Local anaesthetics

Question 1

What are the main types of regional anaesthetics? (2)

Answer 1

• regional peripheral nerve blocks (PNB)
• and neuraxial anesthesia (e.g., spinal and epidural).

Question 2

Contraindications for use of local anaesthesia

Answer 2

Contraindications

• Absolute contraindications:
  
  • Allergies to local anesthetic drugs
• Relative contraindications
  
  • Active inflammation/infection at the injection site
  • Neurological deficits in the area of distribution

Question 3

What does local anaesthesia do?

Answer 3

Local anesthesia reversibly blocks nerve endings and pain conduction near the site of administration (limited area)

Question 4

What are the main types of local anaesthetics? (2)

Answer 4

• topical
• infiltrative

Question 5

What’s the procedure in topical anesthesia?

Answer 5

Topical anesthesia__:

application of gels, ointments, sprays, or patches → anesthetic agent gets absorbed through the skin or mucosa

Question 6

What’s the procedure in infiltration anaesthesia?

Answer 6

Infiltration anesthesia:

injection of local anaesthetic directly into a painful area or one to be operated on

Question 7

Why we should not use local anaesthetics on inflamed tissues?

Answer 7

Effect of local anaesthetics will be very limited on inflamed tissues/abscess

This is due to the acidic environment -> protonation of anaesthetic agent -> it cannot then resolve in the lipids well -> spread of anaesthetic drug to the site of action is then limited

Question 8

Where is (in general) local anaesthetic injected into?

Answer 8

specific nerve or nerve bundle

Question 9

What’s a relative contraindication to local anaesthesia?

Answer 9

Coagulopathy

Question 10

How to identify a specific nerve that we want to use the peripheral block (local anaesthesia) on?

Answer 10

• USS -> needle guided
• nerve stimulation test -> needle emiting eletrical impulses -> stimulation of a nerve -> motor response

Question 11

Two approaches to injecting local anaesthetic drugs

Answer 11

• single shot technique
• catheter with continuous infusion -> if severe post-op pain is expected e.g. knee joint replacement

Question 12

What is epidural anaesthesia?

What agents are injected?

Answer 12

Local anaesthetics with or without opioids are injected into epidural space -> act on spinal nerve root

Question 13

Indications for epidural anaesthesia

Answer 13

• surgeries on lower bodies: knee replacement, hernia, CS, appendectomy, prostate and bladder surgeries,
• labour
• perioperative use (as target analgesia)
• chronic pain management -> spinal stenosis, disc herniation

Question 14

What are absolute contraindications for epidurals?

Answer 14

Epidurals promote circulatory decompensation (their effect on SNS), therefore:

• uncorrected hypovolemia
• increased ICP
• infection at the puncture site

Question 15

What are relative contraindications for epidurals?

Answer 15

• coagulopathy
• spinal deformities
• sepsis, systemic bacteraemia -> as they may spread into intrathecal space
• neurological deficit (disc prolapse, MS, paraplegic syndrome)

Question 16

Site of injection in epidural anaesthesia

What would the needle go?

Answer 16

Epidural:

• can be performed at any vertebral level -> cervical, thoracic, lumbar
• injected into epidural space (between ligamentum flavum and dura matter)

Question 17

Complications of epidural

Answer 17

• Pain at the injection site
• Dural puncture
• Spinal-epidural hematoma
• Epidural abscess
• Hypotension

Question 18

Hypotension following epidural

• Pathophysiology
• Clinical features
• Diagnosis
• Management

Answer 18

Hypotension (after epidural)

Pathophysiology: SNS blockage -> vasodilation and decreased venous return -> reduced cardiac output

Clinical features: dizziness, lightheadedness, nausea, hypotension -> shortly after induction of anaesthesia

Diagnosis: clinical

Management: IV fluids + small doses of epinephrine

Question 19

Where is spinal anaesthesia injected into?

-general components of spinal analgesia

Answer 19

Local anaesthetic with or without opioids with or without alpha adrenergic agonist

Injected into CSF in the lumbar spine -> acts on the spinal cord

Question 20

What is the spinal analgesia used for?

Answer 20

variety of lower body surgeries (lower extremity, pelvic, abdominal, perineal)

Question 21

Injection site in spinal analgesia

Where the needle is inserted into?

Answer 21

• usually below L2 -> to avoid damage to spinal cord
• needle inserted into subarachnoid space -> between arachnoid and pia matter

Question 22

Possible complications of spinal/epidural anaesthesia

Answer 22

• headache - occipital (dura irritated)
• haematoma -> may compress the nerves -> neural dysfunction
• sepsis / aseptic meningitis
• SNS block -> hypovoluemia, hypotension, vasodilation and bradycardia
• urinary retention -> as bladder is atonic after sacral block
  *

Question 23

Overall mechanism of action of local anaesthetics

Answer 23

MoA: block the sensation of pain in the region where they are administrated

Reversible block of sodium channels of the nerve fibres -> conduction of nerve impulses is inhibited

Question 24

Division of local anaesthetic agents (chemical)

Answer 24

• amide group
• ester group

Question 25

Name few agents that belong to the amide group in local anaesthetics

Answer 25

The amide group (lidocaine, prilocaine, mepivacaine, etc.)

*amide group is preferred as it is clinically safer

Question 26

Two examples of local anaesthetic drugs belonging to ester group

Answer 26

Ester group: procaine, tetracaine

Question 27

Complications of local anaesthetic use

Answer 27

• allergy: anaphylaxis or delayed (blister rash)
• vasovagal syncope
• systemic toxicity (in OD or if gets into blood vessel): seizure, metallic taste in the mouth, perioral paraesthesia
• cardiovascular system: bradycardia, AV block, decreased cardiac contractility
• methemoglobinaemia (as local anaesthetics may oxidise haemoglobin to methaemoglobin) -> grey, mottled skin, cyanosis, fatigue