GA - Anaesthesia

Question 1

Why are there so many drugs for GA and sedation?

Answer 1

No single perfect agent
Combos of anaesthetics = used for synergistic and additive therapeutic effects
Risk of increasing adverse effects

Question 2

Why sedation?

Answer 2

Reduce pt anxiety
Increase acceptability to prolonged/extensive procedures - still an effective time limit; <2hrs
Looking for anxiolysis, cooperation, street fitness (may need time to recover before leaving)

Question 3

Why GA?

Answer 3

Extensive/prolonged procedures
Brief painful procedures - Extractions
Total lack of pt cooperation - intellectual impairment, children

Question 4

Drugs available for sedation? Side effects/negatives?

Answer 4

Alcohol - disinhibition, nausea, slow recovery
Tetrahydrocannabinol (THC) - Nausea, illegal
Opiates - europhia, nausea, resp depression
Major tranquillisers - chlorpromazine - profound anxiety, hypotension
Minor tranquillisers - benzodiazepines - drowsiness, prolonged effect

Question 5

Features of oral benzodiazepines?

Answer 5

Long interval, variable, small effect

Often enough for most pts

Question 6

Features of intravenous benzodiazepines?

Answer 6

Competence in IV cannulation
Limited duration of action - repeat doses
Need for monitoring - SpO2 mandatory
Written record - pulse BP SpO2

Question 7

Diazepam features?

Answer 7

Irritant

Skin necrosis

Question 8

Diazemuls features?

Answer 8

Rapid onset
Brief duration of action
Psychoactive metabolites with long half life

Question 9

Midazolam features?

Answer 9

Slower onset
Less predictable effect
Rapid metabolism

Question 10

How do benzodiazepines and barbiturates work?

Answer 10

Bind to GABA receptor
Changes frequency of opening and closing of GABA channel
- Benzodiazepine increases frequency of opening of Cl channel
- Barbiturates increase duration of opening
Membrane hyperpolarised
CNS depression

Question 11

How does propofol work in sedation?

Answer 11

Work at least partly with GABA receptor
Short acting
Fast recovery
Can be used in sub-anaesthetic doses

Question 12

Negatives of propofol as sedation?

Answer 12

No analgesia
Continuous infusion - secure IV access
Expensive delivery system

Question 13

What are the differences between sleep and unconsciousness?

Answer 13

Unrousability
Loss of protective reflexes
= Potential for - aspiration, obstruction, nerve damage due to prolonged pressure

Question 14

What is the process of GA?

Answer 14

Induction
- Rapid pleasant production of consciousness - Iv or gaseous/volatile

Secure airway

• Optimum head position, LMA, ETT
• Endotracheal tube to keep airway open

Maintenance
- Gaseous/volatile or IV
Analgesia
Muscle relaxant

Emergence
- Reversal of muscle relaxation

Question 15

What drugs are used for the induction of GA?

Answer 15

IV:

• Propofol
• Thiopentone
• Ketamine
• Etomidate

Volatile: sevoflurane

Question 16

Characteristics of propofol?

Answer 16

Rapid pleasant onset
Non cumulative
Hypotension (vasodilation)
Painful on injection

Question 17

Characteristics of thiopentone?

Answer 17

Rapid onset
Offset due to redistribution
Slow metabolism
Cumulative
Hypotension (myocardial depression)
Odd complications
- Arterial spasm
- Porphyria
- Anaphylaxis rare but serious

Question 18

Characteristics of ketamine?

Answer 18

Rapid onset
Hypertension
Powerful analgesic
Non cumulative
Muscle rigidity
Unpleasant hallucinations

Question 19

Characteristics of etomidate?

Answer 19

CV stability
Noncumulative
Odd (major) complications
- Inhibition of steroid synthesis 
- Death due to induced addison's

Question 20

How to maintain the airway?

Answer 20

Optimum head position - neck flexed, head extended
Laryngeal mask - does not prevent aspiration
Tracheal intubation - eliminates danger of aspiration BUT
- Use muscle relaxant to overcome laryngeal reflexes = these have side effects
- Suxamethonium
- Atracurium
- Cisatracurium
- Rocuronium
- Pancuronium

Question 21

Features of suxamethonium?

Answer 21

Rapid onset and offset
Depolarising
Muscle pain
Occasional prolonged paralysis
Malignant hyperthermia

Question 22

Atracurium features?

Answer 22

Reliable spontaneous hydrolysis
Histamine release
Hypotension

Question 23

Cisatracurium features?

Answer 23

Not so much histamine release

Slow onset

Question 24

Rocuronium features?

Answer 24

Long duration
Specific reversal agent
Histamine release

Question 25

Pancuronium features?

Answer 25

Medium duration
Tachycardia
Renally excreted
Unchanged

Question 26

How to maintain gaseous/volatile and intravenous anaesthesia?

Answer 26

Gaseous/volatile

• Nitrous oxide
• Isoflurane, sevoflurane, desflurane

Intravenous
- Propofol

Question 27

Issues with nitrous oxide?

Answer 27

Dysphoria

Association with miscarriage

Question 28

Issues with seveflurane?

Answer 28

Acceptable for volatile induction

Question 29

Issues with desflurane?

Answer 29

Rapid onset/offset

Question 30

Issues with propofol?

Answer 30

IV agent - access required
Microprocessor controlled infusion pump - expensive
Can be used for sedation

Question 31

Why do a preop assessment?

Answer 31

Perfect prep prevents poor performance
Max pt safety - optimise pts condition, postpone if necessary
Toxic drugs with significant side effects
- All have lifethreatening effects at therapeutic doses
- CV depressant
- Resp depressant

Question 32

Complications encountered during an operation?

Answer 32

Pt
Anaesthetic
Surgeon

Question 33

What pt problems can occur during an op?

Answer 33

Pre-existing disease

Cardiac

• Aortic stenosis
• Coronary artery disease

Resp

• COPD
• Asthma

Diabetes

• Common
• Associated with renal, CV pathology

Question 34

What history to take for anaesthesia?

Answer 34

Proposed procedure
PMH
- Drugs/allergies
- Surgical: previous GA, problems (pt/fam)
- Medical - cardiac, resp, GI (aspiration risk - Hiatus hernia), renal (impairs drug handling), diabetes
Airway assessment

Question 35

What are the complications of anaesthesia? How to reduce them?

Answer 35

Awareness/OD - agent monitoring: brain func monitors; neuromuscular blockage
Anaphylaxis
Hypoxia - SpO2
Resp depression - CO2 monitoring
Aspiration (preop starvation, intubation)
Peripheral nerve damage (careful positioning)

Question 36

Problems that can occur in surgery? How to treat this?

Answer 36

Haemorrhage - Signs:

• Falling BP
• Rising HR
• Suction container full of blood
• Loads of wet swabs

Tx:
- Permissive loss of haemoglobin (to Hb=80)
Restore circulation with crystalloid
Chloride is the current unfashionable anion