general anesthetics Flashcards
What are the uses of GA?
produce unconsciousness and lack of responsiveness to all painful stimuli.
provide conditions for interventions such as surgery to take place.
control physiology during these processes.
what constitutes an ideal GA?
unconsciousness, analgesia, muscle relaxation, amnesia, brief & pleasant, depth of anesthesia can be altered easily, minimal ADR, large margin of safety
what is an example of combinations which can achieve balanced analgesia
short acting barbiturates, neuromuscular blocking agents, opioids & nitrous oxide
general ADR of GA
depression of respiratory & cardiac performance
What are some examples of inhalation anesthesia?
volatile liquids: halothane, enflurane, desflurane, isoflurane, sevoflurane
gases: nitrous oxide
proposed MOA of inhaled anesthesia
- enhance neurotransmission @ inhibitory synapse through allosterically increasing GABA receptor sensitivity
- depressing neurotransmission @ excitatory synapse by blocking transmission action on NMDA receptor & preventing its activation
what is minimum alveolar concentration (MAC)?
- minimum concentration of drug in the alveolar air that will produce immobility in 50% of patients exposed to painful stimulus
what is the relation of potency to MAC?
low MAC = high anesthetic potency
how to increase absorption of volatile liquids?
- increasing: concentration of GA in inspired air, solubility of GA, blood flow through lungs
list some of the toxic metabolites of GA substances
nephrotoxic: inorganic fluorides of isoflurane, sevoflurane & enflurane
hepatotoxic: metabolite of halothane
what are some of the ADR of halothane?
- dose dependent respiratory depression
- bradycardia and arrhythmia leading to HoTN & dysrhythmia
- halothane-associated hepatitits
when is nitrous oxide used?
analgesia in dentistry and adjunct to supplement analgesic effects of primary anesthetics
what is a major concern of nitrous oxide?
post-operative nausea and vomiting
what is the advantage of combining IV and inhalation anesthetics?
- allows inhalation dose to be reduced
- produce effects that cannot be achieved with inhalation alone
MOA of sodium thiopental (thiopentone)
causes CNS depression by potentiating the action of GABA on GABA receptor gated chloride channel
what are some of the advantages of propofol
- ready made in injectable form, no need for reconstitution
- reduced post operative vomiting
ADR of propofol
- significant CVD effect during induction (HoTN)
- use with caution in elderly, patients with compromised cardiac function and hypovolemics
what is the action of ketamine which results in GA?
dissociative anesthesia
ADR of ketamine
unpleasant psychologic reactions may occur during recovery - may be reduced with pre-med of diazepam/midazolam
name one advantage of halothane
skeletal muscle relaxant (potentiates other relaxants as well), potent (low MAC)
compare isoflurane and halothane
isoflurane has less HoTN and arrhythmic effects; its association with reduced BP is due to decrease in systemic vascular resistance
what are some disadvantages of sevoflurane
- metabolite is nephrotoxic
- unstable when exposed to carbon dioxide absorbents in anesthetic machines, also degrading to a compound that is potentially nephrotoxic
list some examples of IV anesthetics
thiopentone, etomidate, propofol, ketamine, midazolam
name the IV anesthetic which has analgesic properties
ketamine
why are analgesics (eg. NSAIDs, Coxibs, opioids) usually used as adjuncts for GA
this is to reduce anesthetic requirements
what precaution do we need to take when administering barbiturates and muscle relaxants?
must allow barbiturates to clear from IV line before administering muscle relaxants to prevent precipitations
