general anaesthetics

Question 1

what does inhalant GA produce towards painful stimuli?

Answer 1

unconsciousness and analgesia (inability to feel pain)

Question 2

what is needed for inhalant GA to produce therapeutic effects?

Answer 2

inhalant GA must reach CNS concentration sufficient enough to suppress neuronal excitability

Question 3

which has higher potency – inhalant GA with higher or lower minimum alveolar concentration (MAC)?

Answer 3

lower MAC

recall that MAC is minimum concentration of drug in alveolar air that will produce immobility in 50% of patients exposed to a painful stimulus

Question 4

GA mechanism of action

Answer 4

1. enhance neurotransmission at inhibitory synpases by allosterically increasing GABA receptor sensitivity to GABA action. binding of GABA neurotransmitter causes greater entry of Cl- which hyperpolarises cell, making it more difficult to depolarise –> reduces neuronal excitability
2. depressing neurotransmission at excitatory synpases via blocking the NMDA receptor hence preventing glutamate neurotransmitter from acting on and activating NMDA receptor

ref to point 1 (since GABA neurotransmission is inhibitory, this will reduce overall synaptic activity of the brain)

Question 5

list types of inhalant GA

Answer 5

halothane, enflurane, desflurane, isoflurane, sevoflurane, nitrous oxide

Question 6

adverse effects of halothane?

Answer 6

1. respiratory depression at high doses
2. hepatotoxicity
3. relaxation of skeletal muscles
4. depression of cardiac output decreasing blood pressure
5. bradycardia, arrhythmias leading to hypotension and dysrhythmias

Question 7

adverse effects of sevoflurane?

Answer 7

nephrotoxicity

Question 7

halothane has _____ analgesia until patient becomes unconsciousness

Answer 7

little to no analgesia

Question 8

differentiating feature of NO gas

Answer 8

not potent but has high analgesic potency

due to very high MAC, NO alone gives analgesia (and amnesia) but not complete unconsciousness or surgical anaesthesia

hence patients undergoing GA get NO to SUPPLEMENT analgesic effects of primary anaesthetic

Question 9

5 factors affecting inhalant GA action

Answer 9

1. solubility
2. concentration in inspired air
3. rate and depth of pulmonary ventilation
4. pulmonary blood flow
5. arteriovenous concentration gradient in tissue (for uptake)

Question 10

absorption pathway of inhalant GA

Answer 10

first goes to lungs, then to blood, then to brain and other tissues.

the higher the drug’s solubility in blood, the slower the onset because drug will take longer to get to the brain

Question 11

what does intravenous GA produce towards painful stimuli?

Answer 11

unconsciousness ONLY

Question 12

list types of IV GAs

Answer 12

thiopentone (sodium thiopental)
propofol
ketamine

Question 13

specific MOA of each IV GA?

Answer 13

thiopentone + propofol = GABA MOA
ketamine = NMDA MOA

Question 14

2 advantages of IV GAs

Answer 14

1. allows for dose reduction of inhalant GAs
2. can produce effects that cannot be achieved with inhalation alone

Question 15

thiopentone and propofol have __ onset of action and __ duration of action

Answer 15

rapid; very short/short (for propofol)

note that due to the very short/short duration of action, it has to be taken in multiple doses

Question 16

adverse effect of propofol?

Answer 16

hypotension

Question 17

in what type of patients do we use propofol with caution?

Answer 17

1. elderly
2. patients with compromised cardiac function

Question 18

what extra effect does propofol have other than its effect as an anaesthetic

Answer 18

antiemetic (prevents vomiting)

Question 19

difference between ketamine and other IV GAs

Answer 19

1. produces altered consciousness instead of unconsciousness –> patient feels disassociated from environment
2. has analgesic property

Question 20

adverse effects of ketamine

Answer 20

psychologic reactions including hallucination, disturbing dreams, delirium

can be reduced through prescribing diazepam or midazolam

Question 21

anaesthetic adjuncts include…

Answer 21

benzodiazepines (midazolam), alpha-2 adrenergic agonists, analgesics, neuromuscular blocking agents