General anaesthetics Flashcards
1
Q
What is required by an anaesthetic
A
- abolition of sensation
- abolition of pain
- ‘Triad of General Anaesthesia’
- unconsciousness
- analgesia
- muscle relaxation
- multiple drugs
2
Q
What are the stages of anaesthesia
A
- Stage I - analgesia
a) conscious, drowsy, antinociception, amnesia - stage 2 - excitement
a) Loss of consciousness but delirium, irregular cardiorespiration, apnea, spasticity, gagging, vomiting - Stage 3 - anaesthesia
a) regular respiration, loss of reflex and muscle tone - Stage 4 - medullary paralysis
a) depression of cardiorespiration, death
3
Q
What are the characteristics of an idea GA
A
- stable
- potent
- non-toxic
- controllable
- rapid on and off
- adjustable
- minimal cardio-depressant
- minimal respiratory depressant
- non-irritant
- xenon is ideal - why not use it?- Cost – too expensive
4
Q
What are the types of anaesthetics
A
- Inhalation - gasses or vapours
2. Intravenous
5
Q
Describe inhalation method
A
- controllable
- rapid blood-gas exchange
- usually halogenated ethers or hydrocarbons e.g. halothane, isoflurane
- stable, potent
6
Q
Describe intravenous method
A
- injections
- very rapid, short acting
- Induction of anaesthesia
7
Q
What are common anaesthetic procedures
A
- to produce rapid unconsciousness with an intravenous injection of a rapid onset, short acting barbiturate (thiopentone).
- to maintain unconsciousness with one of more inhalation agents (e.g. N2O and Halothane).
- This can be supplemented with an intravenous analgesic agent (e.g. fentanyl)
- produce muscle paralysis with a neuromuscular blocking agent such as the nicotinic antagonist tubocurarine.
8
Q
What drug can be used to provide rapid unconsciousness.
A
- I.V. with rapid, short acting agent e.g. thiopental
9
Q
What is used to maintain unconsciousness.
A
- inhalation agents e.g. N2O and Halothane
10
Q
What is used to supplement analgesia
A
- I.V. e.g. fentanyl.
11
Q
What is used to induce paralysis
A
- neuromuscular block e.g. suxamethonium.
12
Q
What is used as a pre-op anaesthetic
A
- Pre-op (sedation, anxiolysis, amnesia).
2. Midazolam and other benzodiazepines.
13
Q
What are some common inhalation anaesthetics
A
- N2O - rapid, low potency, in combination, obstetrics, analgesic- Used for stage 1 but difficult to maintain
- Volatile halogenated hydrocarbons - Widely used but some side effects especially cardiovascular & nausea
14
Q
Give examples of halogenated hydrocarbons
A
- Halothane - vet use, developing countries, hepatotoxic, hangover
- Enflurane - fast on and off, lower toxicity, epileptogenic
- Halothane and enflurane are not clinically used because of side effects
- Halothane used in developing countries as very cheap
- Isoflurane - non-epileptogenic, cardio and respiratory effects
- Desflurane - v. fast on and off, cardio effects
- Sevoflurane – v. fast, potent, maybe hepatotoxic
- ether (and derivatives), cyclopropane, chloroform- largely obsolete, many side effects, explosive
15
Q
Give examples of common intravenous anaesthetics
A
- Thiopental - barbiturate, very fast on (20 s) and off (10-15 min), non-analgesic, respiratory depression, hangover
- etomidate- rapid metabolism, low cardio-respiratory effects, involuntary muscle jerks
- Propofol - v. rapid metabolism, induction and maintenance, day surgery, most widely used
- Ketamine - slow onset, analgesic, dissociative, hallucinogenic, hypertensive and bradycardic, children & veterinary
- thought children don’t experience hallucinogenic and dissociative affects
- Midazolam and other benzodiazepines- pre-op
