NMBs, Reversal Agents, and Antimuscarinic agents Flashcards
What drugs can decrease pseudocholinesterase activity?
- Echothiopate (glaucoma drug)
- Neostigmine/pyridostigmine (Cholinesterase inhibitors)
- Phenelzine (MAO inhibitor)
- Cyclophosphamide (antineoplastic agent)
- Metoclopramide (Antiemetic)
- Esmolol (B-Blocker)
- Pancuronium (NDMR)
- Oral contraceptives (Various agents)
Bibucaine number
The percentage of inhibition of pseudocholinesterase activity.
Normal activity = 80
Homozygote with abnormal allele = 20
What are some cardiovascular effects of succinylcholine administration?
Act at all Ach receptors causing:
- Possible bradycardia, more likely with second dose. Can be pretreated with antimuscarinic.
- Higher doses can increase heart rate and blood pressure
Absolute contraindications to succinylcholine
Patients with already elevated potassium levels such as burn patients, massive trauma, neurological disorders, stroke, spinal cord injury, Parkinson’s disease, tetanus, cerebral aneurysm, polyneuropathy, Guillain-Barre syndrome, intraabdominal infection, risk of malignant hyperthermia, allergy to succ, [K] > 5.5mEq/L
What are the special considerations of atracurium?
- Metabolized quickly by Ester/Hoffman degradation
- Triggers dose-dependent histamine release, especially >0.5mg/kg
- Avoid in asthmatics
- Laudanosine, a metabolite is associated with precipitation of seizure activity
What are special considerations with cisatracurium?
- Hoffman elimination, 4X more potent than atracurium
- Extenstively less side effects compared to atracurium, does not alter heart rate or have any autonomic effects
What are special considerations with mivacurium?
- Metabolized by pseudocholinesterase similar to succ, so patients with low pseudocholinesterase activity will have prolonged blockade
- Releases histamine to about the same extent as atracurium
- Advantage is a shorter duration of action (20-30min)
What are special considerations of pancuronium?
- Metabolized mainly by the liver, and some of the metabolites are active
- Prolonged in patients with kidney failure, because that is where (40%) is eliminated
- 1 to 2 hours of duration, longest acting NMB
- Causes hypertension and tachycardia because of vagal blockade and sympathetic stimulaiton (avoid in patients with heart disease of any sort)
- Arrythmias can occur, especially with patients on tricyclic antidepresants
- Patients with allergies to bromide may exhibit allergic reactions
What are special considerations of vecuronium?
- Structure is basically pancuronium, minus a methyl group that doesn’t affect potency and reduces the side effects of pancuronium
- Equipotency of pancuronium, and women are 30% more sensitive
What are special considerations of rocuronium?
- No metabolism, eliminated by liver/kidney
- Modestly prolonged by severe liver failure and pregnancy, and elderly due to smaller liver mass
- Better choice for the rare patient in ICU needing prolonged muscle relaxant
- Speedy onset, can be used for RSI
- Has slight vagolytic tendencies
How do you monitor a neuromuscular block?
Use a peripheral nerve stimulator:
- Tetany, twitch, TOF
- Fade - reduction of evoked response indicative of ND block
- Clinical recovery correlates with absence of fade
Recovery index?
Offset speed to recovery from 25% to 75% twitch
Train of four tells you:
-Progressive fade as relaxation increases
Disappearance of:
-4th = 75% block
-3rd = 80-85% block
-2nd = 85-90% block
-1st = 90-98% block
Clinical relaxation requires 75-95% block
A single twitch stimulation tells you:
- The amount of blockage
- Height remains normal until 75% Ach receptors are occupied
- Completely disapears when 90-95% receptors are occupied
When should you administer your NMB reversal?
Recovery of the first twitch
