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Module 9- Respiration > 1/8 General Anaesthesia > Flashcards

1/8 General Anaesthesia Flashcards

1
Q

Name two main general anaesthetic targets and describe how they work.

A

GABA receptor: chloride channel, when open it allows Ca2+ into the cell causing hyperpolarization –> has inhibitory action
NMDA receptor: excitatory amino acid receptor, allows sodium and Ca2+ into cell, ketamine and nitrous oxide will antagonize the receptor (blocking etc.)

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2
Q

Name some other potential targets of general anaesthetic.

A

Two-pore domain K+ channels
Glycine receptors
Na+ channels

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3
Q

What is the overal mechanism of general anaesthetics?

A

Decrease in neurotransmission in the CNS –> loss of consciousness

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4
Q

What is anaesthetsia?

A

Loss of feeling

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5
Q

What is affected by general anaesthesia?

A

The whole body

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6
Q

What is affected by local anaesthesia?

A

Affects part to which it is applied (blocks local sodium channels to prevent excitation)

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7
Q

What is general anaesthesia?

A

A state of reversible unconsciousness with reduced sensitivity and response to stimuli.

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8
Q

What are the three required components needed to achieve general anaesthesia?

A

Unconsciousness
Analgesia
Muscle relaxation

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9
Q

Why do we use anaesthesia in animals?

A

To preform painful surgical/diagnostic procedures
To minimise patient suffering
To reduce risk to the vet and other individuals
To facilitate the procedure by immobilising the patient

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10
Q

Anaesthesia is typically acheived using more than one drug, name the three different categories of drugs used.

A

Premedicant drugs
Induction drugs
Maintenance durgs

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11
Q

What are premedicant drugs?

A

Drugs given prior to a general anaesthetic

Typically a sedative-opioid combination

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12
Q

What are induction drugs?

A

Usually IV agents

Used to achieve the transition from consciousness to unconsciousness

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13
Q

What are maintenance drugs?

A

Usually inhalents

Drugs used to maintain the anaesthetic state

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14
Q

What are the stages of anesthesia?

A

Stage 1: voluntary movement
Stage 2: Involuntary movement/excitation
Stage 3: Surgical anesthesia
Stage 4: Medullary paralysis (death)

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15
Q

What stages of anesthesia do modern drugs aim to avoid?

A

Stage 1 and 2

Almost all general anesthetics have a narrow therapeutic index (careful- want to avoid stage 4 too)

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16
Q

What system do you want to target with anesthetics?

A

CNS

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17
Q

What are the routes of administration for anesthetics?

A

Need to get drug to site of action quickly- crossing cell barriers
- IV, inhalation (other routes too slow)

Lipid solubility a key characteristics in allow drug across cell membranes and around body.

18
Q

What makes the lungs a good drug delivery route?

A

Vast surface area, well perfused with blood supply

Can be used in systemic administration or locally.

19
Q

What characteristics are important in a drug to allow for transport throughout the body (lipid theory)?

A

Receptor/protein targets

Lipid solubility

20
Q

What are the advantages and disadvantages when using IV anesthetic agents for induction of anesthesia?

A

Advantages:

  • rapid smooth induction (minimal excitment)
  • rapid protection of the airways
  • no environmental pollution

Disadvantages:
- IV access required

21
Q

What is it called and what is required when using IV anesthetics for maintenance?

A

Total intravenous anesthesia (TIVA)- meaning that the entire anesthesia process is achieved through IV

Suitable pharmacokinetics are required

22
Q

What are inhalation anesthetic agents typically used for?

A

Maintenance and occasionally to induce anaesthesia

23
Q

What are the advantages and disadvantages of using inhalation agents for maintenance?

A

Advantage:

  • delivery/elimination depends on ventilation
  • rapid adjustment of anesthetic depth (breath-by-breath)

Disadvantages:

  • equipment required (endotracheal tube, carrier gas (O2), vaporiser, breathing system etc.)
  • environmental pollution
24
Q

What are the advantages and disadvantages to using inhalation anesthetics for induction?

A

Advantages:
- IV access can be secured after induction

Disadvantages:

  • Environmental pollution
  • Takes longer and delay in securing airway can be issue
25
Q

Pharmacokinetics of inhalational agents:

What drug properties determine speed of induction/recovery?

A

Blood:gas partition coefficient

  • a low b:g gives rapid induction/recovery
  • indicating whether drug wants to move from alveolar air into blood

Oil:gas partition coefficient
- high o:g gives high potency

26
Q

Pharmacokinetics of inhalational agents:

What physiological factors determine speed of induction/recovery?

A

Alveolar ventilation rate

Cardiac output

27
Q

How does metabolism affect anesthetic agent?

A

Liver- extent depends on agent
Potential toxic metabolites can be produced
- risk to patient and staff

28
Q

How is an inhaled anesthetic agent eliminated?

A

Exhaled- determines duration of action

29
Q

What factors affect the duration of action of IV agent?

A

Redistribution- after being administered, the drug will eventually be redistributed throughout the body, often times in the fat and therefore won’t have any affect on the CNS any more.

Metabolism- liver/elsewhere

30
Q

What effects do general anesthetics have on the nervous system?

A 
Inhibit conduction of action potentials
Inhibit transmission at synapses:
- decrease transmitter release, action of transmitter, and excitability of post-synaptic cell
Brain regions:
- reticular formation 
- hippocampus
31
Q

What effects do general anesthetics have on CVS and respiration?

A

Decrease contractility of isolated heart preparations

Whole animal:

  • effects on cardiac output and blood pressure
  • potentially arrhythmogenic
  • decrease respiration
  • increase arterial pCO2
32
Q

List some IV anesthetic agents used in vet med.

A 
Propofol
Steroid anesthetics (alfaxalone)
Dissociative agents (ketamine)
33
Q

What are some characteristics of propofol?

A

Oil at room temp
Enhance GABA transmission
Short acting, smooth and rapid recovery

Suitable for TIVA

34
Q

What condition may enhance propofols pharmacological effects?

A

hypoproteinaemia

35
Q

What situations do not prolong propofols pharmacological effects?

A

If repeated IV doses administered in dogs (good for mainenance)
In dogs with hepatic dysfunction

prolonged effect may be seen in cats

36
Q

What are some characteristics of Alfaxalone?

A

Enhances inhibitory action of GABA
High therapeutic index
Rapid induction and metabolism
Suitable for TIVA

37
Q

How does Ketamine work?

A

Interrupts NMDA receptors

38
Q

What are some of the side effects of ketamine and what can be done to avoid them?

A

Increased muscle tone
Eyes open/slow nystagmus
Less profound CVS and respiratory depression
Hallucinations

Administer with another drug (sedative)

39
Q

What is Total Intravenous Anesthesia (TIVA)?

A

Anesthesia maintained by intermittent boluses or continuous infusion of an IV agent

40
Q

Why would you use TIVA?

A

Easy to administer
Pharmacokinetics are known
Inhalation anesthetics may be unsuitable for some
Avoids risk to people administering drugs (environmental pollution)

41
Q

List some inhalation anesthetics.

A

Halogenated compounds:

  • halothane
  • isoflurane
  • sevoflurane
  • desflurane

Nitrous oxide

42
Q

What is the minimum alveolar concentration (MAC)?

A

Describes the minimum alveolar concentration at which 50% of patients will not respond to a particular stimulus.

Compares the potency of different inhalation anesthetics.
Relates to the percentage of drug in the inspired air.

Module 9- Respiration (6 decks)

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