General Anaesthetics

Question 1

Define anaesthesia.

Answer 1

Reversible loss of awareness of pain and sensation

Question 2

What are the three main types of anaesthesia?

Answer 2

Local
Regional
General

Question 3

What is stage 1 of anaesthesia?

Answer 3

Induction and administration of analgesia
Reduces response to pain
Conscious but drowsy

Question 4

What is stage 2 of anaesthesia?

Answer 4

Excitement, loss of response to non painful stimuli

Coughing increased, gag reflex

Question 5

What are the concerns of stage 2 anaesthesia?

Answer 5

Choking
Breath holding
Talking
Vomiting
Movement

Question 6

What is stage 3 of anaesthesia?

Answer 6

Desired phase for surgery
Regular respiration
Muscle tone preserved
Progressive shallow breathing

Question 7

What is stage 4 of anaesthesia?

Answer 7

Anaesthetic overdose
Medullary paralysis
Respiration and vasomotor control ceases

Question 8

Describe the ideal parameters of anaesthesia.

Answer 8

Rapid induction and recovery
Avoid stage 2 if possible
Ideally avoid side effects

Question 9

Why are drugs commonly used in combination during anaesthesia? Give examples.

Answer 9

Stages of anaesthesia become less apparent

Different anaesthetics, analgesia, muscle relaxants, anxiolytics

Question 10

What is used for rapid induction?

Answer 10

IV propofol

Question 11

What is used to maintain unconsciousness?

Answer 11

Inhaled nitrous oxide/halothane

Question 12

What can be given as supplementary IV analgesia?

Answer 12

Morphine

Question 13

What is commonly given as a neuromuscular blocker in anaesthesia?

Answer 13

Atracurium

Question 14

What are the benefits of induction and recovery?

Answer 14

Reduced stage 2
Homeostatic reflexes intact
Amnesia

Question 15

What is the theory of lipid pertubation by anaesthetics?

Answer 15

Anaesthetics change the conformation of membrane proteins by changing the environment in which they are dissolved, some specifically affect certain proteins
Adding long carbon chains can reduce the potency

Question 16

What is the protein theory of anaesthetic action?

Answer 16

GABA-A function potentiated, more Cl inions enter the neurone increasing inhibition in the CNS
NMDA receptor function inhibited by blocking glutamate binding
Two pore potassium channel function potentiated

Question 17

What are the most common inhalation anaesthetics?

Answer 17

Nitrous oxide

Isofluorane

Question 18

What are the disadvantages of ether anaesthetics? Where are they used?

Answer 18

Explosive, irritant and cause nausea

Used in 3rd world countries as very cheap

Question 19

What are the advantages of inhalation anaesthetics?

Answer 19

Easy to maintain degree of anaesthesia due to fast air-blood equilibration
Rapid emergence from anaesthesia

Question 20

What are the disadvantages of inhalation anaesthetics?

Answer 20

Cumbersome and expensive apparatus
Administered via mask
Atmospheric pollution by scavengers

Question 21

Discuss the problems with metabolism of inhalation anaesthetics.

Answer 21

Fluranes generate fluoride that causes renal toxicity
Halothane converted to bromide and TFA which is hepatotoxic
Scavenger systems required

Question 22

What is the minimum alveolar concentration?

Answer 22

Measures potency

Concentration required to produce anaesthesia in 50% of patients

Question 23

What is the relevance of blood-gas partition coefficient of inhalation anaesthetics?

Answer 23

Measure of how well the drug dissolves in the blood

Determines rate of induction and recovery

Question 24

What is the relevance of oil-gas partition coefficient of inhalation anaesthetics?

Answer 24

High oil-partition coefficient confers high potency

Lots of anaesthetic will dissolve in fat which is poorly vascularised, leading to slowly resolving ‘hangover’

Question 25

Describe the features of isoflurane.

Answer 25

``` No metabolism Little toxicity Not pro-convulsive Twice the cost of halothane Negative inotrope, can cause hypotension Coronary vasodilator Potentially causes neurodegeneration ```

Question 26

Describe the features of sevoflurane.

Answer 26

``` Described as the anaesthetic of choice Rapid induction Little metabolism Five times cost of halothane Recovery so fast that post-op pain relief is necessary ```

Question 27

Describe the features of nitrous oxide.

Answer 27

Low blood-gas partition coefficient Analgesic at concentrations lower than those causing unconsciousness Introduces more oxygen than pure oxygen would due to density Rapidly leaves blood and tissue Dilates oxygen in lungs for few minutes, transient hypoxia

Question 28

When is nitrous oxide contraindicated?

Answer 28

Pregnancy Pernicious anaemia Scuba diving

Question 29

Describe the formulation of nitrous oxide?

Answer 29

Entonox | 50% nitrous oxide, 50% oxygen

Question 30

What are the advantages of IV anaesthetics?

Answer 30

Rapid induction No stage 2 Simple apparatus Pleasant induction

Question 31

What are the disadvantages of IV anaesthetics?

Answer 31

Level of anaesthesia difficult to control Recovery can be slow Finite duration Vein damage

Question 32

Describe the use of thiopental.

Answer 32

Only normally used for induction Very lipid soluble, crosses BBB quickly Rapid redistribution to highly perfused tissues, slowly distributes into fat Rapid awakening but prolonged hangover Positive inotrope, hypotensioon in hypovolaemic patients Respiratory depression (used in euthanasia)

Question 33

Describe the use of propofol.

Answer 33

Rapid metabolism and recovery compared to other IV Can be continuously infused to maintain anaesthesia Used for day surgery Widely abused by medical personnel

Question 34

Describe the use of ketamine.

Answer 34

``` Dissociative anaesthetic Analgesia and amnesia but patient still partly conscious Increases heart rate Safe in emergency situations High abuse potential ```

Question 35

What are Olney's lesions?

Answer 35

Potential form of brain damage from ketamine | NMDA receptor antagonist neurotoxicity

Question 36

What is neuroleptic anaesthesia?

Answer 36

Combination of antipsychotic andopioid Effects similar to ketamine Not frequently used in humans

Question 37

What is immobilon?

Answer 37

Used in animals Acepromazine and etorphine (neuroleptic anaesthetic) Used in tranquiliser darts and supplied with antidote (revivon) due to potency