Regional Anesthesia Flashcards
4 examples of aminoamide local anesthetics
- lidocaine
- bupivicaine
- ropivicaine
- mepivacaine
(the “i-caine”s)
4 applications for topical anesthesia
- larynx (during intubation)
- splash block prior to wound closure
- corneal (eye exam)
- EMLA cream for skin desensitization (for venipuncture or small mass removal)
potential CNS toxicity signs (5)
- Depression of cortical inhibitory pathways
- Impaired vision
- Tremors/seizures
- CNS depression
- Coma
Describe the MOA of local anesthetics (3 parts)
- Local anesthetic needs to penetrate into the cell to produce the its effects - Blockade of the Na+ channel - Prevents Na+ influx => no depolarization = no impulse transmission
Complication with inferior alveolar n. block
Spread and block of lingual nerve
2 pharmacological compound types of local anesthetics
- aminoesters
- aminoamides
EMLA cream produces anesthesia with a depth of approximately ______
1 cm
BE CAREFUL with infraorbital block in cats and
brachycephalic dogs due to _________
risk of ocular puncture
6 factors influencing the onset of local anesthetics
- lipophilicity
- pKa
- concentration
- dose and volume
- proximity to nerve
- type of nerve
T/F
local infiltration does not target a specific nerve
T
5 factors influencing the duration of local anesthetics
- vascular effect
- tissue blood flow
- vasoconstrictor?
- dose
- affinity to the Na receptor
Landmarks in small animals for epidural anesthesia (3)
- Iliac crest
- Medial sacral crest
- Spinous process of L7
Why is the lumbosacral space used for small animal epidural anesthesia and the sacrococcygeal space used in large animals?
the spinal cord ends at L7 in small animals while in large animals the spinal cord ends at L7
indication for local infiltration anesthesia
Anesthesia for skin and underlying
tissues
_________ anesthetics are hydrolyzed by the cholinesterase enzyme (plasma and liver)
aminoesters
DO NOT use lidocaine with epinephrine when there is not ___________
collateral circulation
________ anesthetics undergo Hepatic metabolism (microsomal
enzymes)
aminoamides
3 target nerves in lumbar paravertebral nerve block
T13, L1, L2
__________ most commonly used in small animals for epidural anesthesia
Lumbo-sacral space
“Loss of Resistance” technique for epidural anesthesia (4)
1. Advance the Tuohy needle until the interarcuate ligament is perceived 2. Remove the stylet and attach the syringe to the hub 3. Apply small pressure to the plunger and advance the needle through the interarcuate ligament 4. The resistance to the injection of air drops suddenly when needle enters the epidural space
CNS signs of LA toxicity will appear before CV signs, except for with __________ toxicity
Bupivacaine
the epidural space is between the ________ and ________
- interarcuate (flavum) ligament
- duramater
what is the benefit of peripheral nerve blocks?
Injection of a small volume of local anesthetic produces a great area of desensitization
Smaller nerve fibers are more susceptible to LA because _____________
shorter length of axon is required to be blocked to halt the conduction completely
Intraneural injections produce _______!!!!
nerve damage
(aminoesters/aminoamides) undergo slower metabolism
aminoamides
2 target structures of local infiltration anesthesia
- free nerve ending
- nociceptors
Local anesthetics are weak _______, therefore in _____ pH they are ionized
- bases
- acidic
with (aminoesters/aminoamides) toxicity from accumulation is more likely
aminoamides
__________: Anesthesia for superficial mucosal
tissues
topical/surface anesthesia
what is the risk of the hanging drop epidural technique
false negatives can occur
2 parts of nociception
- sympathetic stimulation (catecholamine release, ↑ HR and BP)
- stress response (ACTH, ↑ cortisol and blood glucose)
Generally local anesthetic cannot cross the epidermis (exept _____)
EMLA
(aminoesters/aminoamides) are more likely to result in anaphylactoid reactions
aminoesters
why do you want to use small volumes for large animal epidural anesthesia
avoid sciatic nerve block, which will affect motor function of the pelvic limb
What are the medical benefits to the significant reduction of anesthetic and analgesic drugs enabled through pre-emptive analgesia?
Reduction intraoperative complications
hypotension, bradycardia, nausea, GI disturbances
3 methods of finding nerves
- Blindly
- Electrolocation - electric nerve stimulation
- Ultrasound
potential CV toxicity signs (6)
- Bradycardia
- Increased PQ interval
- Increased QRS duration
- Ventricular premature complexes
- Reduction of myocardial contractility
- CV collapse / cardiac arrest
(smaller/larger) and (myelinated/unmyelinated) nerve fibers are more susceptible to local anesthetics
- smaller
- myelinated
2 ways of determining whether the needle is in the epidural space
- Hanging drop technique
- Loss of resistance to injection
local anesthetic toxicity manifests as _______ and ________ signs
- CNS
- Cardiovascular
T/F
Lumbar paravertebral block provides Better analgesia than “inverted L” technique
T
difference between spinal and epidural anesthesia
spinal anesthesia gois into the subarachnoid space while epidural anesthesia
4 examples of aminoester local anesthetics
- procaine
- tetracaine
- benzocaine
- cocaine
Examples of peripheral nerve blocks (5)
- infraorbital
- maxillary
- inferior alveolar (mandibular)
- intercostal
- lumbar paravertebral
3 reasons to provide regional anesthesia
- pre-emptive analgesia
- better intra and postop pain control
- prevents stress response (better immune system activity)
__________ most commonly used in large animals for epidural anesthesia
Sacrococcygeal space
3 reasons a patient may have a high plasmatic level of local anesthetics
- high dose
- direct venous injection
- reduced biotransformation or elimination (liver/renal disease)
Examples of local infiltration blocks
- line block
- intratesticular block
- inverted L
- ring block
Degree of ionization will depend on the ___ and ____ of the tissue
- pKa
- pH
the toxicity of local anesthetics is associated with ___________
high plasmatic levels
_______ is a peripheral nerve block used for flank surgeries in ruminants
lumbar paravertebral block
3 steps of epidural “Hanging Drop” technique
1.Advance the Tuohy needle until the interarcuate ligament is perceived 2.Remove the stylet and fill the hub of the needle with saline 3. When the needle enters the epidural space the drop should be aspirated
Myelinated fibers are more susceptible to be blocked because __________.
LA pools near the
axonal membrane
Order in which nerve sensations are blocked by local anesthetics (6)
- pain
- cold
- warm
- touch
- deep pressure
- motor function
__________: pH at which 50% of a drug is present in its ionized (charged) form and 50% is in its unionized (neutral) form
pKa
2 target structures of topical local anesthesia
- free nerve endings
- nociceptors
3 uses of local infiltration
- Resection of cutaneous or superficial masses
- Surgical closure of lacerations
- Procedures involving an appendage
