Local Anesthetics Flashcards by Giselle Carter

what are the two types of local anesthetics? which has a longer duration of action?

esters (ROR) and amides (RNR); amides have a longer duration of action

How well did you know this?

Not at all

Perfectly

all new local anesthetics are

amides (RNR)

How well did you know this?

Not at all

Perfectly

what do local anesthetics do

block pain without causing unconsciousness

How well did you know this?

Not at all

Perfectly

what is the MOA of local anesthetics

block Na channels -> inhibits APs in all neurons, as well as myocytes

How well did you know this?

Not at all

Perfectly

what is the order in which local anesthetics block

small fibres (ex. pain) are blocked before large fibres (ex. motor)

How well did you know this?

Not at all

Perfectly

where is the receptor for local anesthetics and what does this imply

on the cytoplasmic surface; must diffuse in the cell to produce effect

How well did you know this?

Not at all

Perfectly

why are local anesthetics slower to produce an effect in inflammed or infected tissues

because they are weak bases, so they are protonated and ionized in an acidic environment, which prevents them from diffusing into the cell to block the Na receptor and cause effect

How well did you know this?

Not at all

Perfectly

what combination with local anesthetics can produce necrosis

when lidocaine and epinephrine are used SQ

How well did you know this?

Not at all

Perfectly

why might someone use lidocaine with epinephrine in practice

because lidocaine works until it diffuses away; by combining with a vasoconstrictor (E) we slow its removal and therefore prolong its action

How well did you know this?

Not at all

Perfectly

what are some considerations if you were to use lidocaine with epinephrine

it slows the healing
do not use in end-artery supplied organs (ears, teats, digits, nose, penis…)

How well did you know this?

Not at all

Perfectly

what are the first signs of local anesthetic overdose

drowsiness and muscle twitching

How well did you know this?

Not at all

Perfectly

as plasma concentration of local anesthetics rises what happens

convulsions, unconsciousness, coma

How well did you know this?

Not at all

Perfectly

what is a potential CVS side effect of LAs

blocks excitability of myocardium: AV block and arrhythmia

How well did you know this?

Not at all

Perfectly

what are some examples of lidocaine formulation

injectible +/- epinephrine
gel
spray (ex. for intubating cats)

How well did you know this?

Not at all

Perfectly

what is a consideration before reaching for lidocaine spray in difficult to intubate cats

they are more susceptible to CVS effects and seizures

How well did you know this?

Not at all

Perfectly

what type of LA is lidocaine

an amide (RNR)

How well did you know this?

Not at all

Perfectly

what LA is used for equine nerve blocks

mepivicaine

How well did you know this?

Not at all

Perfectly

why does mepivicaine diffuse better in tissues and what is a consequence of this?

it has a lower pKa -> favours B form (unionized); greater toxicity compared to lidocaine

How well did you know this?

Not at all

Perfectly

what are 3 characteristics of bupivicaine

slower onset (higher pKa) but longer action
4x as potent as lidocaine
greater CVS toxicity so not available as IV

How well did you know this?

Not at all

Perfectly

how does levobupivicaine relate to bupivicaine

it is the s(-) enantiomer

How well did you know this?

Not at all

Perfectly

why is levobupivicaine safer than bupivicaine

does not distribute as well to the CNS or heart

How well did you know this?

Not at all

Perfectly

what is the least irritating LA for eyes

proparacaine

How well did you know this?

Not at all

Perfectly

long term use of proparacaine is related to

corneal sloughing and delayed healing

How well did you know this?

Not at all

Perfectly

what is a “use-dependent block”

lidocaine blocks highly active Na channels more than resting Na channels because, in order to bind to the cytoplasmic part of the Na receptor, it needs to be open (vs. closed, resting sodium channels)

How well did you know this?

Not at all

Perfectly

how does lidocaine have an anti-arrhythmic effect in low concentrations

arrythmias are related to unusual and frequent depolarizations of Na channels in damaged cardiac muscle; lidocaine blocks these random and unusual depolarizations but preserves the less frequent, normally functioning signals via the use-dependent block effect

what should you never use if giving lidocaine systemically

products containing epinephrine (will impact HR and BP)

are esters or amides more resistant to enzymatic activity

amides

T/F amide LAs are more stable under sterilization and temperature extremes

LA enters the nerve fiber as a _________ base and the (ionized/unionized) form blocks conduction by interacting at _______ surface of the _____ channel

neutral/free base; ionized; inner; Na+

local anesthetics with a (higher/lower) pKa have more rapid onset of action

lower

describe what determines the following chemical properties of LAs: - potency - duration - onset of action

potency: lipid-solubility duration: protein binding onset of action: pKa

lidocaine vs bupivicaine: - which has higher potency - which has higher duration of action - which has higher onset of action

bupivicaine for all 3

describe the channel type based on the following affinity of Na: - low - intermediate - high

- low: closed - intermediate: open - high: inactivated

T/F LAs block sensory, motor and autonomic pathways

what is the order of blockage for LAs:

β < C < Αδ< Aα < Aβ

T/F all fibers can be blocked by a LA, but some fibers may NOT be blocked

T/F cats are more sensitive to LA toxicity compared to dogs

put sites in order of fastest to slowest rate of absorption: - SQ - epidural - spinal - intercostal - major nerve block

intercostal > spinal > epidural > major nerve block > SQ

what should you keep a dose below for the following LAs: - lidocaine - bupivicaine

lidocaine: below 8 mg/kg bupivicaine: below 2 mg/kg

T/F most blocks are like IM/SQ injection

With LA toxicity, we see ______ signs before ______ signs, but anesthesia masks _____ signs. Thus, you should watch ____ signs when a patient is anesthetized and ____ signs when a patient is awake

CNS; CVS; CNS; CVS; CNS

in terms of LAs, you can only give ____________ intravenously

lidocaine

LAs: __ blood loss, __ thromboembolism risk, __ perfusion

decrease; decrease; increase

what is the general rule for the dose of LA (mL/kg)

0.2 mL/kg

what are the 8 ways to clinically apply local anesthetics

1) topical 2) regional 3) catheter 4) splash 5) IVRA 6) neuraxial 7) infiltration 8) IV

what is topical administration of local anesthetic

direct application to eyes, skin, mucous membranes, wounds

what are three examples of topical LAs

1) lidocaine spray: facilitates intubation 2) skin: EMLA cream 3) proparacaine for direct application to cornea and conjunctiva

what is a splash block

direct application to surgical site/cavity before closure

what is infiltration

injected into tissue without anatomical concern regarding innervation

what are examples of infiltration

incisional block for laparotomy, ring block

what amount (mL) do you give for infiltration in the following species: - horse/cow - dog/sheep/goat - cat

- horse/cow: 100-200 mL - dog/sheep/goat: 5-15 mL - cat: 1-2 mL

testicular block is an example of

infiltration

inverted L block is an example of

infiltration

where is the LA for a testicular block deposited

spermatic cord and testicular tissue

what is a regional block

when LA is injected adjacent to sensory neurons

what are some examples of regional blocks

- brachial plexus block - sciatic block - RUMM block - retrobulbar block - head block - paravertebral block

what nerves does the retrobulbar block stop

CN II, III, IV, V, VI and the ciliary ganglion

what is the risk with retrobulbar blocks and what do we take from it

can cause proptosis, blindness, globe perforation, retrobulbar hemorrhage; should only use if you are enucleating

what 4 head blocks are performed in small animals every day

1) mental 2) infraorbital 3) maxillary 4) mandibular (inferior alveolar)

what nerves does the brachial plexus block stop

C6-8, T1

what is blocked by the paravertebral thoracolumbar block

T13, L1, L2, L3 dorsal and ventral branches

what 3 nerves do we block in a cornual nerve block and what is the additional nerve if an adult

All: - cornual - infratrochlear - supraorbital Adult: - branches from C2

what is another name for the cornual nerve

zygomaticotemporal

dehorning in goats is different because they receive dual supply from

zygomaticotemporal and infratrochlear

what is IVRA

intra-venous regional anesthesia: IV in a distal limb that has had its blood supply isolated using a tourniquet

what are the two most common neuraxial LAs and what is used more often in vetmed

epidural and subarachnoid: epidural more common in vetmed

what are the 2 epidurals we use

caudal and lumbosacral

what does a lumbosacral epidural block

hindlimb and caudal abdomen as well as motor fibres

how do we commonly administer a lumbosacral block (what drugs)

opioid and lidocaine or bupivacaine

what does a sacrococygeal epidural block

anus, vulva, vagina, perineum, rectum, tail

what is a useful block for feline urethral obstruction

sacrococygeal

what do we commonly use for sacrococygeal block and why

lidocaine: faster onset

what are some applications of IV lidocaine

- analgesia/ MAC reduction - antiarrhythmic - antiinflammatory - anti-endotoxic - good for GI motility - neuropathic pain

because local anesthetics can be cardiotoxic, it is important to monitor (2)

ECG and blood pressure

what are some contraindications for local anesthetics

- infection - allergic reacton - tumors - coagulopathies - cardiac disease