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B33CNS > Anesthetics (Yvonne Mbaki) > Flashcards

Anesthetics (Yvonne Mbaki) Flashcards

1
Q

What is the definition of anesthesia?

A

Provision of insensibility to pain during surgical, obstetric, therapeutic and diagnostic procedures
Involves monitoring and restoration of homeostasis during the post-operative period

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2
Q

How do local anesthetics work?

A

Block generation and conduction of nerve impulses at local contact site, consciousness maintained

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3
Q

What examples are there of local anesthetic drugs?

A

Bupivacaine, lignocaine, ropivacaine

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4
Q

When / why are local anesthetics used?

A

Topical - nasal mucosa / wound margins
Infiltration - vicinity of peripheral nerve endings and major nerve trunks in dental practice
Regional - IV injection leading to numbing of a larger area of the body i.e. in child birth / labour

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5
Q

What is the mechanism of action of local anesthetics?

A

Equilibrium of charged and uncharged LA
The unchanged LA can penetrate the lipid membrane
One in the interstitial fluid of target cells the eqm shifts to charged LA
Charged LA cannot be effluxed from the cell.

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6
Q

How does general anesthetic work?

A

Alters the central neural processing
Readily reversible loss of consciousness with reduced response to pain stimuli and muscle tone
Divided into inhalation and intravenous general anesthetics

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7
Q

What are the ABC stages of anesthesia?

A

A Induction and inhalation or Iv agents used

B Maintenance mainly provided with volatile agents

C Recovery monitoring to assure recovery

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8
Q

What is the first stage in depth anesthesia?

A
  1. Analgesic stage
    Reduces corticol higher function, consciousness not lost but thoughts blurred, reflexes still present
    Smell and pain lost at the end of this stage
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9
Q

What is the second stage in depth analgesia?

A 
2. Excitement Stage 
Corticol inhibitory centres depressed
Increased muscle tone
Vomiting 
Temperature control lost (hypothalamus suppression)
a-rhythm of EEG desynchronized
Respiration increased/ irregular
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10
Q

What is the third stage of depth analgesia?

A 
3. Surgical Anesthesia stage
Slow synchronised EEG rhythms 
Regular, slow breathing
Medullary centres depressed and reflexes lost
Pupils dilated
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11
Q

What is the fourth stage of depth analgesia? (Undesirable)

A
  1. Medullary Paralysis Stage
    Loss of respiration
    EEG waves small/lost
    Death
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12
Q

What types of inhalation anesthesia is there?

A

Gas - nitrous oxide

Volatile liquids - halothane, enflurane, isoflurane, sevoflurane, desflurane

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13
Q

What types of intravenous anesthesia are there?

A 
Inducing agents 
Thiopental
Methohexitone/methohexital
Propofol 
Etomidate

Benzo’s
Diazepam, lorazepam, midazolam

Dissociative anesthesia
Ketamine

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14
Q

What factors provide the ideal inhalation anesthetics?

A 
Stable over a range of temperatures 
Not degraded by light 
Odorless (avoids a cough / irritant) 
Analgesic, anti-emetic and muscle relaxant properties 
Minimal respiratory depression
Minimal cardiovascular effects 
Excreted completely by respiratory system 
Not metabolised or no active metabolites
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15
Q

What is MAC?

A

Minimum alveolar concentration
Measures potency of inhalation analgesics
“Inhaled dose that prevents movement to a standard surgical stimulus in 50% of patients.”

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16
Q

What is the journey of an inhaled anesthetic?

A

Anesthetic gains access into the alveoli (‘windows to the brain’)
Partial pressure is important in driving anesthetic from the respiratory pathway to the brain
A steady state for maintenance of anesthesia is required and this is dependent on partial pressure of alveoli, blood and brain

(1. Alveoli, 2. Transport PP, 3. stable maintenance eqm)

17
Q

What is phase 1 of inhaled anaesthetic administration?

A

Eqm between gas present in functional residual capacity and anesthetic is achieved

18
Q

What is phase 2 of inhaled anaesthetic administration?

A

Uptake and distribution; blood-gas coefficient

19
Q

What are the consequences of high blood-gas partition coefficient?

A

Greater amount of anesthetic must be dissolved in arterial blood in order to equilibrate with the alveoli
e.g. halothane (low MAC - potent)

20
Q

What are the consequences of low bood-gas partition coefficient?

A

Minimal amount of anesthetic must be dissolved in arterial blood in order to equilibrate with the alveoli
e.g. nitrous oxide (high MAC - less potent)

21
Q

What is the relevance of the blood gas partition coefficient?

A

Influence speed of anesthetic induction where nitrous oxide quickly saturates blood but halothane induces anesthesia slowly and has a longer recovery time.

22
Q

What are the factors that affect uptake and distribution in inhaled anesthetics?

A

Blood-gas coefficient
Cardiac output
Alveolar to venous pressure

23
Q

What does a high cardiac output mean in relation to inhaled anesthetics, in comparison to a low cardiac output?

A

High cardiac output: faster removal of anesthetic from alveoli to peripheral tissues - slower access to the brain
Low cardiac output: slower removal of anaesthetic from alveoli to peripheral tissues - faster to gain access to the brain

Influences speed of anesthetic induction

24
Q

How is anesthetic transferred to peripheral tissues from arterial blood?

A

Due to a pressure gradient

25
Q

What happens the higher the concentration of anesthetic?

A

The greater the difference between alveolar (arterial) blood and venous - the higher the uptake and slower induction.

26
Q

What partial pressure must be maintained in surgical anesthesia phase?

A

Pa alveolar, Pa arterial, Pbr brain

27
Q

Which of halothane or nitrous oxide is eliminated from the body quicker?

A

Nitrous oxide eliminated quicker

28
Q

What is the relevance of an anesthetics oil/gas partition coefficient?

A

The lower the MAC the higher the oil/gas partition coefficient because the easier the anesthetic can penetrate to BBB as a more lipophillic drug.

29
Q

What is the journey of an intravenous anesthetic?

A

Once in blood stream some drug binds to plasma proteins and the rest remains free

Drug is transported initially through venous blood then systemic circulation, eventually gaining access to cerebral circulation

A partial pressure gradient permits entry of the anesthetic to the brain where it then exerts its effect

30
Q

What molecules cross the BBB the quickest?

A

Unbound, lipid soluble, unionized drug molecules

31
Q

What is the role and profile of Propofol?

A

INDUCTION
Short acting with onset of action of 30 secs plus rapid recovery
Reduces BP and intracranial pressure
Does not provide analgesia
Accompanied by excitatory phenomena; muscle twitching, yawning, hiccups etc
Some antiemetic effects post recovery

32
Q

What is the role and profile of Thiopental

A

INDUCTION
Fast acting within 1 minute
May cause apnoea, coughing, chest wall spasm, laryngospasm, bronchospasm
Better tolerated agents available

33
Q

What is the role and profile of Etomidate?

A

Hypnotic agent that induces anesthesia but not analgesia

Benefit - little to no effect on cardiovascular system so usually used for sufferers of cardiovascular dysfunction.

34
Q

What is the role and profile of Ketamine?

A

Patient is unconscious but appears awake; induces amnesia - dissociative anesthesia
Increases BP and cardiac output
Potent bronchodilator
Not favored in young adults due to induction of hallucinations

35
Q

What are the proposed mechanisms of general anesthetics?

A

Most activate inhibitory pathways such as GABAa or strychnine-sensitive glycine

Inhibit excitatory mechanisms such as 5HT3, neuronal nicotinic, glutamate NMDA/AMPA

36
Q

What happens to uncharged anesthetic molecules?

A

Concentrate in lipid membranes and cause membrane expansion

37
Q

What are the target sites for general anesthetic?

A

The reticular activating system; arousal, sleep and wakefulness

38
Q

Which medication can be given for practical anesthesia?

A

Premedication
Atropine to reduce secretions
BDZ for sedation

Fast induction
Thiopental IV

Maintain
Isoflurane Inhalation

Muscle relaxation
Neuromuscular blocking drug

Reduce pain
Analgesic opiate; also used post operative

B33CNS (20 decks)

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