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Anesthesiology > Regional Anesthetics > Flashcards

Regional Anesthetics Flashcards

1
Q

What’s the difference between nociception and pain?

A

Pain = perception and awareness of noxious stimulus

Nociception = activation of nociceptors while unconscious

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2
Q

A nociceptive stimulus causes what 2 physiologic processes to occur?

A
  1. sympathetic stimulation - catecholamine release > incr HR/BP
  2. stress response - ACTH release > incr cortisol/BG
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3
Q

What are 3 reasons to provide regional anesthesia?

A
  • pre-emptive analgesia - abolish afferent nociception, reduction of anesthetic/analgesic drugs
    • reduction of intraoperative complications
  • better intra and postoperative pain control - faster return to normal activities
  • prevents stress response - better immune system activity
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4
Q

What is an aminoester?

A
  • hydrolyzed by cholinesterase enzyme
  • causes anaphylactoid reactions

e.g. procaine, tetracaine, benzocaine, cocaine

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5
Q

What is an aminoamide?

A
  • hepatic metabolism (microsomal enzymes)
  • slow metabolism
  • toxicity from accumulation is more likely

e.g. lidocaine, bupivacaine, ropivacaine, mepivacaine

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6
Q

Local anesthetics are essentially what two types of compounds linked together?

A

a lipophilic unit linked to a hydrophilic unit

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7
Q

What is the MOA of local anesthetics?

A
  1. Local anesthetic needs to penetrate into cell to produce its effects
  2. Blockade of Na+ channel
  3. Prevents Na+ influx > no depolarization > no impulse transmission
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8
Q

What are the lipid properties of local anesthetics?

A
  • lipid solubility
    • correlates w/ potency: more lipid soluble = more potent (ie. bupivicaine)
    • facilitates penetration thru nn membranes
    • promotes sequesteration into lipid-soluble compartments (ie. myelin) > slower onset + longer duration of action
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9
Q

What does pKa stand for and what properties does it instill for local anesthetics?

A

pKa = dissociation constant

  • pH at which 50% of drug is present ionized (charged) and 50% is unionized (neutral)
  • unionized = lipid soluble
  • degree of ionization will depend on pKa and pH of tissue
  • local anesthetics are weak bases > ionized in acidic pH
    • local anesthetics are ion trapped in acidic environments
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10
Q

What happens with the local anesthetic effect for a drug like lidocaine with a pKa of 7.8 in infected tissue with a pH of 6.5?

A

Much more of the drug will be ionized when injected into the infected tissue, thus there will be fewer unionized liposoluble molecules available to have an anesthetic effect

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11
Q

What 5 things affect the effect of local anesthetics?

A
  1. pH/pKa
  2. proximity
  3. dose
  4. volume
  5. spread
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12
Q

What 6 things affect the onset of local anesthetics?

A
  1. lipophilicity
  2. pKa
  3. concentration
  4. dose + volume
  5. proximity to nerve
  6. type of nerve
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13
Q

What 5 things affect the duration of local anesthetics?

A
  1. vascular effect
  2. tissue blood flow
  3. vasoconstrictor
  4. dose
  5. affinity to the Na+ receptor
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14
Q

Smaller nerve fiber are ______ susceptible to local anesthetic b/c shorter length of axon is required to be blocked to halt the conduction completely

_______ fibers are more susceptible to be blocked b/c local anesthetic pools near the axonal membrane

A

more; myelinated

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15
Q

Nerve block onset occurs in what order?

A
  1. pain
  2. cold
  3. warm
  4. touch
  5. deep pressure (more evident in long acting LA)
  6. motor function

(Pain —–> motor function)

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16
Q

What is the clinical utility of knowing the order of senstations lost due to nerve block onset?

A

low concentrations of local anesthetic can provide analgesia with mild effects on motor function

17
Q

What 3 things are associated with toxicity of local anesthetics?

A
  • high dose (high plasmatic level)
  • direct IV injection
  • reduced biotransformation or elimination (liver/renal dz)
18
Q

What are potential CNS signs of LA toxicity?

A
  • onset before CV signs (except bupivacaine)
  • depression of cortical inhibitory pathways
  • impaired vision
  • tremors/seizures
  • CNS depression
  • coma
19
Q

What are the CV signs of LA toxicity?

A
  • bradycardia
  • incr PQ interval/QRS duration
  • VPCs
  • reduction of myocardial contractility
  • CV collapse/cardiac arrest
20
Q

What’s one way to ensure you don’t cause LA toxicity?

A

aspirate before injection to rule-out intravascular injection

21
Q

What are the targets and basic principles behind topical/surface anesthesia?

A
  • target structures: free nerve endings, nociceptors
  • anesthesia for superifical mucosal structures
  • generally LA cannot cross epidermis
22
Q

What are some uses for topical/surface anesthesia?

A
  • larynx - avoid laryngospasm during intubation
  • splash block - local application before wound closure, reduce perioperative pain
  • corneal - proparacaine drops - eye exam
  • skin densensitization - EMLA cream (lidocaine + prilocaine) - venipuncture/small mass removal
23
Q

What are the targets and basic principles behind local infiltration?

A

Targets: free nerve endings, nociceptors - does not target specific nerve

  • anesthesia for skin and underlying structures
  • when incisions are deep, all tissue layers are infiltrated
  • injection of LA solution into/around planned sx field
24
Q

What are some uses for local infiltration?

A
  • resection of cutaneous/superficial masses
  • sx closure of lacerations
  • procedures involving an appendage
  • line block - over/around incision line, SQ and underlying tissues have to be infiltrated
  • intratesticular block - castration
  • inverted L - flank laparotomies in ruminants - inj far from incision site, anatomy of incision line not altered, large vol of LA required
  • ring block - around extremity, distal limb, tail, horn
25
Q

What are the principles behind peripheral nerve blocks?

A
  • injection of LA around a periph nn to temporarily block sensory and/or motor functions for perioperative pain control
  • injection of small vol of LA produces great amt of desensitization
  • precision plays important part in success rate - intraneural injections produce nn damage
26
Q

What are some examples and uses for peripheral nerve blocks?

A
  • infraorbital n. block - dental procedures (careful in cats/brachycephalics!)
  • maxillary n. block - dentals, jaw sx
  • inferior alveolar (mandibular) n. block
  • intercostal n. block - 5 points (caudal to rib)
  • lumbar paravertebral n. block - flank sx for ruminants (proximal/distal), better analgesia than inverted L- target nn T13, L1, L2
27
Q

What are the principles and techniques for epidural anesthesia?

A
  • injection of LA in epidural space
  • Epidural space: b/t interacuate (flavum) ligament and dura mater
  • produces segementary analgesia (vol/dose dep)
  • lumbo-sacral space - used in SA (SC ends at L7)
  • sacrococcygeal space - used in LA (SC ends in sacrum)
28
Q

What’s the difference between epidural and spinal anesthesia?

A

spinal - you inject LA in the subarachnoid space

epidural - inject LA outside the dura mater - need to penetrate interarcuate ligament - your landmark as the roof of the epidural space

29
Q

What are your landmarks for epidural anesthesia in small animals?

A
  • iliac crest
  • medial sacral crest
  • spinous process of L7
30
Q

Why must you make sure to only use small volumes of LA when performing a sacrococcygeal or intercoccygeal epidural in large animals?

A

to avoid sciatic nerve block, which would affect function of the pelvic limb

31
Q

What is another name for an epidural needle?

A

a Tuohy needle

32
Q

What are 2 ways to determine if the needle is in the epidural space?

A
  1. hanging drop technique
  2. loss of resistance to injection
33
Q

Describe the hanging drop technique

A
  1. advance Tuohy needle until interacuate ligament is perceived
  2. remove stylet and fill hub of needle with saline
  3. when needle enters epidural space, the drop should be aspirated
  4. false negatives can occur
34
Q

Describe the loss of resistance technique

A
  1. Advance Tuohy needle until the interacuate ligament is perceived
  2. Removed 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 epidural space
35
Q

What are 3 ways of locating the nerves?

A

blindly, using electrolocation (electric nerve stim), U/S

36
Q

What are some issues with blindly finding nerves for LA?

A
  • relies on experience of operator
  • subjective
  • variable success rate
  • higher vol of LA needed
  • higher nerve puncture/damage
  • individual anatomical variation
37
Q

What are the advantages of using electrolocation for LA?

A
  • electrical current used to depolarize the motor component of a mixed nerve
  • high success rate
  • lower volume of LA needed
38
Q

What are the advantages of using U/S to locate nerves for LA?

A
  • real time visualization of nn and vascular structures
  • gold standard
  • high success rate
  • allows visualization of LA spread around nerve

But….

  • expensive equipement
  • learning curve

Anesthesiology (12 decks)

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