Unit 5

Question 1

Alpha fibers

Answer 1

alpha-skeletal muscle motor, proprioception
Beta- touch, pressure
Gamma- Skeletal muscle tone
Delta- fast pain, temp, touch

Question 2

Beta fibers

Answer 2

Preganglionc ANS fibers

Question 3

C fibers

Answer 3

Sympathetic- postganglionic ANS fibers

Dorsal root- slow pain, temp, touch

Question 4

Block onset

Answer 4

1. B
2. C
3. A gamma and A delta
4. A alpha and a beta

Question 5

VGNaC

Answer 5

1 alpha unit
2 betas
Resting (-70 mV): closed
Active (-70 to +35 mV): opens, Na flows outside to inside
Inactive (+35 to -70 mV): closed, inactivation gate until membrane potential reestablished
LA can bind in active and inactive phases- more frequent depol means more time for blockade (use dependent or phasic blockade)

Question 6

Resting membrane potential

Answer 6

-70
3 Na+ out and 2 K+ in

LAs do not impact resting membrane potential or threshold

Question 7

Mechanism of action LA

Answer 7

Weak bases
After injection LA dissociates into uncharge base and ionized, conjugate acid
PKa’s higher than 7.4= > 50% will exist as ionized conjugate acid
Uncharged base enters cell and becomes ionized due to acidic ECF
Only ionized, conjugate acid binds to LA binding site on alpha subunit

Question 8

LA molecule construction

Answer 8

Benzene ring- lipophilic
Intermediate chain- ester or amide (has NH in it)
Tertiary amine- hydrophilic

Question 9

Ester LA’s

Answer 9

No i before Caine suffix
Benzocaine, cocaine, chloroprocaine, procaine, tetracaine
Pseudocholinesterase metabolism
Low allergic potential- cross sensitivity if allergy happens, due to PABA

Question 10

Amide type

Answer 10

I before suffix Caine
Articaine, bupivicaine, etidocaine, lidocaine, mepivicaine, ropivicaine
Hepatic/P450 metabolism
Extremely rare allergies

Question 11

Onset of action

Answer 11

PKA- closer to pH of blood= larger fraction uncharged and able to cross and get to receptor

Dose- give large dose of chlorprocaine cause isn’t very potent even with high pKa
Concentration- higher concentration onset’s quicker

Question 12

Potency

Answer 12

Lipid solubility- can get inside drug and be available to bind to receptor

Intrinsic vasodilating effect- cocaine, chloroprocaine, and ropi dont vasodilate, lido does

Question 13

Duration of action

Answer 13

Protein binding- tissue reservoir to extend DOA, preferably bind to alpha a acid glycoprotein but can bind to albumin

Lipid solubility
Intrinsic vasodilating effect
Addition of vasoconstrictors- prolongs

Question 14

Amide pKa

Answer 14

Bupivacaine- 8.1
Ropivacaine- 8.1
Lido- 7.9
Prilocaine- 7.9

Question 15

Ester pKa’s

Answer 15

Procaine- 8.9
Chloroprocaine- 8.7
Tetracaine- 8.5

Question 16

PKa and LA

Answer 16

Degree of ionization increases as pKA gets further from physiologic pH
Faster onset at pKa close to blood (except chloroprocaine)

Question 17

Benzocaine

Answer 17

PKa 3.5

Unionized at pH yet i has anesthetic activity

Question 18

Site of LA and uptake

Answer 18

I Think Illogical Imposters Can’t Educate But Fabulous Schools Should
IV
Tracheal 
Interpleural
Intercostal
Caudal
Epidural
Brachial plexus
Femoral
Sciatic
Subcutaneous

Question 19

Amide max doses

Answer 19

Bupivicaine 2.5mg/kg, 175mg, with epi 3mg/kg, 175mg
Lidocaine 4.5 mg/kg, 300 mg, with epi mg/kg, 500mg
Ropivicaine 5 mg/kg, 200 mg
Mepivicaine 7 mg/kg, 400mg

Question 20

Ester max doses

Answer 20

Procaine 7mg/kg, 350-600mg

Chloroprocaine 11mg/kg, 800mg

Question 21

Lidocaine toxicity

Answer 21

1-5mcg/mL- analgesia
5-10mcg/mL- tinnitus, perioral numbness, skeletal muscle twitching, restlessness, vertigo, blurred vision, hotn, myocardial depression
10-15mcg/mL- seizures
15-25mcg/mL-  coma, respiratory arrest
>25mcg/mL- cardiovascular collapse

Question 22

CNS factors that increase LAST risk

Answer 22

Hypercarbia
Hyperkalemia- raises membrane potential and makes depolarization more likely
Metabolic acidosis- ion trapping in brain

Question 23

LA cardiac affinity

Answer 23

Bupivacaine>levobupivacaine>ropivacaine>lidocaine

Bupi risk increased with pregnancy, beta blockers, ca channel blockers, dig

Question 24

Cocaine toxicity

Answer 24

Inhibits NE reuptake into nerve terminal- vasoconstrictive properties
SNS stim increases risk
Avoid with MAOIs, TCAs, sympathomimetic drugs
Beware of beta blockade due to unopposed alpha 1 stimulation
Nitro is best but use labetolol or beta blocker with alpha mixed in

Question 25

Lipid emulsion for LAST

Answer 25

Bolus 20% 1.5mL/kg (lean body mass) over one minute Infusion 0.25 mL/kg/min Can repeat bolus up to 2 more times and increase infusion to 0.5 Infusion goes 10min after hemodynamic stability Max dose 10mL/kg in 1st 30 min

Question 26

Lipid MOA

Answer 26

Lipid sink- reservoir to sequester LA Metabolic- increases fatty acid metabolism Inotropic effect- increased Ca influx Membrane effect- impairs binding to VgNaC

Question 27

Avoid in LAST treatment

Answer 27

Beta blockers and Ca blockers

Question 28

Tumescent anesthesia

Answer 28

PE most common causes of death Solution of sodium chloride, lido, epi, and bicarb Max lido dose 55mg/kg Peaks at 12 hours and eliminated in 36 hours

Question 29

Methemoglobinemia

Answer 29

Fe2+ on hemoglobin oxides to ferric form Fe3+-forms methemoglobin Decreases O2 carrying capacity and shifts curve to L Causes- benzocaine, cetacaine, prilocaine, EMLA, nitroprusside, nitroglycerin, sulfa, phenytoin

Question 30

Methemoglobinemia S/S

Answer 30

``` Hypoxia Cyanosis- with normal PaO2 Chocolate colored blood Tachycardia Tachypnea Mental status changes Coma/death ```

Question 31

Methemoglobinemia treatment

Answer 31

Methylene blue: 1-2 mg/kg over 5 min, max dose 7-8 mg/kg Metabolized and reduces methemoglobin to hemoglobin Neonates at high risk

Question 32

EMLA

Answer 32

50/50 lido and prilocaine Analgesia in 1 hour, max effect 2-3 hrs Only to intact skin Infants and kids have risk of methemoglobin

Question 33

EMLA dosing

Answer 33

0-3 months or < 5 kg- 1 g, 10 cmsquared 3-12 months or >5kg- 2 g, 20cmsquared 1-6 years or >10kg- 10g, 100cmsquared 7-12 years or >20kg- 20g, 200cmsquared

Question 34

Prolong duration of action

Answer 34

Epi- alpha 1 agonist, works better on intermediate action LAs Decadron- acts on steroid receptor Dextran- decreases uptake of LAs

Question 35

provide supplemental analgesia

Answer 35

Clonidine- alpha 2 agonism in brain and SC Epi- alpha 2 agonism Opioids- spinal and epidural

Question 36

Drugs that shorten onset time

Answer 36

Sodium bicarb Increases number of lipid soluble molecules Increasing fraction of nonionized base

Question 37

Drugs that improve diffusion through tissues

Answer 37

``` Hyaluronidase Hinders spread of substances through tissues Used in ophthalmic blocks Reduces hematoma size Allergy potential ```