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Anaesthesiology > Local > Flashcards

Local Flashcards

1
Q

Name the 2 classes of local anaesthesia and examples

A

•Amides: lignocaine, bupivocaine
• Esters: cocaine

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2
Q

Compare lignocaine vs bupivocaine (5)

A

Lignocaine: rapid onset, short/moderate duration, rapid tissue penetration, amide bond, less potent and toxic to CNS, less protein binding
Bupivocaine: slower onset, long acting, moderate tissue penetration, amide bond, potent and toxic to CVS (refractory Vfib), more protein binding

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3
Q

Name 2 local side effects/ complications of local anaesthesia

A

• neurotoxic (transient paraesthesia, mild motor weak)
• myotoxic (necrosis)

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4
Q

Name the CNS adverse effects/ complications of local anaesthesia (4)

A

• Initial phase: circum-oral paraesthesia, tinnitus, confusion
• excitatory phase: convulsions
• depressive phase: decreased consciousness, coma, respiratory arrest
Also restlessness, tremor, agitation.
Especially lignocaine! Dose dependant.

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5
Q

Name the CVS adverse effects/ complications of local anaesthesia (3)

A

• Initial phase: hypertension, tachycardia
• intermediary: myocardial depression, decreased co, hypotension
• terminal: vasodilation, severe hypotension, bradycardia, arrhythmia (asystole, vf) refractory V fib
Especially bupivocaine!

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6
Q

Dose of lignocaine for local anaesthesia? And max

A

4 mg/ kg

Max 3-4 mg/ kg without adrenaline, 7 mg with

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7
Q

Toxic Dose bupivocaine for local anaesthesia?

A

2 mg/ kg

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8
Q

What is the chemical structure of local anaesthetics? (3)

A

• Liphophilic phenol ring (highly lipid soluble = potent = decreased onset action )
• amide or ester bridge
• hydrophilic chain

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9
Q

Name 4 amide local anaesthetics

A

• lignocaine
• bupivacaine
• ropivacaine
• levobupivacaine
Prilocaine

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10
Q

Name 4 ester local anaesthetics

A

•Cocaine
• PABA esters
• procaine
• chloroprocaine

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11
Q

Where are local anaesthetics metabolised? (2)

A

• Amides: liver
• esters: pseudocholinesterase in blood (faster and more reliable metabolism)

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12
Q

Name 6 chemical and physical characteristics of local anaesthetics that influence their action

A

• Increased lipid soluble = more potent but slow onset action
• Pka far from normal ph= slow onset
• increased protein binding = longer duration action
• isomerism- L = increased duration, potency, decreased toxicity
• spinal faster than peripheral
• nerve anatomy: diameter, myelinated or not, active

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13
Q

Name 3 physico-chemical properties of lignocaine and how they affect its action

A

• low lipid solubility = low potency
.Pka close to normal (7.9) = faster onset
• protein binding low so won’t last long

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14
Q

Name 3 physico-chemical properties of bupivacaine levo-bupiva and ropivacaine and how they affect its action and onset

A

• High lipid solubility = potent
.Pka far from Normal = slow onset
• High protein binding = long acting

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15
Q

Name 4 side effects cocaine as local anaesthetic

A

•Euphoria paranoia (block reuptake dopamine)
• seizures
• hypertension (intense vasoconstriction) (indirect sympathomimetic, release and block reuptake of na)
• tachycardia

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16
Q

Use of cocaine as local anaesthetic?

A

ENT especially nose due to intense vasoconstriction

17
Q

Prilocaine use?

A

Emla cream: eutetic mixture of local anaesthetic
Added to lignocaine in equal quantities to change melting point. Give skin analgesia within 60 min.
Numb skin for about 2-3h

18
Q

Prilocaine side effect?

A

Methaemoglobinaemia
Don’t use in newborns!

19
Q

What is active metabolite of lignocaine?

A

Monoethylglycinexilidide (megx)
Additive to CNS side effects

20
Q

What is added to spinal bupivacaine and why?

A

80 mg (8 %) glucose or dextrose
Increase baricity (density) of bupivacaine. Heavier than CSF so gravitate to lower spinal regions, smaller dose for denser block.
“Hyperbaric solution”

21
Q

Why would adrenaline be added to local anaesthesia? (3)

A

Vasoconstrictor.
• Decreased absorption of local anaesthetic
• increased safe dose and decrease toxicity
• increased duration action

22
Q

Why would opioids be added to local anaesthesia?

A

Morphine, fentanyl, sufentanil
• increased duration of action of spinal

23
Q

Why would alpha 2 agonists be added to local anaesthesia?

A

Clonidine , dexmedetomidine
• denser sensory block
• prolonged duration action

24
Q

How mix lignocaine?

A

If 1%= 1 g per 100 ml
1000 mg in 100 ml
10 mg per ml

Just add a 0.

25
Q

How mix bupivacaine?

A

0.5% =0,5 g in 100 ml
500 mg in 100 ml
5 mg /ml

Move comma 1 left

26
Q

How calculate dose local anaesthetics for patient?

A

Dose agent x weight = dose patient may receive
Dose patient may receive ÷ mg / kg of agent in vial = dose official

27
Q

Name the 4 sites in order that have increased incidence toxicity from local anaesthesia due to increased absorption

A

• Intercostal
• caudal
• epidural
• brachial plexus

28
Q

Ropivacaine dose? (2)

A

• Epidural and post-op: 0,2% 6-15 ml / h
• surgery: 0,75 - 1% up to 12 ml bolus
Local 2 mg/kg (slightly less toxic than bupiv but otherwise very similar)

29
Q

Treatment of CVS toxicity due to local anaesthetic? (3)

A

V fib: bUpivacaine
Intralipid!!
or Bretilium (not available - antiarrythmic class 3, block release noradrenaline) or K channel opener (pinacidil, bimakalim- improve av conduction but myocardial depression ) (can cause coronary steal in IHD - depression)

30
Q

Treatment of CNS toxicity due to local anaesthetic? (3)

A

Convulsions: lignocaine options:
• BenzO
• thiopentone most effective in theatre
• propofol best!

31
Q

Local anaesthetics work on which channels?

A

Sodium channel blockers

32
Q

What can be used as local instead of bupivacaine to decrease CVS side effects?

A

• Ropivacaine (lower lipid solubility)
• levo-bupivacaine

33
Q

Adverse effect emla cream (prilocaine)

A

Methaemoglobinaemia
(Contraindicated in neonates)

34
Q

Name 4 early signs CNS last

A

• Tinnitus, auditory changes
• perioral numbness
• agitation, confusion, dysphoria
• dizziness, drowsiness,
• metallic taste
• dysarthria ( slurred speech)

35
Q

Name 4 late signs CNS last

A

• Seizures
• respiratory arrest
• decreased consciousness
• coma

36
Q

What colour is Intralipid?

A

White liquid with blue label

Anaesthesiology (24 decks)

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