Nerve stimulator
OVERVIEW
- Nerve stimulator
- aka ‘train of four’ stimulator
USE
Provides an objective measure of neuromuscular blockade
- determine degree of neuromuscular blockade (e.g. during anaesthaesia for a surgical procedure or for ICP control to titrate NMB dosing)
- exclude neuromuscular blockade prior to brain death assessment
- may also be used for regional anesthaesia when performing nerve blocks (alternative or adjunct to ultrasound)
DESCRIPTION
- a peripheral nerve is stimulated by an electrical signal
— current = number of electrons supplied per stimulus
— twitch = muscle response to stimulus - ulnar nerve is most commonly used; alternatives include posterior tibial, facial and peroneal nerve
- ECG dots (ensure good skin contact and current flow)
- Electrodes (black and red)
- Nerve stimulator console
METHOD OF USE
Ulnar nerve
- ECG dots placed
— first dot on the palmar aspect of the wrist 1–2 cm proximal to the wrist
— second dot in the same line 3 cm proximal to the wrist - Electrodes attached
— black (negative) electrode is attached to dot closest to hand (place as close to nerve as possible)
— red (positive) attached to the proximal dot (must be in line to minimise nerve-muscle artefact and ensure maximal stimulation) - stimulator is attached
- voltage is slowly increased starting at 20mA, voltage should not exceed 60mA
- red pulse light indicates voltage conduction
- observe twitching of adductor pollicis (medial adduction of the thumb across the palm)
- ‘Train of four’ (TOF) is commonly used (TOF)
— four electrical currents are delivered at intervals of 0.5 secs
— 1–2 twitches indicates adequate neuromuscular blockade - TOF is typically repeated hourly or as indicated
- do not repeat within 10 seconds to allow recovery of the motor endplate
COMPLICATIONS
- Pain or discomfort
- Incorrect assessment leading to mismanagement (see trouble-shooting below)
OTHER INFORMATION
If no twitches seen check:
- Settings
- Battery
- Connections
- Position and attachment of electrodes
- Site (e.g. obese, thick skin, oedema)
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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