anaesthetics

Question 1

what is a general anaesthetic

Answer 1

act on the brain to produce a loss of sensation - small lipid soluble molecules that pass the BBB, affects synaptic transmission and neuronal excitability

Question 2

what is local anaesthetics

Answer 2

block local nerve trunks

Question 3

what is the reticular formation

Answer 3

complex network of neurons in the brainstem connecting to the hypothalamus, cerebellum and cerebral cortex - arouses cerebral cortex to wakefulness - inhibition causes unconsciousness

Question 4

what are the 4 stages of anaesthesia

Answer 4

1. cortical inhibition - minor procedures
2. excitation/inhibition of cortical neurons - delirium and involuntary movements
3. surgical anaesthesia - 4 planes - gradual loss of respiratory function and muscle tone
4. overdose - resp and circulatory paralysis - death

Question 5

what anaesthetics can be used at induction

Answer 5

ketamine
thiopental
propofol
etomidate

Question 6

what are the pharmacokinetics of thiopental

Answer 6

areas receiving high levels of cardiac output will immediately get high levels of anaesthetic - hours after receiving the drug it is still in fatty tissue - hangover
saturation kinetics - large doses can accumulate and lead to CV/resp depression

Question 7

what are the pharmacokinetics of propofol

Answer 7

rapid onset and rate of distribution - rapidly cleared so no hangover but hard to maintain levels

Question 8

ketamine kinetics

Answer 8

increased BP and HR, no effect on RR
slower onset than propofol and thiopental

Question 9

which inhaled anaesthetics can be used for maintenance

Answer 9

o Halothane
o Isoflurane
o Sevoflurane
o NO
o Desflurane

Question 10

which 2 equilibrium events must occur for an inhaled anaesthetic to be effective

Answer 10

blood - gas
oil - gas

Question 11

what is the blood - gas coefficient and how does it work

Answer 11

Concentration of anaesthetic in the brain mimics that in arterial blood

Question 12

how do low solubility drugs affect the blood - gas coefficient

Answer 12

NO - low partial pressure in alveoli, slow blood absorption - eventual equilibrium

Question 13

how do high solubility drugs affect the blood - gas coefficient

Answer 13

halothane/ether
rapid dissolution into the blood, low alveolar concentration so takes longer to equilibrate

Question 14

what is the oil gas coefficient

Answer 14

transfer of anaesthetic between blood and tissue- majority ends up in fat so can take hours

Question 15

what is halothanes oil-gas coefficient

Answer 15

very high - very fat soluble, more fat the patient has the slower the recovery

Question 16

what two factors affect the rate of induction and recovery when using inhaled anaesthetics

Answer 16

1. alveolar ventilation rate - greater vol of air in - faster equilibrium
2. cardiac output - reduced alveolar perfusion = reduced absorption so faster induction

Question 17

what is the MAC

Answer 17

minimal alveolar concentration required to abolish response to surgical incision in 50% of subjects

Question 18

what are the three proposed targets of anaesthetic

Answer 18

GABAa
glutamate receptors
voltage gated sodium, potassium and calcium channels

Question 19

how do anaesthetics work at GABAa receptors

Answer 19

enhance the effect of GABA on GABAaR
binds to hydrophobic pockets

Question 20

how do anaesthetics work at glutamate receptors

Answer 20

decreases activity (NO- blocks channel pore )
xenon and isoflurane inhibit NMDAR by competing with glycine for its regulatory site

Question 21

how do general anaesthetics work at Voltage gated sodium, potassium and calcium channels

Answer 21

activated by low concentrations of volatile and gaseous anaesthetic to reduce membrane excitability - no response to IV