Pharm Quiz#5

Question 1

Of the phase I and Phase II blocks associated with succinylcholine administration, which is the desirable block?

Answer 1

Phase I

Question 2

What causes a phase I block with succinylcholine administration?

Answer 2

due to prolonged stimulation of acetylcholine receptors—>results in disorganized muscle contractions(fasciculation’s)

Question 3

What is occurring at the cellular level during fasciculation?

Answer 3

acetylcholine receptors become an ion channel, so there is a high flux of K+ out of the cell, and Na+ into the cell, resulting in a membrane potential less than the action potential. After the initial firing, the cells remain refractory.

Question 4

What should be used to diagnose Phase II block due to prolonged NMB? What response will be seen with Phase II block?

Answer 4

PNS prior to giving anti cholinesterase drugs, presence of Phase II block indicated by fade of responses to successive stimuli(preferably “train-of-four”)

Question 5

Reversel of a Phase II block should not be attempted unless(2)?

Answer 5

1. a peripheral nerve stimulator is used
2. spontaneous recovery of muscle twitch has been observed for at least 20 minutes and has reached a plateau with further recovery proceeding slowly.

Question 6

Should the type of block be misdiagnosed, Phase I block will be _____ by an anti cholinesterase agent.

Answer 6

prolonged

Question 7

What are characteristics of Phase II block seen with a PNS?(5)

Answer 7

1. fade of ToF
2. decreased single twitch response
3. fade on tetanus
4. TOF ratio < 0.7
5. post-tetanic facilitation(post-tetanic potentiation)

Phase I ToF ratio-no difference

Question 8

Can a Phase II block be reversed by anticholinesterase drugs?

Answer 8

yup

Question 9

Transition between Phase I and Phase II block is abrupt, occurring with doses > _____.

Answer 9

2-4 mg/kg

Question 10

What is the initial sign of transition from Phase II block to Phase I block?

Answer 10

tachyphylaxis

Question 11

Anticholinesterase drugs _____ Phase II blocks but _____ Phase I blocks.

Answer 11

reverse, worsen

Question 12

What is the anticholinesterase medication typically used to reverse Phase II blocks and why?

Answer 12

edrophonium because its short duration of action

if bock is reversed a longer acting reversal should be considered—>post-op ventilation

Question 13

What is the best reversal agent of a phase II block?

Answer 13

time

Question 14

Patients with genetic resistance to succinylcholine have a shorter duration of action caused by?

Answer 14

accelerated hydrolysis

Question 15

Obese patients require larger doses of succinylcholine due to?

Answer 15

greater plasma cholinesterase activity

Question 16

Myasthenia graves patients may be up to _____ times more resistant to succinylcholine, due to?

Answer 16

2.6, decreased numbers of functional acetylcholine endplate receptors.

Question 17

Atypical plasma cholinesterase is often found after typical succinylcholine doses and cause?

Answer 17

longer than expected duration of action

Question 18

The important variety of atypical plasma cholinesterase are the?

Answer 18

dubucaine related variants

Question 19

What is dubucaine?

Answer 19

an amide local anesthetic that inhibits normal plasma cholinesterase activity 80% and atypical activity 20%

Question 20

What does a Dibucaine # of 80 indicate?

Answer 20

80% inhibition of plasma cholinesterase activity-NORMAL

Question 21

What does a Dibucaine # of 20 mean?

Answer 21

20% inhibition of plasma cholinesterase activity(found in 1 of 3200 patients), means they are HOMOZYGOUS for an atypical plasma cholinesterase variant.

Question 22

In patients with Homozygous atypical plasma cholinesterase variant, how long does succinylcholine usually last?

Answer 22

up to 3 hours in normal doses

Question 23

What does a Dibucaine # of 40-60 indicate?

Answer 23

1/480 patients are heterozygous for atypical plasma cholinesterase. These patients may have prolonged succinylcholine blocks lasting up to 30 minutes.

Question 24

What does a Dibucaine # indicate about plasma cholinesterase?

Answer 24

Indicates quality of plasma cholinesterase not quantity

Question 25

Diminished plasma cholinesterase activity causes….

Answer 25

prolonged duration of action with a single dose of succinylcholine

Question 26

What types of patients have diminished plasma cholinesterase activity?

Answer 26

• patients with heterozygous/homozygous atypical plasma cholinesterase
• pregnancy
• severe liver/kidney disease
• malignant tumors
• infections
• burns
• anemia
• decompensated heart disease
• peptic ulcer
• myxedema
• chronic admin of oral contraceptives
• glucocorticoids
• MAO inhibitors
• irreversible inhibitors of plasma cholinesterase
• echothiophate
• antineoplastic drugs

Question 27

With plasma cholinesterase, slow to absent succinylcholine hydrolysis and prolongation of NMB is see with?(3)

Answer 27

1. decreased hepatic production of plasma cholinesterase
2. drug induced decreases in plasma cholinesterase
3. genetically atypical plasma cholinesterase

only with severe liver disease is plasma cholinesterase production too low to prolong succinylcholine

Question 28

What is the incidence of low plasma cholinesterase?

Answer 28

6% resulting in a longer duration of action

Question 29

Neostigmine lowers plasma cholinesterase {} up to _____ after administration

Answer 29

30 minutes

Question 30

If you reverse, extubate, laryngospasm, give succinylcholine, expect what?

Answer 30

longer duration of action

Question 31

Plasma cholinesterase levels are reduces with(4)

Answer 31

1. insecticides
2. glaucoma
3. myasthenia gravis drugs
4. chemotherapy

Question 32

In younger patients undergoing minor surgery particularly in outpatient setting, what symptoms can be seen?

Answer 32

post-op myalgia in the neck, back and abdomen can occur post succinylcholine, especially with early ambulation

myalgia localized to neck may be wrongly attributed to intubation

Question 33

What attenuates the myalgia sometimes seen with succ administration?

Answer 33

pre-treatment of a non-depolarizer

Question 34

What are the concerns of succinylcholine administration and pregnancy?

Answer 34

• should only be given if absolutely required
• plasma cholinesterase levels are decreased by 24% during pregnancy and for several days postpartum
• a higher proportion of patients will have increased sensitivity to succinylcholine when pregnant than when not pregnant.

Question 35

Factors influencing development of phase II block:

Answer 35

• duration of exposure to drug
• drug concentration
• muscle type(i.e., fast or slow)
• interaction with anesthetics

Question 36

Does the K+/Na+ ATP pump continue while muscle is depolarized?

Answer 36

yup, it increases with increasing intracellular Na+(pumps Na+ out and K+ in)

• pump restores normal inonic balance and membrane potential
• if depolarizing drug present, receptor channels remain open and ion flux through them remains high

Question 37

In a phase II block, the NMJ is _____.

Answer 37

depolarized by a depolarizing relaxant, but membrane potential gradually recovers toward normal, even though junction is still exposed to depolarizers.

NM transmission remains blocked throughout exposure

Question 38

In a phase II block, reversal by a cholinesterase inhibitor is best…….

Answer 38

not attempted, although response to tetanus or ToF sim resembles non-depolarizers.