Myasthenia Gravis

OVERVIEW

  • autoimmune disruption of post-synaptic acetylcholine receptors @ NMJ
  • up to 80% of functional receptors loss
  • typically young woman
  • may have thymus hyperplasia
  • prevalence = 14.2 cases per 100,000

HISTORY

  • mild ptosis -> bulbar palsy and respiratory failure
  • most marked after prolonged exertion
  • severity of MG (duration, functional capacity, doses of medications)
  • dose of steroid and duration
  • may be on immunosuppressive agents, plasmapheresis or immunoglobulin infusion
  • bulbar symptoms
  • upper airway muscle weakness can produce a myasthenic crisis (airway collapse and obstruction + inability to swallow secretions)
  • chewing fatigue
  • significant other cardio/respiratory disease – heart failure, COPD, restrictive lung disease, recurrent aspiration pneumonia

EXAMINATION

  • swallow
  • functional capacity
  • effectiveness of cough
  • jaw closure often weak and cannot be maintained against resistance
  • airway assessment
  • focused RESP and CVS examination
  • evidence of proximal myopathy and strength

Reasons to present to ICU and requiring MV

  • upper airway obstruction
  • inability to clear secretions
  • pneumonia
  • post surgical procedures (including thymetomy resection)
  • tapering of immunomodulatory therapy
  • pregnancy with disease exacerbation

INVESTIGATIONS

Diagnostic

  • edrophonium test (tensilon test)
  • electrophysiological studies
  • EMG
  • Ach receptor and muscle specific receptor tyrosine kinase antibody testing

Respiratory assessment

  • spirometry
  • PEFR
  • CXR
  • ABG

MANAGEMENT

ICU Management

Resuscitate

  • admit to ICU if VC < 25mL/kg, weak cough, not clearing secretions
  • intubate if indicated (airway protection, fatigue, hypercapnic respiratory failure)
  • physio

Specific Therapies

  • cholinesterase inhibitors: pyridostigmine, rivastigmine
  • plasma exchange
  • IVIG
  • corticosteroids (treatment resistant MG crises)
  • restart oral medications as soon as possible (may need IV neostigmine (30mg pyridostigmine:1mg neostigmine) or hydrocortisone if not able to tolerate PO medications)
  • incentive spirometry
  • introduction to physiotherapy
  • GORD/aspiration prophylaxis: H2 antagonists, Na+ citrate, metoclopramide, appropriate starvation

Underlying Cause

  • thymectomy – good analgesia

Intraoperative

  • avoid muscle relaxation if possible (may not be given major abdominal surgery)
  • if required use small titrated doses of NDNMB (10mg atracurium IV boluses)
  • very sensitive
  • plasmapheresis depletes plasma choline esterase levels -> prolonged action of sux, miv, remi + ester based LA’s
  • sux can be used (dose 1.5mg/kg)
  • keep warm
  • use PNS
  • intubation
  • MRSI if indicated
  • controlled ventilation
  • volatile maintenance
  • good analgesia
  • intraoperative hydrocortisone/dexamethasone if indicated
  • avoid reversal if possible (increased risk of cholinergic crisis) -> if need to reverse use standard doses
  • extubate once wide awake and obey commands (able to lift head off pillow for 5 seconds)
  • N/G tube may be required so can have regular medication
  • discussion with neurology about patient degree of optimisation required for surgery
  • plan for post-operative ventilation if required (ICU)
  • plan for analgesic technique as indicated

Predictors of Post operative Ventilation

  • major body cavity surgery
  • duration of disease (> 6 years)
  • history of chronic respiratory disease
  • dose requirements of >750mg/day
  • preoperative VC of <3L

Drugs exacerbating MG

  • neuromuscular blocking drugs
  • antibiotics: aminoglycosides, macrolides
  • CVS drugs: beta-blockers, Ca2+ channel blockers, procainamide, quinidine
  • corticosteroids
  • Mg
  • iodinated contrast
  • d-penicillamine
  • opioids: morphine and pethidine

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and 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 two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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