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NMB
Kevin's Neuromuscular Blockade Lecture (SIUE Nurse Anesthesia)
| 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. |
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toppu2020
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