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General Anaesthesia Flashcards

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1
Q

What is the primary purpose of General Anaesthetics?

A

To produce unconsciousness and a lack of responsiveness to all painful stimuli.

This includes the inhibition of sensory and autonomic reflexes.

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2
Q

What are the components of the triad associated with General Anaesthetics?

A
  • Hypnosis
  • Amnesia
  • Analgesia

These components are essential for effective anaesthesia.

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3
Q

What conditions do General Anaesthetics provide for medical interventions?

A

Conditions for interventions like surgery to take place; skeletal muscle relaxation.

This is crucial for performing surgical procedures safely.

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4
Q

What aspect of patient care is emphasized during the use of General Anaesthetics?

A

Control of physiology.

This includes monitoring and maintaining vital functions during anaesthesia.

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5
Q

What is an important consideration for patient safety during General Anaesthetic reversal?

A

Keep patients safe and alive upon GA reversal.

Reversal of anaesthesia must be managed carefully to ensure patient safety.

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6
Q

Balanced anaesthesia

A

pain relief + unconsciousness + inhibition of reflex

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7
Q

What is the relationship between blood solubility and onset of inhalant GA?

A

The higher the blood solubility, the slower the onset.

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8
Q

What is the purpose of Balanced Anaesthesia?

A

To ensure that induction is smooth and rapid, and that analgesia and muscle relaxation are adequate.

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9
Q

What types of drugs are used in General Anaesthesia (GA)?

A

Drugs are used in combinations, including inhalation anaesthetics and intravenous anaesthetics.

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10
Q

What are the most commonly used drugs in Balanced Anaesthesia?

A
  1. Short-acting barbiturates (for induction of anaesthesia)
  2. Neuromuscular blocking agents (for muscle relaxation)
  3. Opioids and nitrous oxide (for analgesia)
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11
Q

What is the classification of Inhalant GA?

A

volatile liquids and gases.

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12
Q

What are the volatile liquids used in Inhalant GA?

A

Halothane, Enflurane, Desflurane, Isoflurane, Sevoflurane

Halothane is classic

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13
Q

What true gas is used in Inhalant GA?

A

Nitrous oxide

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14
Q

What does Minimum Alveolar Concentration (MAC) indicate?

A

It is an index of inhalation anaesthetic potency; low MAC = high anaesthetic potency.

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15
Q

How is Minimum Alveolar Concentration (MAC) defined?

A

It is defined as the minimum concentration of drug in the alveolar air that will produce immobility in 50% of patients exposed to a painful stimulus.

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16
Q

Which inhaled GA has the highest MAC?

A

NO

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17
Q

Other factors affecting MAC

A

age, condition, concomitant administration of other drugs

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18
Q

What must an inhalation anaesthetic reach to produce therapeutic effects?

A

CNS concentration sufficient to suppress neuronal excitability.

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19
Q

What factors influence the concentration of anaesthetic in the blood?

A
  1. Concentration of anaesthetic in inspired air
  2. Solubility of GA
  3. Blood flow through lungs
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20
Q

What happens if any of the factors influencing anaesthetic concentration increase?

A

The rate of GA uptake into blood increases.

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21
Q

What determines the distribution of general anesthetics (GA)?

A

Distribution is determined by regional blood flow, which dictates which tissues receive GA.

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22
Q

Which tissues receive general anesthetics quickly after administration?

A

Brain, liver, lungs, heart, muscle, and gastrointestinal (GI) tissues.

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23
Q

How are inhalation anesthetics eliminated?

A

Inhalation anesthetics are eliminated almost entirely via the lungs with minimal hepatic metabolism.

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24
Q

Mode of elimination of inhaled GA?

A

Lungs as expired air with limited hepatic metabolism

factors determining uptake also determine elimination eg. blood flow rate to the brain

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25
Why do anesthetic levels in the brain drop rapidly when administration is stopped?
Because blood flow to the brain is the highest, leading to a rapid drop in anesthetic levels.
26
What should be noted about some anesthetic metabolites?
Some metabolites can be toxic.
27
What are examples of toxic metabolites from anesthetics?
Inorganic fluorides of isoflurane and enflurane are nephrotoxic; halothane is hepatotoxic.
28
What is Halothane?
First modern inhaled anaesthetic, standard for comparison
29
What are the properties of Halothane?
Volatile liquid, non-flammable and non-irritating
30
What is the potency of Halothane?
Potent (MAC 0.75%)
31
What is the rate of onset and recovery for Halothane?
Medium rate of onset and recovery
32
Does Halothane provide analgesia?
Little or no analgesia until unconsciousness supervenes
33
What effect does Halothane have on respiration?
Causes respiratory depression dose-dependently
34
How does Halothane affect blood pressure?
Decreases B.P. due to depression of cardiac output ## Footnote Bradycardia and arrhythmia may also occur leading to hypotension and dysrhythmia
35
What effect does Halothane have on skeletal muscle?
Relaxes skeletal muscle and potentiates skeletal muscle relaxants
36
What is a potential adverse effect of Halothane?
May lead to halothane-associated hepatitis
37
What is the smell of Isoflurane?
Isoflurane has a pungent smell.
38
What is the potency of Isoflurane?
Isoflurane is potent with a MAC of 1.4%.
39
What is the rate of onset and recovery for Isoflurane?
Isoflurane has a medium rate of onset and recovery.
40
How does Isoflurane compare to halothane?
Isoflurane is similar to halothane but with less hypotension and arrhythmia.
41
What effect does Isoflurane have on blood pressure?
Isoflurane decreases blood pressure mainly due to a decrease in systemic vascular resistance.
42
What is the potency of Sevoflurane?
Sevoflurane is potent with a MAC of 2%.
43
What is the rate of onset and recovery for Sevoflurane?
Sevoflurane has a more rapid rate of onset and recovery.
44
How is Sevoflurane metabolized?
Sevoflurane is metabolized in the liver to release inorganic fluoride, which is nephrotoxic.
45
What happens to Sevoflurane when exposed to carbon dioxide absorbents?
Sevoflurane becomes unstable when exposed to carbon dioxide absorbents in anaesthetic machines, degrading to a potentially nephrotoxic compound.
46
What is the state of Nitrous Oxide?
It is an odourless gas.
47
Is Nitrous Oxide flammable?
No, it is non-flammable.
48
What is the onset and recovery profile of Nitrous Oxide?
It has a rapid onset and recovery but lacks potency (MAC 105%).
49
What effects does Nitrous Oxide provide when used alone?
It provides analgesia and amnesia but not complete unconsciousness or surgical anaesthesia.
50
How is Nitrous Oxide used in General Anaesthesia (GA)?
Patients undergoing GA receive nitrous oxide to supplement the analgesic effects of the primary anaesthetic.
51
In what situations is Nitrous Oxide used alone?
It is used as an analgesic agent (e.g., dentistry, during delivery).
52
What is a major concern associated with Nitrous Oxide?
Postoperative nausea and vomiting.
53
What is an induction agent?
An induction agent is a substance that induces unconsciousness.
54
Does an induction agent keep you asleep for a long time?
No, it does not necessarily keep you asleep for very long!
55
What effect do most induction agents have on respiration?
Most agents depress respiration – you will need to take over ventilation of patients.
56
Can intravenous agents be used alone?
Yes, they may be used alone or to supplement the effects of inhalation agents.
57
What are the advantages of using inhaled and intravenous anaesthetics together?
1. Permit dosage of the inhalation agent to be reduced, and 2. Produce effects that cannot be achieved with an inhalation alone.
58
What is Thiopentone?
Thiopentone, also known as Sodium thiopental, is a barbiturate with extremely high lipid solubility.
59
How quickly does Thiopentone induce unconsciousness after IV administration?
Unconsciousness occurs 10-20 seconds after intravenous administration.
60
What is the duration of action for a single dose of Thiopentone?
The duration of action is ultra-short
61
What are the implications of liver cirrhosis on Thiopentone's action?
Liver cirrhosis can result in prolongation of clinical action due to slow elimination and large volume of distribution.
62
How is Thiopentone metabolized and excreted?
Thiopentone is extensively bound to plasma protein, with less than 1% excreted unchanged.
63
What is the mechanism of action for Thiopentone?
Thiopentone causes CNS depression by potentiating the action of the neurotransmitter GABA on the GABAA receptor-gated chloride ion channels.
64
What is Propofol?
The most common IV anaesthetic used in Singapore, ready made in injectable form, no need to re-constitute (unlike thiopentone).
65
How does the induction rate of Propofol compare to thiopentone?
Induction rate is similar to thiopentone, and recovery is more rapid (patients move sooner and feel better).
66
What are the uses of Propofol?
Used both for induction and maintenance.
67
What is the onset time for Propofol?
Rapid onset
68
What is the duration of action for Propofol?
Short duration of action because of rapid redistribution from brain to other tissues.
69
In what type of surgery is Propofol extensively used?
Extensively used in 'day surgery'.
70
What is required for extended effects of Propofol?
Needs continuous, low-dose infusion for extended effects.
71
What effect does Propofol have on postoperative vomiting?
Reduced postoperative vomiting (may be related to an anti-emetic action).
72
What cardiovascular effects occur during induction with Propofol?
Significant cardiovascular effect during induction (decrease in blood pressure and negative inotropic) – hypotension.
73
In which patients should Propofol be used with caution?
To be used with caution in elderly patients, patients with compromised cardiac function, and hypovolemic patients.
74
Which GA results in dissociative anaesthesia?
Ketamine
75
Effects of Ketamine
sedation, immobility, analgesia, amnesia ## Footnote rapid induction; responsiveness to pain lost
76
Where is ketamine metabolised?
liver ## Footnote excreted in urine and bile
77
Why is ketamine suited for continuous infusion without prolonging DOA?
Large Vd and rapid clearance
78
adverse effects of ketamine and how to reduce them?
unpleasant psychologic reactions during recovery ## Footnote premedicate with diazepam / midazolam anxiolytic
79
Why is ketamine used in 3rd world countries?
It is the only IV GA with analgesic property

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