Lecture 11 - General Anaesthetics Flashcards
what is the dose response curve for general anaesthetics?
it is a very steep dose response curve
what is general anaesthetic potency proportional to?
liquid solubility
what are the three ways for chemicals to be administered?
- inhalation
- intravenous
- physical
lipid solubility theory for general anaesthetics
work at the level of the plasma membrane to either cause volume expansion or increase lipid fluidity
what is the Meyer-Overton rule?
anaesthetic effect is proportional to molar concentration of agent in liquid
what did binding experiments with general anaesthetics conclude?
there was a limited number of sites for general anaesthetics which resulted in the idea that specific receptors were involved.
where are binding sites accessible for general anaesthetics?
within the cellular membrane
general anaethetics interaction with ion channels
- increase action of GABA at GABAa receptors.
where do volatile general anaesthetics bind to?
the interface of alpha and beta subunits of GABAa
or activate two pore domain K channels causing hypnotic effect
where do intravenous general anaesthetics bind?
only on the beta subunit of GABAa
what blocks NMDA receptors
ketamine and nitrous oxide
what is the action if general anaesthetics?
inhibits action potentials by decreasing inward currents of voltage gated sodium channels. also interferes with exocytotic process of neurotransmitters
what is the effect of general anaesthetics on neurotransmission at low concentrations?
- synaptic transmission in CNS is decreased
- decreased reticular information causing unconsciousness
- inhibition of neurotransmission in hippocampus causing short term amnesia.
- inhibition of thalamic sensory relay nuclei parts of cortex causing analgesia
- volatile anaesthetics can inhibit spinal reflexes
what is the effect of general anaesthetics at high concentrations?
- results in loss of motor control, reflexes, respiration and autonomic regulation.
- in absence of artificial respiration results in death
first stage of anaesthetic (analgesia)
reduced responsiveness to a normal painful procedure
second stage of anaesthetic (excitement)
- patient has exaggerated reflexes where they gag or kick out.
this stage is dangerous for the person doing the procedure
third stage of anaesthetic (surgical anaesthesia)
- unconsciousness
- patient has lost all reflexes
- short-term amnesia
fourth stage of anaesthetic (medullary paralysis)
- loss of cardiovascular reflexes and respiratory paralysis
- needs to be rapidly controlled
what are the advantages of intravenous anaesthetics?
- rapid induction and easy to administer
characteristics of propofol (intravenous)
used for maintenance of anaesthesia and has rapid metabolism. rapid recovery so less ‘hangover’ can be useful for short surgery.
characteristics for thiopental (barbiturate)
induction is 20 seconds and lasts 10 minutes because of redistribution but causes respiratory depression
characteristics of etomidate (intravenous)
offers advantage of having less cardiovascular depression
disadvantages of intravenous administration
pain at site of injection and complex pharmacokinetics. has a hangover due to accumulation in body fat
characteristics of ketamine
- acts as a dissociative anaesthetic and causes sensory loss
- NMDA channel blocker
- causes hallucinations
- increased intracranial pressure which is a hazard.
