Local Anesthetic Techniques Flashcards
what is the most common anesthetic and how long does it last?
2% lidocaine, it has an onset time of 3-5 minutes with an intermediate duration of 1-2 hours
what are alternatives to lidocaine?
mepivacaine (1-2 hours)
bupivacaine (4-6 hours)
how might lidocaine be used in field anesthesia?
Its commonly used with short term anesthesia for analgesic effects when its injected into the cord and then you let it sit during the final scrub
When xylazine and ketamine are used for field castrations what type of lidocaine block should you use for a smooth recovery?
intratesticular, intravenous lidocaine delayed recovery
what do we use for topical anesthesia of the eye?
proparacaine with an onset of 15s, duration 15-30 minutes
Explain the Auriculopalpebral block
This blocks motor function of the eye by infiltrating the caudal aspect of the zygomatic arch and causes paralysis of the eyelids
Explain the supraorbital block
This is a sensory block to most of the upper eyelid. Go dorsal to the medial canthus to find the supraorbital foramen and inject in and over it.
name a few of the other local anesthetics of the eye
lacrimal, infratrochlear and zygomaticofacial
infraorbital I block
Analgesia of the upper lip and nose. To perform this inject over the infraorbital foramen by palpating the nasal notch and facial crest.
Infraorbital II block
Desensitize teeth to 1st molar, maxillary sinus, roof of nasal cavity, skin to medial canthus. To perform thread the needle into the infraorbital foramen.
Maxillary Block
All upper teeth, sinuses and nasal cavity are blocked. To perform insert a 3.5 inch needle ventral to zygomatic process, dorsal to vessels, caudal 1/3 of eye and 90 degrees
Mandibular Block
All mandibular structures are blocked. The lateral canthus and the mandibular cheek teeth can be used to located the block. A 20 ga 6 inch needle rostral to the angle of the mandible is used to inject 15-20ml local.
Mental I block
This provides analgesia of the lower lip when you inject 5ml over the mental foramen
Mental II block
Analgesia of the lower incisors and caudal to the 3rd premolar by threading the needle into the foramen
what are some contraindications for epidurals?
- infection at puncture sites
- +/- sepsis
- uncorrected hypovolemia
- anticoagulation rx
- anatomic abnormalities
describe the epidural space
the epidural space is within the spinal canal outside of the visceral later of the dura matter, it is not the subarachnoid space which is the site of CSF collection
lumbosacral epidural
This is easier as a subarachnoid than an epidural and is fast/controlled flank anesthesia. This is less commonly used and more difficult. It can result in dural puncture and CSF tap AND has a higher risk of motor blockade and ataxia
caudal epidurals
These are simple to do and preserve locomotor function of the hindlimb. There is no risk of dural puncture or CSF and less risk of motor blockade and ataxia
T/F: you can block the skin before an epidural with 2% lidocaine
T
what needles/spinal needles/epidural catheters are recommended for epidurals?
18G 1.5 inch needles, don’t reuse needles or use a catheter for repeated or long term use
landmarks for a lumbosacral subarachnoid
This is the same landmarks as for CSF collection. Go 1-2 cm caudal to a line drawn from the cranial edge of tuber sacrale and dorsal midline with a 17.5cm 18G spinal needle
landmarks for a caudal epidural
palpate Co1-Co2 as the first midline depression caudal to the sacrum which is the first movable coccygeal articulation when the tail is raised and lowered
when should epidural catheters be placed?
in scenarios when you need continuous analgesia like pelvic fractures, hindlimb fractures, septic joints, etc.
what do you use for epidurals?
local anesthetics, alpha 2 agonists, opioids (morphine, butorphanol), ketamine
Lidocaine as an epidural causes __ blockade and is typically __ ml per 500kg horse with a rapid onset of __ and a __ minute duration
Lidocaine as an epidural causes motor blockade and is typically 6-8 ml per 500kg horse with a rapid onset of 6-10 minutes and a 60-90 minute duration
what alphas 2 can we add to an epidural that may work synergistically and prolong analgesia?
Xylazine: 3-4 hour duration
Detomidine: 1-2 hour duration
how do opioids work as epidurals?
they inhibit pain transmission in the dorsal horn of the spinal cord so you can walk around but can’t feel it aka they provide analgesia without motor blockage. This is useful for intra and postoperative analgesia of the perineum and hindlimb.
ex. morphine and butorphanol
morphine is a __ agonist with a __ onset of __ min and __ duration and may help decrease __ needs during surgery. __ morphine is cheaper and can be administered at a lower volume so its good for one time use while __ morphine is expensive and administered in a large volume but better for repeated admin.
morphine is a pure agonist with a short onset of 1-5 min and 6-16 hour duration and may help decrease halothane needs during surgery. Regular morphine is cheaper and can be administered at a lower volume so its good for one time use while Preservative - free morphine is expensive and administered in a large volume but better for repeated admin.
T/F: butorphanol is very effective as an epidural agent
F, it has variable reports of efficacy
ketamine in an epidural provides __ somatic but __ visceral analgesia with a fast onset of __ minutes and short duration of __ minutes.
ketamine in an epidural provides good somatic but poor visceral analgesia with a fast onset of 1-5 minutes and short duration of 30-75 minutes.
how might combining drugs benefit epidural usage?
The combination may act synergistically and prolong anesthesia or provide better analgesia than one agent along. Using multiple also minimizes the side effects of the individual drugs
Opioids + alpha 2 agonists
most commonly morphine is used and will have a faster onset with the alpha 2’s. With this combo you can give the full dose of each drug and this can be useful for long term pain management
Alpha 2 agonists and locals
Be careful with the dose of the local to prevent ataxia and decrease the dose by 30%. This combo is useful for standing surgery and has a prolonged effect over local anesthetic along
common epidural drug combos
xyalzine/lidocaine
morphine/detomidine
butorphanol/lidocaine
