ICU Acquired Weakness (ICUAW)

OVERVIEW

  • ICU Acquired Weakness (ICUAW) includes critical illness myopathy (CIM), critical illness polyneuropathy (CIP), or a mixture of both (myopathy is typically predominant)
  • very common in the mechanically ventilated (25-60% in those mechanically ventilated for > 7 days)
  • increasing body of evidence that ICUAW leads to poor quality of life and persistent weakness lasting long after ICU discharge

PATHOPHYSIOLOGY

Multifactorial pathogenesis may involve:

  • axonopathy, not demyelinating
  • mitochondrial dysfunction
  • microvascular ischaemia
  • sodium channelopathy
  • catabolism
  • immobility

RISK FACTORS

  • sepsis
  • systemic inflammation
  • poor glycaemic control
  • steroids
  • neuromuscular blocking agents
  • immobility
  • malnutrition
  • female sex
  • pre-existing sarcopenia

CLINICAL FEATURES

  • onset is typically about 1 week into a critical illness
  • Sensation is preserved (deficits can be present with axonopathy; difficult to assess in ICU due edema and coma)
  • Symmetrical deficits
  • Mostly proximal weakness
  • Reflexes are present, though diminished
  • CSF findings are normal
  • Cranial nerve function and autonomic nervous system function are usually intact
  • CK may be raised if myopathy is present
  • Nerve conduction studies (if performed) show normal conduction velocities with decreased compound muscle action potentials (CMAPs)
  • score of <48 on the MRC sum score (MRC-SS) of muscle strength is diagnostic of ICUAW

INVESTIGATIONS

Investigations are often not necessary, however they may be required depending on the possible differential diagnoses and implications for management and prognosis

Laboratory

  • CK (mildly elevated – and transiently so – in critical illness myopathy (not so with critical illness neuropathy)
  • UEC
  • B12 level
  • Acetylcholine receptor antibodies (for myasthenia gravis)
  • Inflammatory markers (e.g. CRP)
  • Lumbar puncture

Imaging

  • CXR (evidence of malignancy causing Eaton-Lambert syndrome)
  • MRI of the brainstem and spine

Special tests

  • Nerve conduction studies andelectromyography: CIP shows sensorimotor axonopathy with decreased compound muscle action potentials (CMAP) and sensory-nerve action potentials, but preserved conduction velocities (CV). CIM shows reduced amplitude and increased duration of CMAPs. ICUAW often is a mixture of CIP and CIM.
  • Muscle biopsy if no satisfactory explanation is found

DIFFERENTIAL DIAGNOSIS

Key differentials of ICU-acquired weakness

  • Critical illness polyneuropathy
    • presents around a week into a critical illness, typically with limb weakness and atrophy, reduced tendon reflexes, loss of peripheral sensation to touch and pain, preservation of CN function, electrophysiological studies -> motor and sensory neuropathy, biopsies -> axonal degeneration and denervation -> atrophy of muscles
  • Residual paralysis
    • exclude using peripheral nerve stimulation (minimal response to TOF, PTc)
  • Residual sedation
    • calculation of dose, duration and ability to clear medications (response to antagonism; naloxone, flumazenil)
  • Acute myopathy
    • risk factors = neuromuscular blockage and corticosteroids, motor findings with no sensory abnormalities, CK elevated, electrophysiological testing -> myopathy, muscle biopsy -> loss of thick filaments
  • Spinal cord lesions
    • associated with a sensory level and hyperreflexia
  • Brain stem problems
    • cranial nerve lesions
  • Guillain-Barre syndrome
    • ascending motor weakness, loss of reflexes, some peripheral sensory deficits, pain, post-viral, high protein in CSF, responsive to Ig and plasmapheresis

Differential diagnosis of rapidly progressive limb weakness (with or without respiratory failure)

  • CNS
    • Encephalitis, acute disseminated encephalomyelitis, transverse myelitis, brainstem or myelum compression, leptomeningeal malignancy
  • Motor neurons
    • Poliomyelitis, West Nile virus anterior myelitis, amyotrophic lateral sclerosis, progressive spinal muscular atrophy
  • Plexus
    • Neuralgic amyotrophia, diabetes mellitus
  • Nerve roots
    • Guillain-Barré syndrome, acute onset chronic inflammatory demyelinating neuropathy, Lyme disease, cytomegalovirus-related radiculitis, HIV-related radiculitis, leptomeningeal malignancy
  • Peripheral nerves
    • Guillain-Barré syndrome, acute onset chronic inflammatory demyelinating neuropathy, iatrogenic, toxic, critical illness myopathy-neuropathy, vasculitis, diphtheria, porphyria, thiamine deficiency, porphyria, Lyme disease, metabolic or electrolyte disorders (hypokalaemia, phosphataemia or magnesaemia, hypoglycaemia)
  • Neuromuscular junction
    • Myasthenia gravis, botulism, intoxication
  • Muscles
    • Critical illness myopathy-neuropathy, mitochondrial disease, acute rhabdomyolysis, polymyositis, dermatomyositis

MANAGEMENT

  • intensive glycaemic control
  • minimise use of corticosteroids and neuromuscular blockade
  • physiotherapy – consider including early mobilisation
  • electrical muscular stimulation (EMS)
  • minimise sedation
  • electrolyte replacement
  • optimise nutrition
  • ventilator weaning

PROGNOSIS

Short term

  • increased ventilation
  • increased ICU stay
  • increased mortality

Long term

  • most recover to be able to walk independently
  • small amount have mild disability
  • 30% have severe quadriparesis, quadriplegia or paraplegia

References and Links

LITFL

Journal articles

  • Deem S. Intensive-care-unit-acquired muscle weakness. Respir Care. 2006;51:(9)1042-52; discussion 1052-3. [pubmed]
  • Dhand UK. Clinical approach to the weak patient in the intensive care unit. Respir Care. 2006 Sep;51(9):1024-40; discussion 1040-1. [PubMed] [Free Full Text]
  • Fan E, Cheek F, Chlan L, et al. An official American Thoracic Society Clinical Practice guideline: the diagnosis of intensive care unit-acquired weakness in adults. Am J Respir Crit Care Med. 2014;190:(12)1437-46. [pubmed]
  • Hermans G, De Jonghe B, Bruyninckx F, Van den Berghe G. Interventions for preventing critical illness polyneuropathy and critical illness myopathy. Cochrane Database Syst Rev. 2009;(1)CD006832. [pubmed]
  • Hermans G, De Jonghe B, Bruyninckx F, Van den Berghe G. Clinical review: Critical illness polyneuropathy and myopathy. Crit Care. 2008;12:(6)238. [pubmed]
  • Khan J, Burnham EL, Moss M. Acquired weakness in the ICU: critical illness myopathy and polyneuropathy. Minerva Anestesiol. 2006;72:(6)401-6. [pubmed]
  • Kress JP, Hall JB. ICU-acquired weakness and recovery from critical illness. N Engl J Med. 2014;370:(17)1626-35. [pubmed]
  • Truong AD, Fan E, Brower RG, Needham DM. Bench-to-bedside review: mobilizing patients in the intensive care unit–from pathophysiology to clinical trials. Crit Care. 2009;13:(4)216. [pubmed] [PMC free article]

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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