Chapter 5- Sedation, General Anesthesia, and Analgesia Flashcards
Why is it preferred to use regional anesthesia than general anesthesia in farm animals?
Due to practical and financial reasons
Which is the most commonly used local anesthetic solution in farm animals?
Lidocaine
What is the analgesic duration of lidocaine in farm animals?
90-180 minutes
True/False: Lidocaine is the only local anesthetic solution licensed for use in farm animals in the US
True
How soon and for how long can proparacaine hydrochloride desensitize the cornea after application?
Within 30 seconds and for 10-15 minutes
Auriculopalpebral block in cows
1. Anatomy
2. Amount
3. Action
- Palpable along the zygomatic arch, ventral to the zygomaticoauricularis muscle and to the zygomatic process of the temporal bone caudal to the coronoid process
- Infiltrate 5-15 mL
- Motor-only desensitization causing akinesia of the corresponding eyelid
Peterson block
1. Anatomy
2. Amount
3. Action
4. Notes
- Using a 3.5 inch 18G needle. In a space delineated by the zygomatic process of the frontal bone, the zygomatic process of the temporal bone, the frontal process of the zygomatic bone, and the rostral edge of the coronoid process of the zygomatic bone. The needle should be advanced to the pterygopalatine fossa toward the foramen orbitorotundum at a depth of 7-10 cm
- 15 mL of lidocaine
- Desensitizes the oculomotor, trochlear, and abducens nerves and the 3 branches of the trigeminal nerve (ophthalmic, maxillary, and mandibular). Complete motor and sensory block of the eye, except the eyelid
- More challenging than the retrobulbar block, but less chances for hemorrhage, penetrating the globe, damage to the optic nerve, or injection into the meninges.
Retrobulbar block
1. Anatomy
2. Amount
3. Action
4. Notes
- Using a 3-4 inch, 18 G needle curved. Penetrate the eyelids at medial and lateral canthus at the dorsal and ventral orbital rims while using the fingers to reflect the globe away. Advance through the conjunctiva in a curve medially to the orbital apex
- 15 mL of lidocaine divided in the 4 sites
- Desensitize all ocular muscles and the optic nerve
- Possible damage to the globe, intraneural meningeal injection, retrobulbar hemorrhage, damage to the optic nerve
Anesthesia for dehorning
1. Cattle
2. Goats
- Anesthesia of the cornual nerve
- Anesthesia of the cornual nerve, the cornual branch of the zygomaticotemporal nerve, and branches of the infratrochlear nerve
Anesthesia for disbudding in cattle
1. Anatomy
2. Amount
3. Action
4. Notes
- Palpable along the ventrolateral aspect of the frontal ridge, halfway between the lateral canthus and the base of the horn
- 5-10 mL
- The cornual nerve is a branch of the zygomaticotemporal nerve, part of the trigeminal nerve
- In older cattle a hemicircunferential block of the caudal aspect of the horn base might be needed to block the cutaneous branches from the second cervical spinal nerve
Anesthesia for disbudding in goats
1. Anatomy
2. Amount
3. Notes
- A) The cornual branch of the zygomaticotemporal nerve is desensitized at a location half way between the lateral canthus of the eye and the lateral base of the horn, as close as possible to the ridge of the supraorbital process. B) The branches of the infratrochlear nerve are blocked with a line block half way between the medial canthus of the eye and the medial base of the horn, dorsal and parallel to the dorsomedial margin of the orbit.
- Both with 2-3 mL
- Use a low amount of lidocaine in goats due to their extreme sensitivity to lidocaine toxicity. Max dose of 10 mg/kg. In kids, divide 1 mL in the four sites to desensitize the bud
What are some disadvantages of a line block technique? (5)
- Increase surgical bleeding
- Delayed healing
- Incomplete anesthesia in deeper tissues
- Risk of toxicity
- Inability to extend the incision
Inverted L infusion technique
First, inject along the last rib and then horizontally just ventral to the transverse processes with multiple subcutaneous injections (1 cm deep) and deeper muscle injections (2-7 cm deep)
What region does the paravertebral block provide analgesia to?
Entire flank region potentially
Which spinal nerves are blocked?
Last thoracic (T13) and first two lumbar (L1-L2)
Dorsal approach technique for the paravertebral block
Palpate the ends of the tranverse processes, the puncture site is abaxial to the transverse process between T13-L1, L1-L2, and L2-L3. Inser a 3.5 inch needle ventrally until the transverse process is encountered (~5-7 cm), then walk the needle off the cranial edge of the process and advance ventrally to penetrate the costotransverse ligament and intercostal membrane. After penetration, usually palpable as a pop, inject 10-15 mL of lidocaine per site.
A What is an alternative to the dorsal paralumbar block?
A distal paravertebral block can be performed by inserting the needles parallel to the tip of transverse processes dorsally and ventrally at the processes of L1-L2 and L4
What should you consider when performing epidural anesthesia in cattle to avoid damage to the inner thigh musculature?
Have excellent footing and hobble the hind legs
What are the common approaches for epidural anesthesia in cattle?
- Sacrococcygeal (S5-Cx1)
- First coccygeal (Cx1-Cx2)
Epidural anesthesia procedure
The location is located by palpating the dorsal spinous process of the sacrum and coccygeal vertebrae while moving the tail up and down. A 22g, 2 inch needle is inserted directly on midline with the bevel cranially until a pop is felt.
Which space would be more straightforward for an epidural injection since it is usually larger?
Intercoccygeal
What are some indicatives of penetrating the epidural space?
- Hanging drop
- Loss of resistance
Recommended lidocaine dose, Onset time and duration of the effect
- 10 mL/ 100 kg (0.2 mg/kg)
- 10-20 minutes
- 30-150 minutes
What combination of medications has shown to potentiate the duration of the epidural?
Xilazine 0.03 + Lidocaine 0.2 mg/kg diluted to 5 mL of sterile saline
What is the onset of action and duration of xylazine + lidocaine combination?
Onset of 3-4 minutes and duration of ~100 minutes
What is the Bier block?
Is IV regional anesthesia
The regional anesthesia using the Bier block will last as long as ____
The tourniquet is in place
Which vessels can be used for the Bier block and how much should you infuse?
Can infuse up to 30 mL of 2% lidocaine
1. Dorsal metacarpal/metatarsal
2. Palmar/plantar digital vein
3. Dorsal digital vein
4. Lateral saphenous vein
For how long can the tourniquet be safely left in place for regional IV anesthesia?
For up to 90 minutes
What branches provide innervation to the udder?
Branches originating from L3-L4 (Caudal aspect of the udder); Branches originating from L1-L2 (Cranial aspect)
What blocks should you perform to provide anesthesia to the udder?
A paravertebral block and epidural block
What can be a consequence of performing a paravertebral block and an epidural block?
Weakness of the pelvic limbs
True/False: For procedures that involve the external teat surface a ring block or IV anesthesia is usually adequate
True
For procedures affecting the cistern, what block can be sufficient?
Infiltration of anesthetic solution directly to the cistern
What do you need to do when applying the anesthetic to the cistern to prevent any milk during the infusion?
A tourniquet can be placed to the base of the teat
