BASIC - ANAESTHESIA

Question 1

Definition of local anaesthetics?

Answer 1

o Any technique to induce the absence of sensation in a specific part of the body
o Topical or local administration

Question 2

Mechanism of local anaesthetics?

Answer 2

o Block transmission of nerve impulse transiently
o Inhibit Na channels in axon preventing the transmission of nerve impulses
o Sensory information blocked at site of application and does not reach brain

Question 3

Types of local anaesthetics? What are they joined by?

Answer 3

o Composed of two groups
 Lipid-soluble hydrophobic aromatic group
 Charged, hydrophilic amide group
o Joined by either:
 Ester link
• Procaine, amethocaine (Ametop), cocaine, benzocaine, tetracaine
 Amide link (most common)
• Lignocaine, bupivacaine (longer-acting), levobupivacaine, ropivacaine, mepicaine, prilocaine

Question 4

Examples of long-acting anaesthetics?

Answer 4

 Bupivacaine, levobupivacaine, ropivacaine

Question 5

Examples of short-acting anaesthetics?

Answer 5

 Prilocaine, lignocaine, cocaine

Question 6

Administration of local anaesthetics?

Answer 6

o	Topical – EMLA, Ametop
o	Mucosal – ENT procedures
o	Tissue infiltration
o	Peripheral nerve block
o	Plexus block
o	Epidural
o	Spinal

Question 7

Common doses of lidocaine, bupivacaine, prilocaine, ametop? With adrenaline?

Answer 7

o Lignocaine (3mg/kg) with adrenaline (7mg/kg)
o Bupivacaine/Levobupivacaine (2mg/kg) with adrenaline (2mg/kg)
o Prilocaine (6mg/kg) with adrenaline (9mg/kg)
o Tetracaine/Amethocaine (each tube 1.5g sufficient for 6x5cm)

Question 8

Calculate number of mls of bupivacaine 0.25% safe for 60kg woman?

Answer 8

 60kgx2mg/kg = 120mg
 0.25% means 2.5mg/ml
 120/2.5 = 48ml maximum of bupivacaine

Question 9

Definition of LA toxicity?

Answer 9

 Occurs when too much LA enters circulation

Question 10

Presentation of LA toxicity?

Answer 10

 Light-headedness, dizziness drowsiness
 Tingling around lips, fingers or generalised
 Metallic taste, tinnitus, blurred vision
 Confusion, convulsions and coma
 Bradycardia, hypotension, cardiovascular collapse

Question 11

Management of LA toxicity?

Answer 11

 Discontinue injection
 Call for help
 ABCDE – 100% O2, maintain airway
 IV access
 Control seizures – IV midazolam/diazepam, propofol
 Consider use of Intralipid as per AAGBI guidelines: reduces concentration of free local anaesthetic

Question 12

Uses of spinal/epidural anaesthesia?

Answer 12

 Anaesthesia for operations to lower half of body
• Obstetrics (C-sections)
• Orthopaedics (hip/knee replacement)
• General surgery, urology, gynaecology
 Analgesia (epidural, for intra-operative and up to 72 hours post-operative analgesia)
• No respiratory distress so advantage over opioids

Question 13

Properties of epidural anaesthesia?

Answer 13

• LA +/- opioid via epidural catheter
• Slower onset 15-30 mins
• Effect reliant on catheter position
• Less motor-block
• Duration of anaesthesia up to 72 hours

Question 14

Position of epidural anaesthesia?

Answer 14

 Can be done at any level, risky if above L1

Question 15

Position of spinal anaesthesia?

Answer 15

 Spinal block can go L2-S2
 Made most often L4/5, L3/4, L2/3
 Chose lowest level possible to minimise spinal cord damage

Question 16

Properties of spinal anaesthesia?

Answer 16

• Single shot injection of small volume (~2/3mls LA +/- opioid) into CSF
• Rapid onset (5-10mins)
• Predictable and reliable
• Dense block, particularly motor
• Duration of anaesthesia 2-3 hours

Question 17

Anatomy - when does spinal cord end? When does subarachnoid space end? When does epidural space end?

Answer 17

o Spinal cord ends L1 in adults
o Subarachnoid space ends S1 in adults
o Epidural space ends at sacrococcygeal hiatus