Local Anesthetic Techniques Flashcards
What are the main benefits to local and regional anesthesia?
-allows for examination and procedures without general anesthesia (bypasses risk of induction and recovery)
-provides analgesia without systemic side effects
-can be combined with sedation to provide balanced analgesia
What is the main local anesthetic used in veterinary medicine and what are its main characteristics? What are the other options?
-2% lidocaine is used most commonly
-duration is around 1-2 hours
-onset in 2-5 minutes
-very inexpensive
Other options: mepivacaine which lasts 1-2 hours or bupivacaine which lasts 4-6 hours
T/F: IV lidocaine is a good thing to add when performing painful procedures to provide analgesia
False- does not help
- actually delays recovery
Why is sedation and local anesthesia required for examination, diagnostic and minor surgical procedures in the eyes of horses?
Horses often clamp their eyelids really tight together making it impossible to do an exam let alone operate on their eyes
-without sedation they will not tolerate the exam and will be fighting everything you are doing to them
What drug is recommended for topical anesthesia for the eyes of horses?
Proparacaine: onset 15 s, duration 15-30 min
-not appropriate for ongoing pain relief
What block is used to block the motor innervation to the eyelids to perform an eye exam?
Auriculopalpebral
- use 25 ga 1 inch needle, and inject 1-2 mLs
-infiltrate the caudal aspect of the zygomatic arch
What sensory block can you add if you want to desensitize an area of the eyelid prior to a procedure?
Supraorbital block will desensitize most of the upper eyelid
- inject in and over the supraorbital foramen (just dorsal to the medial canthus)
If you want to desensitize the entirety of the upper eyelid, what blocks would you perform along with the supraorbital block? What if you want to desensitize the lower eyelid?
Lacrimal- gets the lateral 25% of the upper lid
Infratrochlear- gets the 25% of the medial upper lid
For lower lid, perform the zygomaticofacial block
What does the infraorbital block 1 desensitize? What are the landmarks?
What about the infraorbital block 2?
1: Provides analgesia of the upper lip and nose
- inject over the infraorbital foramen
-palpate the nasal notch and facial crest and inject in between the two (use 4-5 mL of local)
2: desensitizes teeth to first molar, maxillary sinus, roof of the nasal cavity, skin to medial canthus
- thread the needle into the infraorbital foramen
-standing horses do not tolerate this well
What does the maxillary block desensitize? How is it performed?
Blocks all upper teeth, sinuses and nasal cavity
-insert a 3.5 inch needle ventral to the zygomatic process, dorsal to the vessels at 90 degree angle
-inject 15-20 mLs
Hard to perform on standing horse
What does the mandibular block desensitize? How is it performed?
Blocks all mandibular structures
-blocks everything up to the lateral canthus down
-palpate mandibular notch and slide needle under mandible
-use 20 ga 6 inch needle, inject rostral to angle of mandible (insert 10-15 cm) and inject 15-20 mL of local
What does the mental block 1 desensitize? How is it performed?
What about the mental block 2?
1: Provides analgesia of the lower lip
-inject 5 mL over the mental foramen
-palpate by pushing the tendon of the depressor labi inferioris dorsally
2: provides analgesia of the lower incisors and caudal to the premolars
-must thread the needle into the foramen
-inject 5-10 mL
What are the main indications for performing an epidural?
For procedures involving the rectum, vagina, perineum, urethra and bladder
-obstetric manipulations (if foal is dead)
-analgesia of stifles and hocks
-intraop - can decrease MAC
What are the contraindications for performing an epidural?
-infection at the puncture site
-+/-sepsis
-uncorrected hypovolemia
-anticoagulation reaction (if on aspirin)
-anatomic abnormalities
Where is the epidural space?
Within the spinal canal but outside the visceral layer of the dura matter
- not the subarachnoid space- deeper (if you hit this, would be a spinal)
Why are caudal epidurals performed more in horses than lumbosacral epidurals?
Lumbosacral epidurals are hard- often will hit subarachnoid space. Want to use this for flank procedures. You need special equipment and aseptic technique
Caudal epidurals are simple to perform, no special equipment is needed, and you can preserve the locomotor function of the hindlimb
How should you prep a horse for an epidural?
-need proper restraint
-horse should be standing squarely
-clip and prep the skin
-use sterile gloves and supplies
-can block the skin with 2% lidocaine
What are the landmarks for a lumbosacral spinal?
-same landmarks as for CSF collection
-1-2 cm caudal to a line drawn from the cranial edge of the tuber sacrale and dorsal midline
-need a 17.5 cm 17 g spinal needle- being vertical in all planes is important
What are the landmarks for a caudal epidural?
- palpate co-1 and co2 as the first midline depression caudal to the sacrum
- also the first moveable coccygeal articulation when the tail is raised and lowered
Describe the 2 different techniques for performing a caudal epidural
Technique 1: use 18 ga 1.5 inch needle
-enter the center of the space perpendicular to the skin
-may feel popping as the interarcuate ligament is penetrated
Technique 2: a 5-7.5 inch 18 ga spinal needle
- insert at the caudal part of the interspace at above 30 degrees parallel to horizontal plane
-can be useful if the horse has had multiple epidurals
Compare and contrast the caudal and lumbosacral epidurals
Caudal: preferred site, easier and safer, no risk of dural puncture or CSF tap, less risk of motor blockade and ataxia
Lumbosacral: less commonly used, more difficult, can result in dural puncture and CSF tap, high risk of motor blockade and ataxia
What equipment do you need to perform an epidural?
-needles, spinal needles, or epidural catheters
-needles are recommended for one time administration
-catheters recommended for repeated or long-term use
Describe the two techniques to ensure you are in the right spot for an epidural
1: hanging drop- Go through just the skin with 18 ga 1.5 inch needle, once through skin full hub with saline and then advance until the drop is sucked in
When would you use an epidural catheter?
When continuous epidural analgesia is needed
-best for repeat dosing
-use 17 ga huber point directional needle with stylet
-be aware that catheters can cause local inflammation and necrosis
Examples: pelvic fractures, hindlimb fractures, septic joints
