Test 2: Non-depolarizing Muscle Relaxants Flashcards
How to calculate Lean Body Weight (easy).
IBW (men) = height in cm - 100
IBW (women) = height in cm - 105
LBW = IBW x 1.3
How many subunits do NDMR need to bind to in order to render the channel useless?
NDMR only needs to bind to one alpha subunit to render channel useless.
Is NDMR a competitive or noncompetitive blockade?
Competitive blockade. Increased Ach can knock this off the receptor.
Where do NDMR interrupt the action potential?
Interrupts Ach binding to the nAchR.
-Prevents channel from ever opening
The more potent a NDMR, the _____ its speed of onset.
The more potent a NDMR, the slower its speed of onset.
Explain the relationship between potency, dose, and onset of action.
-Greater potency = lower dose
-Lower dose = decreased drug delivery to the NMJ
Increased potency = smaller dose = longer onset
The larger the dose, the ____ speed of onset.
Larger dose = increases the speed of onset
-Increases the potential for side effects
-Prolongs the duration of blockade.
What is the effect of volatile agents on dosage of NDMR?
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.
What is the effect of a NDMR on another NDMR?
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)
What are the s/sx associated with Histamine release?
-Bronchospasm
-Skin Flushing
-Tachycardia
-Hypotension from peripheral vasodilation
Atracurium and Mivacurium esp at high doses
-Decreased by slow injection rates and pretreatment with antihistamines
What are the Cardiovascular effects associated with NDMR?
-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)
T/F: Older NDMR agents blocked the nAchR of autonomic ganglia.
True.
-Blocked the sympathetic nervous system response to hypotension
-Tubocurarine and Metocurine
What is the effect of hypothermia on NDMR blockade?
Hypothermia prolongs blockade by decreasing metabolism and delaying excretion.
What is the effect of respiratory acidosis on NDMR blockade?
-Potentiates the block
What electrolyte imbalances will augment a NDMR?
-Hypokalemia
-Hypocalcemia
-Hypermagnesemia
Why does Hypermagnesemia augment a NDMR?
Magnesium inhibits the entry of Ca++ into the presynaptic membrane (Causes relaxation).
What is important to know with NDMR dosing with neonates?
-Increased sensitivity secondary to immature neuromuscular junctions
-Greater extracellular space = larger volume of distribution
-Not necessary to decrease/increase the dose
What is important to know with NDMR dosing with Cirrhotic Liver Disease/Chronic Renal Failure?
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).
Why does the dose of NDMR need to be increased in burn patients?
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.
How should you change your dose of NDMR with hyperkalemia?
-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)
How should you change your dose of NDMR with hypokalemia?
-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)
What is a Priming Dose?
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
What is a Defasciculating Dose?
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)
What does PNS monitoring help prevent?
-over/under dosing
-Residual paralysis in recovery/PACU
Subjective measurement
What should repeat doses of muscle relaxant be guided by?
-PNS
-Clinical Signs (SV, movement, etc)
Clinical signs may precede twitch response.
-Differing sensitivities to MR’s between muscle groups or PNS malfunction
What is the first indicator of seeing diaphragmatic movement?
Curare cleft on CO2 waveform
What drugs are the Benzylisoquinolones?
-Mivacurium
-Atracurium
-Cisatracurium
What drugs are the Steroids?
-Pancuronium
-Vecuronium
-Rocuronium
What is important to know with NDMR and elderly patients?
-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)
What is important to know with NDMR and obese patients?
-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
