Chapter 23: Local Anesthetics

Question 1

classification of local

Answer 1

esters and amides

Question 2

MOA of local

Answer 2

Suppress pain by blocking sodium channels and by blocking impulse conduction along axons​

Question 3

selectivity of anesthetic effects

Answer 3

Only in neurons located near the site of administration​

Suppress pain without generalized depression of nervous system ​

Question 4

time course of local

Answer 4

Onset of local anesthesia​

The ability of an anesthetic to penetrate the axon membrane is determined by three properties:​
Molecular size​
Lipid solubility​
Degree of ionization at tissue pH​
local of small size, high lipid sol, and low ionization cross membrane rapidly and have fast onset.

Termination of local anesthesia​
Impact of regional blood flow -high BF = carried away fast. low BF = prolonged effects

Question 5

local + vasoconstrictors

Answer 5

Use with vasoconstrictors​

Epinephrine: Decreases local blood flow, delays systemic absorption of the anesthetic, prolongs anesthesia, and reduces the risk of toxicity​
absorption of epi itself can cause toxicity -> palpitations, nervousness, HTN. can use a and b adrenergic antagonists to control this.

​

Question 6

Local ADRS

Answer 6

Central nervous system: Excitation followed by depression​

Cardiovascular: Bradycardia, heart block, reduced contractile force, cardiac arrest, and hypotension​

Allergic reactions​

Methemoglobinemia

Question 7

local allergic rxn

Answer 7

range from dermatitis to anaphylaxis
more likely with ester type
no cross sensitivity bw ester and amide

Question 8

methamoglobinemia from local

Answer 8

seen with topical, liquid, sprays, gels benzocaine
Hb is modified such that it cannot release O2 to tissues. can result in death.
benzocaine contraindicated in pt under 2y. use caution in older children and older adults when applied to mucous membranes.

Question 9

lidocaine

Answer 9

Most widely used local anesthetic​

Topical and injectable applications​

Effects extended if given with epinephrine​

Also used for cardiac dysrhythmias

amide

onset less than 2 min, duration ~ 1hr

Question 10

topical locals

Answer 10

Grouped according to route​

Topical: Lidocaine, tetracaine, and cocaine​ -can use on skin and mucous membranes

Systemic toxicity​

Question 11

injectable locals

Answer 11

Carries significant risk and requires special skills​

Severe systemic reactions may occur; equipment for resuscitation should be immediately available​

Intravenous line should be in place to permit rapid treatment of toxicity​

lido, bup, mep, prilo, rop, pro. chloropro, tetra

Question 12

systemic tox s/sx

Answer 12

bradycardia, heart block, cardiac arrest
sz, resp depression, coma

Question 13

min systemic tox of local

Answer 13

Application guidelines:​
Apply smallest amount needed​
Avoid application to large areas​
Avoid application to broken or irritated skin​
Avoid strenuous exercise, wrapping the site, and heating the site, all of which can accelerate absorption by increasing skin temperature​

Question 14

epidural anes

Answer 14

Injecting a local anesthetic into the epidural space​

Anesthetic can reach the systemic circulation in significant amounts​

Lidocaine and bupivacaine

Question 15

spinal anes

Answer 15

Injecting local anesthetic into the subarachnoid space​

Injection is made in the lumbar region below the termination of the cord​

Bupivacaine, lidocaine, and tetracaine​

Question 16

Epidural, spinal ADRs

Answer 16

Hypotension​

Autonomic blockade may disrupt function of the intestinal and urinary tracts, thereby causing fecal incontinence and either urinary incontinence or urinary retention​

“Spinal” headaches ​

Question 17

infiltration

Answer 17

Infiltration: Injecting a local anesthetic directly into the immediate area of surgery or manipulation​

Question 18

nerve block

Answer 18

Nerve block: Injecting a local anesthetic into or near nerves that supply the surgical field but at a site distant from the field itself​

Question 19

iv regional

Answer 19

Intravenous regional: Employed to anesthetize the extremities (i.e., hands, feet, arms, and lower legs) but not the entire leg