NMBDs: Non-depolarizing (Exam III) Stephen's Cards Flashcards
What are the 4 main differences between all of the non-depolarizing muscle blockers?
- Onset;
- Duration of action;
- Rate of recovery;
- Metabolism
What is the MoA of non-depolarizing blockers?
- Pre-junctional sites → block ACh release;
- Post junctional → Compete with ACh at nACh-R for alpha subunits → no conformational change
Which type of neuromuscular blocking drug will cause a conformational change of the nicotinic ACh receptor?
Succinylcholine
What are the characteristics of a non-depolarizing block?
- ↓ twitch response to a single stimulus;
- Unsustained response (fade) to continuous stimulus;
- TOF ratio < 0.7;
- Post-tetanic potentiation;
- Potentiation of other non-depolarizing drugs;
- Antagonism by anticholinesterase drugs;
- No fasciculations during onset
Why would you not give an intubating dose of rocuronium and then give vecuronium as the rocuronium starts to offset?
Non-depolarizing neuromuscular blockers will potentiate each others effects.
When would you use a priming dose of a non-depolarizing paralytic?
ONLY with succinylcholine to avoid its side effects (fasciculations, eye weakness, etc.)
What is fade?
Fade suggestssomefibers are contracting while some are blocked (muscle contraction is all or nothing)
What causes the adverse CV effects of non-depolarizing blockers?
- Release of histamine;
- Effects at cardiac muscarinic receptors;
- Effects on nACh-R at autonomic ganglia
Why do the adverse CV effects of non-depolarizing blockers vary between patients?
- Underlying diseases
- Pre-op meds
What is the “Autonomic Margin of Safety”?
Essentially Therapeutic Index
Difference between dose thatproducesblockade (ED95) and dose thatcreatescirculatory effects.
Which non-depolarizing blocker has a required dose that both causes blockade and adverse CV effects?
Pancuronium
Essentially no therapeutic index
What adverse event have non-depolarizing blockers been shown to have in critically ill patients?
When does this occur?
- Critical Illness Myopathy
- Weeks to months after NMBD discontinuation
Who is most often affected by critical illness myopathy?
- Had MODS for > 6 days;
- Usually had an aminosteroid NMBD;
- Administered Glucocorticoids prior to NMBD
Why is critical illness myopathy thought to occur?
Possible ↓ clearance or active metabolites
Which volatile gasses exhibit a dose-dependent enhancement of NMBDs?
Why is this?
- Desflurane > Sevoflurane > Isoflurane
- Thought to occur due to solubility allowing rapid movement into muscular partition/compartment.
What drug classes and/or drugs will enhance or prolong neuromuscular blockade?
- Diuretics
- Corticosteroids
- Metoclopramide
- Local Anesthestics
How does Magnesium affect non-depolarizing blockers and SCh?
Why is this thought to occur?
Enhances blockade
- ↓Release of ACh and
- ↓sensitivity to ACh
How will sympathomimetics such as ephedrine or epinephrine affect NMBDs?
↓ onset time (Drug works faster)
How will sympatholytics such as esmolol affect NMBDs?
↑ onset time (Drug works slower)
How does Hypothermia affect non-depolarizing blockers?
Does this occur for CYP450 metabolism or hoffman elimination?
Hypothermia will increase NMBD duration
This occurs whether the process is CYP450 dependent or hoffman elimination dependent
How doesacute hypokalemiaaffect non-depolarizing blockers?
↓ Vᵣₘ
- Resistance to depolarizing NMBDs
- Sensitivity to non-depolarizing NMBD’s
How does acute hyperkalemia affect non-depolarizing blockers?
↑ Vᵣₘ
- Sensitivity to depolarizing NMBDs;
- Resistance to non-depolarizing NMBDs
With ↑K⁺ we are sensitive to succ & resistant to roc
How do burns affect non-depolarizing blockers?
Burns patients within the 10 - 60 day time from burn will have a resistance to NMBDs.
What percentage of the body needs to be affected by burns to cause altered response to non-depolarizing blockers?
- 30% BSA or >
For a patient with burns needing intubation, how can we offset the resistance to non-depolarizing blockers the burn causes?
1.2 mg/kg dose of Rocuronium
Explain how paresis/paralysis will affect neuromuscular blocking drugs effects.
The more “paralyzed” = more resistant
Ex. Paralyzed leg (most resistant) > unaffected side of a person who suffered a stroke > person who never had a stroke or any paresis whatsoever.
Which depolarizing/non-depolarizing blocker is the most likely to cause allergic reactions? Which is least likely to cause reaction?
SCh (most) > Pancuronium, Vecuronium, Rocuronium > Cisatracurium (least)
What organic functional group makes a cross sensitivity reaction possible for depolarizing/non-depolarizing blockers?
- Quaternary ammonium group
How can a patient get an allergic reaction from a depolarizing/non-depolarizing blocker on their 1st exposure?
Due to prior sensitization →Soaps/cosmetics (women > men)
How does Gender affect non-depolarizing blockers? MoA?
- Women more sensitive (need 22% less Vec or 30% less Roc) and have greater drug duration.
- MoA: likely muscle mass
What is the most common long acting NMBD?
Pancuronium (Pavulon)
What is the intubating dose, onset and duration of Pancuronium?
- Dose: 0.1mg/kg;
- Onset: 3-5 minutes;
- Duration: 60-90 minutes
How is the majority of Pancuronium eliminated?
- 80% eliminated unchanged in urine
What patients would you not want to use pancuronium on?
Liver and Kidney cases (prolonged elimination and metabolism).
What changes in metabolism of Pancuronium do we see with a liver disease patient?
- Increased VD
- Larger initial dose is needed
- Prolonged E½ time
What CV effects do we see with Pancuronium?
Sympathomimetic:
- ↑ HR;
- ↑ MAP;
- ↑ CO;
What occurs with norepinephrine after pancuronium administration?
- ↑NE release
- ↓NE reuptake
Compared to pancuronium, what duration of action do intermediate-acting NMBDS have?
Approximately 1/3 duration of action
Compared to pancuronium, what cardiovascular effects do intermediate-acting NMBDS have?
Minimal/absent cardiovascular effects
After administering any intermediate-acting neuromuscular blocker, when you be able to reverse its effects via an cholinesterase-inhibitor?
Approximately 20min post administration
What is the intubating dose, onset, and duration of Vecuronium?
- Intubating Dose: 0.1 mg/kg
- Onset: 3-5 minutes
- Duration: 20-35 minutes
What is the main way Vecuronium is metabolized?
- CYP450’s
- 3-desacetylvecuronium 50-80% as potent (but rapidly converted to metabolite with 1/10 the effects)
How does metabolism of Vecuronium change with the elderly?
- ↓ volume of distribution (less muscle mass);
- ↓ plasma clearance (less hepatic flow / delayed recovery with infusions)
Is vecuronium a great drug for those with liver or kidney problems?
Nope
- Hepatic metabolism
- Renal dysfunction = ↑E½
How does metabolism of Vecuronium change with an obstetric patient?
- Insignificant effects to fetus;
- ↑ clearance in 3rd trimester (progesterone);
- ↑ duration early postpartum (give IBW)
What will respiratory acidosis post administration of vecuronium do?
Prolong NMJ blockade
When is respiratory acidosis that occurs after Vecuronium administration a concern?
With post-operative hypoventilating patients (ex. post-opioid administration)
What is the normal intubating dose, onset and duration of Rocuronium?
- Dose: 0.6 mg/kg
- Onset: 3-5 minutes
- Duration: 20-35 minutes
What is the RSI intubating dose, onset and duration of Rocuronium?
- Dose: 1.2 mg/kg
- Onset: 1-2 minutes
- Duration: 60-90 minutes
How is Rocuronium excreted?
Unchanged in bile
Why will Rocuronium have a longer DoA in the elderly or with liver failure patients?
Due to ↓ clearance and ↑ Vd
What percentage of Rocuronium is excreted renally?
10-30% → only marginally affected by renal failure
Roc is good for CKD patients?
What is the intubating dose, onset and duration of Cisatracurium?
- Intubating Dose: 0.1 mg/kg;
- Onset: 3-5 minutes;
- Duration of action: 20-35 minutes
What is unique about the metabolism of Cisatracurium?
Recovery from infusion is NOT affected by time.
How is cisatracurium metabolized?
Hoffman Elimination
What changes occur in Cisatracurium when used in an elderly patient? What changes occur in an obese patient?
- Elderly: Slight delay in onset d/t CO;
- Obese:Duration of action prolonged IF dosed at actual body weight d/t ↑ Vd
What changes occur in Cisatracurium when used in an obese patient?
Duration of action prolonged IF dosed at actual body weight d/t ↑ Vd
What is the intubating dose, onset and duration of Mivacurium?
- Intubating Dose: 0.15 mg/kg;
- Onset: 2-3 minutes (Conditions less desirable);
- Duration: 12-20 minutes
How is mivacurium cleared from plasma?
Via Plasma cholinesterases
Which two NMBDs cause histamine release?
- Atracurium
- Mivacurium (with massive overdoses)