Lecture 11 - General Anaesthetics

Question 1

what is the dose response curve for general anaesthetics?

Answer 1

it is a very steep dose response curve

Question 2

what is general anaesthetic potency proportional to?

Answer 2

liquid solubility

Question 3

what are the three ways for chemicals to be administered?

Answer 3

1. inhalation
2. intravenous
3. physical

Question 4

lipid solubility theory for general anaesthetics

Answer 4

work at the level of the plasma membrane to either cause volume expansion or increase lipid fluidity

Question 5

what is the Meyer-Overton rule?

Answer 5

anaesthetic effect is proportional to molar concentration of agent in liquid

Question 6

what did binding experiments with general anaesthetics conclude?

Answer 6

there was a limited number of sites for general anaesthetics which resulted in the idea that specific receptors were involved.

Question 7

where are binding sites accessible for general anaesthetics?

Answer 7

within the cellular membrane

Question 8

general anaethetics interaction with ion channels

Answer 8

• increase action of GABA at GABAa receptors.

Question 9

where do volatile general anaesthetics bind to?

Answer 9

the interface of alpha and beta subunits of GABAa
or activate two pore domain K channels causing hypnotic effect

Question 10

where do intravenous general anaesthetics bind?

Answer 10

only on the beta subunit of GABAa

Question 11

what blocks NMDA receptors

Answer 11

ketamine and nitrous oxide

Question 12

what is the action if general anaesthetics?

Answer 12

inhibits action potentials by decreasing inward currents of voltage gated sodium channels. also interferes with exocytotic process of neurotransmitters

Question 13

what is the effect of general anaesthetics on neurotransmission at low concentrations?

Answer 13

• 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

Question 14

what is the effect of general anaesthetics at high concentrations?

Answer 14

• results in loss of motor control, reflexes, respiration and autonomic regulation.
• in absence of artificial respiration results in death

Question 15

first stage of anaesthetic (analgesia)

Answer 15

reduced responsiveness to a normal painful procedure

Question 16

second stage of anaesthetic (excitement)

Answer 16

• patient has exaggerated reflexes where they gag or kick out.
  this stage is dangerous for the person doing the procedure

Question 17

third stage of anaesthetic (surgical anaesthesia)

Answer 17

• unconsciousness
• patient has lost all reflexes
• short-term amnesia

Question 18

fourth stage of anaesthetic (medullary paralysis)

Answer 18

• loss of cardiovascular reflexes and respiratory paralysis
• needs to be rapidly controlled

Question 19

what are the advantages of intravenous anaesthetics?

Answer 19

• rapid induction and easy to administer

Question 20

characteristics of propofol (intravenous)

Answer 20

used for maintenance of anaesthesia and has rapid metabolism. rapid recovery so less ‘hangover’ can be useful for short surgery.

Question 21

characteristics for thiopental (barbiturate)

Answer 21

induction is 20 seconds and lasts 10 minutes because of redistribution but causes respiratory depression

Question 22

characteristics of etomidate (intravenous)

Answer 22

offers advantage of having less cardiovascular depression

Question 23

disadvantages of intravenous administration

Answer 23

pain at site of injection and complex pharmacokinetics. has a hangover due to accumulation in body fat

Question 24

characteristics of ketamine

Answer 24

• acts as a dissociative anaesthetic and causes sensory loss
• NMDA channel blocker
• causes hallucinations
• increased intracranial pressure which is a hazard.

Question 25

characteristics of inhalation anaesthetics

Answer 25

• only route of entry and exit is via lungs
• easy to control the concentrations
  easily cross alveolar membrane
  small amount of toxicity due to limited metabolism

Question 26

what does low blood solubility cause?

Answer 26

causes rapid induction and recovery because of concentration in alveolar space is equal to concentration in inspired air. equilibrates more rapidly with concentration in blood

Question 27

what does high lipid solubility cause?

Answer 27

increases potency but slows down recovery and equilibration in fat is much slower

Question 28

how is malignant hyperthermia triggered?

Answer 28

exposure to certain drugs used for general anaesthetics like volatile anaesthetic agents

Question 29

what does malignant hyperthermia cause?

Answer 29

drastic and uncontrolled increase in oxidative metabolism in skeletal muscle, which overwhelms bodys capacity to supply oxygen, remove CO2 and regulate temperature

Question 30

what can malignant hyperthermia lead to if not treated?

Answer 30

circulatory collapse and death

Question 31

how is malignant hyperthermia treated?

Answer 31

Dantrolene used to treat it as a ryanodine receptor antagonist and muscle relaxant given

Question 32

what type of disorder is malignant hyperthermia?

Answer 32

inherited as an autosomal dominant disorder