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PMCOL 343 Final Exam Latest Update
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PMCOL 343 Final Exam LatestUpdate
A-beta fibers - Answer - respond to gentle mechanical stimuli
A-delta fibers - Answer - respond to noxious mechanical stimuli
- fast conduction
C fibers - Answer - respond to noxious heat or chemical stimuli
- slowly conducting
What is nociception? - Answer - neural encoding of noxious stimuli
What is pain? - Answer - unpleasant sensory and emotional experience associated with
actual or potential tissue damage
Analgesic Definition - Answer - blocks the sensation of pain without blocking other
modalities
What is the difference between local and general anaesthetics? - Answer - local
anaesthetics block nerve conduction and all sensation
- general anaesthetics cause unconsciousness, do not always produce analgesia
What is hyperalgesia? - Answer - enhanced response to painful stimulus
What is allodynia? - Answer - generation of a painful response by an innocuous stimuli
What is acute pain/first pain? - Answer - nociceptive stimuli leads to acute pain via
activation of nociceptive pathways
- A-delta fibers
- good pain
- if causes inflammation then it is carried by C-fibers (chronic pain)
- treated with/prevented by local anaesthetics
- less than 3 months
What is chronic pain? - Answer - mild, musculoskeletal pain
- treated with non-steroidal anti-inflammatory drugs (NSAIDS)
,- ongoing pain caused by release of
--> bradykinin
--> histamine acid metabolites
--> prostaglandins
- good pain
- if more than 3 months (outlasts normal healing process)
What is deep pain? - Answer - deep to body surface, poorly localized associated with
major trauma
- treated by major analgesics (opioids)
- good pain
What is neuropathic pain? - Answer - pain induced by injury to the somatosensory
system
- nerve injury or NS infections
- ex: phantom limb pain, shingles, diabetic neuropathy
- develops slowly and OUTLASTS healing of original injury
- not good pain??
What occurs if peripheral nerve injury pain is left untreated? - Answer - leads to
centralization of pain
--> pain becomes chronic and hard to treat
What are the structural requirements of local anaesthetics? - Answer - aromatic residue
- ester/amide linkage to alkylamino group
- weak bases
What are examples of local anaesthetics with ester linkages? How are they hydrolyzed?
- Answer - cocaine
- procaine
--> hydrolyzed by plasma cholinesterase
--> half life in blood of less than one minute
What are examples of local anaesthetics with amide linkages? How are they hydrolyzed?
- Answer - lidocaine
,--> hydrolyzed by P450 enzymes in liver (if you have liver disease then it can be more
toxic)
What is the mechanism of action of local anaesthetics? - Answer - block Na+ channels
(increased threshold for AP firing)
- must become neutral to enter membrane
- enters channel from inside
- use-dependent block (higher probability of blocking if more active)
How does pH influence local anaesthetic efficacy? - Answer - low pH (high H) pushes the
reaction towards the cationic form which can't enter the membrane to block Na+
channels
How does pKa of a local anaesthetic influence its own efficacy? What are some
examples? - Answer - smaller pKa has a faster rate of onset because more uncharged
molecules are "ready to go" and pass through membrane to block Na+ channels
- Mepivacaine has a faster rate of onset than Procaine because it has a smaller pKa
When administered local anaesthetics, vasoconstrictors like adrenaline are often
added. What is the purpose of this? - Answer - limit systemic absorption (especially if
applied to highly vascularized area)
- increase local anaesthetic concentration at site of action
- counteract tendency for local anaesthetics to cause vasodilation
What are some factors that affect nerve fiber susceptibility for local anaesthetics? -
Answer 1. fibre diameter
- C- A-delta fibers most susceptible
- lowest safety factor for conduction
2. firing frequency (fire more = more susceptible)
3. spike width (broad spikes = more chances for entry)
How can systemic absorption of local anaesthetics lead to toxicity? - Answer -
hypotension (direct effects on smc in b.vessel)
- cardiac depression (Na+ block in heart) esp with bupivacaine
What are the CNS effects of local anaesthetics? - Answer - sleepiness,
light-headedness, auditory disturbances, restlessness
- high conc = nystagmus (uncontrolled eye movements), shivering, convulsions
, - very high conc = CNS depression
What are the characteristics of general anaesthesia? - Answer - analgesia
- amnesia
- loss of consciousness
- inhibition of sensory and autonomic reflexes
- skeletal muscle relaxation
What are the characteristics of an ideal general anaesthetic agent? - Answer - smooth
and rapid induction
- rapid recovery
- wide margin of safety
- limited adverse effects
What are some of the adverse effects of general anaesthetics? - Answer - vomiting
- CV depression
- respiratory depression
- respiratory irritant effect of volatile (gas) anaesthetics
- toxicity
What types of anaesthetics are used for minor procedures? - Answer - oral sedatives +
regional local anaesthesia
What types of anaesthetics are used for conscious sedation? - Answer -
benzodiazepines + opioid analgesics
- can respond to verbal commands, patent airway
What are the preoperative medications? - Answer - sedatives that have anxiolytic and
amnesia properties
- muscle relaxants (d-tubocurarine)
- atropine (to limit mucous secretions)
What is used to induce anaesthesia? - Answer - via IV
- thiopental
- propofol
- etomidate or
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