Local Anesthetics

Question 1

What is the general effect of all local anesthetics?

Answer 1

Local anesthetics bind to sodium channels in nerves to block nerve transmission

Question 2

What kinds of nerves are easiest to block?

Answer 2

• Myelinated
• Small
• High firing frequency

Question 3

What is the function of Aδ nerves?

Answer 3

Pain

Cold temprature

Question 4

What is the function of Aβ nerves?

Answer 4

Tactile

Proprioception

Question 5

What is the function of Aα nerves?

Answer 5

Motor

Question 6

What is the function of B nerves?

Answer 6

Preganglionic Sympathetic

Question 7

What is the function of C nerves?

Answer 7

Visceral Pain

Question 8

What is the order in terms of easiest to hardest nerves to block in the type A nerves?

Answer 8

δ > β > α

Question 9

In terms of the nerves overall, what are the easiest to hardest nerves to block?

Answer 9

B > A > C

Question 10

What is the onset time of LAs dependent upon?

Answer 10

pH and pKa

High pH will increase the speed of onset.

Question 11

What is the potency of LAs dependent upon?

Answer 11

Lipid solubility

As lipid solubility increases the potency of the LA will increase.

Question 12

What is the duration of effect of LAs dependent upon?

Answer 12

Local protein binding NOT plasma binding

Increased protein binding will mean longer duration of action.

Question 13

What can be added to LAs to increase the speed of onset?

Answer 13

NaHCO3

Question 14

What can be added to LAs to localize them to the area?

Answer 14

EPI used to vasoconstrict to keep the drugs locally to the injection area

Question 15

Is EPI useful in localizing LAs that are highly protein bound?

Answer 15

No because vasoconstriction would not be useful for localization when proteins are already functioning in that role

Question 16

What Na+ gates are open at rest?

Answer 16

h open

m closed

Question 17

What Na+ gates are open at activation?

Answer 17

h open

m open

Question 18

What Na+ gates are open at inactivation?

Answer 18

m open

h closed

Question 19

What is the function of A𝛄 nerves?

Answer 19

Muscle tone

Question 20

What are the first signs of spinal/epidural anesthesia?

Answer 20

􏰁 Sympathectomy>sensory>motor

Question 21

What are the first signs of peripheral anesthesia?

Answer 21

First sign may be lack of proximal muscle coordination - finger to nose

Question 22

What are the LA esters?

Answer 22

Cocaine
Procaine
Tetracaine
Benzocaine

Question 23

What are the LA amides?

Answer 23

Lidocaine

Bupivicaine

Question 24

Where does binding occur on the Na receptor?

Answer 24

Binding occurs on the cytoplasmic (inside) side of the receptor so LA must traverse the membrane. Only the uncharged can cross but the charged form is the active form.

Question 25

What are some contraindications to LA use?

Answer 25

Bacteremia Pre-existing neurologic disease Abnormal coagulation

Question 26

Where is LA administered for spinal?

Answer 26

Needle inserted at L3 - L5 and the drug is deposited around cauda equina

Question 27

Where is LA administered for epidural?

Answer 27

Any level is possible and the site of action is the nerve roots

Question 28

What are the respiratory effects of LA at the thoracic level?

Answer 28

􏰁Minimal reduction in vital capacity with abdominal muscle | paralysis but the loss of proprioception can be upsetting to patient as they cannot feel their own breathing

Question 29

What are the respiratory effects of LA at the high spinal level?

Answer 29

BP will be reduced due to B type nerve block that causes the brainstem to trigger suppression of respiration. NEVER due to phrenic nerve paralysis

Question 30

How is respiratory arrest due to LA effects treated?

Answer 30

Vasopressors and supportive ventilation

Question 31

What are the cardiovascular effects of neuraxial LA?

Answer 31

Arterial dilation and decrease in BP and decrease in HR due to decreased filling.

Question 32

How are LA esters eliminated?

Answer 32

Plasma cholinesterase

Question 33

How are LA amides eliminated?

Answer 33

Liver via cytochrome P450

Question 34

What is the toxicity of LA on neurons?

Answer 34

Can inhibit inhibitory neurons that will lead to increased excitatory neuron action

Question 35

How are LA induced seizures treated?

Answer 35

Benzodiazepines | Succinylcholine

Question 36

How is LA toxicity prevention performed?

Answer 36

Fractionated injection with intermittent aspiration to make sure you are not in a blood vessel Use of epinephrine as intravascular marker

Question 37

What is a treatment for LA toxicity?

Answer 37

Intralipid. It is lipophilic and creates a “sink” that LA can be sequestered into

Question 38

What is a common side effect of neuraxial anesthesia?

Answer 38

Postdural puncture headache (PDPH) is a common complication of neuraxial anesthesia its incidence is influenced by many factors