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)
References and Links
CCC Neurocritical Care Series
Emergencies: Brain Herniation, Eclampsia, Elevated ICP, Status Epilepticus, Status Epilepticus in Paeds
DDx: Acute Non-Traumatic Weakness, Bulbar Dysfunction, Coma, Coma-like Syndromes, Delayed Awakening, Hearing Loss in ICU, ICU acquired Weakness, Post-Op Confusion, Pseudocoma, Pupillary Abnormalities
Neurology: Anti-NMDA Encephalitis, Basilar Artery Occlusion, Central Diabetes Insipidus, Cerebral Oedema, Cerebral Venous Sinus Thrombosis, Cervical (Carotid / Vertebral) Artery Dissections, Delirium, GBS vs CIP, GBS vs MG vs MND, Guillain-Barre Syndrome, Horner’s Syndrome, Hypoxic Brain Injury, Intracerebral Haemorrhage (ICH), Myasthenia Gravis, Non-convulsive Status Epilepticus, Post-Hypoxic Myoclonus, PRES, Stroke Thrombolysis, Transverse Myelitis, Watershed Infarcts, Wernicke’s Encephalopathy
Neurosurgery: Cerebral Salt Wasting, Decompressive Craniectomy, Decompressive Craniectomy for Malignant MCA Syndrome, Intracerebral Haemorrhage (ICH)
— SCI: Anatomy and Syndromes, Acute Traumatic Spinal Cord Injury, C-Spine Assessment, C-Spine Fractures, Spinal Cord Infarction, Syndomes,
— SAH: Acute management, Coiling vs Clipping, Complications, Grading Systems, Literature Summaries, ICU Management, Monitoring, Overview, Prognostication, Vasospasm
— TBI: Assessment, Base of skull fracture, Brain Impact Apnoea, Cerebral Perfusion Pressure (CPP), DI in TBI, Elevated ICP, Limitations of CT, Lund Concept, Management, Moderate Head Injury, Monitoring, Overview, Paediatric TBI, Polyuria incl. CSW, Prognosis, Seizures, Temperature
ID in NeuroCrit. Care: Aseptic Meningitis, Bacterial Meningitis, Botulism, Cryptococcosis, Encephalitis, HSV Encephalitis, Meningococcaemia, Spinal Epidural Abscess
Equipment/Investigations: BIS Monitoring, Codman ICP Monitor, Continuous EEG, CSF Analysis, CT Head, CT Head Interpretation, EEG, Extradural ICP Monitors, External Ventricular Drain (EVD), Evoked Potentials, Jugular Bulb Oxygen Saturation, MRI Head, MRI and the Critically Ill, Train of Four (TOF), Transcranial Doppler
Pharmacology: Desmopressin, Hypertonic Saline, Levetiracetam (Keppra), Mannitol, Midazolam, Sedation in ICU, Thiopentone
MISC: Brainstem Rules of 4, Cognitive Impairment in Critically Ill, Eye Movements in Coma, Examination of the Unconscious Patient, Glasgow Coma Scale (GCS), Hiccoughs, Myopathy vs Neuropathy, Neurology Literature Summaries, NSx Literature Summaries, Occulocephalic and occulovestibular reflexes, Prognosis after Cardiac Arrest, SIADH vs Cerebral Salt Wasting, Sleep in ICU
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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