Local Flashcards
Name the 2 classes of local anaesthesia and examples
•Amides: lignocaine, bupivocaine
• Esters: cocaine
Compare lignocaine vs bupivocaine (5)
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
Name 2 local side effects/ complications of local anaesthesia
• neurotoxic (transient paraesthesia, mild motor weak)
• myotoxic (necrosis)
Name the CNS adverse effects/ complications of local anaesthesia (4)
• 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.
Name the CVS adverse effects/ complications of local anaesthesia (3)
• Initial phase: hypertension, tachycardia
• intermediary: myocardial depression, decreased co, hypotension
• terminal: vasodilation, severe hypotension, bradycardia, arrhythmia (asystole, vf) refractory V fib
Especially bupivocaine!
Dose of lignocaine for local anaesthesia? And max
4 mg/ kg
Max 3-4 mg/ kg without adrenaline, 7 mg with
Toxic Dose bupivocaine for local anaesthesia?
2 mg/ kg
What is the chemical structure of local anaesthetics? (3)
• Liphophilic phenol ring (highly lipid soluble = potent = decreased onset action )
• amide or ester bridge
• hydrophilic chain
Name 4 amide local anaesthetics
• lignocaine
• bupivacaine
• ropivacaine
• levobupivacaine
Prilocaine
Name 4 ester local anaesthetics
•Cocaine
• PABA esters
• procaine
• chloroprocaine
Where are local anaesthetics metabolised? (2)
• Amides: liver
• esters: pseudocholinesterase in blood (faster and more reliable metabolism)
Name 6 chemical and physical characteristics of local anaesthetics that influence their action
• 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
Name 3 physico-chemical properties of lignocaine and how they affect its action
• low lipid solubility = low potency
.Pka close to normal (7.9) = faster onset
• protein binding low so won’t last long
Name 3 physico-chemical properties of bupivacaine levo-bupiva and ropivacaine and how they affect its action and onset
• High lipid solubility = potent
.Pka far from Normal = slow onset
• High protein binding = long acting
Name 4 side effects cocaine as local anaesthetic
•Euphoria paranoia (block reuptake dopamine)
• seizures
• hypertension (intense vasoconstriction) (indirect sympathomimetic, release and block reuptake of na)
• tachycardia
Use of cocaine as local anaesthetic?
ENT especially nose due to intense vasoconstriction
Prilocaine use?
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
Prilocaine side effect?
Methaemoglobinaemia
Don’t use in newborns!
What is active metabolite of lignocaine?
Monoethylglycinexilidide (megx)
Additive to CNS side effects
What is added to spinal bupivacaine and why?
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”
Why would adrenaline be added to local anaesthesia? (3)
Vasoconstrictor.
• Decreased absorption of local anaesthetic
• increased safe dose and decrease toxicity
• increased duration action
Why would opioids be added to local anaesthesia?
Morphine, fentanyl, sufentanil
• increased duration of action of spinal
Why would alpha 2 agonists be added to local anaesthesia?
Clonidine , dexmedetomidine
• denser sensory block
• prolonged duration action
How mix lignocaine?
If 1%= 1 g per 100 ml
1000 mg in 100 ml
10 mg per ml
Just add a 0.
How mix bupivacaine?
0.5% =0,5 g in 100 ml
500 mg in 100 ml
5 mg /ml
Move comma 1 left
How calculate dose local anaesthetics for patient?
Dose agent x weight = dose patient may receive
Dose patient may receive ÷ mg / kg of agent in vial = dose official
Name the 4 sites in order that have increased incidence toxicity from local anaesthesia due to increased absorption
• Intercostal
• caudal
• epidural
• brachial plexus
Ropivacaine dose? (2)
• 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)
Treatment of CVS toxicity due to local anaesthetic? (3)
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)
Treatment of CNS toxicity due to local anaesthetic? (3)
Convulsions: lignocaine options:
• BenzO
• thiopentone most effective in theatre
• propofol best!
Local anaesthetics work on which channels?
Sodium channel blockers
What can be used as local instead of bupivacaine to decrease CVS side effects?
• Ropivacaine (lower lipid solubility)
• levo-bupivacaine
Adverse effect emla cream (prilocaine)
Methaemoglobinaemia
(Contraindicated in neonates)
Name 4 early signs CNS last
• Tinnitus, auditory changes
• perioral numbness
• agitation, confusion, dysphoria
• dizziness, drowsiness,
• metallic taste
• dysarthria ( slurred speech)
Name 4 late signs CNS last
• Seizures
• respiratory arrest
• decreased consciousness
• coma
What colour is Intralipid?
White liquid with blue label
