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Principles of anaesthesia > Maintenance of general anaesthesia > Flashcards

Maintenance of general anaesthesia Flashcards

1
Q

Key components of GA

A

Unconsciousness
Analgesia
Muscle relaxation
Vegetative depression

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2
Q

Types of anaesthesia

A

Local/regional anaesthesia
○ Peripheral nerve blocks
○ Extradural anaesthesia
○ Splash block
○ Local infiltration/wound catheters

General anaesthesia
○ Inhalation
○ Injection
○ Or a combination of the two

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3
Q

Maintenance of anaesthesia

A

Keeping patient asleep throughout the procedures
○ w/o nociception
○ w/o movement
○ w/o awareness

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4
Q

How to assess level of anaesthesia

A

Muscle tone
Jaw tone
Palpebral reflex
Corneal reflex (if doesn’t have this it will be dead soon)
Nystagmus (common in horses)
Eye position
Lacrimation

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5
Q

Guedel anaesthetic staging

A

Awake
Stage II
Stage III
- Light (plane I)
- Medium (plane 2)
- Deep (plane 3)
Stage IV

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6
Q

Stage II anaesthesia

A

Normal breaths but irregular breath-holding

Normal size pupil

Eyeballs up

Palpebral and corneal reflexes present

Lacrimation present

Still responds to surgical stimulation

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7
Q

Light (plane I) stage III anaesthesia

A

Normal breathing with regular pattern

Pupils constricted

Eyeballs down

Palpebral may be present, corneal present

Lacrimation may be present

Likely still responds to surgical stimulus

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8
Q

Medium (plane 2) stage III anaesthesia

A

Shallow breathing - more reduced intercostally, regular pattern

Pupils slightly dilated

Eyeballs slightly further up than if light but still down

Palpebral absent, corneal present

No lacrimation

May respond to surgical stimulation

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9
Q

Deep (plane 3) stage III anaesthesia

A

Very shallow, jerky breathing - no intercostal movement

Pupils very dilated

Eyeballs up

May not have corneal reflex if very deep

No lacrimation

No response to surgical stimulation

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10
Q

Stage IV anaesthesia

A

No breathing

No iris visible - just pupil

Eyeballs up

No corneal reflex

About to die

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11
Q

Central eyes and palpebral reflex present during surgery

A

Too light

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12
Q

Central eye and no palpebral when under GA

A

Too deep

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13
Q

What are most inhalational anaesthetics?

A

Halogenated hydrocarbons

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14
Q

Mode of action of inhalational anaesthetics

A

Don’t 100% know

Interaction with lipid-membranes

Binding to specific sites in proteins

GABAa-receptors

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15
Q

Main effect of inhalational anaesthesia

A

Hypnosis - NOT analgesic

Deep enough they won’t react but still feel pain

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16
Q

What does MAC stand for?

A

Minimum alveolar concentration

17
Q

What is the MAC?

A

The concentration of vapour needed in alveoli of the lungs to prevent movement/motor response in 50% of subjects in response to surgical (pain) stimulation

18
Q

What is the MAC used for?

A

To assess the potency of anaesthetic inhalants (the lower the more potent) - gives a rough idea of what a specific patient needs

19
Q

How can you measure the alveolar concentration of an inhalant in a clinical setting?

A

The end tidal concentration (e.g. et(iso) is close to the alveolar concentration

20
Q

What do partial pressure changes of inhalational anaesthetic in the alveoli influence?

A

Partial pressure changes in the brain

Rate of induction/recovery

21
Q

What do partial pressures of inhalational anaesthetics in the brain influence?

A

Depth of anaesthesia

22
Q

Side effects of inhalational anaesthesia

A

Cardiovascular depression
- myocardial depression (negative inotropy)
- peripheral vasodilation
- depression of tissue autoregulation
- CNS depression (reduction in sympathetic tone)

Sensitisation of myocardium to arrhythmogenic effects of catecholamines

Respiratory depression

Trigger malignant hyperthermia

Hepatoxic (metabolised in the liver)

23
Q

Nitrou oxide properties

A

Highly insoluble in blood -> rapid induction

2nd gas effect - takes other gases with it e.g. pulls oxygen out of brain and blood at the end of anaesthesia

Diffusion in gas filled spaces/cavities - don’t use in large animals

24
Q

Effects of nitrous oxide

A

Analgesic (NMDA receptors, opioid system)

Anaesthetic: MAC > 100% so cannot give enough of it, can only be used in combniation

No absorption with activated charcoal

25
Q

Carrier gases for inhalational anaesthesia

A

Oxygen
Air
Nitrous oxide

26
Q

Hazards of inhalational anaesthesia

A

Occupational hazard
- mutagenesis/teratogenesis
- miscarriage, congenital malformations
- kidney/liver damage

Threshold limits
- need good ventilation

Scavenging of exhaust gas
- active: central vacuum
- passive: hoses to connect machine with atmosphere
- activated charcoal: absorption

Pollution of the environment
- greenhouse gases

27
Q

Delivery of inhalant anaesthesia

A

Initial (5-10min)
- high fresh gas flow (4l/min)
- vaporizer setting 2-3%

Second phase
- reduction in FGF to min required (often around 1l/min)
- adjust depending on depth

End
- Just switch it off
- exchange gas in system (empty rebreathing bag)

28
Q

Ways of administering injectable anaesthetic agents

A

Constant delivery of agent (TIVA)

Repeated bolus of anaesthetic agent

29
Q

Constant delivery of injectable anaesthetic agent

A

Total intravenous anaesthesia (TIVA)

Advantages:
- stable plane
- plasma concentration in constant range

Disadvantages:
- Accurate delivery
- Equipment needed

30
Q

Repeated bolus of injectable anaesthetic agents

A

Advantages:
- does not require syringe driver

Disadvantages:
- Unstable plane of anaesthesia
- Dosing interval and regime variable
- Repeated over-/underdosing

31
Q

Propofol for maintenance

A

CRI: 0.1-0.5mg/kg/min

Slower metabolism in cats

Toxic effects of benzylalcohol (if with preservatives)

32
Q

Alfaxalone for anaesthetic maintenance

A

CRI: 0.05-0.2mg/kg/min

Ventilatory support might be necessary

No accumulation

Recovery can be rough

33
Q

Ketamine for anaesthetic maintenance

A

Cumulative

Active metabolite

Sub-anaesthetic doses peri-operatively for analgesia

10-20 mcg/kg/min (lower if concious)

34
Q

Drug combinations to achieve anaesthetic triad

A

Alpha 2 agonist

Peripheral/central muscle relaxants

Anaesthetic agents or adjuvants

35
Q

‘Triple drip’ for large animals

A

Muscle relaxant (guaifenesin, midazolam)

Sedative (alpha 2 agonist)

Anaesthetic (ketamine)

36
Q

Partial intravenous anaesthesia (PIVA)

A

Combination of inhalational anaesthesia and injectable anaesthetics for maintenance of anaesthesia

37
Q

Agents used to partial intravenous anaesthesia

A

Opioids (fentanyl CRI)

Ketamine

Liddocaine

Alpha 2 agonists (ideally short acting)

Principles of anaesthesia (9 decks)

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