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Anesthesia > Local Anesthesia > Flashcards

Local Anesthesia Flashcards

1
Q

What is the mechanism of action of local anesthetics? What does this result in?

A

lipophilic. unionized local anesthetic crosses the phospholipid membrane and dissociates into the ionized form, binding to and blocking voltage-gated Na+ channels = initial opening followed by stabilization

suppression of action potential in excitable tissues, increased firing threshold, lengthened refractory period = prevented conduction and propagation of nerve impulses as concentration increases

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2
Q

What amino ester is used as a local anesthetic? What is onset, potency, and duration like

A

Procaine - 8.9 pKa

  • 10-20 min
  • low potency
  • short duration (30-60 mins)
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3
Q

What are 2 short-acting amino amides used as local anesthetics?

A

LIDOCAINE (7.9) - 5-10 min onset, intermediate potency and duration of action (60-120 mins) —> good for laceration repair

MEPIVACAINE (7.7) - 5-10 min onset, intermediate potency and duration of action (90-180 mins)

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4
Q

What are 2 longer acting amino amides used as local anesthetics?

A

BUPIVACAINE (8.1) - 10-20 min onset, high potency, long duration of action (180-360 min)

ROPIVACAINE (8.1) - 10-20 min onset, high potency, long duration of action (120-240 min)

should be onboard well in advance

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5
Q

What fibers are affected by lidocaine, bupivacaine, and ropivacaine?

A

LIDOCAINE - non-specific, blocks all fiber types

B/R - sensory > motor

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6
Q

How does the location of nerve bundles affect onset of action of local anesthetics?

A
  • superficial nerve bundles are penetrated first
  • proximal areas blocked sooner than distal areas

(femoral-sciatic = knee before tarsus)

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7
Q

How does myelination affect onset of action of local anesthetics?

A

small myelinated and unmyelinated fibers blocked before large myelinated fibers

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8
Q

What affects the discharge rate of local anesthetics?

A

local anesthetics’ higher binding affinity for open and inactivated channels compared to activated channels (phasic or use-dependent blockade)

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9
Q

What is the order of the first 5 neuron types in the blockade? What do they result in?

A
  1. B - increased skin temperature
  2. A delta, C - pain relief, loss of temperature sensation
  3. A gamma - loss of proprioception
  4. A beta - loss of sensation to touch and pressure
  5. A alpha - loss of motor function

pain relief before blocked motor function

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10
Q

What are the recommended doses of lidocaine in dogs, cats, horses, and cattle?

A
  • DOGS: 2-6 mg/kg
  • CATS: 0.5-1 mg/kg
  • HORSES/CATTLE: max 6 mg/kg
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11
Q

What are the recommended doses of mepivacaine in dogs, cats, and horses?

A
  • DOGS: 5 mg/kg
  • CATS: 2-3 mg/kg
  • HORSES: max 5-6 mg/kg
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12
Q

What are the recommended doses of bupivacaine in dogs, cats, and horses?

A
  • DOGS and CATS: 2 mg/kg
  • HORSES: 2 mg/kg (toxic at 4 mg/kg)
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13
Q

What are the recommended doses of ropivacaine in dogs and cats?

A
  • DOGS: 2 mg/kg
  • CATS: 1.5 mg/kg
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14
Q

What toxicities are associated with the use of IV lidocaine?

A
  • CNS: seizures, nystagmus, muscle twitching, hypoventilation, respiratory arrest
  • CV signs: depressed myocardial automaticity, reduced refractory period duration, reduced contractility and conduction velocity
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15
Q

What CV are associated with lidocaine and bupivacaine/ropivacaine? What ECG changes are expected?

A
  • LIDOCAINE: hypotension
  • B/R: profound arrythmias

wide or inverted QRS, bradycardia, VPCs, V-tach

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16
Q

What is the best treatment to avoid local anesthesia toxicity? What supportive therapy is recommended?

A

avoid IV administration

  • oxygen
  • anti-seizure medication
  • IV fluids
  • vasopressors, inotropes
  • anticholinergics
  • antiarrhythmics (bretylium magnesium)
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17
Q

What is lipid rescue?

A

Intralipid - 20% IV lipid emulsion to extract the lipid soluble local anesthetic from aqueous plasma phase and make it unavailable to tissues

  • bolus 4 mL/kg followed by 0.5 mL/kg/min for 10 mins
18
Q

What formation of local anesthetics should be used for epidurals? What technique is recommended?

A

preservative-free

  • sterile technique
  • aspirate before injection and anytime the needle is repositioned
  • if there is resistance to injection, STOP - most likely in the nerve bundle
19
Q

How can resistance to injection be detected for local anesthetics?

A

use a 3 mL syringe and have an air bubble to watch for compression

  • note: dental blocks are done with 1 mL syringe, so detection is difficult
20
Q

What vasoconstrictor is used as an adjunct? Alpha-2 agonist? Opioid? What do they do?

A

epinephrine - increases intensity and duration of block

dexmedetomidine - enhances local anesthetic duration of action

buprenorphine - enhances peripheral nerve blcoks cia sodium channel mechanism

21
Q

How is sodium bicarbonate used as an adjunct?

A

decreases pain on injection, but not likely to speed up onset of action

22
Q

What risk is associated with epinephrine usage as adjuncts?

A

ischemic damage to nerve and surrounding tissues (vasoconstrictor!)

23
Q

What are the most common adjuncts used as local anesthetics? Why are they commonly diluted?

A

opioids and dexmedetomidine (variable use among clinicians due to variable effectiveness in different species)

when max dose is reached, it allows for large areas of distribution without increasing dose any more

24
Q

What is sarapin?

A

biologic derived from pitcher plant used as a local anesthetic, usually for chronic pain - limited data available

25
Q

What is Nocita?

A

liposome encapsulated bupivacaine given in the fascial plane and slowly released over 72 hours (cat dose 2x > dog dose)

  • DON’T SHAKE, disrupts liposomes
26
Q

Surgical pain flow chart:

A
27
Q

What block is used for the perineal region? What effect does it have?

A

sacrococcygeal block (coccygeal epidural)

doesn’t block pelvic limb motor function, but blocks the perineum (can go further down the tail for amputations)

28
Q

What are 3 buprenorphine options for cats?

A
  1. standard buprenorphine given IV, IM, or OTM
  2. Simbadol given SQ (high concentration, 24 hours)
  3. Zorbium given transdermal (higher concentration, 3-4 days)
29
Q

How is Zorbium part of the feline TGH analgesic plan?

A

transdermal buprenorphine (sit for 30 mins) with 3-4 days duration at 20 mg/mL

30
Q

What are 4 options for tibial plateau leveling osteotomy (TPLO) for cruciate rupture?

A
  1. epidural opioid
  2. epidural local anesthetic
  3. epidural opioid + local anesthetic
  4. nerve stimulator or ultrasound-guided femoral and sciatic nerve blocks with local anesthetic
31
Q

What are 5 effects of epidurals for TPLOs?

A
  1. motor impairment
  2. potential loss of sympathetic function with cranial migration
  3. risk of infection in epidural space
  4. urinary retention
  5. failure/ineffective due to technique
32
Q

What are 4 effects of nerve blocks for TPLOs? What technique is best?

A
  1. potential for duration longer than 6-8 hours with loss of limb function
  2. potential for nerve damage with intraneural injection
  3. risk of IV injection and toxicity
  4. failure/ineffective due to technique

US gives better localization/visualization

33
Q

What are 5 contraindications for epidurals?

A
  1. coagulopathy
  2. fractures
  3. dermatitis, skin infections, or lesions at site
  4. meningitis, myelitis, encephalitis, sepsis
  5. shock and hypovolemia
34
Q

When should dental nerve blocks be given? What agent is most commonly use?

A

after radiographs identify needed extractions and 10-20 mins before procedure

Bupivacaine - 0.1-0.25 mL/site with max dose of 0.1 mg/kg

35
Q

What are the 4 basic dental blocks performed?

A
  1. maxillary
  2. infraorbital
  3. mandibular
  4. mental
36
Q

What types of block techniques are used for otic blocks?

A
  • soaker catheter
  • nerve blocks
  • Nocita
37
Q

What blocks are used for enucleations?

A

retrobulbar or peribulbar nerve blocks with 0.1-0.2 mg/kg of Bupivacaine or Lidocaine

38
Q

What limb block is able to be done visually? What technique is done for incisions?

A

ring blocks

line blocks

39
Q

What is risk associated with in Bier (IV) blocks? What 2 things should be avoided?

A

sudden infusion of local anesthetic into vasculature c

  1. use in cats
  2. > 1 hour use of tourniquet (ischemia!)
40
Q

What are intrapleural blocks most commonly used for? In what animals are they avoided?

A

thoracic-associated pain and pancreatitis

CATS have a higher toxicity concern due to the proximity of the agent to the heart and large vessels

41
Q

Lateral thoracotomy, example protocol:

A

Anesthesia (40 decks)

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