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Systems: Specialities AB > Anaesthetics: Principles and Pharmacology > Flashcards

Anaesthetics: Principles and Pharmacology Flashcards

1
Q

What does anaesthesia mean?

A

Without feeling/ perception

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2
Q

What is general anaesthesia?

A
  • An anaesthesia which produces insensibility in the whole body, usually causing unconsciousness
  • Caused be centrally acting drugs
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3
Q

What is regional anaesthesia?

A
  • An anaesthesia which produces insensibility in an area or region of the body
  • Caused by local anaesthetics applied to nerves supplying the relevant area
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4
Q

What is local anaesthesia?

A
  • An anaesthesia which produces insensibility in only the relevant part of the body
  • Caused by local anaesthetic applied directly to the tissues
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5
Q

What types of drugs have been developed to be used in anaesthesia?

A
  • Inhalational anaesthetics
  • Intravenous anaesthetics
  • Muscle relaxants
  • Local anaesthetics
  • Analgesics
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6
Q

What advancements have been made in anaesthetic techniques and equipment?

A
  • Tracheal intubation
  • Ventilation
  • Fluid therapy
  • Regional anaesthesia
  • Monitoring
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7
Q

What is the triad of anaesthesia?

A
  • Analgesia
  • Hypnosis
  • Relaxation
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8
Q

What agents assist in relaxation during anaesthesia?

A
  • Muscle relaxants
  • Local anaesthetics
  • General anaesthetic agents
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9
Q

What agents assist in analgesia during anaesthesia?

A
  • Local anaesthetics
  • Opiates
  • (General anaesthetic agents)
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10
Q

What agents assist in hypnosis during anaesthesia?

A
  • General anaesthetic agents

- (Opiates)

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11
Q

What is meant by balanced anaesthesia?

A
  • Using multiple agents to do different jobs
  • Doses are titrated separately and are therefore more accurate to requirements
  • Helps to prevent overdose
  • Allows flexibility
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12
Q

What problems does polypharmacy present?

A

Increased chance of drug reactions/ allergies

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13
Q

What problems does muscle relaxation present?

A
  • Requirement for artificial ventilation

- Means of airway control

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14
Q

What problems does separation of relaxation and hypnosis present?

A

Risk of awareness

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15
Q

How do general anaesthetic agents work?

A
  • Interfere with the neuronal ion channels
  • Hyperpolarise the neurones making them less likely to fire
  • Inhalational agents dissolve in the membranes to have a direct physical effect
  • IV agents work by allosteric binding to GABA receptors to open chloride channels
  • Leads to loss of cerebral function from most complex to most primitive
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16
Q

What care is required when a patient is under general?

A
  • Airway management
  • They have an impairment of respiratory function and control of their breathing
  • Cardiovascular monitoring
  • General care of an unconscious patient
  • Long drawn out resus
17
Q

What are the features of IV anaesthesia?

A

Rapid onset of LOC
-1 arm to brain circulation

Rapid recovery

  • Due to the disappearance of the drug from circulation
  • Redistribution vs metabolism
18
Q

How does the concentration of IV agent differ in tissue over time?

A
  • Decreases in blood and vessel rich organs
  • Rapid increase then slower decrease in viscera
  • Slow increase and decrease in muscle
  • Slow increase in fat
19
Q

What are inhalational agents composed of?

A

Halogenated hydrocarbons

20
Q

How are inhalational anaesthetics administered?

A
  • At induction given at high levels to create concentration gradients (lungs>blood>brain)
  • They therefore cross the alveolar BM easily
  • The arterial concentration equates closely to alveolar partial pressure
21
Q

What is MAC?

A
  • Minimum alveolar concentration
  • The concentration of drug required in the alveoli to produce anaesthesia
  • Low number= high potency
22
Q

What are the features of inhalational anaesthetics?

A

Induction
-Slow

Maintenance
-Can be used to prolong duration and therefore very flexible

Awakening

  • Stop inhalational administration
  • Washout using gas agent minus the anaesthetic to reverse concentration gradient
23
Q

What sequences of anaesthesia can be used?

A
  • Inhalational induction and maintenance
  • IV induction and maintenance

Most common
-IV induction and inhalational maintenance

24
Q

What IV agents are used?

A
  • Propofol

- Opiate (remifentanil)

25
Q

What effect does GA have on the CVS centrally?

A

Depresses cardiovascular centre

  • Reduces sympathetic outflow
  • Negative inotropic/chronotropic effect on heart
  • Reduced vasoconstrictor tone leading to vasodilation
26
Q

What effect does GA have on the CVS directly?

A
  • Negatively inotrophic
  • Vasodilation leading to decreased peripheral resistance
  • Venodilation leading to decreased venous return and cardiac output
27
Q

What effect do all anaesthetic agents have on the respiratory system?

A

They are respiratory depressants so they:

  • Reduce hypoxic and hypercarbic drive
  • Decrease tidal volume and increase rate

Paralyse cilia

Decrease FRC

  • Lower lung volumes
  • VQ mismatch
28
Q

What are the indications for muscle relaxants?

A
  • Ventilation and intubated patients
  • When immobility is essential
  • Body cavity surgery
29
Q

What problems can arise when using muscle relaxants?

A
  • Awareness
  • Incomplete reversal can lead to airway obstruction and ventilator insufficiency in the immediate post op period
  • Dependence on airway and ventilator support
30
Q

Why is intraoperative analgesia used?

A
  • Prevention of arousal
  • Opiates contribute to hypnotic effect of GA
  • Suppression of reflex responses to painful stimuli e.g. tachycardia , hypertension
31
Q

Why may regional anaesthetic be used intraoperatively?

A

It has no direct sedative effects but can allow for lighter GA by eliminated painful surgical stimuli

32
Q

What physiological effects do local and regional analgesia have?

A
  • Retention of awareness / consciousness
  • Lack of global effects of GA
  • Derangement of CVS physiology proportional to size of anaesthetised area
  • Relative sparing of respiratory function
33
Q

What is the limiting factor in the used of locals?

A

Toxicity

34
Q

Why is toxicity high in locals?

A
  • IV injection given
  • Tissue absorption > rate of metabolism = high plasma levels leading to vasoconstriction which in turn reduces absorption
35
Q

What does toxicity of locals depend on?

A
  • Dose
  • Rate of absorption (site dependent)
  • Patient weight
  • Drug used
36
Q

What are some signs and symptoms of local anaesthetic toxicity?

A
  • Circumoral and lingual numbness and tingling
  • Light-headedness
  • Tinnitus, visual disturbances
  • Muscular twitching
  • Drowsiness
  • Cardiovascular depression
  • Convulsions
  • Coma
  • Cardiorespiratory arrest
37
Q

How do local differential blocks work?

A

Due to the differential penetration into different nerve types
-Myelinated, thick fibres are relatively spared
-Motor fibres spared relatively preventing paralysis
Pain fibres blocked easily

38
Q

What are all effects of regional anaesthetics including neuraxial blocks due to?

A

Sympathectomy

39
Q

What physiological effects do neuraxial blocks have on the respiratory system?

A
  • Inspiratory function relatively spared
  • Expiratory function relatively impaired (cough dependent on abdominal muscle function)
  • Decrease in FRC
  • Increased V/Q mismatch

Systems: Specialities AB (19 decks)

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