General anaesthetics Flashcards
Name 5 desirable qualities of general anaesthesias
Loss of consciousness at low concentrations, suppression of reflex responses at high concentrations, amnesia, analgesia, muscle relaxation.
Name 4 gaseous general anaesthetics
NO, diethyl ether, halothane, enflurane
Name 2 IV general anaesthetics
Propofol and etomidate.
What is the Meyer/Overton Correlation?
What are the problems with this theory?
Anesthetic potency increases in DIRECT PORPORTION with oil:water partition coefficient.
Problems: minute changes to bilayer at relevant concentrations. How would they change membrane concnentrations.
How do IV general anaesthetics, like etomidate and propofol work?
IV general anaesthetics, like etomidate and propfol, usually ALTER SYNAPTIC FUNCTION. They AGONIZE GABAa receptors. Stimulating the B3 component supresses reflexes and a5 stimulation causes amnesia.
How do gaseous general anaesthetics, like diethyl ether and halothane work?
Gaseous general anaesthetics work by ALTERING SYNAPTIC FUNCTION- they agonize GABAa receptors (stimulating a1 supresses reflexes) and the ANATAGONIZE NMDA receptors and DERCEASE FIRING RATE of nAChRs. Gaseous general anaesthetics also DECREASE NEURONAL EXCITIILITY by agonizing background potassium channels, prolonging neuronal hyperpolarization.
How do general anaesthetics induce loss of consciousness?
They depress excitability of thalamocortical neurones (GABAa stimulation, both, and TREK channel opening, gaseous only) as well as influence reticular activating system (by decreasing firing rate of nAChR, gaseous only).
How do general anaesthetics supress reflex responses?
Via GABAa stimulation: IV stimulate B3 and gaseous stimulate a1.
How do general anaesthetics induce amnesia?
By decreasing synaptic transmission in the hippocampus and the amygdala e.g. IV general anaeathtsics stimulate GABAa a5 subunits.
Compare the distribution of IV and inhalational general anaesthetics?
Once administrated, the IV GAs can freely access the brain and their half life is almost entire dependent on the metabolism by the liver.
For inhaled GAs, it depends on the blood:gas partition coefficient- low means GOOD penetration.
A high blood:gas partition coefficient means poor penetration–> a high blood plasma level means it will take a long time to reach equilibrium with the brain partial pressure, so a slow onset.
Comapre the use of IV and inhalational general aneasthetics
Inhalational (NO, diethyl ether, enflurane) are RAPIDLY ELIMINATED and you have RAPID CONTROL on the depth of aneathesia.
IV (propfol, etomidate) have FAST INDUCTION and cause LESS COUGHING.
So use propofol for induction, enflurane for maintenance.
What could you use as adjuncts propofol and eflurane and why?
Opoids for pain relief e.g. iv fentanyl
NMJ blocker for muscle relazation e.g. suxemethonium
BDZs for amnesia e.g. IV midazolam.
