Name 3 potential theories of how inhalant anesthetics works (the receptors they may act on)
1) GABA
2) two-pore K
3) glycine
What is MAC?
the concentration of vapor in the lungs that is needed to prevent movement in 50% of subjects in response to surgical pain stimulus
Mac is an index of?
potency
Why is MAC hard to translate from research to clinical setting? (3)
1) use only inhalants (don’t account for pre-meds or injectables)
2) use only healthy animals
3) MAC varies by each patient
Give the MAC for:
1) ISO
2) SEVO
1) 1.3–1.6
2) 2.3–2.6
Two things that increase MAC?
hyperthermia
CNS stimulants
4 things that decrease MAC?
pregnancy
hypothermia
extremes of age (young and old)
Other anesthetic agents (pre-med or injectable)
Name 7 things that DO NOT change MAC
duration of anesthesia gender anticholinergics (atropine) pH PaCO2 PaO2 BP
Name the beneficial side effects of inhalants as dose increases (4)
1) unconsciousness
2) muscle relaxation
3) loss of nociceptive response
4) loss of sympathetic response
Two effects of anesthetics on:
1) CV system
2) respiratory system
CV system:
1) decreases CO (myocardial depression)
2) decreases systemic vascular resistance (vasodilation)
Respiratory:
1) decreases minute ventilation (shallow breaths)
2) decreased response to increased CO2
Are inhalants metabolized by the body?
NO
Neural process of encoding noxious stimuli
Nociception
Name the 5 stages of pain pathway
1) transduction (detection and conversion to AP)
2) transmission (AP to spinal cord)
3) modulation (amplified or suppressed)
4) projection (sent to brain)
5) perception
Which area of the brain is involved with perception of pain?
Cortex (thalamus encodes meaning to the pain)
Concerning A-delta fibers, describe:
1) myelination status
2) size of receptive field
3) type of pain transmitted
1) lightly myelinated
2) small receptive field
3) rapidly transmits sharp, localized, transient pain
Concerning C- fibers, describe:
1) myelination status
2) size of receptive field
3) type of pain transmitted
1) unmyelinated
2) large receptive field
3) slowly transmit generalized, burning, throbbing, and persistent pain
Which neurons are involved with:
1) acute, high-intensity stimuli (incisional)
2) tissue injury and inflammation
3) injury to peripheral sensory nerves (neuropathic)
1) A-delta (also C fibers)
2) C fibers
3) A-beta; also C fibers
Pain due to a stimulus which does not normally provoke pain
allodynia
Two substypes of neuropathic pain; define neuropathic pain
central
peripheral
pain caused by injury to or dysfunction of somatosensory nerves
What are 4 signs of neuropathic pain?
hyperalgesia
allodynia
chronicity
Failure of traditional analgesics
Glutamate receptors (AMPA & NMDA) in:
1) physiologic state
2) neuropathic state
1) AMPA–active
NMDA–inactive
2) AMPA–sensitized
NMDA–active
What 4 categories are used in the AAHA to assess pain?
1) loss of normal behavior
2) expression of abnormal behavior
3) reaction to touch
4) physiologic parameters
3 classes of drugs that can be used to treat peri-operative incisional pain?
Opioids
Alpha-2 agonists
Local/regional anesthetics
What type of pain can lidocaine be used for?
peripheral neuropathic pain (blocks the bad Na channels)
Name 2 drugs used for central neuropathic pain and their MOAs
1) Ketamine–>NMDA receptor antagonist
2) Gabapentin (Ca channel blocker)
Drugs that are naturally derived from opium
Opiate
Which is a broader term:
Opioid or opiate?
opioid (includes naturals AND synthetics)
Name the two clinically relevant opioid receptors and where they exist in highest concentration
1) Mu (MOP)–highest in dorsal horn (lower in brain)
2) Kappa (KOP)–highest in brain (sedation); lower in dorsal horn
Which step in the pain transmission pathway do opioids effect and where?
modulation @ dorsal horn & midbrain (descending inhibitory tracts)
Differentiate:
1) potency
2) efficacy
1) AMOUNT of substance needed to achieve desired affect
2) ABILITY of substance to achieve a desired affect
Three clinical effects of mu agonist?
analgesia
mild sedation
excitement (depending on spp. and dose)
Which mu agonist is associated with histamine release?
Morphine
Rank the mu agonists (5) by increasing potency
Morphine=methadone
Hydromorphone
Fentanyl
Remifentanil
Fentanyl & Remi are equal in potency
this is also the order of longest to shortest duration of action AND longest to shortest time to onset
Why does remifentanil have such a short duration of action?
it’s brokendown by tissue esterases
Describe butorphanol’s interactions at the mu and kappa receptors & it’s clinical effects
Mu–antagonist (inhibits full mu agonists)
Kappa–agonist
causes sedation & mild analgesia
Naloxone is a ?
opioid ANTAGONIST
3 causes of peripheral neuropathic pain
1) sensitization of peripheral nociceptors
2) direct nerve injury
3) alteration in Na channels (lower threshold or spontaneous activation)
Opioids stimulate receptors in which 2 areas to cause sedative effects
Midbrain
forebrain
13 side effects of opioids
1) decreased ventilation
2) apnea after bolus
3) vomiting
4) reset body temp
5) panting (dogs)
6) cough suppression
7) immunosuppression
8) decreased HR
9) histamine release
10) delayed gastric emptying
11) alterations in peristalsis
12) defecation
13) miosis/mydriasis
Buprenorphine is a _____
partial agonist (ceiling effect & reduces effects of full Mu agonists)
