)
Objective pain assessment: Research/Clinical utilization- what is a force plate used for?Lameness evaluation (measures how much wight animal puts on limbs, mainly used in research setting)
Objective pain assessment: Nociceptive assays- types? (4)Electrical
Thermal
Mechanical
Chemical
What is an electrical nociceptive threshold assay testing?Nociceptive withdrawal reflex (put current through muscle, at certain level the animal will try to withdraw limb)
What is a chemical nociceptive threshold assay testing?Length of time (latency) it takes the animal to lift/bite at limb as a reaction to a noxious chemical (e.g. Formaldehyde, complete Freund's Adjuvant, capsaicin)
What is a mechanical nociceptive threshold assay testing?Force needed to see a reaction e.g. Von Frey Filaments (basic probe), Balloon models (use in hollow organs-inflate), tourniquets, force measuring devices
What is a thermal nociceptive threshold assay testing?How high a temperature before animal reacts- hot plate, tail flick (infrared heats), Hargreaves test (put the jacket thingy on a horse and wait to see skin twitch)
What would the characteristics of a perfect pain score be? (8)Easy to apply
Objective
Covers frequency/intensity/quality/duration (sensory pain components)
Reliable: intra-observer repeatability (same person should have same result before and after) & inter-observer reproducibility (2 people should get the same result)
Sensitive
Species-specific
Language-specific
(Breed specific)
What are the unidimensional subjective pain assessment scales? (4)Simple descriptive scale (SDS)
Numerical rating scale (NRS)
Visual analogue scale (VAS)
Dynamic interactive visual analogue scale (DIVAS)
What are the multidimensional subjective pain assessment scales? (2)Composite measure pain scales (CMPS)
Facial action coding system (FACS)
Characteristics of the Simple descriptive scale (SDS)Simple to use
4-5 descriptors
Not sensitive in detecting small changes in pain intensity
Inter-observer variability
What does the SDS scale look like?No pain--Mild pain--Moderate pain--Severe pain--Very severe pain--Worst imaginable pain
Characteristics of the Numeric rating scale (NRS)Numbers rather than descriptors
Inter-observer variability
What does the NRS scale look like?0 (No pain)--1--2--3--4--5--6--7--8--9--10 (Worst imaginable pain)
Characteristics of the Visual analogue scale (VAS)Simple
Inter-observer variability
What does the VAS scale look like?0mm (No pain) ------------------------------------100mm (Worst possible pain for this procedure)
Characteristics of the Dynamic interactive visual analogue scale (DIVAS)Same concept as VAS
Observe animal from a distance
Approaching
Interacting
Palpation of wound and surrounding area
What are the benefits of multidimensional pain scales?Incorporate intensity and affective component of pain
Refine observations
There are several categories, with a weighted score within each
More objective, less observer variability (ideally)
What must be known to construct a multidimensional pain scale?Normal behavior (also must be validated)
Which pain dimension does behavioral response fall under?Affective (emotional)
Characteristics of the Composite measure pain scales (CMPS)Observing the patient without interacting, then while interacting
Observing patient's response to palpation of surgical site
What is the purpose of a numerical score with a CMSP?Cut-off for analgesic intervention (decide at what point it would be appropriate to give pain relief)
What are the validated CMPS she mentions?Glasgow Composite Measure Pain Scale (dog)
UNESP-Botucatu multidimensional composite pain scale (cat)
PASPAS Colic Pain Score (horse)
EAAPS Scale 1 + 2 (horse)
MCOPS (horse)
The Glasgow pain scale is validated for _____ ____ in ____ (species)?Acute pain, Dogs
Characteristics of the Glasgow pain scaleBased on specific behavioral signs
Identified 279 expressions/words associated with pain in the dog
47 descriptors in 7 behavioral categories
Low interpretation bias by observer
The 7 behavioral categories of the Glasgow pain scalePosture
Comfort
Vocalization
Attention to the wound
Demeanor, response to humans
Mobility
Response to touch
The UNESP-Botucatue scale is the ONLY valudated scale for _____ ____ in ____ (species)Acute pain, Cats
Why are there multiple validated pain scales for horses?Colic pain is different from orthopedic/somatic pain
Most recent advance in recognition of subtle behavioral changes associated with pain:Investigation of facial expressions
Facial action coding systems (FACS) are most focused on?Animal's face when assessing pain (changes in facial appearance resulting from muscle actions)
Examples of FACS?Mouse/Rat/Rabbit grimace scale, Facial Assessment of Pain EQQUUSbFAP (lol), EquiFACS (The Equine Facial Action Coding System), Horse grimace scale, Equine Pain Face, MaqFACS....
Some features of equine facial expressions of pain:Asymmetrical/low ears, or held stiffly backwards
Angled eye, tension above eye
Withdrawn, tense stare
Square-like nostrils
Muzzle tension (strained mouth and pronounced chin)
Tension of mimic muscles/chewing muscles
Challenges with using facial expressions fo evaulate pain?Not static
Not all identified features present at all time (false positive)
Requires experience with species
Challenges assessing chronic pain?Requires owner compliance & education (they need to accurately assess)
There are periods of pain free & intense pain (more variability)
PLATTER = ?PLan (patient-speficic pain assessment, tx plan)
Anticipate (preventive/ASAP analgesia)
TreaT (according to type, duration, intensity)
Evaluate (Pain assessment!!! preferably objective)
Return (modify/discontinue tx)
memorize

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