General Anesthetics Flashcards
Can you give sodium channel blockers as general anesthetic
NO! Heart has sodium channels -> will block them everywhere
How to suppress CNS
activate GABA
NMDA receptor antagonists
glycine inhibition
What drugs get to brain faster: lipophilic or lipophobic
lipophilic
What does GA cause
muscle relaxation, loss of autonomic reflexes, analgesia, anxiolysis
reversible loss of sensation
what does suppression of amygdala do
removes fear, anxiety, emotion, memory
What happens if you suppress activity of medulla
medulla is vasomotor center -> will suppress cardiac and respiratory center -> only want to do this to a certain point
Two types of GA
inhaled
IV
what is balanced anesthesia
both inhaled and IV together
properties of inhaled anesthetics
distribute well to all body parts
become concentrated in fatty tissue
CNS primary site of action
At low concentrations, inhaled anesthetics act as
GABAa positive allosteric modulators (increase activity of GABA channels)
At high concentrations, inhaled anesthetics act as
GABAa receptor agonists
GABA agonist vs modulator
agonist increases duration of opening
modulator increases frequency of opening
Four stages of anesthesia
stage 1: Analgesia - amnesia, euphora
stage 2: excitement - excitement, delirium, combative behavior
Stage 3: surgical anesthesia - unconsciousness, regular respiration, decreasing eye movement
Stage 4: medullary depression - respiratory arrest, cardiac depression and arrest, no eye movement
primary site of action for GA
CNS
What stage of anesthesia is the goal
stage 3, avoid stage 4 (in both inhaled and IV)
Minimum alveolar concentration (MAC)
alveolar partial pressure (minimum concentration) of anesthetic vapor that is able to prevent motor responses to a surgical incision in 50% of patients (analogous to ED50)
What happens when you increase MAC
increase partial pressure
MAC is inversely/proportionately related to potency
inversely
LOW MAC = high potency and vice versa
potency = 1/MAC
Wide or narrow TI for inhaled (isoflurane example)
narrow TI
TI = lethal pressure 50/MAC
What dictates inhaled anesthetic potency
lipophilicity
Greater lipophilicity equals
greater potency and greater rate of absorption
What dictates rate of anesthetic induction
rate of gas absorbed into lungs
Lower rate of absorption equals
faster anesthesia induction
lower rate of absorption allows anesthetic to build up in alveoli, leading to
faster onset of anesthesia
If gas remains in lungs then you get faster/slower rate of absorption
faster
highly lipophilic inhaled agents do what
penetrate alveoli -> go to capillaries -> distribute to body -> not as much goes to the brain -> slower anesthetic induction
low lipophilic inhaled agents do what
high concentration builds up in alveoli -> goes to blood -> goes to brain -> faster anesthetic induction
Inhaled anesthetic agents
Nitrous oxide desflurane sevoflurane enflurane isoflurane halothane methoxyflurane
Nitrous oxide
MAC = 1.01
rapid onset and recovery
desflurane
MAC = 0.06
poor induction agent, rapid recovery
sevoflurane
MAC = 0.02
rapid onset and recovery
enflurane
MAC = 0.0168
medium rate of onset and recovery
Isoflurane
MAC = 0.0114
medium rate of onset and recovery
Halothane
MAC = 0.0077
Medium rate of onset and recovery
Methoxyflurane
MAC = 0.0016
very slow onset and recovery
The lower the MAC
the more potent the agent
The more potent the agent
the more lipophilic
The more lipophilic the agent
the higher rate of absorption
The higher the rate of absorption of the agent
the SLOWER the onset of anesthesia
Balanced anesthesia
several anesthetic agents used simultaneously
allows physician to achieve potency and rapid induction/recovery in controlled manner
What will mixture of nitrous oxide and isoflurane produce
NO = rapid induction
Iso = potent
NO will anesthetize pt quickly and Iso will ensure deep anesthesia
simultaneous removal of the drugs will cause person to wake up (NO = rapid recovery) but be groggy (Iso = medium recovery)
IV agents used for
rapid induction of anesthesia
administered with inhaled
IV agents
ultra short acting -> barbiturates (thiopental)
Propofol: ultra-short, rapidly distributed and metabolized
Barbiturates
ultra short acting
high lipid solubility
Thiopental and Methohexital
Benzodizepines
-pams and -zolams
given to cause sedation, relaxation, amnesia prior to administration of other GA
Do benzo’s have faster or slower onset of action than barbs or propofol
Slower, but still adequate for surgical anesthesia
What can benzo’s be reversed by
flumazenil
Propofol
powerful GABAa positive allosteric modulator (increases time channel open)
ultra short, but rapidly distributed and metabolized -> faster recovery
most commonly used IV anesthetic
Opioid analgesics
fentanyl, sufentanil, alfentanil, and remifentanil are used in combo
bind mu receptors in brain and spinal cord -> suppress midbrain/raffe nucleus
which two opioids have rapid onset of action and can be used in combo with barbiturates as an anesthetic
Alfentanil and remifentanil
