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CPT > L12 - Anaesthetics > Flashcards

L12 - Anaesthetics Flashcards

1
Q

2 types of anaesthesia

A

General - patient in unconscious

Local - conscious and regional - blocks compartment

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2
Q

Types of general anaesthetic

A

Inhaled (volatile)

Intravenous

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3
Q

Conscious sedation

A

Use of small amounts of anaesthetic or benzodiazepines to produce a sleepy like state

  • maintain verbal contact but feel comfortable
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4
Q

Stages of anaesthesia

A
  1. Premedication - patients feels drowsy on ward
  2. Induction - normally intravenous but may be inhaled
  3. Intraoperative analgesia - opioid
  4. Muscle paralysis - to facilitate intubation, ventilation and stillness
  5. Maintenance
  6. Reverse muscle paralysis and recovery - postoperative analgesia
  7. Provisions for postoperative nausea and vomiting
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5
Q

How does inhaled anaesthesia work?

A

A percentage of the volatile anaesthetic is in the vaporiser

Fresh air goes in and anaesthetic comes out

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6
Q

What is volatile anaesthesia normally made from?

A

Fluoridated hydrocarbons

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7
Q

What is the most potent anaesthetic?

A

Phenol

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8
Q

Xenon

A

high concentration - noble gas but good anaesthetic as neuroprotective

Used in children

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9
Q

Guedel’s sign stage 1

A
  • Analgesia phase
  • conscious
  • normal muscle tone
  • Normal breathing
  • slight eye movement
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10
Q

Stage 2 guedel’s sign

A 
Excitement phase 
Unconscious 
Paradoxical excitement 
Normal to markedly increased muscle tone 
Erratic breathing 
Moderate eye movements 
Delirium can occur
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11
Q

Stage 3 Guedel’s sign

A

Surgical anaesthesia (4 levels)

Muscle tone:

  • slightly relaxed - normal breathing - slight eye movements
  • moderately relaxed - slower breathing - no eye movements
  • markedly relaxed - even slower breathing - no eye movements
  • markedly relaxed - just the odd breath - no eye movements
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12
Q

Stage 4 Geudel’s sign

A

Respiratory paralysis
Flaccid muscle tone - need intubation
No eye movements

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13
Q

Glabellar reflex

A

Tap eyes/ forehead but no response

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14
Q

Anaesthesia

A

Analgesia
Hypnosis - loss of consciousness
Depression of spinal reflexes
Muscles relaxation

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15
Q

Patient response to increasing conc of anaesthetic

A
  1. Memory loss
  2. Loss of consciousness (shortly after)
  3. Immobility
  4. Loss of cardiovascular response
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16
Q

MAC

A

Minimum alveolar concentration

  • alveolar concentration at 1 atm at which 50% of subjects fail to move to surgical stimulus
  • at equilibrium, the alveolar concentration = the concentration at the spinal cord
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17
Q

Why can’t potency be measured for volatile anaesthetic

A

At room temperature, the anaesthetic would vaporise

18
Q

Blood: gas partition

A

in the blood- measure solubility

  • low value = fast induction and recovery
19
Q

Oil: gas partition

A
  • In fat
  • determines potency and slow accumulation
  • high solubility = high potency
  • as most targets are surrounded by fat e.g. phospholipid membranes
20
Q

Factors increasing MAC

A
  • Age - infants
  • Hyperthermia - has less likely to dissolve and more likely to evaporate
  • pregnancy
  • alcoholism
  • central stimulants
21
Q

Factors decreasing MAC

A

Age - elderly
Hypothermia
Other anaesthetics and sedatives
Opioids (MAC sparring)

22
Q

Nitrous oxide

A
  • analgesic - anaesthetic effect via NMDA
  • MAC sparring
  • lower side effects
  • if nitrous oxide used, less anaesthetic can be given as better carrier than air
23
Q

GABA A receptors

A

Majority of anaesthetics use GABA receptors (major inhibitory transmitter)

  • ligand gated Cl- channel causing Cl- influx and hyperpolarisation
24
Q

GABA activity

A

Anxiolysis
Sedation
Anaesthesia

25
NMDA receptors
Xenon Nitrous oxide Ketamine - inhibit excitatory NMDA receptors - block excitation via glutamate
26
Anaesthesia effect on the reticular formation
Anaesthesia blocks connectivity Depresses: - thalamus - less sensory processing - hippocampus - impaired memory processing - brainstem - impaired resp and CVS function
27
Anaesthetic effect on spinal cord
Depresses the dorsal horn (afferent spinothalamic pathway) - causing analgesia Depresses motor neuronal activity
28
Intravenous general anaesthetics
Propofol - rapid Barbiturates (rapid) Ketamine - slower
29
When are intravenous general anaesthetics used?
For induction | Can be used as sole anaesthetic in TIVA - total intravenous anaesthesia
30
How does general intravenous anaesthetic work?
All target GABA except ketamine which potentials NMDA - affects RAS
31
How is intravenous anaesthetic potency measured ?
Plasma conc to achieve a specific end point - e,g. Loss of eyelash reflex - mixed anaesthesia = bolus to the end point then switch to volatile - can mix and match depending on side effects - TIVA - defined PK value based algorithm to infuse at a rate to maintain set point, prices by a bolus
32
When is local anaesthetic used ?
``` Dentistry Obstetrics - child birth Regional surgery - patient is awake Post op - wound pain Chronic pain management ```
33
Local anaesthetic examples
Lidocaine Bupivacaine Ropivacaine Procaine
34
Characteristics of local anaesthetics
- Lipid soluble - more potent - Lower pKa - faster time of onset - Chemically linked by ester or amide bond - plasma is full of esterases therefore quickly metabolised and short duration of action - protein binding - higher will increase the duration of action
35
Structure of local anaesthetic
Aromatic ring and amine linked via: - Ester bond - short duration of action - amide bond - longer duration of action
36
Bupivacaine mechanism of action
Infuse into wound Binds to voltage gated Na+ channels inside Prevents Na+ influx Decreases depolarisation- blocks response to pain Block small myelinated (afferent) nerves therefore nociceptors and sympathetic block Use dependent block - higher activity, the more depolarisation
37
Lidocaine and bupivacaine
Bupivacaine is more soluble therefore more potent It acts longer as it is more protein bound Both have amide linker so last longer than procaine which has an Easter linker
38
Regional anaesthesia features
- Blocks nerve so patient remains awake and selectively anaesthetises a part of the body - local anaesthetic or opioid used
39
Nerves of the upper extremity
Interscalene Supraclavicular Infraclavicular Axillary
40
Nerves of the lower extremity
Femoral Popliteal Sciatic nerve Saphenous
41
General anaesthesia side effects
- post operative nausea and vomiting - hypotension - post operative cognitive dysfunction - 65+ yrs old with long standing anaesthesia e.g. hallucinations + confusion - chest infection - as not coughing or ambulating
42
Local and regional anaesthetic side effects
Na+ channel blockers - inappropriate dose can cause asystole

CPT (23 decks)

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