2021A09 Explain the onset and offset of neuromuscular block at the diaphragm, larynx and adductor pollicis after an intubating dose of vecuronium. What are the clinical implications of these differences?

 

List:

·        Intro

·        Table

·        Graph

·        Implications

 

Intro:

Definitions

·      ED95: dose that produces 95% depression of single twitch height in adductor pollicis

·      2 x ED95: intubating dose

Summary

Adductor pollicis vs diaphragm/larynx:

·      Slower onset

·      Greater peak effect

·      Slower offset

 

Table:

 

Diaphragm and Larynx (D&L)

Corrugator supercilii (CS)

Adductor pollicis (AP)

Physiology:

 

 

 -Blood flow

 -ACh release

 -AChR density

 -AChE activity

Clinical effect:

 

 

 -Onset speed

↑ (25% faster)

 -Peak effect

 -Offset speed

↑ (33-50% faster)

 

Graph:

 

Implications:

Where to look

·     CS: medial eyebrow (not orbicularis oculi)

·     AP: thumb & forefinger (not hypothenar eminence)

Induction

·     CS: intubate at TOF count = 0

·     AP: intubate at TOF count = 1 (?)

Maintenance

If immobility essential:

·     CS: titrate against TOF count = 0

·     AP: titrate against PTC

·     Administer relaxant by infusion

Emergence

·     CS: ahead of D&L. TOF count by inspection.

-> risk of residual curarisation

·     AP: lag behind D&L. TOF ratio by accelerometry.

-> Reversal at TOF count 4

-> Extubate at TOF ratio >0.9

 

References:

https://pubs.asahq.org/anesthesiology/article/117/5/934/13433/Neuromuscular-MonitoringMore-than-Meets-the-Eye

https://link.springer.com/content/pdf/10.1007/BF03019373.pdf

 

 

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