Clinical: Farm Animal Local Blocks Flashcards
Indications for horn blocks:
- dehorning/disbudding
- horn injury
- inappropriate horn growth
Cornual n. block
- branch of lacrimal n. which is a branch of opthalmic division of trigeminal n.
Horn blocks in adults
- cornual branch of intratrochlear n., branch of trigeminal
- frontal n., branch of supraorbital n.
- nerves are close enough together than if one n. is blocked, the other is likely to be blocked
- Cutaneous branches of cervical n. –> SQ infiltration around the horn
Local anaesthetics for horn blocks?
2% lidocaine 5-10 mls (cascade)
Procaine + adrenaline (Adrenacaine)
Also give NSAID
Complications w/ horn block?
- block not 100% effective (variation in path of n., inaccurate assessment of depth, pass thru apneurosis of temporalis m. caudal to ridge –> no analgesia, misplacement of needle)
- pain on injection –> mvmt of animal –> misplacement of agent
Horn blocks in goats differ from cows by…
- wider n. supply to horn
- horn base is larger
Risk of doing horn block in neonate goat?
- immature resp & CV systems
- easily become hypothermic
- risk of hypoglycaemia
- sensitivity of alpha-2 agonists
Cornual branch of zygomaticotemporal block in goats
- laterally located behind caudal ridge of supraorbital process
- halfway btw lateral canthus & lateral edge of base of horn
- 2% lidocaine, 2-3 ml or adrenocaine 1-1.5 cm deep w/ 22-25 G needle
Cornual branch block of infratrochlear nerve in goats?
- medial, dorsomedial margin of orbit
- 2% lidocaine, 2-3 ml or adrenocaine 22-25G needle at 0.5 cm depth
Retrobulbar block indications
- enucleation sx
- corneal sx
Drugs for retrobulbar block?
- 10-15 ml 2% lidocaine (Cascade)
- Procaine (Adrenacaine) - Licensed
Retrobulbar block anaesthetises
cornea
lid (upper/lower)
Technique of Retrobulbar block
- 4-point (upper & lower lids 12/6 o’clock, lateral/medial canthus 3/9 o’clock)
- 1-point
Signs of satisfactory retrobulbar block
- corneal analgesia
- mydriasis
- proptosis
Complications of a retrobulbar block
- Penetration of the globe
- orbital haemorrhage
- damage to optic n.
- oculocardiac reflex
- inj into optic n. meninges
- inj into systemic circulation
Peterson block is used for
Anaesthesia of the eye in cattle
Peterson eye block desensitizes the nerves responsible for…
- sensory & motor fxn of all structures of the eye, except the eyelid
- Nerves: oculomotor, trochlear, abducent, trigeminal n.
Landmarks for Peterson eye block
- Cranially: supraorbital process
- ventrally: zygomatic arch
- Caudally: coronoid process of the mandible
Indications for Peterson block
- enucleation sx
- safer than retrobulbar block
- anaesthetises the eye & orbit w/ immobilisation of the globe
Drug used for Peterson block
10-15 ml 2% lidocaine
Auriculopalpebral anaesthetises…
motor nerve supply to orbicularis oculi muscle
Localisation of auriculopalpebral
- runs from base of ear aong facial crest
- ventral to eye, giving off its branches on the way
The auriculopalpebral provides
- no analgesia
- used in conjunction w/ topical analgesia (2% lidocaine)
Line block
Infusion of local anaesthetic into the incision site to desensitise a select area of the paralumber fossa
Line block technique
- SQ inj
- Inj into deep muscle layers
toxic dose of lidocaine in line block for small ruminants? cattle?
Small ruminants: 5 mg/kg
Cattle: 10 mg/kg
Disadvantages of a line block
- poor analgesia of deep layers
- distorts Sx site
Inverted L Block
blocks tissue bordering caudal aspect of rib 13 & ventral aspect of transverse processes of lumbar vertebrae
Indications for inverted L block
- Caesarians
- some laparotomies
Advantages of Inverted L block
- local anaesthetic away from operating site (minimal oedema & haematoma risk)
- easy
- good when transverse process not easily palpable
Disadvantages of Inverted L block
- high vol of local anaesthetic
- toxicity
- increased cost
- variable analgesia, esp to deep layers
Proximal Paravertebral block
desensitises dorsal & ventral n. roots T13-L4
Proximal paravertebral block causes…
scoliosis of the spine (muscle relaxation) & warming of skin
How long does it take for onset of proximal paravertebral blocks?
onset 20 mins
How do you check the efficacy of a proximal paravertebral block?
- skin becomes hyperaemic
- local anaesthetic causes vasodilation
- lateral curvatiure of the spine towards the anaesthetised side
- test w/ forceps prior to Sx
Distal paravertebral block
desensitises dorsal & ventral rami of the spinal n. T13-L4
The distal paravertebral block does not cause
scoliosis
Advantages of distal paravertebral block
- lack of scoliosis
- easier
- more consistent results
Disadvantages of distal paravertebral block
- larger doses of anaesthetic needed
- variations in efficiency caused by variation in anatomic pathways of the nerves
Caudal epidural is used for…
- obstetrics
- Sx procedures involving: tail, perineum, anus, rectum, vulva & vagina, prepuce & scrotum
What vol of lidocaine should be used in a caudal epidural?
Lidocaine 0.5 ml/45 kg
IVRA (Bier Block)
Provides analgesia of the digits
Indications for a IVRA/Bier block
- Sx of the distal limb
Drug used for Bier block/IVRA
20 ml of 2% lidocaine
Advantages of Bier Block (IVRA)
- simple
- rapid onset & recovery
- single injection site
- minimal blood in Sx field
- may also administer antibiotics
Disadvantages of Bier Block (IVRA)
- lateral recumbency often req’d
- haematoma formation at site of inj
- damage to nerve underneath tourniquet
- local anaesthetic toxicity when tourniquet released
