wk1- intro to LA

Question 1

uses for LA

Answer 1

1. diagnostic
2. therapeutic
3. surgery

Question 2

modes of delivery of LA

Answer 2

1. topical
2. infiltrative
3. ring block
4. peripheral nerve block
5. EMLA
6. iontophoresis

Question 3

define LA and how do they work

Answer 3

reversible loss of sensation in an area of the body

they block sodium ion channels so sodium cannot flow into neurons
this inhibits the transmission of APs along individual neurons

Question 4

anatomy of LA

Answer 4

aromatic ring- confers lipid solubility

intermediate linkage- permits classification and mode of metabolism (amide or ester)

terminal amine- charged or uncharged to make it water or lipid soluble

Question 5

types of LA

Answer 5

amide
ester

Question 6

ester

metabolism, toxicity, allergy, stability, onset of action, pKa

Answer 6

M: rapid by protein cholinesterase
T: less likely
A: more likely
S: photo/temp labile
O: slower
pKa: higher (8.5-8.9)

Question 7

amide

metabolism, toxcity, allergy, stability, onset, pKa

Answer 7

M: slower, by the liver
T: more likely
A: less likely
S: very stable
O: moderate to fast
Pka: Close to 7.4

Question 8

types of esters

Answer 8

cocaine
chloroprocaine
tetracaine

Question 9

types of amides

Answer 9

bupivacaine
lidocaine
ropivacaine

Question 10

LA and physiochemical properties

Answer 10

LA- weak base that needs to be unionised to reach site of action inside the neuron

then dissociation causes it to become in ionised form that binds to sodium ion channel once inside neuron

Question 11

unpronated LA molecules can what

Answer 11

pass through cell membranes because theyre lipophilic

Question 12

what is a proton

Answer 12

H plus

Question 13

if pH decreases (more acidic)

Answer 13

more protons

Question 14

if pH increses (more alkaline)

Answer 14

less protons

Question 15

define pKA

Answer 15

pH where drug is 50% ionised and unionised

Question 16

if the pH is low what does that mean for the LA drug in the body

Answer 16

the higher the amount of drug present in unionised form which can more rapidly penetrate the nerve cell membrane and cause a faster onset of action

Question 17

what nerve fibers are effected by LA, what order is sensation lost

Answer 17

greatest effect is on automatic and small myelinated nerve fibers than large myelinated fibres

C-unmyelinated, B-unmyelinated, A delta (small myelinated)

order of nerve sensation loss

1. pain
2. temp
3. touch
4. deep pressure
5. motor

Question 18

how many nodes have to be blocked

Answer 18

more than 1 as AP can skip over a blocked node called saltatory conduction

Question 19

what makes onset of time faster?

Answer 19

the closer the pKa is to tissue pH (7.4), the more unionised form which causes a faster rate of onset

Question 20

what speeds up onset?

Answer 20

alkalinisation (eg bicarbonate)

Question 21

duration of LA depends on

Answer 21

1. lipid solubility (greater action)
2. molecular size (greater protein binding)
3. protein binding (greater action)

Question 22

injecting LA near vascular sites will result in

Answer 22

loss of LA as it is removed by systemic circulation too quickly

Question 23

maximum safe dose can be increased by the addition of what and why

Answer 23

adrenaline

delays the absorption of LA and prolongs its effects through vasocontriction in area of injection and confining LA to that region

Question 24

when is adrenaline contraindicated

Answer 24

peripheral nerve block where there is no contralateral arterial supply (feet/digits) as it can cause prolonged ischaemia leading to necrosis of tissue

Question 25

complications of LA

Answer 25

-failure of use
-infection
-allergy/anaphylaxis
-drug interactions
-toxicity

Question 26

difference between absolute and relative OD

Answer 26

absolute- dose too large, absorbed into CVS more rapidly than liver can remove it

relative- dose is fine, injection technique causes elevation

Question 27

signs of overdose (mild-mod)

Answer 27

lightheaded, restless, metallic taste numbness, visual/hearing disturbances, loss of consciousness

Question 28

signs of overdose (mild to high)

Answer 28

1. tonic clonic siezure activity
2. generalised CNS depression
3. depressed BP, HR, resp rate

Question 29

common allergic reactions to LA

Answer 29

urticaria (wheals)
angioedema

typically occurs within 1 hour

Question 30

when is signed consent required for LA

Answer 30

not when given without surgical intervention

yes when being used as primary treatment (chronic neurological pain)

Question 31

documentation of LA includes

Answer 31

1. site of injection
2. time of injection
3. LA drug name and concentration
4. dose delivers- Mg
5. batch number
6. exp date
7. any adverse reaction noted

Question 32

minimum safety requirements

Answer 32

2 people in room
adrenaline
telephone

alcohol wipes
neurotip
sharps box

as well as clinical aprons/gloves

Question 33

thicker needles used for

Answer 33

drawing up solutiont

Question 34

thinner needles used for

Answer 34

injecting

Question 35

higher the gauge means

Answer 35

thinner the needle

eg 14 gauge - thicker than 27 gauge