Critical illness neuropathy Flashcards
What is critical illness (poly)neuropathy (CIP)?
one of three classifications of intensive-care unit acquired weakness (ICUAW) the others being critical illness myopathy (CIM) and critical illness neuromyopathy (CINM)
What is intenstive-care unit acquired weakness?
a clinically detected weakness in critically ill patients in whom there is no plausible aetioloy other than critical illness
What are 4 aspects to the mechansims proposed to cause critical illness polyneuropathy?
- Microvascular alterations
- Metabolic alterations
- Electrical alterations
- Bionenergetic failure
How are microvascular alterations thought to cause critical illness polyneuropathy?
increase in e-selectin expression, vasodilation, increased capillary permeability, extravasation and endoneural oedema which results in hypoxia
How are metabolic alterations thought to contribute to the mechanism of critical illness polyneuropathy?
production of toxic factors such as cytokines, hyperglycaemia, hormone imbalance, hypoalbuminaemia, amino acid deficiency and activation of proteolytic pathways
How are electrical alterations thought to contribute to critical illness polyneuropathy?
ion channel dysfunction, cell depolarisation, inexcitability, altered calcium homeostasis and changes in excitation-contraction coupling
How is bio-energetic failure thought to contribute to critical illness polyneuropathy?
anti-oxidant depletion, increase in reactive oxygen species, mitochondrial dysfunction and apoptosis
Overall how are all the factors thought to work together to cause critical illness polyneuropathy?
the endoneural oedema resulting from increased permeability may impair energy delivery to the axon followed by axonal death
direct toxic effects and mitochondrial dysfunction evoked by hyperglycaemia may contribute to this process
What are 12 risk factors for critical illness polyneuropathy?
- Sepsis
- SIRS
- Multi Organ Failure (MOF)
- Female Gender
- Duration of Organ Dysfunction
- Duration of ICU Stay
- Ionotropic Support
- Renal Failure
- Low Serum Albumin
- Hyperglycemia
- Neuromuscular Blockades
- Corticosteroids
What are 7 clinical features of critical illness neuropathy?
- Muscle weakness
- absent facial weakness - cranial nerves rarely affected
- Muscle weakness - in a third
- Reduced muscle reflexes - decrease over time
- Difficulty in weaning from ventilator
- Sensory loss - difficult to assess with sedated/intubated patient
- Impaired consciousness
What is the nature of muscle weakness in critical illness neuropathy?
- predominantly in the lower extremities
- symmetrical, flaccid weakness
- reduced limb movement following painful stimulus to the distal limb
What are 5 aspects of the investigations to perform in critical illness neuropathy?
- MRC to assess muscle strength - out of total score of 60. 48/60 designates ICUAQ or significant weakness. <36/48 indicates severe weakness
- Nerve conduction studies
- EMG
- Biomarkers: creatine kinase, plasma levels of neurofilaments
- Biopsy: not commonly performed
What will nerve conduction studies show in critical illness neuropathy? 3 things
- reduced compound muscle action potential (CMAP)
- sensory nerve action potentials (SNAPs) may be reduced
- nerve conduction velocity usually normal or minimally reduced
Despite not being routinely performed, what will biopsy show in critical illness neuropathy?
- features of denervation and reinnervation with small muscle fibres
- fibre-type grouping
- fibre group atrophy with widespread axonal degeneration of both motor and senosry nerves
- thick filament loss commonly associated with critical illness myopathy (CIM)
What are 5 key aspects of the management of critical illness neuropathy?
- Glycaemic control: intensive insulin therapy for hyperglycaemia
- Optimising nutrition
- Treatment of sepsis
- Avoid neuromuscular blockades: hepatic or renal failure, hypermagnesaemia, metabolic acidosis and concomitant use of certain antibiotics (aminoglycosides and clindamycin)
- Physiotherapy
