General Anaesthetics Flashcards
Who was Horace Wells?
A dentist who noticed the effects of nitrous oxide when it was used in the circus. He thought it would be good for tooth extraction as it would make the patients less responsive. He did the experiment himself
Who was William Morton?
Used ether as a medical drug for pain, was a dentist. Along with a surgeon, Warren, he used ether on a patient and performed the surgery with an audience using ether. The surgery was succesful
Who was Simpson?
Read the paper of a phd student Robert Glover; he had used chloroform on dogs and reported the effect on their CNS
Simpson tested chloroform on humans in order to alleviate pain in labour but was criticised by not giving any credit to Glover and for being ‘unethical’
What are the two main classifications of general anaesthetics?
Chemical and physical
What is a physical general anaesthetic?
Examples include low atmospheric pressure, hypothermia. Not commonly used in humans but used in amphibians and flies
How can chemical general anaesthetics be administered?
Inhaled or intravenous
What factor determines how safe a general anaesthetic is?
Its lipid solubilty - if it is lower it is safer eg nitrous oxide
Halothane has a high lipid solubility so you only need a little bit of it for there to be an effect
Where do volatile general anaesthetics bind?
They bind at the interface of the alpha and beta subunits of GABAa
Where do intravenous general anaesthetics bind?
They bind to the beta subunit of GABAa
What receptors does ketamine block?
NMDA
What is the effect of low concentrations of GAs on nuerotransmission?
Neurotransmission in the CNS decreases, it causes inhibited reticular formation and causes a loss of consciousness. The hippocampus is affected causing short term amnesia?
What is the effect of high concentrations of GAs on nuerotransmission?
Causes decreased conduction in both the PNS and CNS. This ma cause the loss of motor control, reflexes, respiration and autonomic regulation
What are the four stages of anaesthesia?
1) Analgesia
2) Excitement stage
3) Surgical Anaesthesia
4) Medullary Paralysis
What happens in analgesia (first step)?
There is a reduced responsiveness to pain, nitrous oxide reaches this stage well so it is good for dental procedures
What happens in excitement (second stage)?
This is a dangerous state, there may be a loss of consciousness due to reticular formation inhibition, reflexes are exaggerated particularly due to incision eg flailing limbs, coughing, gagging and causes eratic breathing
This stage wants to be avoided
What happens during surgical anaesthesia (third stage)?
Unconsciousness, loss of response to painful stimuli, loss of reflexes and short term amnesia
Relaxed muscle tone
What happens during medullary paralysis (forth stage)?
Loss of cardiovascular reflexes and respiratory paralysis which can cause death
This stage wants to be avoided
What are the properties of an ideal anaesthetic?
Rapid induction causing loss of unconciousness
Analgesia
Muscle relaxation
Rapid recovery
What are the advantages of intravenous anaesthetics?
Easy to administor, rapid induction (20-30 secs), Propofol has rapid metabolism, good for induction of anaesthesia, rapid recobery and less ‘hangover’ so appropriate for day case surgery
What are the disadvantages of intravenous anaesthetics?
Pain at the site of injection, complex pharmacokinetics, thiopental has high lipid solubility rapid induction, but also short duration of action due to redistributon and hangover may be caused due to accumulation in body fat
There are side effects such as respiratory depression and cardiovascular depression
Why are inhaled general anaesthetics good?
You can lower the concentration given easily, you can change the amount of gas inhaled and it has low toxicity and little metabolism
Ryanodine receptors may be activated during GA administration. What are the effects of this?
Malignant hyperthermia - muscles contract, oxygen is depleted from other cells, massive increase in body temperature, may be inherited as a mutation
What does ketamine cause?
Sensory loss, analgesia and amnesia
When is ketamine used?
In peadiatrics and vetinary surgery
List some examples of inhalation anaesthetics
Nitrous oxide, isoflurane, desflurane and sevoflurane
When might inhaled GAs be problematic?
If the lungs are damaged or diseased
Speed and recovery from GA will depend on what?
Solubility in blood and fat
