General Anaesthetics Flashcards
what is anaesthetic?
• Anaesthesia = “without sensation”
– reversible loss of awareness of pain
what are the different types of anaesthetic?
- local
- regional
- general
what is local anaesthetic?
– patient remains conscious
– cheaper, safer
– Used in different ways to give surgeon ability to work on different parts of the body
what is regional anaesthetic?
– larger area of the body involved
– Can numb a whole arm
what is general anaesthetic?
– Loss/change of consciousness (central effect)
– major surgery can take place
– This is the type you could use to remove appendix/tumours
what is stage 1?
– Induction/analgesia
– Reduced responses to pain
– Conscious but drowsy
– Varies dependent on the agent ether»haloethene
The time a patient spends in stage 1 depends greatly on what drug they have been given. Some of the older drugs have a longer period of time within stage 1.
what is stage 2?
– Loss of response to stimuli
– Responses to pain preserved
– Gag reflex, coughing can increase
– This can lead to concerns of choking, holding breath, talking, vomiting during the surgery
This is a dangerous phase as you have things a patient may do which would cause harm. We want to minimise the time a patient has in this stage, if you increase the dose you can get to stage 3 quicker.
what is stagw 3?
– Surgical anaesthesia
– Regular respiration
– Possibly some reflexes as muscle tone is preserved
– Movement ceases
– Progressive shallowing of breath
this is the level stable steady state where you can do surgey without worrying too much about the patient. As long as you maintain the level of the drug, you won’t have too many issues with the patient. However, if the dose is too large you might get shallowing of patients breath.
what is stage 4?
– Anaesthetic overdose
– Medullary paralysis
– Respiration and Vasomotor control ceases
This is an OVERDOSE. Lose the control of the body and the patient will stop breathing. Unless you do something the patient will die.
what are the pharmacokinetics of GA?
• We would like rapid induction and rapid recovery
• We would prefer to avoid stage 2 – get them as quickly through this as possible
• We want the, to be in stage 3 in stable state until the surgery is done
• We would prefer the patient not to die in stage 4
• We would prefer to avoid side-effects – help them recover as quickly as possible.
There is no single drug which can achieve all of these goals
what are modern GA?
• rapid induction of unconsciousness; i.v. propofol.
o Get to therapeutic levels in plasma very quickly and this will give you rapid indiuction so you get past stage 2 quickly
• maintenance of unconsciousness and production of anaesthesia; inhaled N2O/halothane
• supplementary i.v. analgesic e.g. morphine
• neuromuscular blocker e.g. atracurium – this is for abdo surgery
• Fast induction and recovery (anxiety, hangover), reduces time stage II, homeostatic reflexes remain intact, amnesia not a bad thing to not remember surgery
o This is why sometimes you use i/v for induction and then move to inhaled as this is able to maintain over a longer period of time
how do GA work?
– Alter function of neurones – Structures very diverse o Argues against unified theory – Lipid theory – Protein theory
what is lipid perturbation?
• Was originally thought to be an effect on lipid alone, but was later interpreted in terms of changing the conformation of membrane proteins by changing the environment in which they are dissolved.
• However, this doesn’t completely work:
o Chain cut-off
o Adding long carbon chains can REDUCE potency
o ?a binding cavity of some sort
• Physical chemistry shows anaesthetics don’t change membranes that much
• Stereoselectivity of anaesthetic actions – membrane action fluidization is not a good explaination
• Some anaesthetics specifically affect certain proteins
what is the protein theory?
- Targets on membrane proteins, the binding sites for the anaesthics are probably situated in the lipid bilayer and the way it works it by dissolving in the bilayer, accessing the protein and then changing the structure and the function of the protein.
- GABA A = inhibitory ligand gated ion channels
- Potassium channels open you get hyperpolarisation
- NMDA are excitatory and general anaesthics inhibit these proteins
- Volatile anaesthics seems to act on all three receptors these are the ones you inhale
what is the function of GABA?
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