LA and ultrasound Flashcards
1
Q
what is the lipophilic portion of a LA
A
- benzene ring
- it is necessary for activity
2
Q
ester chemical structure
A
-CO-
3
Q
amide chemical structure
A
-NHC-
4
Q
what is the hydrophilic portion of LA
A
- quaternary amine
5
Q
intracellular pH
A
7.0
6
Q
extracellular pH
A
7.4
7
Q
s enantiomer
A
left = sinister
8
Q
r enantiomer
A
right = rectus
9
Q
what are pure isomers
A
- they only have one type of enantiomer (s or r)
- ropivacaine and levobupivacaine (both s)
10
Q
benefit of s enantiomer
A
- less neuro and cardio toxic
11
Q
MOA of LA
A
- inhibits Na channels by binding to alpha subunit, slowing rate of depolarization not allowing threshold potential to be reached
- binds in activated and inactivated states
- binds on internal part of channel
- weak binding
12
Q
frequency dependent blockade
A
- only has access when receptor is open
- nerves with more activity = faster blockade
13
Q
what is Cm
A
- minimum concentration to produce blockade
14
Q
factors that effect Cm
A
- larger diameter increases Cm
- high frequency and higher pH decreases Cm
15
Q
Cm for motor to sensory
A
- Cm for motor is twice sensory = sensory block with no motor
16
Q
Cm epidural vs spinal
A
- unchanged Cm
- direct access to nerves = less amount
17
Q
how many node of Ranvier must be blocked
A
- at least 2, preferably 3
18
Q
order of blockade with fibers
A
- B fibers (preganglionic SNS fibers)
- C and A-delta fibers (pain, temp, touch) (afferent)
- A-gamma fibers
- A-beta fibers
- A-alpha fibers
19
Q
order of blockade “senses”
A
- autonomic
- temp
- pain
- touch
- pressure
- motor
- vibration
- proprioception
20
Q
what is a weak base pK value
A
7.6 - 8.9
21
Q
base plus acid =
A
- more ionized
- just about physiological pH = >50% ionized
- locals with pks nearest physiologic pH = faster onset
22
Q
what form can cross the lipid bylayer
A
un-ionized
23
Q
what is the weak acid local
A
- benzocaine
- pKa of 3.5
24
Q
pKa of lidocaine
A
7.9
25
alkalinization
- adding bicarb raises pH closer to pKa = faster onset by 3-5 min
26
distribution of LA
1st uptake into lungs
2nd distribution into high perfused areas (heart, brain, kidneys)
3rd low perfused areas (muscle, fat)
- amides are more widely distributed
27
protein binding of LA
- bupivacaine and ropivacaine highly bound
- lido not as much
- proteins are to large to cross the placenta
28
why is placental transfer of LA important
- causes ion trapping
- unionized LA crosses placenta and hits low fetal pH = drug becomes ionized and cant cross back = toxicity in fetus
29
what is potency of LA related to
- lipid solubility
- more lipid soluble = easier to cross lipid by-layer
30
what is the onset of a LA related to
- state of ionization (most important)
- lipid solubility
31
DOA is related to
- protein binding & lipid solubility
- higher affinity to proteins and lipids = stronger attachment = drug remains close to Na channels to act longer
32
metabolism of amides
- mainly hepatic
- minimal renal
33
amide LA clearance fastest to slowest
- fastest = prilocaine
- intermediate = lido & mepivicaine
- slowest = etidocaine, bupivacaine, ropivacaine
34
metabolism of esters LA
- rapid hydrolysis from cholinesterases in plasma and liver
- cocaine is an exception, in liver
35
ester LA clearance fastest to slowest
- rapid = chloroprocaine
- intermediate = procaine
- slow = tatracaine
36
what are the metabolites of ester LA
- paraaminobenzoic acid (PABA) (causes allergies)
37
what local injection site contains little to no cholinesterase enzyme
- CSF
- must wait until drug goes into systemic circulation
38
plasma cholinesterase is inhibited
- deficiency
- liver disease
- increased BUN
- parturients
- chemo pts
39
Epi as an additive
- marker for intravascular injection
- 1:200,000 or 5mcg/ml
- limits systemic absorption (decrease toxicity)
- no effect to onset, prolongs DOA
40
which 2 LA have no vasodilator activity
- cocaine
- ropivacaine
41
pH of lido 2%
6.5
42
pH of lido 2% w/epi
4.5
43
what are the effects of mixing locals
effects are additive not synergistic
faster onset and longer DOA
44
max dose of bupivacaine
plain = 175 mg (2.5 mg/kg)
w/epi = 225 mg (3 mg/kg)
45
max dose of etidocaine
plain = 300 mg (4mg/kg)
w/epi = 400 mg (5mg/kg)
46
max dose of lidocaine
plain = 300 mg (4.5 mg/kg)
w/ epi = 500 mg (7mg/kg)
47
max dose of mepivacaine
plain = 300 mg (4.5 mg/kg)
w/ epi = 500 mg (7mg/kg)
48
max dose of prilocaine
plain = 500 mg (6 mg/kg)
w/epi = 600 mg (9mg/kg)
49
max dose with ropivacaine
plain = 200 (2.5mg/kg)
w/epi = 200 (2.5 mg/kg)
50
max dose of chloroprocaine
plain = 800 (12mg/kg)
w/epi = 1000 (15mg/kg)
51
max dose of cocaine
plain (3 mg/kg)
52
max dose of procaine
plain = 500 (7 mg/kg)
w/epi = 600 (8 mg/kg)
53
max dose of tetracaine
plain = 100 (1.5 mg/kg)
w/epi = 200 (2.5 mg/kg)
54
Hadzic's progression
- signs from toxic effects of LA
- vertigo
- tinnitus
- ominous feelings
- circumoral numbness
- garrulousness
- tremors
- myoclonic jerks
- convulsions
- coma
- CV collapse
55
systemic levels are related to BF of tissues (fastest to slowest)
- IV
- tracheal
- intercostal
- caudal
- paracervical
- epidural
- brachial plexus
- subarachnoid
- subcutaneous
(in time i can please everyone but suzi and sally
56
transient neurological symptoms (TNS)
- pain in lower back, buttocks, and posterior thighs
- sign of neurotoxicity
- highest risk with intrathecal lido
57
cauda equina syndrome
- diffuse injury across lumbosacral plexus
- bowel and bladder sphincter dysfunction
- paraplegia
- related to lido
58
anterior spinal artery syndrome
- lower extremity paresis and variable sensory deficit
59
cardiotoxicity w LA
- more resistant that CNS (3x blood concentration than seizures)
- profound hypotension
- bupivacaine may see CV before CNS @ (8-10 mcg/ml)
60
treatment of LA toxicity
- 100% fiO2
- benzos
- avoid propofol, vasopressin, CCB, BB, LA
- decrease epi to <1 mcg/kg
- lipid emulsion 20%
61
lipid emulsion dosing
-1.5 ml/kg LBW
- infusion @ .25 ml/kg/min, double rate if CV still unstable
- upper limit: 10ml/kg over first 30 min
62
methemoglobinemia
- hemoglobin oxidized to methemoglobin (cant carry O2)
- treatment = methylene blue 1-2mg/kg IV over 5 min, do not exceed 7.8 mg/kg
