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Locoregional anaesthesia Flashcards

1
Q

Uses of locoregional anaesthesia

A

Improves perioperative pain management

Decreases opioid consumption

Improves patient welfare (quicker recover, lesser side effects)

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2
Q

General pharamacology of local anaesthetics

A

Most are an aromatic lipophilic end, an intermediate ester or amide linkage, and a hydrophilic portion

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3
Q

Classifications of local anaesthetics

A

Amino-esters
- procaine
- chloroprocaine
- benzocaine
- tetracaine

Amino-amides
- prilocaine
- lidocaine
- mepivacaine
- bupivacaine
- ropivacaine

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4
Q

Mechanisms of action of local anaesthetics

A

Ion channel blockers

Usually interrupt inward Na+ currents through the voltage gated Na+ channels

This impedes depolarisation and consequently nerve excitation and conduction

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5
Q

Where is the binding site for local anaesthetics?

A

Located on the a-subunit of the Na+ channel pore and is accessible from the intracellular side

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6
Q

Amino-esters

A

Procaine

Benzocaine

Tetracaine

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7
Q

Procaine

A

Used to perform infiltrations and nerve blocks for short procedures e.g. disbudding

Quick onset

Brief duration (30-60min)

Might cause allergic reactions

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8
Q

Benzocaine

A

Exclusively for topical use and for fish anaesthesia in water

Fast acting

Short lasting

Methemoglobinaemia has been reported as a side effect

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9
Q

Tetracaine

A

Suitable for topical anaesthesia

Commonly used in ophthalmic preparations and creams for cutaneous application

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10
Q

Amino amides

A

Prilocaine

Lidocaine

Mepivacaine

Bupivacaine and levobupivacaine

Ropivacaine

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11
Q

Prilocaine

A

Most commonly used as a topical agent prior to IV catheterisation e.g. EMLA cream

Low systemic toxicity

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12
Q

Lidocaine

A

Most versatile an most widely used

Fast onset

Moderate duration

Relatively mild toxicity

Can be used for regional anaesthesia and CRIs

Anti-arrhythmic and intrinsic vasodilative properties, anti-inflammatory effects, prokinetic activity

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13
Q

Mepivacaine

A

Very similar to lidocaine

Duration of effect extends up to 2h

Commonly used for infiltration anaesthesia in various animal species

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14
Q

Bupivacaine and levobupivacaine

A

Highly lipophilic

Potency about 4x that of lidocaine

Long duration of action (4-8hr)

Slow onset (20-30mins)

Suitable for infiltrations, neuraxial use, and peripheral nerve blocks

Not used topically or IV due to high cardiotoxic potential

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15
Q

Ropivacaine

A

Chemically related to mepivacaine and bupivacaine

Same clinical use, onset, and duration as bupivacaine

Marginally shorter sensory blockade (up to 6h) and slightly lower degree of effect at similar potencies

Affects vascular tone - concentrations below 0.5% causes vasoconstriction, concentrations over 1% causes vasodilation

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16
Q

Techniques used for nerve blocks

A

Blind
- based on use of anatomical landmarks

Nerve stimulator guided
- for mixed peripheral nerves to identify sensor component

Ultrasound guided
- increasingly common

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17
Q

Adverse effects of local anaesthesia

A

Also block voltage dependent K+ and Ca2+ channels

Block Na+ channels in the brain and heart - neurotoxicity and cardiotoxicity

Neurotoxicity increases with lipid solubility and potency (BBB penetration). Depression, excitation, seizures

Cardiotoxicity increases with dosage and potency. Tachyarrhythmias e.g. ventricular tachycardia. However supraconvulsant doses of lidocaine profpoundly inhibit cardiac conduction resulting in bradyarrhthmias (prolonged PR and QRS intervals) - causes cardiac arrest at high doses

Methaemoglobinaemia is associated with prilocaine, procaine, lidocaine, and topical use of benzocaine. Neonates are predisposed to developing this due to red cell immaturity

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18
Q

Topical use of local anaesthesia

A

Application of drugs on intact skin or mucous membranes

Drug penetrates the stratum corneum of the epidermis or mucosal layers respectively

Most common forms are eye drops, oral sprays, creams for cutaneous use

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19
Q

Infiltrations of local anaesthetics

A

Commonly used for perioperative analgesia

Peri-incisional subcutaneous, periodontal, intratesticular etc. or more targeted injections in proximity to specific peripheral nerves

Intra-articular injections are commonly used especially prior to or after stifle surgeries

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20
Q

Peripheral nerve blocks

A

Used for dental blocks
- infra-orbital
- maxillary
- mandibular
- retrobulbar

Brachial plexus block to desensitise the thoracic limb distal to the elbow (sensory and motor)

Combine sciatic-femoral nerve block used to dessentitise the pelvic limb distal to the stifle

Intravenous regional anaesthesia more popular for large species where you don’t want lingering motor dysfunction in the upper limbs

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21
Q

Benefits of peripheral nerve blocks

A

Monolateral motor block

No risk of CV side effects

No risk of spinal cord damage

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22
Q

Risks and cons of peripheral nerve blocks

A

Peripheral nerve damage

Toxicity

Needs expensive equipment

23
Q

Maxillary nerve block

A

Desensitises teeth and soft tissues of the upper jaw

For tooth extraction during dentals

Can be more tricky in some breeds due to larger muscles

24
Q

Mandibular nerve block

A

Desensitises teeth and soft tissue of the lower jaw

Useful for tooth extration during dentals

Insert needle medial to bony prominence on mandible

25
Infraorbital nerve block
Desensitises soft tissues of upper jaw Teeth desensitised only with the deep approach (to reach the maxillary nerve) Used for soft tissue surgery e.g. tumour removal or minor teeth surgery
26
Mental nerve block
More distal branch of mandibular nerve Desensitises the soft tissues of the lower jaw Teeth not fully desensitised
27
Brachial plexus nerve block
At level of axilla Sensory and motor block of the thoracic limb distal to the elbow Techniques - electric nerve stimulator guided - ultrasound guided (dorsal recumbency, linear probe between sternum and scpula, needle inserted with implant technique)
28
Sciatic-femoralis nerve block
Sensory and motor nerve block to the pelvic limb distal to the stifle joint Electrical nerve stimulator and US guided techniques
29
Sciatic nerve block
Sensory and motor innervations of hind limbs Two components - tibial (stifle flexion) - common peroneal (stifle and tarsus extension) Landmarks - greater trochanter of femur - ischiatic tuberosity Common volumes used: 0.1-0.2 ml/kg US guided has a more distal approach
30
Femoral nerve block
Put patient with limb to be blocked uppermost Identify using the femoral artery - nerve should be just cranial (nerve stimulator guided) US-guided - ientify within femoral triangle (artery, vein, nerve)
31
Neuraxial anaesthesia
Includes both nitrathecal and epidural administrations LA are often combined with other classes of analgesics like opioids, alpha 2s, and ketamine - enhances the sensory block May be used for procedures involving the pelvic limbs, the pelvic cavity, or the caudal abdomen
32
Epidural anaesthesia
Access at the intervertebral junctions Just above the meningeal sheaths Landmarks: ilium wings and processus spinosus of L7 vertebral body Inject slowly (30-60s), pressure is negative Should not get any CSF through the needle
33
Intrathecal anaesthesia
Into the CSF Quick onset, short duration CSF will come through needle
34
Epidural vs intrathecal anaesthesia
Epidural + less invasive + lower risk of iatrogrenic damage to spinal cord - harder to identify correct needle positioning Intrathecal + faster action - CSF has high turnover so shorter lasting action
35
Drugs suitable for neuraxial anaesthesia
Local anaesthetics (beware of motor block) Opioids (morphine) Alpha 2s (medetomidine, xylazine) Ketamine (preservative free) Steroids (to treat chronic inflammatory pain)
36
Role of locoregional anaesthesia in large animals
Many clinical procedures performed in the standing animal under sedation ○ Eye enucleation (cattle, horses) ○ Perineal surgeries (mare) ○ Abomasal displacement (cattle) ○ Dental (horses) Restrictions in the use of systemic analgesics (opioids) in food animals Neuraxial not used as often due to lasting motor blocks which can cause management problems and also stress and welfare problems
37
Commonly used local anaesthetics used in large animals
Procaine is approved for food producing animals in Europe (Lidocaine in USA) but other commonly used under cascaed - bupivacaine - levobupivacaine - ropivacaine - mepivacaine
38
Nerves of interest for loco-regional anaesthesia in large animals
Trigeminal nerve - maxillary - mandibular - ophthalmic Infraorbital nerve (horses) Maxillary block (horses) Mandibular nerve block (horses) Mental nerve block (horses) Retrobulbar block (horses) Infratrochlear/lacrimal nn. (goats) Cornual n. (cattle)
39
Infraorbital block in horses
For procedures involving nares, the soft tissues of the naso-labial region and the periodontal tissues (partial or no analgesia of the teeth)
40
Maxillary block in horses
For both the soft tissues of the maxillary region and the teeth of the upper jaw
41
Mandibular nerve block in horses
For both the soft tissues of the mandibular region and the teeth of the lower jaw
42
Mental nerve block in horses
Provides analgesia to the soft and periodontal tissues of the rostral mandibular region Desensitises a limited area and not really the teeth
43
Retrobulbar block in horses
Ultrasound guided Make sure not to stick the needle into the eye globe Usually do this before enucleation due to the high risk of damage to the eye globe (going to be removed anyway but still makes the surgery harder) Block the optic nerve as a side effect blocking vision Will also block branches of the ophthalmic nerve and the oculomotor nerve to block sensory innervation
44
Blocks for dehorning goats
Infratrochlear/lacrimal nerves (cornual branches) Anatomical landmarks - zygomatic arch - temporo-mandibular joint
45
Blocks for dehorning cattle
Cornual nerve Often accomplished with a blind ring block around the area of interest
46
Peripheral nerve blocks for the abdominal wall
Inverted L block Paravertebral block - dorsal approach, US guided, blind approach
47
Anaesthesia for the flank region (large animals)
A line delimited by the paralumbar fossa is desensitised with local anaesthetics Also called 'inverted L block' Commonly used in cattle, rarely in horses Indicated for: rumenotomy, c-section, cystotomy Applies to both L/R flanks depending on surgical procedures
48
Paravertebral block - dorsal approach (large animals)
The nerves providing innervation to the flank and abdominal wall are blocked at their spinal emergence in proximity of the vertebral column/spinal cord Used in both horses and cattle Blind approach more common, an ultrasound-guided approach has been developed for cattle Anatomical landmarks - last rib and transverse processes of L1, L2, and L3 Insert needle dorsal to ventral, parallel to the vertebral column and perpendicular to transverse processes
49
Intravenous regional anaesthesia of the limbs in cattle
Injected in a peripheral vein of the area of interest, after application of a tourniquet Will diffuse in the target area but systemic absorption is limited by the temporarily decreased perfusion Tourniquet should be removed after 30 mins Old technique still widely used in cattle Advantages: easy to perform, cheap, no need for expensive equipment, effective Disadvantages: risk for iatrogenic vascular/nerve damage, only local anaesthetic suitable for IV use can be used (lidocaine), only for cattle (risk of laminitis in horses)
50
Epidural in large animals generally
Anatomical landmarks: processus spinosus of last lumbar vertebra and ilium wings for lumbosacral epidural; processus spinosus of C1 and C2 and sacro-coccygeal junction for coccygeal epidural Aseptic preparation of the area
51
Epidural in horses and ruminants
Insert the needle percutaneously with a 45-90 degree angle (with respect to the vertebral column) Remove the stylet and apply a drop of saline at the hub of the needle Slowly forward the needle through the subcutaneous and muscular layers 'loss of resistance' or 'pop' sensation when the ligamentum flavum is crossed Check for blood contamination/bleeding Inject over 30-60 seconds
52
Epidural in goats
Easy identification of anatomical landmarks- prominent bony processes Local anaesthetics more commonly used compared to horses and cattle (motor block easier to manage in small ruminants) Usually performed under light sedation
53
Epidural in cattle
Identification of anatomical landmarks easier than in horses Be aware of motor block when using local anaesthetics (especially lumbosacral approach Usually performed under light sedation
54
Epidural in horses
Similar considerations as for cattle with respect to approach and use of local anaesthetics Technically more difficult owing to well developed gluteal and lumbar muscles in equine species Usually performed under sedation Don't want to inject lumbosacrally due to motor block but not full desensitisation anywhere else

Principles of anaesthesia (9 decks)

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