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NMB

Kevin's Neuromuscular Blockade Lecture (SIUE Nurse Anesthesia)

QuestionAnswer
Where do the motor neurons originate from the spinal cord? anterior (ventral) horn
Where do the sensory neurons originate from the spinal cord? posterior (dorsal) horn
What type of neurons are the motor and sensory? somatic
What are the 3 components of the NMJ? 1) presynaptic terminal 2) synaptic cleft 3) motor end plate
Where are the Ach receptors located in the NMJ? 1) motor end plate 2) presynaptic membrane (positive feedback potentiation of ACh release via exocytosis)
How many Ach must bind to NAChR for opening of channel? 2 Ach. One for each alpha subunit.
What are the steps for neuromuscular transmission? AP at nerve terminal Opening of voltage-gated Ca2+ channel Ca2+ enters nerve terminal ACh released Presynaptic potentiation Ach binds to motor end plate NAChR channel opens allowing Na+ and Ca2+ in while K+ out
What enzyme terminates NT action? True cholinesterase or Acetylcholinesterase
What are the products of ACh and ACh-ase? 1) choline 2) acetate
What happens to the motor end plate when ACh action is terminated? Repolarization
What happens to the choline molecules once they are broken down by ACh-ase? transported back into nerve terminal to resyntheize ACh.
Name the 2 types of NMB? 1) depolarizing 2) non-depolarizing
Name the only depolarizing agent and how long does it work? succinylcholine (anectine) 10 min
What are the three classes of NDNMB, their length of action, and name examples in each category. Short-acting (10 min): Mivacurium Intermediate-acting (40-60 min): Atracurium, Cisatracurium (Nimbex), Vecuronium, Rocuronium (Zimuron) Long-acting ( > 1 hr): Doxacurium, Pancuronium, Pipecuronium
Which agent should be used for RSI? Succinylcholine. difficult airway, full stomach
Name 3 ways to produce NM relaxation 1) NMBA 2) Regional Anesthesia 3) High MAC (> 2 MAC)
Which enzymes break down succinylcholine? Pseudocholinesterase or Plasma Cholinesterase or Butyrocholinesterase
What compartment does metabolism of succinylcholine occur? blood stream
What compartment does metabolism of Ach occur? NMJ
What keeps the muscle unable to contract with depolarizing agent? Inactivation gate of voltage-gated sodium channel remains closed because motor end plate unable to repolarize due to succinylcholine remaining on NAChR receptor. (Since Succ not metab. by ACh-ase, remains on NAChR longer = prolonged depolarization)
What process needs to occur before succinylcholine can be metabolized? succinylcholine must diffuse down concentration gradient from NMJ to blood stream.
What is the mechanism of action for NDNMB? competitive inhibition = channel can't open
How does the nerve stimulator work? INDIRECTLY determines relaxation of musculature by stimulating action potential in the nerve which travels to NMJ. (If you stimulate the muscle instead of the nerve, you will always have a response because NMJ is bypassed and that is where NMB work)
Name the sites where NMB can be monitored? 1) aductor pollicis (ulnar nerve) 2) orbicularis occuli (Facial nerve (CN VII)) 3) 1st dorsal interosseous muscle in hand 4) abductor of little finger 5) nerves of foot
What is the landmark for the facial nerve? stylomastoid foramen
What is the order in which muscle function returns after NMB? 6) Aductor pollicis 5) Eye muscles. 4) Extremities. 3) Trunk (from the neck muscles downward through the intercostals). 2) Abdominal muscles. 1) Diaphragm. *Adductor policies returns last, but facial nerve may be more reliable
Name 5 modalities for monitoring NMB. 1) single twitch 2) TOF 3) tetanus 4) post-titanic count 5) DBS
Single Twitch Duration: 0.1 to 0.2 msec Frequency:0.1 to 1 Hz Purpose: qualitative assessment *not very reliable * 75-80% receptors may still be occupied with normal response.
Train of Four Duration: 0.5 msec Frequency: 2 Hz Purpose: following recovery of blockade * 3 twitches represents a 75% block. * 2 twitches represents an 80% block. * 1 twitches indicates a 90% block. * 0 twitches indicates a 99-100% block.
How is TOF expressed? TOF is ratio of 1 twitch to last twich. For example last twitch is 1/3 as big as first, would be documented as .33
Tetanus Duration: 5 sec * Observe for tetanic fade. * Should be used sparingly for deep block assessment. * Painful. * 70% of receptors may be occupied with a normal reading. No fade.
Post-Tetanic Count Give 5 seconds of tetany at 50 Hz. Allow for a 3 second pause. Deliver multiple single twitches at 1 Hz. * only when TOF or DBS absent * count less than 8 indicates deep block. * Number of twitches inversely correlate with reversal of NMB.
DBS Duration: Put more simply, two short bursts of 50 Hz tetanus separated by 0.75 seconds. * Useful during onset, maintenance, and emergence More sensitive means of assessing nondepolarizing blockade. (due to less receptor occupation than TOF)
Should response to PNS be determined visually? No. It should be done tactile.
Response w/ 99-100% occupied Complete paralysis (no twitches in TOF)
Response w/ 95% occupied Diaphragm moves ( no twitches in TOF)
Response w/ 90% occupied Abdominal relaxation adequate (1 twitch present in TOF)
Response w/ 75-80% occupied Tidal volume returns to normal or greater than 5ml/kg (single twitch is as strong as baseline)
Response w/ 70-75% occupied No palpable fade in TOF, useful as a gauge of recovery
Response w/ 60-70% occupied No palpable fade in double burst stimulation, more sensitive than TOF indicator
Response w/ 50% occupied Passes inspiratory pressure test, at least –40 cm H2O; head lift for 5 seconds, sustained strong handgrip; sustained bite (very reliable indicator)
Which PNS modality is best and most sensitive? DBS
What are the characteristics of a Phase I Block? Fascinations, No fade, Decrease in amplitude of twitches, Decreased amplitude to tetany, No post-titanic potentiation, Block are potentiated by anti cholinesterase drugs, Block antagonized by NDNMB (but will still have paralysis --> phase II block)
What happens which reversal agent given during phase I block? block potentiated
Can succinylcholine cause a phase II block? Yes. With overdose. (6 mg/kg).
What are the characteristics of a Phase II block? Will have fade, No fasciculation's, Block antagonized with anticholinesterases, Posttetanic potentiation, Amplitude of single twitch contractions decreases with increasing intensity of block
What is responsible for phase I block converting to phase II block? ion channels on motor end plate close and end plate repolarizes. (unknown reason)
Why do facial muscles become paralyzed first with NMB? blood flow greatest to head and neck.
Where is offset and recovery best monitored and why? ulnar nerve. because it recovers last, so you will end up reversing patient later, which is preferable.
Do the protective reflex muscles of the pharynx and upper esophagus recover before the diaphragm, larynx, hands, or face? No. The protective reflexes recover after all of these muscles.
How long does recovery take after return of 1 twitch? 30 minutes
How long does recovery take after return of 2-3 twitches? 4-5 min (intermediate agents) 10-12 min (long-acting agents)
How long does recovery take after return of 4 twitches? 5 minutes
What is the minimum amount of twitches for reversal of NDNMB? 2 twitches
Is DBS or TOF better for assessing readiness for reversal? DBS
Does spontaneous breathing mean adequate reversal? No.
Created by: toppu2020