Lecture 18 & 19: Locoregional Anesthesia (Exam 3) Flashcards
(65 cards)
1
Q
Why should I use a local block
A
- General ax prevent the perception of pain but it doesn’t stop the transduction, transmission, & modulation of pain
- LA block the initiation & conduction of action potentials in nerve fibers
2
Q
T/F: LA should always be considered as part of a multi-modal analgesic plan
A
True
3
Q
Describe the admin of LA
A
- Can be pr, intra, or post op
- Administering prior to sx will decrease the stress response
- Often allows sx to be performed in a px w/o the use of general x (more used in Large animals)
- Reduces the amount of induction & maintenance drugs req if given before surgical stimulation
- When given prior to surgical stimulation it can reduce the potential for dev of “wind up” pain
4
Q
What is the MOA of LA
A
- Analgesia is a direct result of the NA ion channel being blocked & the membrane being stabilized
- Blockade occurs from inside the nerve cell
- Nerve cell depolarization is prevented which block the conduction of nerve impulses
5
Q
What happens to the px when given LA
A
- Has a dose dep loss of sensory, motor, & autonomic fxn
- This effect is transient as the local ax is metabolized or hydrolyzed
6
Q
What do LA do to small diameter (C & Ag) nerve fibers
A
- Blocks preferentially prior to large myelinated fibers
- Loss of sensation occurs w/ varying degrees of loss of motor fxn
- C > Ag > Ay / Ab / Aa
7
Q
What is the order that sensation disappears
A
- Pain
- Cold
- Warmth
- Touch
- Joint
- Deep pressure
8
Q
How does the lipid solubility of an LA changes its effects
A
- High lipid soluble = more potent effects
- Increased solubility = increased duration of effect
- Speed of onset of the LA is inversely proportional to the drugs lipid solubility & pKa
9
Q
How does the protein binding ability of an LA changes its effects
A
More highly protein bound LAs have a longer duration of action
10
Q
T/F: Decreasing the concentration of LA in a given area will increase the duration of analgesia
A
False; increasing the concentration
11
Q
How does the systemic absorption of an LA changes its effects
A
- As systemic absorption increases (like due to vasodilation) the duration of the effect decreases
- Lidocaine causes vasodilation so it has a shorter duration of action
12
Q
List some ester local ax
A
- Procaine
- Tetracaine
- Benzocaine
13
Q
List some amide local ax
A
- Lidocaine
- Mepivacaine
- Bupivacaine
- Ropivacaine
- Lidocaine + prilocaine
14
Q
Describe lidocaine
A
- Commonly used LA w/ a fast onset time (low pKa of 7.9)
- Short duration of action b/c of low protein binding & ability to cause vasodilation
- Min damage or irritation to tissue
- Safe to give IV @ clinical doses
- Effects when given IV: ax sparing, augments analgesia, antiarrhythmic, GI promotility, anti inflammatory, & antishock
15
Q
What is pKa (dissociation constant)
A
The pH @ which 50% of an acid or base is in the ionized state
16
Q
What is the pKa of most LAs
A
They are mostly bases w/ a pKa btw/ 8 & 9 so they are mostly ionized @ a pH of 7.4
17
Q
What happens to LAs in an acidic environment? What about alkaline?
A
- Acidic: The drug shifts to the ionized
- Alkaline: Drug shifts to an unionized form
18
Q
Describe Mepivacaine
A
- Commonly used LA in equine for diagnostic nerve blocks in lameness exams
- Faster onset time compared to lidocaine (pKa of 7.6)
- Highly protein bound so longer duration of action than lidocaine
- Less irritation or tissue damage
- Absence of vasodilator effects so no need to use w/ epinephrine
19
Q
Describe Bupivacaine
A
- Longer time to onset compared to lidocaine b/c of high pKa (8.1) & increased lipid solubility
- Longer duration of action b/c of high protein binding
- Margin of safety is the lowest compared to lidocaine, mepivacaine, & ropivacaine
- Greater concern for system cardiotoxicity so it should never be given IM
20
Q
Describe bupivacaine liposome injectable suspension
A
- Nocita provides extended release of bupivacaine for up to 72 hours
- FDA approved in 2016 to control pain in dogs having cranial cruciate ligament sx
- Use a moving needle infiltration tech being sure to inject in all layers of tissue
21
Q
Describe ropivacaine
A
- Similar chemical properties as bupivacaine (is the pure s-(-) enantoiomer)
- Less CV & CNS toxicity than bupivacaine
- Concentration dep onset time (low -> similar to bupivacaine & high -> similar onset to mepivacaine)
- Similar duration of action to bupivacaine
- More expensive the bupivacaine
22
Q
Fill out the chart:
A
23
Q
What happens if you combine local anesthetics
A
- Results can be unpredictable & duration of action shorter
- Need to pay attention to toxic Dosages
- Don’t do it
24
Q
What can be additives to LAs
A
- Opioids
- Alpha 2 agonists
- Ketamine
25
Describe opioids
* Preservative free morphine commonly admin w/ LA for epidural or spinal ax
* Analgesia can last up to 24 H
* Has systemic side effects that can occur
26
Describe alpha 2 agonists
* Small doses of xylazine, medetomidine, & dexmedetomidine used in certain LA techs to improve analgesia & duration of action
* Can have systemic side effects
27
Describe ketamine
* Enhances analgesic effects by blocking NMDA, sodium, & potassium channels
* Side effects may include an increase in HR & BP
28
How does epinephrine effect LAs
* Vasoconstrictor
* May be added to increase duration of action b/c it delays absorption
* Can potentially reduce toxicity of LA
* Never use on distal extremities b/c may cause tissue necrosis
29
How does Hyaluronidase effect LAs
* Used to hasten onset time
* Could lead to more systemic absorption & toxicity
* Duration of block may be decreased
* May be utilized in exotics (reptiles)
30
How does sodium bicarbonate effect LAs
* Added to lidocaine to reduce pain on injection
* Possible enhance the effect of the LA by increasing diffusion across nerve cell membrane
31
What are general consideration for the use of LA
* Always aspirate for blood prior to injecting to prevent serious complications
* Never inject if you feel resistance (this will decrease the chance of intraneural injection)
* Carefully select the correc gauge (smaller is generally better) needle & length for a particular px
* Be sure to use sterile needles & solutions for each px
* Allow adequate time after admin for the onset of the block before proceeding w/ a painful procedure
* Understand the potential risks of doing the LA tech as well as species specific toxic doses prior to admin
* Label the syringe & do no interchange drugs
32
What are neurologic toxic effects of LA
* Sudden alteration in mental state or sedation
* Agitation
* Muscle twitching
* Nystagmus
* Seizures
* Coma
33
What are cardiorespiratory effects of LAs
* Respiratory arrest
* Cardiac dysrhythmias
* Hypotension due to vasodilation
* Myocardial depression/cardiac toxicity
* Death
34
What is required to produce signs of CV system toxicity than to produce CNS toxicity
Larger doses
35
What are some other potential effects?
* Methemoglobinemia more likely to occur in a cat
* Don't recommend using in a px that are hypotensive or in show (cause increased vasodilation due to sympathetic blockade -> CV collapse)
* Contraindicated to use a local ax tech in a px w/ coagulopathy due to possible hemorrhage
* Inhalant ax decreases metabolism of lidocaine in cats
* Allergic rxn are rare but could occur w/ the use of ester type LA
36
Haw can you tx LA systemic toxicity
* Usually see CNS signs before CV unliss bupivacaine was given IV or the px has decreased hepatic fxn
* Stop admin of the LA
* Start CPR if cardiac arrest
* Anticonvulsants
* Supplemental oxygen, intubation, & ventilation
* Cont moinitoring of ECG & blood pressure
* Consider IVF, vasopressors, inotropes, & antiarrhythmics as needed
* IV lipid emulsion therapy
37
What are some species specific considerations of LAs
* Cats have limited ability to metabolize LA so they are more susceptible to toxicity from lidocaine & bupivacaine
* Cats are @ an increased risk for dev methemoglobinemia & heinz body anemia w/ certain local ax
* Avoid use of benzocaine in ferrets & other small exotics
* Carefully calculate dosages for kids & lambs if dehorning or castration procedure planned (easy to overdose them b/c small body mass & high vascularization of horn bud)
38
What basic equipment is needed
* needle (27 to 18 g; 2 to 9 cm)
* Syringes (1 to 20 mL)
39
What advanced equipment is needed for LAs
* Peripheral nerve stimulators used to improve accuracy of LA blocks
* Insulated needles w/ injection port
* Ultrasound
* Epidural catheter kit
40
Describe an infiltration of LA
* Line block: going right to the side of the incision
* Field block for biopsy
* Splash block for enucleation
* Ring block in cats for declaw
* Inverted L block used more in food animal
* Diffusion catheter is placed in the incision during closure
41
Describe intercostal blocks
* Indications: analgesia for thoracotomy, rib fractures, & prior to chest tube placement
* Landmarks: Caudal edge of rib (avoid vein & artery), as proximal to the spine as feasible to anesthetize the region distal to injection, block 2 to 3 IC spaces cranial & caudal to the areas affected for better results due t overlapping nerve supply, & avoid depth of needle going past rib as it may penetrate the pleura
42
Describe an interpleural block (intrapleural block)
* For post op management of thoracotomy/sternotomy to provide analgesia to the thoracic cavity & cranial abdominal cavity
* Can do a one time block or place an indwelling thoracic drain/catheter for repeated blocks
43
Describe an intraperitoneal block
* Provides analgesia to the abdominal cavity (specifically viscera) LA applied in the abdomen prior to closing the linea alba
44
Describe a intratesticular block
* Split 2mg/kg lidocaine btw/ the 2 testicles
* Can be performed in cats, just decrease dose by half
* Can reserve a small amount for pre-scrotal line block in dogs
* Clip & prep the surgical area
* Use a 22-25 g needle
* Aspirate prior to injection
* Lidocaine travels up the spermatic cord to achieve max effect in a few mins
45
Describe a retrobulbar block
* Provides ax to the eye including the conjunctiva, cornea, & uvea
* Complications include hematoma, IV injection, nerve damage, & subarachnoid injection
* Use with caution
46
Describe an auriculotemporal nerve & great auricular nerve block
* Provides analgesia for the external ear canal & auricular pinna
* Could produce temporary paralysis of nerves which prevents the patient from blinking so recommended to lubricate the eye every 2 hours
47
Describe a mental nerve block
For procedures involving rostral mandible & associated teeth, & rostral lower lip
48
Describe an infraorbital nerve block
* For procedures involving the rostral part of the maxilla (skin, lip, maxilla, maxillary teeth, palate, & nasal cavity)
* Effectiveness of block depends o whether the injection is made inside the foramen or only @ the entrance
49
Describe a maxillary nerve block
* For procedures involving the maxilla, upper teeth, nares/nasal cavity, palate, & upper lip
* Could perform bilaterally for a rhinoscopy
50
Describe a mandibular nerve block (inferior alveolar)
For procedures involving the mandible, lower lip, & dental extractions
51
Describe a brachial plexus block
* Can provide analgesia to the elbow & structures distal to it (accuracy improved w/ peripheral nerve stimulator)
* Risk of hemorrhage or IN injection, pneumothorax, & Horners syndrome
52
Desribe a radial/ulnar/median/musculocutaneous block (RUMM block)
* Provides ax to distal thoracic limb (carpus & paw)
* Simple to perform once you locate the anatomy
53
Describe a cervical paravertebral block
* Provides analgesia & muscle relaxation to upper thoracic limb (including the proximal shoulder & humerus)
* Difficult to perform
54
Describe an IV regional anesthesia block (bier block)
* Access vein in leg (cephalic or saphenous) distal to tourniquet site
* Desanguinate limb by wrapping w/ an esmarch bandage (start distal & wrap prox)
* Inject lidocaine IV (max effect in 5 to 10 min)
* Never leave tourniquet on more than 90 mins
55
Describe a femoral/saphenous nerve block
* Commonly comboed w/ the sciate nerve block to achieve ax of the pelvic limb (distal to mid femur)
* The use of the ultrasound decreases the time for completion of the block
* The rate of complications & also less LA is used
56
Describe a sciatic nerve block
* This block alone is sufficient to perform sx of the foot & hock
* Always combine the two blocks for surgeries involving the stifle
57
What is used for a pelvic limb regional ax blocks
Bupivacaine combined w/ dexmedetomidines most commonly used
58
What does an ultrasound guided transverse abdominis plane block (TAP) do
Provides analgesia to the ventral & lateral abdominal wall including skin, mammary glands, abdominal sub Q tissue, & abdominal muscles/ parietal peritoneum
59
Describe a lumbosacral epidural & spinal blocks
* Useful in ortho sx of the hindlimb & also for abdominal exploratory sx
* Blocks sensory, motor, & sympathetic fibers
* Decreases concentration of inhalant agent (MAC reduction) & causes muscle relaxation
* Post op analgesia for 12 to 24 H
* Clip & steril pre w/ sterile gloves
* Use preservative free morphine
* 20 to 22 gauge spinal needle
60
Describe the epidural & its landmarks
* Cranial border of the wings of the ilium
* Line connecting the wings crosses dorsal spinous process of L7
* Directly caudal feel depression of lumbosacral jxn (L7-S1)
* Sternal or lateral recumbency
* Place needle in center of depression on dorsal midline. Direct bevel of needle rostrally
* Advance the needle until it penetrates ligamentum flavum (popping sensation)
* If bleeding occurs the needle probably has been advanced too far
* Test dose .5 to 1 ml of air or saline to test for resistance. Aspirate gently to insure needle is not in vein
* Inject slowly over 1 to 2 mins
* If CSF present 1/2 the total volume of drug is admin as a spinal or intrathecal
61
What are some of the contraindications of an epidural
* Px w/ increased intracranial pressure
* Clotting disorder
* Hypovolemic px
* Degenerative central or peripheral axonal disease
* Anatomical abnorms
* Skin infections @ the epidural space
62
What is a caudal epidural
* Newer tech described to facilitate catheterization in male cats w/ urethral obstruction (or other perineal procedures)
* Avoids the need to induce general anesthesia in compromised px & also provides pain relief
63
Describe intra-articular blocks
* Usually inserted sterilely after joint exploration & closure
* Can use lidocaine or bupivacaine
* Morphine is useful for chronically inflammed joints
64
What are some topical LAs
* Lidocaine patches
* Topical cream
* Proparacaine ophthalmic solution
* Lidocaine sprayed on the larynx
* LA applied to the urethra
65
What are the tips for success w/ LA tech
* Have the appropriate equipment readily ava
* Review anatomy for your px
* Understand LA drug pharmacology
* Know what the potential complications & contraindications are for each tech used
* Have a tx plan prep in case of complications
* Prepare another plan for analgesia in case you block doesn't work or block is contraindicated for your px current status
* Practice, practice, practice
* Keep up w/ current literature
