Anesthetic Pre-medications - analgesics Flashcards
what is the purpose of analgesics as premedication
to minimize or abolish pain during and following surgery
opioids as pre-medications
- surgical manitulations produce a larghe number of pain signals and stimulate the RAS pathway in the medulla
- opioids inhibit pain signal so the patient doesnt wake up
- used because general anesthetics do not inhibit pain signal generation
why is administering opioids as a premedication safer than maintaining unconsiousness with higher doses of general anesthetic
- higher doses would inhibit all brain activity including respiration and CV function
Opium (the poppy) contains what compounds
- morphine
- codeine
- heroin
- hundreds of other chemicals
major and minor sites of opioid receptors
major = pain pathways
minor = most other organ systems
what are the possible uses of opioid drugs
Analgesia (manage pain) - most known for
sedation
cough suppression
treatment of diarrhea
true or false: opioids are used thoughout all steps of the general anesthesia protocol
true
opioid receptor families that mediate analgesia
Mu: mediates/prevents severe pain, most side effects
Delta
Kappa
opiod receptor that produces dysphoria
sigma
analgesia vs dysphoria
analgesia: pain reduction
dysphoria: terror, hallucinations, state of unease
types of opioid drugs
morphine
codeine
fentanyl
heroine
oxycodone
hydrocodone
hydromorphone
Opioids - mechanism of analgesic effects
- pre-synaptic stimulation: inhibits opening of Ca2+ channel - inhibit release of NT
- no Ca2+ = no neurotransmission
- post-synaptic stimulation: opens K+ channel - inhibit depolarization
- no K+ = hyperpolarozation
- overall = inhibit neurotransmission in pain pathways
stimulation of the Mu opioid receptor leads to…
- analgesia - intense
- euphoria
- miosis (pupil constriction)
- respiratory depression
stimulation of the delta opioid receptor leads to…
- analgesia
- respiratory depression
stimulation of the kappa opioid receptor leads to…
- analgesia - moderate
stimulation of the sigma opioid receptor leads to…
- dysphoria
- hallucinations
- respiratory and vasomotor stimulation
- *stimulated by some opioids and some non-opioids (e.g. ketamine)
properties of opioid drugs
- can stimulate opioid receptors maximally or weakly
- some are agonists at one receptor and antagonists at another
Fentanyl vs. Pentazocine
- Fentanyl = full mu agonist
- Pentazocine = full kappa agonist and partial mu agonist
- pentazocine is like a competetive antagonist to fentanyl
Pentazocine at the Mu receptor
- produces weak analgesic effect
- when present, prevents fentanyl from binding which produces a string analgesic effect
- when administered together weaker effect than fentanyl alone
pharmacokinetics of opioids
- weak bases
- Phase I and II metabolism with high first-pass effect
- cocaine is a “pro drug” that is metabolized to morphone - depends on persons CYP2D6 activity
Physiological effects in the CNS of full Mu agonists
- analgesia
- sedation
what opioids are known to be full Mu agonists
morphine
fentanyl
Physiological effects in the CV system of full Mu agonists
- little effects at normal doses
- morphone may cause histamine release - causes hypotension
Physiological effects in the respiratory system of full Mu agonists
- dose-dependent depression of respiratory system
- more intense effect when combined with a general anesthetic
- repiratory arrest (overdose = death)
- supress cough reflec
how can you reverse respiratory depress caused by opioid overdose
naloxone
Physiological effects in the GI system of full Mu agonists
- constipation: reduced propulsion in large bowel
- biliary colic: bile duct sphincter constriction
- nausea and vomitting
Physiological effect in the urinary system of full Mu agonists
- bladder ohincter tine increased, causing urgency to urinate but difficult
clinical use for full Mu agonists
treat moderate to severe pain
clinical use for opioid (Mu agonist) + a sedative
profound sedation prior to surgery
clinical use for a Kappa agonist
mild to moderate pain
clinicale use for codeine
anti-tussive (prevent seizure)
clinical use for loperamide
anti-diarrheal
Fentanyl - example of an opioid as pre-medication
- full Mu agonist
- used for pain releif
- most common opioid for pre and post operative analgesia (IV administered)
- constipation is common
- for chronic pain administered as a transdermal patch
Naloxone - example of an opioid antagonist
- binds and blocks Mu receptor (competitive inhibition)
- treatment for opioid overdose
- reverse profound sedation
- treat circulatory shock due to endogenous opioids
Carfentanyl - opioid used for sedation and imobilization
- used to immobilize large animals
- extremely fatal
- reversal agent (naloxone) required for recovery to occur
- Etorphine is a drug like carfentanyl but used for wildlife
opioids as anti-diarrheal medication
- e.g. Loperamide and Diphenoxylate
- reduce propulsive gut motility
- constrict anal sphincter
- less addictive than other opioids
