general anaesthesia Flashcards
what do anaesthetics bind to?
There are no anaesthetic specific receptors; the only common feature between them is their high lipid solubility. They tend to bind to the hydrophobic pockets of proteins
what increases the potency of a GA?
the presence of an ethyl group, the presence of a halogen substitution the presence of unsaturation?
what decreases the potency of a general anaesthetic?
the presence of a hydrophilic group
why does the potency of alochols as anaesthetics decrease after decanol?
this probably reflects the binding pocket size
what is MAC
this is the minimum alveolar concentration of safe level of anaesthetic which when at equilibrium will prevent movement in response to a painful stimuli in 50% of individuals (basically and ED50)
what is the relationship between MAC and potency
the higher the MAC the lower the poteny
explain how different drugs with different blood solubilities have different rates of onset
the lower the blood solubility, the quicker the rate of onset. this is because equilibrium will be attained quicker, as the concentration of drug within the alveoli does not vary dramatically.
concentration in blood at equilibrium - MAC * blood/gas partition
what are the four stages of anaesthesia?
- analegsia (but not all anaesthetics are analgesic at sub-anaesthetic levels.
- excitement and delirium
- surgical anaesthesia
- overdose
medullary depression and can lead to death
when is ketamine used?
this is used in dissociative anaesthesia, but this has a problem with abuse
why has propofol replaced thiopentone?
that’s because thiopentone is a short acting barbiturate therefore, has the risk of dependance
what is special about IV anaesthesia?
can be used for induction anaesthesia they also produce anaesthesia before equilibrium has been reached. the peak quickly in blood but also have a rapid offset because blood redistributed to less well perfused areas
why may anoxia occur during recovery from anaesthesia?
due to the fink effect
- that is nitrous oxide moves back into alveolus down its concentration gradient and this dilutes the axes within the alveolus
why is premedication used peri-operatively?
prevent parasympthomemimetic effects of anaesthesia and to prevent anxiety or pain
why may affect the rate of offset of GA?
the amount of adipose tissue the patient has, this is because blood flows slowly through adipose tissue, and because of the high lipid solubility of the inhalation anaesthetics some will deposit there. this will cause hangover effects/
why may affect the rate of offset of GA?
the amount of adipose tissue the patient has, this is because blood flows slowly through adipose tissue, and because of the high lipid solubility of the inhalation anaesthetics some will deposit there. this will cause hangover effects
