Lecture 7 Pathophysiology and Assessment Flashcards
What is Pain?
In animals, an aversive sensation & feeling associated with actual or potential tissue damage
What are the Negative Physiologic Sequela of pain & Stress
- ↓ Pulmonary function
- atelectasis -> pneumonia
- ↑ muscle tension,↓ lung compliance
- Cardiovascular
- ↑ HR, BP⇒ ↑ myocardial work
- ↓ Immune function
- ↑ WBC
- ↓ lymphocytes & killer T cells
- Endocrine -↑ stress hormones
- ↑ catecholamines, aldosterone, AT II, ACH, cortisol, glucagon
- Coagulation
- ↑ platelet adhesion,↓ fibrinolysis
- Activation of coagulation cascade
- GI & GU
- ↑ sphincter tone, ↓ muscle tone
- Immobility, inappetence, insomnia
- What is the Pre-emptive Pain Score
- Is it tailored to individual?
- Does it assess response to therapy?
- Assign degree of pain based on underlying pathology, procedure performed & amount of tissue trauma involved
- No Pain
- Mild pain
- Moderate pain
- Severe pain
- Not tailored to individual
- not useful in assessing response to therapy
- What are the 2 Types of Pain
- How is each pain described (how it feels)?
- Somatic – Originates from damage to bones, joints, muscle or skin
- described as localized, constant, sharp
- Visceral – Arises from stretching, distention or inflammation of viscera
- described as deep, aching, without good localization
- Neuropathic – Originates from injury or involvement of the PNS or CNS
- described as burning or shooting
- +/- neurological deficits
What is the order of pain transmission
- Transduction
- Transmission
- Modulation
- Projection
- Perception
- Where in the body does transduction occur?
- How does transduction happen
- Occurs at tissue level
- Specialized nerve endings (nociceptors) transform mechanical, thermal, chemical stimuli into action potentials
- Release of local inflammatory mediators
What are the 2 types of nociceptors in transduction
- Aδ nociceptors
- C-fiber nociceptors
Which drugs work at the transduction level?
- Non-steroidal anti-inflammatory drugs (NSAIDS)
- Local Anesthetics
- Opioids (peripheral opioid receptors)
- Aδ nociceptors are low, high or both thresholds?
- are they polymodal or use a single stimuli?
- What types of stimuli?
- Low or high threshold
- high threshold respond only to tissue threatening/damaging stimuli
- Polymodal or single stimuli
- mechanical, chemical, thermal
- Aδ nociceptors discharge at rates greater than or less than c-fibers?
- How does the pain feel with these receptors?
- Discharge at rates > than C-fibers
- more discriminative information to CNS
- Sharp, pricking pain of ‘first pain’
- C-fiber nociceptors are low, high or both thresholds?
- are they polymodal or use a single stimuli?
- Is there a large number in skin, muscle, joints or viscera
- All high-threshold
- polymodal
- Large # in skin, muscle, joints, few in viscera
- C-fiber nociceptors are fast or slow onset?
- What do they signal?
- Slow onset, ‘second’ pain; burning, aching
- Signals tissue damage/inflammation => sensitizes/activates ‘silent/sleeping’ Aδ and C fibers
What happens during the transmission phase
Action potential is transmitted via sensory nerves to dorsal root ganglion => via dorsal root nerves to grey matter of spinal cord
Which drugs work at Transmission level
- Local Anesthetics
- α-2 agonists
What are the types of nerves that do transmission
- Aβ
- non-noxious sensory information
- myelinated
- Aδ
- non-noxious & noxious info
- myelinated
- C
- Unmyelinated
- Noxious info only
What happens in the modulation phase?
- Synapse with neurons in dorsal horn of spinal cord grey matter
- Impulses are amplified or suppressed
- Neurotransmitters act on excitatory/inhibitory receptors (AMPA, NMDA/GABA, glycine)
What drugs work at the Modulation level
- NSAIDS
- Local Anesthetics
- Opioids
- α-2 agonists
- NMDA antagonists
- NK-1 antagonists
- Tricyclic anti-depressants
- Anticonvulsants
- What happens in the projection phase
- What tracts does it go through? (1 main one)
- Nociceptive information conveyed to brain by nerve tracts
- Tracts:
- Spinothalamic tract**
- Spinoreticular tract
- Spinomesencephalic Tract
- Spinohypothalmic tract
What happens in the perception phase
Integration, processing, recognition of sensory information occurs in multiple areas of brain
What drugs work at the perception phase
- Opioids
- α-2 agonists
- NMDA antagonists
- NK-1 antagonists
- Tricyclic anti-depressants
- Anticonvulsants
- Benzodiazepines
- Phenothiazines
- Anesthetics
- Inhalants
- Injectable
What are the 3 parts of the brain that perception happens in
- Reticular Activating System
- Periaqueductal gray area
- Thalamus
Explain what happens in the Reticular activating system for perception
- integration of sensory experience
- mediates motor, autonomic, endocrine response
Explain what happens in the periaqueductal gray area in perception
- transfers info to thalamus/hypothalamus
- relay for descending facilitative/inhibitory modulation
- Descending facilitation important in chronic pain syndromes
Explain what happens in the thalamus in perception
transfers information to cerebral cortex & limbic system
- Once the thalamus sends information to the cerebral cortex and limbic system, what is the area that percieves fear and axiety?
- Emotion?
- Memory?
- Amygdala => fear, anxiety
- Cingulate gyrus => emotion
- Hippocampus => memory
What are the Basic Tenets of pain management
- Pre-emptive pain management
- => Analgesics must be given BEFORE painful stimulus to help prevent central nervous system ‘wind-up’
- Classification of severity & types of pain
- Followed by intra/post op
- Customized, multi-modal approach
- Adjunct analgesic drugs & modalities
- ‘one size fits all approach’ may not work for all patients
- Patient evaluation, reassess analgesic plan => intra/post-op
All to decrease peripheral & central sensitization/ ‘wind-up’
What is Peripheral Sensitization
- Tissue damage releases chemical mediators =>
- recruit inflammatory cells =>
- ‘Sensitizing Soup’ =>
- ↓ excitation threshold, activates silent nociceptors =>
- ↑nociceptive input to spinal cord
What are 2 ways to prevent peripheral sensitization (drug and a technique)
- NSAIDS
- ***Good Surgical Technique***
What is Central Sensitization
- Frequent, severe, prolonged activation of nociceptors =>
- leads to ↑ excitatory neurotransmittors (glutamate, Substance P) in dorsal horn of spinal cord =>
- activates NMDA, NK, AMPA receptors =>
- ↑signal molecules, gene expression, neuroplasticity =>
- chronic pain
What is Multi-modal Pain Management
Use variety of drugs & techniques => affects different receptors & levels of pain pathway
Why do you do a Multi-modal Pain Management
- ↑ efficacy & ↓ dose of each drug
- ↓ doses, ↓ side effects =>
- eg. respiratory depression, hypotension
- Can you use physiologic data to do pain assessment?
- Vocalization?
- Physiologic data can be misleading
- Heart rate could be low but still painful
- respiratory rate, pupil size, cortisol
- Not really because Vocalization can be caused by:
- Pain, anxiety, dysphoria, nursing care needs
What are the 2 mentioned Behavior based Pain Scales in class (there are more out there)
- Glasgow Composite
- Colorado State APS
are Behavior based Pain Scales subjective or objective
All have a subjective component
What are Pain Behaviors in Dogs that can be used to assess pain
- Body posture/activity
- Reluctance to move/lie down
- Changing positions/restlessness
- Vocalization
- Facial expression/appearance
- Appetite/bowel,urinary habits
What are Pain Behaviors in cats that can be used to assess pain
- Hunched position with head low, ‘humpy cat’
- Facial expression
- Squinted eyes, ‘squinty cat’
- Sitting quietly, seeking no attention
- Trying to hide, back of cage
- Resentment at being handled, palpation
- Presence/absence of normal behaviors (grooming)
- Interactive behavior
What does the Glasgow Composite Measure Pain Scale measure
- Behaviors based on vet questionnaire
- Two parts: observation, interaction
- ↓ observer bias, easy to use
- Presence/absence of specific behaviors
- Reassess analgesic plan
- 6/24 or 5/20
- A section is about lameness so if the animal is laying down you dont do that part and asess out of 20
- 6/24 or 5/20
What are limitations to Glasgow Composite Measure Pain Scale
- Only dogs
- Does not consider prior demeanor
- No assessment of level of sedation
What does the CSU Acute Pain Scale measure
- observation/interaction
- Psychological/behavioral signs of pain
- Has a section for Non-assessment in sleeping patients
- Alert to ‘unarousable’
- Evaluates body tension
- ‘reassess analgesic plan’ > 1.5 – 1.75
The UNESP-Botecatu pain score assesses what things?
- Miscellaneous behaviors
- Reaction to palpation of surgical site
- Reaction to palpation of abdomen
- Vocalization
- Posture
- Comfort
- Activity
- Attitude
- Arterial Blood Pressure
- Appetite
What are Pain Behaviors in Horses that have abdominal pain
- Dullness, depression, lowered head carriage
- Rigid stance, reluctance to move
- Fixed stare, flared nostrils
- Rolling, looking/kicking at abdomen
What are Pain Behaviors in Horses that have lameness pain
Weight shifting, abnormal weight distribution
Pointing/hanging of limb
What is the equine pain face
- Lowered ears (the distance between the ears increases at the base)
- Contraction of the muscle above the eye (m. levator anguli oculi medialis)
- Tense stare
- Nostril dilated in the medio-lateral direction
- Edged shape of the muzzle with lips pressed together and flattened chin
- Tension of the facial muscles
What are Pain Behaviors in food animals
- Postural stance – ‘statue stance’ after castration, abnormal tail carriage
- Ear flicking, head shaking/scratching – dehorning pain
- Foot stomping, easing of quarters, scrotal licking – castration pain
- Distress calls
- Escape behaviors
- Pressure Alogometry
- Thermal sensitivity
- Should PRN (as needed) Analgesia be used?
- Why or why not?
- No
- Dose/interval based on:
- underlying disease, surgical procedure
- level of pain expected
- Dose according to pharmacokinetic/dynamic recommendations for specific drug/species
- Patient pain evaluation
Patients should not have to ‘prove’ pain for analgesics
- Should Analgesics be withheld in sleeping patients?
- Why or why not?
- Don’t withold!
- Because:
- Adequate pain control => resting comfortably, sleeping
- Dose according to pharmacokinetic/dynamic recommendations for drug/species
- Allow to rest after response to treatment established
- Pain evaluation
- ‘unarousable’
- Should patients be woken up to evaluate pain?
- Why or why not?
- Not if they are just sleeping
- Why:
- Many analgesic drugs also cause sedation
- Sleep/rest is important for post-op patients
- Warm, dry, clean, quiet environment, day/night light cycle
- Patients must be arousable
- Evaluate level of sedation & adequacy of analgesia after expected onset of action of analgesic drug
If a patient is unarousable what should be done and why?
- Assess for level of consciousness
- Best done after expected onset of action of analgesic drug(s)
- Risk of hypoventilation & hypoxemia, gastro-esophogeal regurgitation & aspiration pneumonia
