Prac 5. Local anaesthesia

How should you prepare the area for local anaesthesia?

Before administration clip and scrub the area to be anaesthetised

What block would you recommend for dehorning?

Cornual block

What is the main indication for an inverted L block?

Standing laparotomy

What are your landmarks for an inverted L block?

Start: - Just below 2nd lumbar vertebrae - Just below transverse processes caudally - Just behind last rib cranially

Describe how you would perform an inverted L block?

Start: - Just below 2nd lumbar vertebrae - Just below transverse processes caudally - Just behind last rib cranially - Inject local as withdrawing the needle SC, IM ensuring that deeper structures have also been infiltrated using a fan-wise infiltration - Repeat the process at regular distance intervals to ensure complete coverage - Works in 10-15min

How would you perform a retrobulbar nerve block?

- 2 or 4 point ie: - 2 = medial and lateral canthus - 4 = + upper and lower eyelid

What is the purpose of a teat cistern infusion?

- Anaesthesia of mucosal surface only ie. polyps, teat pea removal

What is the goal of the retrobulbar nerve block?

- Analgesia of cornea - Mydriasis - Proptosis

How would you perform IV regional anaesthesia?

- Apply tourniquet above - Catheterise vein of distal limb (20-22G) - Local administered (10-30ml) - Works in 15 min and lasts until the tourniquet is in place (max 60-90min) - Slowly release the torniquet

How could you perform anaesthesia of the eyelid?

- Auriculopalpebral nerve block (motor) - Supra orbital - Line block

What local anaesthesia would you add when performing dehorning of larger cattle with developed horns/bulls?

- Block 1st and 2nd cervical nerves - Additional 5-10ml - Partial ring at the base of horn, caudal aspect of horn

What is the purpose of the auriculopalpebral nerve block?

- Blocks m orbicularis oculi and prevents the eyelids from moving - Note - no analgesia (akinesia only!)

Which cranial nerves play a role in the eye?

- CNV (opthalmic branch) supplies: * globe * conjunctiva * 3rd eyelid * part of upper and lower eyelids - CNII, IV, VI * extraocular muscles - CNVII (auriculopalpebral n/branch( * eyelids

Which nerves are blocked by the Petersen nerve block?

- CNV mandibular, maxillary and opthalmic branches (lower, upper and 3rd eyelid), median canthus, eyeball - CNIII, IV and VI (ocular muscles)

What are the downsides to doing a line block?

- Changes tissue structure - Causes local inflammation - Delayed healing

What are the land marks for caudal epidural anaesthesia (CEA)?

- Co1-Co2 or one caudal

What are the cons of local and regional anaesthesia compared with GA?

- Cooperative patient or proper restraint needed - May require sedation - Requires knowledge of anatomy

Describe what an epidural anaesthesia comprises:

- Deposition of the local into the extradural space - Needle enters the spinal cord but does not penetrate meninges - Caudal and cranial possible (posterior and anterior)

How would you perform an inverted V block?

- Gently inject local as withdrawing the needle SC-IM to ensure that deeper structures have also been infiltrated, using a fan wise infiltration - Use 2-6ml/teat - Works in 10-15 min

How would you perform a teat ring block?

- Gently inject local as withdrawing the needle in fan wise infiltration at 4-6 sites around the teat base - 10-20ml local per teat - Works in 10-15 min - Tourniquet not essential

Which areas are anaesthetised via the infraorbital block?

- Half of rostral face ie: - Incisors and cheek teeth (up to M2) - Nostril, nasal septum - Upper lip - Muzzle --> facilitates surgery or placement of nose ring

What are your landmarks for auriculopalpebral nerve block?

- Halfway between the base of the ear and the lateral canthus - End of the zygomatic arch - Just caudal to palpable large blood vessels - Inject 5-10ml and should work in 5-10min

How would you perform a line block?

- Infiltrate the line of surgical incision using a fan wise infiltration - Usually 2ml/cm local - Works in 10-15 min

How would you perform a teat cistern infusion?

- Infuse 10ml local using a teat cannula - works in 5-10 min

How would you perform an IV teat block?

- Inject 5-7ml of local into any of the visible superficial veins - Works in 5 mins - Lasts until tourniquet taken off (max 45-60min - release slowly)

Where should you NOT inject local anaesthetic?

- Into infected tissuse - IV (except in the limbs when performing IVRA) - With epinephrine as teat anaesthesia (ischaemic necrosis)

What types of teat blocks can you perform on cattle?

- Inverted V block - Teat ring block - Teat cistern infusion - Intravenous teat block

What are the pros of local and regional anaesthesia over GA?

- Less toxicity - Decreased risk due to recumbency - Less equipment needed

What is regional anaesthesia?

- Local anaesthetic injected around a large nerve trunk (ie. regional nerve block), into the epidural space or intravenously

Describe the effects of a caudal epidural anaesthestic after low and high doses:

- Low dose blocks tail, anus, perineum, vulva, caudal vagina, portion of perineum - High dose also portion of thighs and half pelvis

What technique would you use to anaesthetise the infraorbital n?

- Nerve is difficult to palpate, so go rostral to the facial tuberosity and draw a line from the nasomaxillary arch to the second molar - Inject 20-30ml local and repeat on opposite side as required

Describe the technique used when performing a CEA?

- Palpate tail up and down for proper placement - 18G 1.5 inch needle inserted at 45 degrees - 1ml/100kg - Can add xylazine - Works in 10-20 min, lasts 1-2 hours (4-8 if you add xylazine) - For prolonged anaesthesia can use a small diameter epidural catheter

How would you perform a distal paravertebral nerve block?

- Palpate transverse processes of 1st, 2nd and 4th lumbar vertebrae - Inject 1-2ml local at the tip of each process - At each process insert 4-6 inch needle: 1. Parallel and dorsal to the processes, injecting 5-10ml local as a bolus and 5-10ml as the needle is withdrawn 2. Parallel and ventral to the processes repeat

Describe the area blocked by the paravertebral nerve block:

- Perineural injection of local at spinal nerves T13, L1 & L2 as they emerge from the spinal column - Provides analgesia and anesthesia of the whole area including peritoneum

How would you provide the best complete anaesthesia to the eye?

- Petersen and auriculopalpebral nerve blocks combined

Describe the basics of teat anaesthesia:

- Provide adequate restraint - Sedation often recommended - Placing elastic band around teat base - For short interventions, tourniquet

What are the risks associated with the retrobulbar nerve block?

- Sudden death if local infused intraoptically - Haemorrhage - Cardiac dysrhythmias (oculocardiac reflex)

Where is the Peterson nerve block performed?

- Temporal fossa * just above the pterygopalatine fossa * in front of the foramina orbitorotundum Landmark = notch created by: - Cranially = supraorbital process - Ventrally = zygomatic arch - Caudally = coronoid process of mandible

When is an inverted V block useful?

- Used for teat sx and accidental limb wounds

What nerve blocks might you use if you were performing surgery on the eyeball and/or third eyelid?

-Retrobulbar nerve blcok - Petersen nerve block - Local infiltration of base of 3rd eye lid

Describe landmarks for the Cornual block:

Inject 5-10ml local relatively superficially 1-3 cm toward the horn base, midway between the lateral canthus of the eye and base of the horn, behind the lateral ridge of the frontal bone

What are the landmarks for a cranial epidural:

L6-S1