ICU-Acquired Weakness

Epidemiology

  • History: unexpected prolonged ventilatory failure with acute weakness was first reported in status asthmaticus patients treated with concomitant corticosteroids and paralytics [MEDLINE]
    • Subsequent reports were noted in patients with sepsis/inflammation even without the use of corticosteroids or paralytics
    • Studies have variably called these entities critical illness polyneuropathy, critical illness polymyopathy, ICU-acquired paraesis, etc
  • Incidence by EMG/NCV: 25%-50% of patients who require >7 days of ICU care and the majority of patients who develop systemic inflammatory response syndrome (SIRS) can be demonstrated to have EMG/NCV abnormalities consistent with ICU-acquired weakness
    • These abnormalities occur early in the course, accumulate during the course of the illness, and usually affect both nerves and muscles
  • Incidence by Neurologic Exam: 33% of critically ill patients exhibit weakness on clinical exam

Risk Factors

  • Immobilization
  • Severity of Illness
  • Corticosteroid Exposure
  • Neuromuscular Blocker Exposure
    • Paralytics are commonly used in the ICU to facilitate rapid-sequence intubation (RSI), facilitate mechanical ventilation, reduce oxygen consumption, and control intracranial pressure
    • Prolonged paralysis has been observed with use of these agents, especially in the setting of hepatic or renal dysfunction
      • Prolonged paralysis may be seen for days-weeks after use of pancuronium and vecuronium in the setting of renal failure
      • Due to clearance in plasma, atracurium and cisatracurium are not associated with prolonged paralysis due to delayed clearance
    • However, a systematic review indicates that short-term use of paralytics (not exceeding 48 hrs) in ARDS did not significantly increase the rate of ICU-acquired weakness [MEDLINE]
  • Sepsis
  • Prolonged Mechanical Ventilation
    • Mechanical ventilation alone (without inflammation or sepsis) can weaken respiratory muscles (termed “ventilator-induced diaphragmatic dysfunction”
      • May be related to absence of neural stimulation and/or muscle contraction
      • Diaphragm may be more sensitive than other muscles to the effects of critical illness
      • In animal studies: the diaphragm weakens within the first 1-3 days of mechanical ventilation
      • Stimulating the diaphragm to contract attenuates some of the loss in strength -> suggests that partial ventilatory support (rather than full ventilatory support) may be a better strategy in mechanically-ventilated patients
  • Hyperglycemia: some studies have demonstrated decreased incidence of ICU-acquired weakness with tight glucose control

(TNF alpha and IL-6 levels are not associated with ICU-acquired weakness)


Diagnosis

  • Electromyogram (EMG) + Nerve Conduction Velocity (NCV): decreased compound muscle action potential, increased action potential duration, fibrillation potentials, positive sharp waves, and normal conduction velocity
  • Muscle Biopsy (usually not necessary): primary axonal degeneration, type II muscle fiber atrophy, thick filament (myosin) loss, occasional necrotizing myopathy

Diagnostic Algorithm

  • Globally Impaired Mentation (despite sedative washout) -> CNS studies
  • Focal Central Neuro Deficit -> CNS studies
  • Focal Peripheral Neuro Deficit -> EMG+NCV (with or without muscle biopsy)
  • Intact Mentation + Symmetric Weakness (with facial muscle sparing) -> if no improvement, consider EMG+NCV (with or without muscle biopsy)

Clinical

Neurologic Manifestations

  • Symmetric Extremity Weakness
    • May be severe
    • May persist for months in some cases (although a subset of patients may rapidly improve over days-weeks)
    • Proximal>distal impairment
    • Sparing of facial muscles
    • Handgrip strength may serve as an easy screening test for ICU-acquired weakness

Pulmonary Manifestations

  • Acute/Chronic Hypoventilation (see Acute Hypoventilation, [[Acute Hypoventilation]] and Chronic Hypoventilation, [[Chronic Hypoventilation]])
    • ICU-acquired weakness often affects the respiratory muscles and is associated with increased ventilator-dependence

Treatment

Prevention

  • Minimization of Use of Corticosteroids: if possible
  • Minimization of Use of Paralytics: if possible
    • Neurostimulator Train-of-Four Monitoring: shown to decrease the amount of paralytic administered and the recovery time from paralytics (although this benefit is not seen with the use of atracurium and cisatracurium)
      • Probably should be used routinely
  • Daily Interruption of Sedation and Paralysis: indicated
  • Early Mobilization/Physical Therapy: indicated

Prognosis

  • ICU-acquired weakness is associated:
    • Increased ICU Length of Stay
    • Increased Hospital Length of Stay
    • Increased Mortality Rate

References

  • Neuromuscular blockade in the intensive care unit. More than we bargained for. Am Rev Respir Dis. 1993 Jan;147(1):234-6 [MEDLINE]
  • ICU-acquired weakness. Chest 2007; 131:1541-1549
  • Early intensive care unit mobility therapy in the treatment of acute respiratory failure. Crit Care Med 2008; 36:2238–2243
  • Early exercise in critically ill patients enhances short-term functional recovery. Crit Care Med 2009; 37:2499-2505
  • Intensive care unit-acquired weakness. Crit Care Med 2010; 38:779-787
  • Functional Disability 5 Years after Acute Respiratory Distress Syndrome. NEJM 2011; 364:1293-1304
  • Neuromuscular blocking agents in acute respiratory distress syndrome: a systematic review and meta-analysis of randomized controlled trials. Crit Care. 2013 Mar 11;17(2):R43 [MEDLINE]