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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
Q

NMDA receptors

A

Xenon
Nitrous oxide
Ketamine

  • inhibit excitatory NMDA receptors
  • block excitation via glutamate
26
Q

Anaesthesia effect on the reticular formation

A

Anaesthesia blocks connectivity

Depresses:

  • thalamus - less sensory processing
  • hippocampus - impaired memory processing
  • brainstem - impaired resp and CVS function
27
Q

Anaesthetic effect on spinal cord

A

Depresses the dorsal horn (afferent spinothalamic pathway) - causing analgesia

Depresses motor neuronal activity

28
Q

Intravenous general anaesthetics

A

Propofol - rapid
Barbiturates (rapid)
Ketamine - slower

29
Q

When are intravenous general anaesthetics used?

A

For induction

Can be used as sole anaesthetic in TIVA - total intravenous anaesthesia

30
Q

How does general intravenous anaesthetic work?

A

All target GABA except ketamine which potentials NMDA

  • affects RAS
31
Q

How is intravenous anaesthetic potency measured ?

A

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
Q

When is local anaesthetic used ?

A 
Dentistry 
Obstetrics - child birth 
Regional surgery - patient is awake 
Post op - wound pain 
Chronic pain management
33
Q

Local anaesthetic examples

A

Lidocaine
Bupivacaine
Ropivacaine
Procaine

34
Q

Characteristics of local anaesthetics

A
  • 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
Q

Structure of local anaesthetic

A

Aromatic ring and amine linked via:

  • Ester bond - short duration of action
  • amide bond - longer duration of action
36
Q

Bupivacaine mechanism of action

A

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
Q

Lidocaine and bupivacaine

A

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
Q

Regional anaesthesia features

A
  • Blocks nerve so patient remains awake and selectively anaesthetises a part of the body
  • local anaesthetic or opioid used
39
Q

Nerves of the upper extremity

A

Interscalene
Supraclavicular
Infraclavicular
Axillary

40
Q

Nerves of the lower extremity

A

Femoral
Popliteal
Sciatic nerve
Saphenous

41
Q

General anaesthesia side effects

A
  • 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
Q

Local and regional anaesthetic side effects

A

Na+ channel blockers - inappropriate dose can cause asystole

CPT (23 decks)

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