General Anaesthetics

Question 1

Who was Horace Wells?

Answer 1

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

Question 2

Who was William Morton?

Answer 2

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

Question 3

Who was Simpson?

Answer 3

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’

Question 4

What are the two main classifications of general anaesthetics?

Answer 4

Chemical and physical

Question 5

What is a physical general anaesthetic?

Answer 5

Examples include low atmospheric pressure, hypothermia. Not commonly used in humans but used in amphibians and flies

Question 6

How can chemical general anaesthetics be administered?

Answer 6

Inhaled or intravenous

Question 7

What factor determines how safe a general anaesthetic is?

Answer 7

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

Question 8

Where do volatile general anaesthetics bind?

Answer 8

They bind at the interface of the alpha and beta subunits of GABAa

Question 9

Where do intravenous general anaesthetics bind?

Answer 9

They bind to the beta subunit of GABAa

Question 10

What receptors does ketamine block?

Answer 10

NMDA

Question 11

What is the effect of low concentrations of GAs on nuerotransmission?

Answer 11

Neurotransmission in the CNS decreases, it causes inhibited reticular formation and causes a loss of consciousness. The hippocampus is affected causing short term amnesia?

Question 12

What is the effect of high concentrations of GAs on nuerotransmission?

Answer 12

Causes decreased conduction in both the PNS and CNS. This ma cause the loss of motor control, reflexes, respiration and autonomic regulation

Question 13

What are the four stages of anaesthesia?

Answer 13

1) Analgesia
2) Excitement stage
3) Surgical Anaesthesia
4) Medullary Paralysis

Question 14

What happens in analgesia (first step)?

Answer 14

There is a reduced responsiveness to pain, nitrous oxide reaches this stage well so it is good for dental procedures

Question 15

What happens in excitement (second stage)?

Answer 15

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

Question 16

What happens during surgical anaesthesia (third stage)?

Answer 16

Unconsciousness, loss of response to painful stimuli, loss of reflexes and short term amnesia
Relaxed muscle tone

Question 17

What happens during medullary paralysis (forth stage)?

Answer 17

Loss of cardiovascular reflexes and respiratory paralysis which can cause death
This stage wants to be avoided

Question 18

What are the properties of an ideal anaesthetic?

Answer 18

Rapid induction causing loss of unconciousness
Analgesia
Muscle relaxation
Rapid recovery

Question 19

What are the advantages of intravenous anaesthetics?

Answer 19

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

Question 20

What are the disadvantages of intravenous anaesthetics?

Answer 20

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

Question 21

Why are inhaled general anaesthetics good?

Answer 21

You can lower the concentration given easily, you can change the amount of gas inhaled and it has low toxicity and little metabolism

Question 22

Ryanodine receptors may be activated during GA administration. What are the effects of this?

Answer 22

Malignant hyperthermia - muscles contract, oxygen is depleted from other cells, massive increase in body temperature, may be inherited as a mutation

Question 23

What does ketamine cause?

Answer 23

Sensory loss, analgesia and amnesia

Question 24

When is ketamine used?

Answer 24

In peadiatrics and vetinary surgery

Question 25

List some examples of inhalation anaesthetics

Answer 25

Nitrous oxide, isoflurane, desflurane and sevoflurane

Question 26

When might inhaled GAs be problematic?

Answer 26

If the lungs are damaged or diseased

Question 27

Speed and recovery from GA will depend on what?

Answer 27

Solubility in blood and fat