ICU-acquired weakness (ICUAW) designates clinically detected weakness in critically ill patients in whom there is no plausible etiology other than critical illness. Patients with a suggestive history who are able to participate in a comprehensive bedside neuromuscular examination can be given this diagnosis.
Electrophysiology testing, direct muscle stimulation, and biopsy may be necessary to characterize neuromuscular injury in the patient who is unable to participate in a comprehensive neuromuscular examination, is failing to improve function despite weeks of therapy, or for the patient with asymmetric weakness.
When conducted, advanced testing, particularly electrophysiology tests, can characterize the specific phenotype of ICUAW including critical illness polyneuropathy, critical illness myopathy, a combination of the two (polyneuromyopathy), or prolonged neuromuscular blockade.
The exact epidemiology of ICUAW is unknown. Studies show that 46% of patients with sepsis, multiorgan failure, or prolonged mechanical ventilation are diagnosed with ICUAW. In patients undergoing mechanical ventilation for 7 days or more, 25% develop ICUAW.
Factors associated with the diagnosis of ICUAW include the presence of multisystem organ dysfunction, sepsis, SIRS, and hyperglycemia and the duration of mechanical ventilation. The only known therapy to prevent ICUAW has been strict glycemic control with insulin; however, adverse events with this therapy have impacted widespread utilization.
Many patients admitted to the intensive care unit (ICU) develop a syndrome of neuromuscular dysfunction characterized by generalized muscle weakness and an inability to be liberated from mechanical ventilation. Since this syndrome occurs in the absence of preexisting neuromuscular disease, it is believed to reflect illnesses or treatments occurring in the ICU. Early reports described two categories of acute, acquired neuromuscular dysfunction: polyneuropathy (during sepsis and multisystem organ failure)1,2 and myopathy (particularly in patients with acute respiratory failure who received glucocorticoids and/or neuromuscular blocking agents [NMBAs]).3,4 Decades of research on this acquired nerve and muscle injury has characterized specific phenotypes via comprehensive physical examination, electrophysiologic testing, and histopathology. Overall, the spectrum of neuromuscular disorders acquired in the ICU is collectively referred to as “ICU-acquired weakness” (ICUAW) (Fig. 85-1).5
Classification of intensive care unit-acquired weakness. CIM, critical illness myopathy; CINM, critical illness neuromyopathy; CIP, critical illness polyneuropathy; NMJ, neuromuscular junction.
The rising incidence and societal burden of critical illness—such as sepsis and the acute respiratory distress syndrome (ARDS)6–8—coupled with declining case fatality rates and an aging population,9,10 suggests that the number of patients with ICUAW and its sequelae may be substantial and likely to grow. Accordingly, intensivists must have familiarity with the presentation of ICUAW, recognize when to conduct advanced testing, and understand the diagnostic tests involved. Although currently limited in scope, measures designed to prevent or attenuate ICUAW must be considered and implemented.
CRITICAL CARE SURVIVORSHIP AND ICUAW
Critical care outcomes research ...