Anaesthesia

Question 1

What are the 4 stages of Guedel’s signs?

Answer 1

Stage 1: analgesia and consciousness

Stage 2: unconscious, breathing is erratic but delirium could occur leading to excitement phase

Stage 3: surgical anaesthesia (4 levels)

Stage 4: respiratory paralysis and death

Question 2

For volatile compounds what do we use to describe potency? Explain what this term means?

Answer 2

Minimum Alveolar Concentration (MAC) Alveolar concentration at which 50% of subjects fail to move to surgical stimulus

Question 3

At equilibrium, alveolar concentration = _______ concentration

Answer 3

spinal cord

Question 4

What factors affect induction and recovery from anaesthesia?

Answer 4

Partitian coefficients -Blood: Gas -Oil: Gas

Question 5

How does the amount of adipose tissue in a patient effect their induction and recovery from anaesthetic compounds?

Answer 5

Compounds have a greater ability to partition into fat which means it will accumulate in the adipose tissue Can take a long time for obese patients to wake up

Question 6

What factors affect MAC and how do they affect it?

Answer 6

Age (high in infants, lower in elderly) Hyperthermia (increased) Hypothermia (decreased) Pregnancy (increased) Alcoholism (increased) Central stimulants (increased) Other anaesthetics and sedatives (decreased) Opioids (decreased)

Question 7

Why is nitrous oxide often added to other volatile agents

Answer 7

Induce amnesia and hypnosis - “volatile sparing agent” Allows use of reduced doses of antetheic Therefore reduces the side effect profile

Question 8

What does the Meyer-Overton correlation show?

Answer 8

Anaesthetic potency in relation to lipid solubility

The greater is the lipid solubility of the compound in olive oil the greater is its anaesthetic potency

Question 9

Anaesthetic potency correlates to which two factors?

Answer 9

Lipid solubility

GABA_A receptor interaction

Question 10

Which receptor is a critical target for anaesthetics?

Which type of channel is this?

Answer 10

GABA_A

Ligand gated ion channel for Cl- conductance

Question 11

All anaesthetics potentiate GABA_A medicated Cl- conductance to depress CNS activity besdies which 3 drugs?

Answer 11

Xe

N₂O

Ketamine

Question 12

How does anaethetic interaction with GABA_A receptors cause CNS depression?

Answer 12

Binding to the receptor causes increased permeability to chloride

This casues chloride to enter the cell

The cell becomes hyperpolarised

Becomes difficult to get an action potential

Question 13

Anaethetics modulate the balance between excitation by _____ and inhibiton by _____

Answer 13

glutamate

GABA

Question 14

Which areas of brain circuitry are affected by anaethetics?

How do each of these relate to their use in surgery/intubation?

Answer 14

Reticular formation depression - loss of connectivity + sensory information

Hippocampus depression - loss of memory

Brainstem depression - respiratory and some CVS depression

Spinal cord depression at dorsal horn - analgesia

Depression of motor neurone activity - MAC

Question 15

What are the main IV anaethetics?

Which receptors to they bind to elict their effects?

Answer 15

Propofol - GABA_A

Barbituates- GABA_A

Ketamine - NMDA

Question 16

The main IV anaethetics are given IV for what purposes?

Answer 16

Induction

Total IV Anaethesia (TIVA)

Question 17

How do we describe IV anaesthetic potency?

Answer 17

Plasma concentration to achieve a specific end point (e.g. loss of eyelas reflex, Bispectral Index (BIS))

Induction: Bolus to end point (sleep)

TIVA: defined PK based algorithm to infuse at a rate to maintain set point

Question 18

Name some examples of local anaethetics

Answer 18

Lidocaine

Bupivacaine

Ropivacaine

Procaine

Question 19

How does the dissociation constant (pKa) relate to the time of onset of local anaethetics?

Answer 19

The lower the pKa, the faster the onset

Question 20

How does bupivacaine (a local anaethetic) work in wound analgesia?

Answer 20

Blockage of voltage-gated sodium channels

Cannot produce an AP

Blocks small myelinated nerves (afferents) in perferance= nociceptive and sympathetic block

Question 21

Compared to Procaine, is Bupivacaine more or less potent and how does its duration of action compare?

Answer 21

More potent + longer duration of action

Question 22

Which drugs can be used to generate a regional “block”?

Answer 22

Local anaethetics (e.g. lidocaine)

Opioids

Question 23

What are the main side effects from general anaethesia?

Answer 23

Post-operative nausea and vomitting (PONV)

Hypotension

Post-operative cognitive dysfunction (POCD)

Chest infection