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
- Mechanical ventilation alone (without inflammation or sepsis) can weaken respiratory muscles (termed “ventilator-induced diaphragmatic dysfunction”
- 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
- 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)
- 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]