6. NMBAs Flashcards
What are NMBAs
neuromuscular blocking agents
When to re-dose
if re-dose is needed, use low dose titrated to effect (to centralize eye) Cannot recover a paralyzed patient, AchEi requires partial metabolism to reverse (3 twitches with TOF/spontaneous breathing)
act on the ____ receptor at the ____
Nicotinic Ach at the NMJ
effect of nmba?
paralysis (interrupt transmission at the NMJ)
only affects skeletal muscle
Two different mechanisms?
- Nondepolarizing
- NO short acting
- Intermediate acting: atracurium, rocuronium
- we don’t use the long acting ones - depolarizing
- succinylcholine (not used often)
advantage over ach
only one molecule is needed to block receptor (competitive antagonist)
termination of effect of nmba?
redistribution/metabolism/excretion
reversal agent - inc. Ach concentration
two types of non depolarizing nmbas?
- bensylisoquinolinium compounds
- can cause H release
- don’t rely on liver for metabolism, eliminated into blood and met with plasmatic esterases
ex/ atracurium - steroidal compounds:
- met by liver
atracurium v. cis atracurium
atracurium is a mixture of 3 groups (cis is the most potent one)
- Laudanosine is liver toxic, product of hoffman elimination, causes seizures
- H release
- cis-atracurium needs much lower dose -> less H release and less laudonosine production
Hoffman elimination is __ and ___ dependent
pH and temperature
without these, metabolism is prolonged
vecuronium
metabolite has some nmba properties, met in liver
no H release
rocuronium
derived by vecuronium, less potent, needs high dose, faster onset
reversal of nondepolarizing nmbas
- AchE inhibitors, they compete with NMBA at the NAch receptor, CANNOT be used to reverse a DEEP block
- neostigmine, edrophonium
- acts on MAchR -> bradycardia, bradyarrthythmia (pre-treat with atropine) - Encapsulating agents. Can reverse deep block, no CV effects, super expensive not used
succinylcholine
- depolarizing NMBA
- two Ach molecules together, initially activates receptor and causes fasiculations
- followed by flaccid paralysis
met by butrylcholinesterase (psuedocholineresterase) - giant dose, fast
- used for ET in humans because quick and goes away fast
- tremors start in front and move to back
side effects of succinylcholine
- MAchR - bradycardia or ANS ganglia - tachycardia/hypertension
- Hyper K
- Myoglobinuria (due to muscle contraction)
- inc. IOP (muscle contraction)
- MH
only indication is
muscle relaxation
often used for which surgeries?
- OCULAR surgery
- different sensitivities (high is highly sensitive - Fracture reduction
- improvement of surgical field
- preventing cough during intubation
- facilitation of mechanical ventilation
- C section (doesn’t cross placenta) provide analgesia
- rapid intubation in cat
3 Rules of NMDAs
- use with hypnotic and analgesic
- use IPPV
- Monitor anesthetic depth - ONLY with HR
MAC awake
(0.8) half of that asleep (1.3)
exclude ________ before extubating
residual paralysis
how do we assess muscular response?
visual, tactile
MMG, EMG,
**AMG
AMG
acceleromyography
stimulation patterns - train of four (TOF)
T1/T4 is TOF ratio 100% is no paralysis (4 twitches)
*need 3 twitches to reverse
reverse if patient is breathing?
yes! they can still be partially paralysed, reverse!
anesthetic drugs can act ______ with NMBAs
synergistically! muscle relaxers!
