Test 2: Non-depolarizing Muscle Relaxants

Question 1

How to calculate Lean Body Weight (easy).

Answer 1

IBW (men) = height in cm - 100
IBW (women) = height in cm - 105

LBW = IBW x 1.3

Question 2

How many subunits do NDMR need to bind to in order to render the channel useless?

Answer 2

NDMR only needs to bind to one alpha subunit to render channel useless.

Question 3

Is NDMR a competitive or noncompetitive blockade?

Answer 3

Competitive blockade. Increased Ach can knock this off the receptor.

Question 4

Where do NDMR interrupt the action potential?

Answer 4

Interrupts Ach binding to the nAchR.
-Prevents channel from ever opening

Question 5

The more potent a NDMR, the _____ its speed of onset.

Answer 5

The more potent a NDMR, the slower its speed of onset.

Question 6

Explain the relationship between potency, dose, and onset of action.

Answer 6

-Greater potency = lower dose
-Lower dose = decreased drug delivery to the NMJ

Increased potency = smaller dose = longer onset

Question 7

The larger the dose, the ____ speed of onset.

Answer 7

Larger dose = increases the speed of onset
-Increases the potential for side effects
-Prolongs the duration of blockade.

Question 8

What is the effect of volatile agents on dosage of NDMR?

Answer 8

NDMR required doses may be decreased by 15% in the presence of volatile agents.
-Volatiles enhance NMB. They don’t provide skeletal muscle relaxation. These relax smooth muscle: Bronchodilation, etc.

Question 9

What is the effect of a NDMR on another NDMR?

Answer 9

A NDMR will augment another NDMR (usually). Can induce with Roc/Succ and then switch to Vec as it has a longer profile (if something happens and procedure is much longer as you had planned)

Question 10

What are the s/sx associated with Histamine release?

Answer 10

-Bronchospasm
-Skin Flushing
-Tachycardia
-Hypotension from peripheral vasodilation

Atracurium and Mivacurium esp at high doses
-Decreased by slow injection rates and pretreatment with antihistamines

Question 11

What are the Cardiovascular effects associated with NDMR?

Answer 11

-Histamine effects (tachycardia, hypotension)
-Release of prostacyclin, which prevents the formation of the platelet plug in primary hemostasis (the opposite of thromboxane)
-Effects at Cardiac muscarinic receptors (usually undermined by propofol effects). Vagolytic response = tachycardia (Pancuronium is #1)

Question 12

T/F: Older NDMR agents blocked the nAchR of autonomic ganglia.

Answer 12

True.
-Blocked the sympathetic nervous system response to hypotension
-Tubocurarine and Metocurine

Question 13

What is the effect of hypothermia on NDMR blockade?

Answer 13

Hypothermia prolongs blockade by decreasing metabolism and delaying excretion.

Question 14

What is the effect of respiratory acidosis on NDMR blockade?

Answer 14

-Potentiates the block

Question 15

What electrolyte imbalances will augment a NDMR?

Answer 15

-Hypokalemia
-Hypocalcemia
-Hypermagnesemia

Question 16

Why does Hypermagnesemia augment a NDMR?

Answer 16

Magnesium inhibits the entry of Ca++ into the presynaptic membrane (Causes relaxation).

Question 17

What is important to know with NDMR dosing with neonates?

Answer 17

-Increased sensitivity secondary to immature neuromuscular junctions
-Greater extracellular space = larger volume of distribution
-Not necessary to decrease/increase the dose

Question 18

What is important to know with NDMR dosing with Cirrhotic Liver Disease/Chronic Renal Failure?

Answer 18

Cirrhotic liver disease/chronic renal failure result in an increased volume of distribution (Vd) and a lower plasma concentration for a given MR.
-Increased loading dose for DL and intubation secondary to increased Vd (drugs are hydrophilic - stay in water space. Will need more. Increased LD to get effects)
-Decreased maintenance doses secondary to disease and decreased clearance (need fewer maintenance doses).

Question 19

Why does the dose of NDMR need to be increased in burn patients?

Answer 19

Dose must be increased in burn patients due to the resistance at the Motor End Plate caused by:
-Increased protein binding
-Up-regulation of the receptors.

Question 20

How should you change your dose of NDMR with hyperkalemia?

Answer 20

-RMP is increased (Less negative, closer to threshold)
-Easier to depolarize
-Avoid Succ
-Need increased dose of NDMR (will have more muscle activity to suppress as it’s easier to depolarize)

Question 21

How should you change your dose of NDMR with hypokalemia?

Answer 21

-RMP is decreased (MORE negative, farther from threshold)
-Harder to depolarize
-Will need increased dose of Succ
-Need decreased dose of NDMR (block should be prolonged/enhanced as it is harder to depolarize)

Question 22

What is a Priming Dose?

Answer 22

Using a NDMR as the priming dose and a NDMR as the induction dose
-Give 10-15% of the usual intubating dose (usually Roc) first, about 5 min before induction.
-Idea is that you can prime some receptors, so that uptake is faster of other receptors when you intubate. (just done to speed it up)
-May produce distress (feels difficult to breathe), dyspnea, diplopia, & dysphagia
-O2 desat in patients with marginal pulmonary reserve
-Not commonly done in practice

Question 23

What is a Defasciculating Dose?

Answer 23

Administration of a NDMR 5 minutes before succinylcholine
-Can prevent certain side effects: fasciculations, muscle pain/myalgias, inc Intragastric pressure/LES tone, increased ICP
-MUST increase the dose of Succ (1.5 - 2.0 mg/kg)

Question 24

What does PNS monitoring help prevent?

Answer 24

-over/under dosing
-Residual paralysis in recovery/PACU

Subjective measurement

Question 25

What should repeat doses of muscle relaxant be guided by?

Answer 25

-PNS
-Clinical Signs (SV, movement, etc)

Clinical signs may precede twitch response.
-Differing sensitivities to MR’s between muscle groups or PNS malfunction

Question 26

What is the first indicator of seeing diaphragmatic movement?

Answer 26

Curare cleft on CO2 waveform

Question 27

What drugs are the Benzylisoquinolones?

Answer 27

-Mivacurium
-Atracurium
-Cisatracurium

Question 28

What drugs are the Steroids?

Answer 28

-Pancuronium
-Vecuronium
-Rocuronium

Question 29

What is important to know with NDMR and elderly patients?

Answer 29

-Dec onset time due to slower circulation times
-DOA of Roc/Vec is prolonged due to decreased hepatic & renal clearance and increased Vd
-DOA is unchanged in Cis/Atracurium (more reliable)

Question 30

What is important to know with NDMR and obese patients?

Answer 30

-DOA of Roc/Vec is likely to be prolonged
-Cis/Atracurium is unchanged (more reliable)
-Cisatracurium is preferred over Atracurium due to no Histamine release
-Dose at Ideal Body Weight