Question | Answer |
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. |