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Pharmocolgy > P11: General Anaesthetics > Flashcards

P11: General Anaesthetics Flashcards

1
Q

What are the 3 main effects of GA

A

Sedative
Hypnotic
Analgesic

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2
Q

What are sedatives, hypnotics and analgesics

A
  • Sedative - compound that reduces irritability or excitation
  • Hypnotic - compound that induces sleep
  • Analgesic - compound that reduces pain sensation without loss of consciousness
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3
Q

Name typical GAs in use

A 
Desfluorane
sevofluorane 
Fentanyl
Propofol
Thiopentone
Isofluorane
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4
Q

What are the 4 stages of Anaesthesia

A
  1. Analgesia Stage
  2. Excitement Stage
  3. Surgical Anaesthesia Stage
  4. Medullary Depression Stage
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5
Q

What happens in the 3rd plane of the Analgesia Stage

A

Complete analgesia and amnesia, disorientation, vertigo/ataxia, increased respisation, BP and HR

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6
Q

What happens in the excitement stage of anaesthesia

A

Loss of consciousness to automatic breathing

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7
Q

What can happen to respiration in the surgical anaesthesia stage

A

Automatic respiration to respiratory paralysis

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8
Q

What happens in the first plane of surgical anaesthesia

A

Cessation of eye movements, loss of swallowing reflex

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9
Q

What happens in the second plane of surgical anaesthesia

A

Laryngeal reflex lost, tear secretion increases, regular deep breathing, response to skin stimulation lost

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10
Q

What happens in the third plane of surgical anaesthesia

A

Progressive intercostal paralysis, diaphragmatic respiration persists, pupils dilated and light reflex lost

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11
Q

What happens in the fourth plane of surgical anaesthesia

A

Complete intercostal and diaphragmatic paralysis (apnea)

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12
Q

What happens in the medullary depression stage

A

Stoppage of respiration to death - medullary paralysis = respiratory depression, vasomotor collapse and death

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13
Q

What can be used to prevent many of the changes found in the stages of anaesthesia

A

Neuromuscular blockers

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14
Q

What is the lipid theory of GA mechanisms

A
  • Relationship between lipid solubility and anaesthetic potency
  • Anaesthesia occur if solubilisation of the GA in the lipid bilayer causes a redistribution in membrane lateral pressure
  • Ion channels in particular are highly sensitive to membrane lateral pressure
  • Increased pressure prevents channels opening limiting neural excitation
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15
Q

What is the protein theory of GA mechanisms

A
  • Specific targeting of CNS receptors

- GABA, Glycine, 5-HT and ionotropic glutamate receptors and voltage gated ion channels

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16
Q

What are the 2 major classes of GA and give examples of each

A

Intravenous - propofol, thiopnetone

Inhalation -

  • Gaseous - Nitrous Oxide
  • Voltaile liquids - desfluorane, sevofluorane, isofluorane, halothane
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17
Q

Define the Minimum Alveolar Concentration (MAC)

A

Steady state partial pressure (%) of an inhalational agent required for immobility of 50% of subjects exposed to a noxious stimulus (surgical incision)

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18
Q

What is the Minimum Alveolar Concentration (MAC) used for

A
  • Provides a means to compare the potency of the various inhalational agents
  • Serves as a guide to determining dose
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19
Q

50% of the MAC dose (MAC awake) gives what response from patients

A

50% of patients can be woken

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20
Q

100% of the MAC (MAC) dose gives what response from patients

A

50% of patients wont move at surgical incision

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21
Q

130% of the MAC dose (ED95) gives what response from patients

A

95% of patients will not move at surgical incision

22
Q

150-200% of the MAC dose (MAC-BAR) gives what response from patients

A

50% of patients have blocked autonomic responses

23
Q

Describe the characteristics of sevoluorane and its MAC value

A 
Rapid-acting
Volatile liquid anaesthetic
Non-irritant
Rapid recovery
MAC - 2.1%
NB - has largely replaced halothane
24
Q

Describe the side effects of sevofluorane

A
  • Can trigger malignant hyperthermia
  • Can increase intracranial pressure
  • Little effect on heart rhythm compared with other volatile anaesthetics
25
Q

Describe the mechanism of sevofluorane

A
  • Positive allosteric modulator of GABAa receptors
  • NMDA receptor antagonist
  • Potentiates glycine receptor activity
  • Inhibits nicotinic ACh and 5-HT3 receptors
26
Q

Describe the characteristics of isofluorane and its MAC value

A
  • Rapid-acting volatile liquid anaesthetic
  • Analgesic and Muscle relaxer
  • Usually used to maintain anaesthesia induced by other agents
    MAC - 1.15%
27
Q

What are the vascular effects produced by isofluorane

A
  • Increased incidence of coronary ischaemia
  • Heart rate can rise, particularly in younger patients
  • Systemic vascular resistance can decrease, reducing arterial pressure and cardiac output
28
Q

What are the potential side effects of isofluorane

A
  • Bronchial secretions = coughing and laryngospasm
  • Malignant hyperthermia
  • Post-operative cognitive dysfunction
29
Q

What type of anaesthetics are triggering factors for malignant hyperthermia

A

Most inhalational anaesthetics

30
Q

What is the first sign of malignant hyperthermia

A

Elevated CO2 production

31
Q

What is malignant hyperthermia characterised by

A
  • Hypermetabolism in skeletal musculature
  • Muscle rigidity
  • Muscle injury
  • Increased sympathetic nervous system activity
  • Hyperkalaemia
32
Q

How is malignant hyperthermia treated

A

Intravenous administration of dantrolene (suppresses exciation-contraction coupling in muscles) and supportive therapies (cooling, oxygen)

33
Q

What is the MAC of nitrous oxide

A

104% - would cause asphyxia

34
Q

Where is Nitrous oxide used

A

In combination with other anaesthetics - allows a reduction in dosage

Dental/obstetric preparation - entonox, a 50:50 mix with oxygen

35
Q

Describe the characteristics of nitrous oxide as an anaesthetic

A 
Inhaled and excreted via the lungs
Rapid onset of action
Good analgesic actions
Causes euphoria
No signicicant effects on respiration, liver, kidney or GI tract
36
Q

What are the most important injection anaesthetics

A

Propofol and thiopentone

37
Q

How is IV injection better than other injection routes

A

Faster, more stable and more reliable

38
Q

Describe the characteristics of propofol

A

Rapid onset and metabolism (hepatic)

N.B. Used for induction and maintenance of anaesthesia

39
Q

What is given with propofol

A

Given alongside lidocaine

Supplemented by nitrous oxide or opioids

40
Q

What are the side effects of Propofol

A
  • Respiratory Depression
  • Hypotension due to peripheral vasodilation
  • Induction of cardiac dysrhythmia
  • Can induce priapism in males
41
Q

Describe the characteristics of Thiopentone

A
  • Barbiturate with high lipid solubility
  • No analgesic properties
  • Smooth and rapid induction of anaesthesia
42
Q

Describe the mechanism of Propofol

A

Potentiates inhibitory GABAa receptor activity, slowing the channel-closing time and by blocking voltage gated sodium channels

43
Q

How is the action of thiopentone terminated

A

Terminated by redistribution into adipose tissue, rapid recovery from anaesthesia but produces prolonged sedation

44
Q

What are the side effects of thiopentone

A
  • Induces respiratory depression and hypotension
  • Lack of analgesic effects may result in increased SNS on recovery: tachycardia, sweating, tachypnea, raised BP, pupil dilation
  • Narrow margin between anaesthesia and cardiovascular depression
45
Q

Describe the mechanism of Thiopentone

A 
Binds GABAa
Nicotinic
5-HT3
Glycine receptors
(all ion channels)
46
Q

What kinds of pre-medications are used before GAs

A

Anti-emetics
Opioid analgesics
Benzodiazepines

47
Q

Give examples of anti-emetics and where the act

A

Droperidol, Domperidone (DA D2 antagonists)

Acts in CTZ in brainstem

48
Q

Give examples of Opioid analgesics used as pre-medications and what they do

A

Alfentanil, fentanyl, remifentanil

Pre-surgical pain relief, sedation, reduction in GA dosage

49
Q

Side effects of opioid analgesics as pre-medications

A

Respiratory and cardiovascular depression, emesis

50
Q

Give examples of Benzodiazepines used as pre-medications and what they do

A

Diazepam, lorazepam

Anxiolytic/sedative, amnesia, little respiratory and cardaic depression

Pharmocolgy (22 decks)

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