Neuromuscular Blockers Flashcards
What do neuromuscluar blocking drugs do?
Interrupt nerve impulses at the NMJ
What is the result of a neuromuscular block?
Complete paralysis of striated muscles with no analgesia and retained consciousness
What are some indications for NMBs?
- Positioning eye centrally
- Relaxation of respiratory muscles (ICU patients)
- Relax muscles for neurological or orthopedic surgeries
- Aid in intubation (humans)
What are the components of balanced anesthesia?
- Unconsciousness
- Stop reflexive movements/muscle relaxation
- Analgesia
Is mechanical ventilation required when using NMBs?
Yes, due to paralysis of respiratory muscles, spontaneous ventilation ceases
What systems need to be monitored when using NMBs?
Cardio, respiratory, oxygenation
What are the only two indications of noxious stimulation when using NMBs?
Tachycardia and high blood pressure
When should NMBs not be used?
- No ability to ventilate or monitor
- Insufficient analgesia during surgery
- As a sole agent for procedures or euthanasia
What is the MOA of depolarizing NMBDs?
Nicotinic ACh receptor agonist causing membrane depolarization
What is the MOA of non-depolarizing NMBDs?
Competitive antagonist on nicotinic ACh receptors stabilizing muscle membranes
What is the order of muscle relaxation?
Ocular muscles > Everything else (larynx observed esp) > Diaphragm
What are some factors that influence the effect of NMBDs?
- Hypothermia
- Electrolyte abnormalitites
- Acid-base disorders
- Age
- Thermal burn
What are some drugs that potentiate NMBD effects?
- Inhalation anesthetics
- Aminoglycoside antibiotics
- Local anesthetics
- Cardiac antiarrhythmic drugs
- Diuretics
- Magnesium
What is succinylcholine mainly used for?
Human intubation
Historically used as euthanasia drug (inhumane)
What is seen in Phase-1 block with succinylcholine?
Muscle fasciculation then paralysis
What is seen in Phase-2 block with succinylcholine?
Non-depolarizing blockade after prolonged/high dosages
What are some adverse effects of succinylcholine?
- Cardiac arrhythmias
- Hyperkalemia
- Fasciculation, myalgia, myoglobinuria
- Elevated intra-ocular and intra-gastic pressures
- Malignant hyperthemia
Cumulative effects are less likely with what type of NMBDs?
Non-depolarizing
Which type of NMBDs have less adverse effects?
Non-depolarizing
Do non-depolarizing NMBDs have cardiovascular side effects?
Little to none
What is the major metabolite in atracurim and what does it do?
Laudanosine, decreases seizure threshold
What is atracurium eliminated by?
Plasma esterase enzymes- plasma pH and temp dependent
Can atracurium cause histamine release at high doses?
Yes
Cisatracurium represents what percentage of atracurium mixtures?
15% oft he 10 isomer mixture
How is cistracurium elimated?
80% Hofmann elimination- organ dependent
Which NMBD is the first choice in vet med?
Rocuronium
What is rocuronium antagonized by?
Sugammadex- usually not needed
How is rocuronium eliminated?
Mostly liver, partially kidneys
What must be monitored closes when recovering patients with MNBDs on board?
Respiration
What are sites of peripheral nerve stimulation in the dog/cat?
Peroneal and ulnar nerves
What are sites of peripheral nerve stimulation in the horse?
Facial and peroneal nerves
What are the stimulation patterns? (5)
- Single twitch
- Train of four
- Tetanic stimulation
- Post-tetanic count stimulation
- Double burst stimulation
What is single twitch stimulation used for?
Determine minimum necessary current to evoke maximal movement response prior to injecting NMBDs
aka Supramaximal stimulus
What is train of four stimulation used for?
Determine how deep the blockade is
With train of four: the first twitch is the largest and the last is the smallest
What does this indicate?
Partial blockade
What will you see on a train of four stimulation with complete blockade?
No response
A TOF ratio of what suggests acceptable recovery from blockade?
> 0.9
What kind of NMBDs are not recommended to antagonize?
Depolarizing NMBDs: succinylcholine
What kind of drugs can be used to andtagonize NMBDs?
Ancetylchonlinesterase inhibitors- increased ACh at the NMJ
Edrophonium over neostigmine
What drug is used to REVERSE rocuronium?
Sugammadex
How does sugammedex reverse rocuronium?
Rocuronium binds with sugammadex’s lipophilic core
