Local Anaesthetic and Anaesthesia

Question 1

Function of local anaesthetics

How do they work?

Answer 1

Reversible local inhibition of nociception
-can target specific nerves or areas of skin

Pass across lipid membrane => become ionised
Binds to Na channels => blocks Na entry, inhibits AP
Preferentially blocks small diameter, myelinated, high frequency fibres

Question 2

Contraindications of local anaesthetics

Answer 2

Past allergic reactions
FHx of malignant hyperthermia
Inflammed, infected tissue - unlikely to work due to low pH of tissue

Question 3

What would you need to consider with the dosages

Answer 3

Dose varies by LA
Concentration of solution expressed as %

1% = 10mg/ml

Max dose calculations need patient weight and LA conc

Question 4

When would you use adrenaline with LA

When would you not use adrenaline

Answer 4

Improved local hemostasis by VC => prolongs LA effect by reducing tissue absorption
Works instantly

High doses => increased ischemia, tachycardia, HTN, arrythmia risk

CI

• end arteries (fingers)
• caution in poor peripheral circulation (Raynauds, diabetes, PVD)

Question 5

Equipment needed

Answer 5

Sterile gloves, drapes
Alcohol wipe
Sharps bin
Gauze
Needle
LA solution

Question 6

Preprocedure for LA use

Answer 6

Consent after explaining risks and benefits
CI check

Aim to numb skin, prevent pain but they may still feel movement, pressure

LA administration will be painful but quickly settles

Question 7

Method for LA injections

Answer 7

Draw up LA, remove air bubbles
Clean skin using alcohol wipe
Insert needle through skin and dermis into subcut
Aspirate to check location of needle, you don’t want to see any blood

Inject LA slowly
Advance needle to cover larger area within subcut space

Question 8

Postprocedure for LA use

Answer 8

Monitor for signs of LA toxicity

Inform patient of likely duration of action and advice to protect area until sensation returns

Question 9

Types of LA

Answer 9

Local infiltration => LA injected directly around site to create area of numbness

Ring block => LA injected around digital NVB of fingers

Nerve block => LA injected around specific nerve

Topical LA => cream on skin under adhesive dressing

Bier Block => IV regional anaesthesia of Prilocaine

Eye drops => used in opthalmology for emergencies and surgery

Question 10

Potential complications of LA

Answer 10

Pain

Allergic reaction, anaphylaxis

LA toxicity

• CNS toxicity
• CV toxicity

Methaemoglobinemia esp with prolicaine

Question 11

Signs of CNS toxicity

Answer 11

Decreased inhibitory neuron activity

• perioral parasthesia
• tinnitus
• visual changes
• lightheaded, dizzy
• tongue numb, metal taste
• seizures
• anxiety, confusion

If severe
-inhibition of cardioresp centers in medulla => resp failure, arrythmias, cardiac arrest, hypotension, coma

Question 12

Management of LA toxicity

Answer 12

Remove toxic agent
Call senior/anaesthetists
ABCDE assessment
-O2 and vetilation if needed
-BZ for seizures

Lipid emulsion antidote bolus and infusion

• 1.5mL/kg IV over 1 min
• Infusion 0.25ml/kg/min

Question 13

Signs of CV toxicity

Answer 13

Decreased myocardial activity, contractility

• bradycardia
• hypotension
• arrythmias
• cardiac arrest

Question 14

Signs of neuromuscular toxicity

Answer 14

Decreased muscle excitability, myotinic effects

Question 15

Signs of methaemoglobinaemia

Management

Answer 15

Cyanosis
High RR
Confusion, LOC
Dizzy

ABC management with O2
IV methylene blue antidote
-1-2ml/kg over 5mins