NM Blockade Monitoring Flashcards
Anatomy involved in muscle contraction
Anterior horn of SC –> Motor Neuron contains presynaptic terminal –> Synaptic Cleft/space –> Skeletal Muscle Fiber via NM junction contains motor end plate.
Describe Nicotinic Ach Receptor
Located in jxnl folds of synaptic cleft. Contain 5 sub units 2 alpha, 1 beta/delta/epsilon. Activation req 2 alpha sub units to bind with 2 Ach molecules.
NM transmission process
Act potential reaches synaptic terminal, Ca channels open and cause release of Ach into synaptic cleft. 2Ach bind to 2 alpha subunits. Open channel and allow Na influx into motor end plate and cause action potential propagation down nerve.
Succinylcholine properties
Resembles 2 Ach molecules, activates motor end plate then causes desensitization. Does not allow end plate repolarization so no act potentials can happen.
Non-Depolarizers / “Intubating dose” is 2x ED95
Benzylquinolones - cis/atra-curium. Steroidal - Curae drugs. Comp antagonist for Nic Ach receptors, bind to alpha sub units. Short, IM, long acting. 30/ 30-60 / 60+ min
Phase 1 Block
“Depolarizing” block - muscle fasciculations precede blockade. Decr single twitch height, No fade to tetanus (sust response to tetanic stim), TOF, double burst. No post-tetanic potentiation. Block potentiated by antiAch drugs, antagonized by NDMB.
Phase 2 Block
“NonDepolarizing Block” - absence of fasciculation. decr single twitch height, Fade with tetanus, TOF, double burst. Has post-tetanic potentiation. Block may appear with rept Succs dosing.
NDMB reversal process
Neostigmine 0.05mg/kg max of 5mg. Increases Ach available, anti-musc Rx must be given. glycopyrrolate in 5:1 ratio with neostig. Glyco dose 0.01 mg/kg, will offset bradycardia, bronchoconstriction, salivation d/t incr Ach d/t neostig.
Indications for PNS
assess dept of NM block / assess paralysis during induction / assess for reversal/extubation readiness / assess for block before re-dosing.
PNS locations
Orbicularis oculi - muscle of eye via facial nerve CN7, post-lat to orbit, eyebrow moves. Adductor pollicis - muscle of thumb via ulnar nerve. Flexor hallucis - muscle of big toe via post tib nerve.
Facial nerve
Ideal for intubation readiness, best location for blockade onset at larynx. 2-3cm post-lat to orbit.
Ulnar nerve
Black lead distal on nerve. Red lead proximal 2-3cm. Best location for maintenance monitoring, emergence/recovery. Hand muscle more sensitive to muscle relaxant.
Post Tib nerve
ideal for when bed is rotated, provider access only to foot of bed. causes plantar flexion.
Patterns of Stimulation
Single twitch / TOF (count and ratio) / Tetanus / Double burst (DBS) / Post-tetanic count (PTC)
NDMB - has fade with each twitch, no fasc
DepMB - equal depression of all twitches, no fade, fasc present.
Reasons for Fade
NDMB - 1) competes for Ach rec subunits, unable to sustain contraction once Ach utilized and replaced by NDMB. 2) NDMB block Ach receptors on presynaptic nerve which has neg FB on Ach release with rept stimulation.
Single Twitch - Initial Threshold for Stim & Supramaximal (2.75-3x ITS, 10-20% above maximal)
All or none repsonse, if muscle moves when stim, less than 100% paralysis exists. Delivered “supramaximal”, 0.1-1Hz, 1-10 secs apart. Inital threshold maybe determined but not useful clinically.
TOF - count and ratio
Most commonly used nerve stim. 2Hz per 2 seconds. Count x/4 or ratio first to fourth twitch height. Fade indicative of phase 2 block.
TOF ratio
Requires four twitches to be present. Twitch 4 / Twitch 1. Sensitive between 70-100% blockade. at 0.9 ratio (1/4 twitches nearly equal) laryngeal muscles are intact. TOFr 0.9 recovery is present.
TOF count
4/4 - 70% or less. 3/4 75-80% block. 2/4 80-85% block. 1/4 90% block. 0/4 100% block. Intra op goal is 85-95%, 1-2 twitches.
Tetanus
Cont current 50-100Hz x5 sec straight. Painful! Assesses deep block. Fade with >75% block, no fade = <75% block. 100Hz maybe better at detecting fade.Use when other tests are equivocal, dont repeat this test.
Double burst stimulation
Analog to TOF, 2 short bursts 50Hz, 3/4 sec apart. Two twitches is better than 4 at detecting fade. Use at deeper levels of block, 2nd twitch fade = TOFr < 0.6 = significant blockade present.
Post Tetanic Count
Only used for assess severe/deep block, not used unless known severe paralysis is known as other tests have no twitch. 50Hz x5 secs followed by single twitches. Mobilizes Ach, presence of twitch count allows measuring intensity of block. Less twitches = more intense block. <8 twitch count means deep block.
