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MBBS II HNNS > L20 - General anaesthetics > Flashcards

L20 - General anaesthetics Flashcards

1
Q

Diff. between anaesthesia and analgesia?

A

 Anaesthesia = absence of all sensation (including pain, proprioception, etc.)

 Analgesia = no pain

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2
Q

Diff between general anesthesia and regional?

A

 General anaesthesia (GA) = loss of all sensation + CONSCIOUSNESS***

 Regional anaesthesia (RA) = absence of all sensation in one part of body (e.g. arm)

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3
Q

What constitutes ‘balanced anesthesia’?

A
  1. Unconsciousness (general anaesthesia)
  2. Analgesia (local anaesthesia)
  3. Muscle relaxation (neuromuscular blockers)
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4
Q

List the antedotes to NMB, Opioids and anesthetics?

A 
NMB = neostigmine
Opioid = naloxone
Anesthesia = NO ANTEDOTE
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5
Q

RECEPTOR THAT ANESTHETICS ACT ON?

A

GABA-A receptors at inhibitory synapses

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6
Q

List the modulators that act on GABA-A receptors at inhibitory synapses? (7) BBAAPPS

A

Barbiturate site: anesthetics (e.g. pentobarbital)
Benzodiazepine site

Anesthetic / alcohol site
Antagonists (e.g. bicuculine) at GABA site

Picrotoxin site: convulsants (e.g. TBPS)
Propofol site

Steroid site: anesthetics (e.g. alfaxalone)

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7
Q

Compare ED50 to LD50 in general anesthetics?

A

Very close

ED95 and LD05 overlap

Potentially highly lethal

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8
Q

Explain why general anesthetics can be lethal?

A

Too deeply asleep:

1) Tongue falls back > blocks nasal, oral passage to trachea > airway obstruction > suffocation
2) Lose protective airway reflex: e.g. vomitus goes to trachea, lungs > aspiration pneumonitis

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9
Q

Metabolism of Thiopentone (thiopental) at physiological pH and storage form?

A

Storage form in sodium bicarbonate solution = pH >10, ionized sulfide, highly water-soluble

Injection&raquo_space; Unstable non-ionized protonated sulfide&raquo_space; rapid conversion to highly lipid-soluble form at pH7.4 (readily crosses blood-brain barrier)

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10
Q

Describe the distribution of Thiopentone (thiopental) after injection?

A

Long terminal t1/2 (12h), but almost 0 concentration in brain at 5h due to uptake, fast redistribution to:

  • Vessel-rich group: concentration in highly perfused organs (e.g. brain): concentration drops FAST
  • Muscle, fat: concentration increase slowly over time

Even if terminal t1/2 is long, patient can wake up in 10 mins due to fast redistribution

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11
Q

Is Thiopental context-sensitive? How is level of thiopental maintained?

A

Highly context sensitive !!

Rapid redistribution, so constant injection is needed&raquo_space; leads to high accumulation

Time for CNS conc. to drop after repeated admin is much higher than expected

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12
Q

List some Cardiovascular, respiratory, CNS side effects of thiopental?

A
  • Mean arterial pressure decrease, HR increase
  • Respiration decrease
  • Cerebral blood flow and ICP decrease
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13
Q

What is the most commonly used general anesthetic? How is it stored?

A

Propofol In lipid solvent

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14
Q

Compare terminal t1/2 of propofol to thiopental? Compare context- sensitivity?

A

propofol = 4.8 hours, much shorter t1/2 than thiopental (12 hours)

Propofol = very little context sensitivity

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15
Q

Implication of little context sensitivity in propofol? WHy is it good?

A

infused safely for long surgeries

Predictable wake up time

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16
Q

What is the technique for injecting propofol?

A

Target controlled infusion (TCI):

Based on body weight, height

varies infusion rate over time to maintain plasma and Brain concentration within therapeutic window

17
Q

Effects of general anesthesia at increasing dosages?

A

Increasing dosage = increasing CNS depression:

Sedation > drowsiness > sleep > anesthesia

18
Q

List some Cardiovascular, respiratory, CNS side effects of propofol? Contraindication?

A

Systemic vascular resistance, HR, MAP decrease

Respiration decrease

Cerebral Blood flow decrease

Dont use in patients with heavy bleeding or low BP

19
Q

Advantage of Ketamine over propofol? Disadvantage?

A

Good for hypotensive patients because of increase in HR, Peripheral resistance, BP

Strong hallucination, strange nightmares&raquo_space; severe mental ADR

20
Q

Compare terminal t1/2 of ketamine to propofol and thiopental?

A

Much shorter than propofol

Ketamine t1/2 = 3 hours

21
Q

List some Cardiovascular, respiratory, CNS side effects of Ketamine?

A
  • INCREASE cardiac contractility, systemic vascular resistance and MAP (not decrease like propofol and thiopental)
  • Decrease resp.
22
Q

Advantage and disadvantage of Etomidate vs propofol?

A

Good for heart bypass surgery due to no increase in HR or MAP

Significant vomiting and nausea + CNS excitation

23
Q

List 5 IV general anesthetics?

A 
Thiopental 
Propofol 
Ketamine 
Etomidate 
Methohexital
24
Q

Give another preparation of general anesthetic apart from IV GA? Give 5 examples?

A

Inhaled general anaesthetics via vaporizers (not commonly used now)

halogenated ethers:

  • Not gases but very volatile liquids
  • E.g. desflurane, sevoflurane, isoflurane, Nitrous oxide, Xenon
25
Q

Overview of how variable bypass vaporizer works?

A

Carrier gas > Goes into vaporizing chamber > Bypass channel add set amount of bypass air > exit

26
Q

Define Minimum alveolar concentration?

A

Alveolar concentration of the inhaled agent

which prevents movement in response to a standard painful stimulation in 50% of subjects

27
Q

Relate age to Minimum alveolar concentration?

A

MAC target changes with age

Younger = harder to anesthesize, need higher conc.

Older = easier to anesthesize

28
Q

Relate MAC to Oil:gas partition coef. ?

A

Log is inversely proportional to log of oil:gas partition coefficient

Increase Oil:gas partition coef. = decrease in MAC: Meyer- Overton correlation

Potency is related to lipid solubility

29
Q

Define blood: gas partition coef.? What determines the wash-in?

A

Time taken for inhaled gas to reach alveolar and diffuse into circulation at alveolar capillary
» Higher the number, the less time taken to reach target concentration

Wash-in = Alveolar concentration (FA)/ inhaled concentration (FI), modulated by Ventilation rate
» Determines the onset of inhaled agent

30
Q

Relate ventilation rate to speed of inhaled gas wash-in?

A

Higher ventilation = increase speed of wash-in = faster build-up of inhaled gas in blood

31
Q

Relate cardiac output to speed of inhaled gas wash-in?

A

Increase cardiac output = DECREASE speed of wash in = slower build-up of inhaled gas in blood

32
Q

List the CVS side effects of inhaled anesthetics?

A

Decrease Cardiac output, systemic vascular resistance, MAP
Decrease respiration
Increase HR***

Similar to thiopental

33
Q

Describe the elimination rate of inhaled anesthetics?

A

Very slow metabolism, mostly remained unmetabolized

Mostly wake up by exhaling the agent to lower the plasma conc

MBBS II HNNS (57 decks)

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