Lecture 12 - Local Anaesthetics

Question 1

Onset of action?

Answer 1

proportional to the amount of free base at physiological pH i.e. the pKa

Question 2

Protein binding in anaesthetics?

Answer 2

proportional to duration of action - Bupivacaine > Ropivacaine > Lignocaine > Prilocaine

Question 3

Metabolism of different anaesthetic types?

Answer 3

esters - plasma cholinesterases; amides - liver metabolism therefore dependent of liver blood flow

Question 4

Lignocaine?

Answer 4

amide, low lipid solub., low pka (fast onset), low protein binding (short duration), ideal for short surgical procedures

Question 5

Bupivacaine?

Answer 5

amide, high lipid soluble, high pka (slower onset), high protein binding (longer duration), ideal for nerve blocks for analgesia

Question 6

Cocaine?

Answer 6

ester, topical to nose for vasoconstriction

Question 7

Prilocaine?

Answer 7

amide, safest agent, used in Bier’s block

Question 8

Ropivacaine?

Answer 8

amide, slow onset, long acting, all round similar to bupivacaine but les cardiac toxicity

Question 9

L.A toxicity?

Answer 9

allergic reactions (rare w amides), dose dependent neuro and cardiac toxicity (CC:CNS ratio for cardiac saftey), typically occurs due to accidental IV infusion

Question 10

Maximum safe dose - lignocaine?

Answer 10

5mg/kg, 7 w adrenaline

Question 11

Maximum safe dose - Bupivacaine?

Answer 11

2mg/kg, 3 with adrenaline

Question 12

Prilocaine?

Answer 12

600mg

Question 13

Topical to skin use?

Answer 13

emla (eutectic mixture of LAs), useful for children IV

Question 14

Topical to mucous membrane?

Answer 14

cocaine, lignocaine spray; instrumentation of nose, outh or pharynx

Question 15

Soft tissue infiltration?

Answer 15

minor interventions (moles) and post operative pain

Question 16

Peripheral nerve blocK?

Answer 16

infiltrate specific nerve e.g. brachial plexus for arm surgery, mixed nerves have smalelr sensory parts affected quicker

Question 17

Spinal anaesthesia?

Answer 17

below L2, profound m and s blockade, can perform knee or hip replacements or C sections

Question 18

Epidural anaesthesia

Answer 18

through epidural space rather than spine, can be left in for days of use rather than hours, option for motor blockade or not