Local anaesthetic

Question 1

What is analgesia

Answer 1

Absence of sensibility to pain, particularly the relief of pain without loss of consciousness (paracetamol/ibuprofen)

Question 2

What is anaesthesia

Answer 2

Partial or complete loss of sensation, with or without loss of consciousness, a result of disease, injury or administration of an anaesthetic agent, usually by injection or inhalation

Question 3

What is local anaesthesia

Answer 3

A temporary loss of sensation in one small area of the body caused by special drugs called anaesthetics. Patient is conscious, but without feeling in the areas of the body treated with anaesthetic

Question 4

What is paresthesia

Answer 4

Abnormal sensation - spontaneous or evoked

Question 5

What is dysesthesia

Answer 5

Unpleasant abnormal sensation, spontaneous or evoked

Question 6

What is hypoesthesia

Answer 6

Reduced perception of stimulus or decreased sensation

Question 7

What is the mechanism of action of local anaesthetic

Answer 7

• Sodium channels open when a signal passes down an axon
• The local anaesthetic is unionised
• Local anaesthetic blinds to the bottom of the receptor, Na+ ions can not move through so the message is not passed

Question 8

What is the specific receptor theory

Answer 8

• Local anaesthetic drug binds to specific receptors within the sodium channel producing physical obstruction to entry of sodium ions
• It binds to a closed gate and maintain it in the closed position
• This leads to a reversible block of action potential propagation

Question 9

What are the 2 categories of LA

Answer 9

Amino amides and amino esters

Question 10

Describe amino amides

Answer 10

• Metabolised by the liver - used regularly everyday
• Lidocaine - manufacturers advise caution in patients with liver disease and several renal dysfunction

Question 11

Describe amino esters

Answer 11

Metabolised by pseudochlorinesterase in the blood to form para-aminobenzoic acid - can cause an allergic reaction therefore not as widely used

Question 12

What are ideal properties of local anaesthetic

Answer 12

• Specific and reversible action
• Non irritant, no permanent damage to tissues
• No allergic reaction or systemic toxicity
• Rapid onset of action
• Potent
• Stable in solution
• Not expensive

Question 13

What are different types of local anaesthetic

Answer 13

Esters + amides

Question 14

What are the characteristics of lidocaine

Answer 14

• Most common
• Very effective

Question 15

What are the characteristics of prilocaine

Answer 15

• Most common
• Very effective

Question 16

What are the characteristics of articaine

Answer 16

• Better diffusion
• Fast onset
• Hydrolysed quickly

Question 17

What are the characteristics of mepivacaine

Answer 17

• Plain
• Very short acting

Question 18

What are the characteristics of bupivacaine

Answer 18

• Slow onset but long duration - 2 hours pulpal anaesthesia

Question 19

Describe vasoconstrictors

Answer 19

• Decrease the blood flow
• Lowers aesthetic concentration in blood so decreases risk of toxicity
• Increases length of action of local anaesthetic
• Decreases amount of bleeding at operation site

Question 20

Describe the role of adrenaline and epinephrine

Answer 20

Care in ischaemic heart disease (inadequate blood supply)

Question 21

Describe the role of felypressin

Answer 21

Avoid in pregnancy

Question 22

Describe safety procedures for the operator

Answer 22

• Don’t rush
• Dont re-sheath or re-use
• Discard of sharps appropriately

Question 23

Describe safety procedures for the patient

Answer 23

• Soft tissue trauma
• Nerve trauma
• Intravascular injection

Question 24

What are some causes of failure of local anaesthetic

Answer 24

Operator dependent:
- Choice of technique and solution
- Poor technique
Patient dependent:
- Anatomical
- Pathological
- Psychological