Page 1125 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

764 PART 6: Neurologic Disorders

One widely cited catalyst for attention to the burden of neuromuscular
is unable to participate in a comprehensive neuromuscular examina- weakness was the comprehensive observations of a cohort of survivors
tion, is failing to improve function despite weeks of therapy, or for the of acute respiratory distress syndrome (ARDS) published in 2003.
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patient with asymmetric weakness. These 109 survivors were young (median age, 45 years), had few pre-
• When conducted, advanced testing, particularly electrophysiology tests, existing comorbidities, and were severely ill (median APACHE II
can characterize the specific phenotype of ICU-AW including critical score, 23). Their critical illness was marked by prolonged mechanical
illness polyneuropathy, critical illness myopathy, a combination of the ventilation (median duration, 21 days) and ICU and hospital lengths
two (polyneuromyopathy), or prolonged neuromuscular blockade. of stay (median duration, 25 and 48 days, respectively). Despite severe
• The exact epidemiology of ICUAW is unknown. Studies show that acute lung injury, serial follow-up examination during the first year
after ICU discharge demonstrated restoration of lung function. Lung
46% of patients with sepsis, multiorgan failure, or prolonged mechan- volumes and spirometry normalized by 6 months and carbon monoxide
https://kat.cr/user/tahir99/
ical ventilation are diagnosed with ICUAW. In patients undergoing diffusion capacity improved to 72% predicted at 12 months. In contrast,
mechanical ventilation for 7 days or more, 25% develop ICUAW. all 109 patients reported poor function attributed to the loss of muscle
• Factors associated with the diagnosis of ICUAW include the presence bulk, proximal weakness, and fatigue. One year after ICU discharge, the
of multisystem organ dysfunction, sepsis, SIRS, and hyperglycemia median distance walked in 6 minutes was 66% of predicted and only
and the duration of mechanical ventilation. The only known therapy 49% of patients had returned to work.
to prevent ICUAW has been strict glycemic control with insulin; how- More recently, the same cohort was characterized at 5 years after ICU
ever, adverse events with this therapy have prevented its utilization. discharge. All patients reported subjective weakness and decreased
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exercise capacity when compared to function before ICU admission.
Although there was no evidence of clinical weakness on examination,
the median distance walked in 6 minutes remained lower than expected
INTRODUCTION based on age and sex (76% predicted). By the fifth year, 77% of patients
had returned to work; however, patients often required a modified
Many patients admitted to the intensive care unit (ICU) develop a syn- work schedule, gradual transition back to work, or job retraining. In
drome of neuromuscular dysfunction characterized by generalized muscle addition, patients were plagued with the psychological ramifications of
weakness and an inability to be liberated from mechanical ventilation. their severe illness; more than half of survivors experienced at least one
Since this syndrome occurs in the absence of preexisting neuromuscular episode of physician-confirmed depression or anxiety.
disease, it is believed to reflect illnesses or treatments occurring in the ICU. Others have reported similar findings of post-ARDS debilitation.
Early reports described two categories of acute, acquired neuromuscular Specifically, an observational trial of 112 ARDS survivors without
dysfunction: polyneuropathy (during sepsis and multisystem organ fail- baseline impaired physical function noted a 66% cumulative incidence
ure) and myopathy (particularly in patients with acute respiratory failure of physical impairment during 2 year follow-up. This impairment,
1,2
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who received glucocorticoids and/or neuromuscular blocking agents). defined as the acquisition of two or more dependencies in instrumental
3,4
Decades of research on this acquired nerve and muscle injury has char- activities of daily living, had greatest incidence by 3 months after
acterized specific phenotypes via comprehensive physical examination, discharge and was associated with longer ICU stay and prior depressive
electrophysiologic testing, and histopathology. Overall, the spectrum of symptoms. More recently, a comprehensive 1 year follow-up of patients
neuromuscular disorders acquired in the ICU is now collectively referred enrolled in a randomized controlled trial of nutritional strategies
to as “ICU-acquired weakness” (ICUAW) (Fig. 83-1). 5 in patient with ARDS demonstrated that survivors, regardless of
The rising incidence and societal burden of critical illness—such as nutritional strategy, experienced substantial impairments in endurance
sepsis and the acute respiratory distress syndrome —coupled with (as defined by six minute walk test) and cognitive function. 15
6-8
declining case fatality rates and an aging population, suggests that Acquired neuromuscular weakness and loss of function have been
9,10
the number of patients with ICUAW and its sequelae may be substantial measured in other contexts of critical illness, including severe sepsis
and likely to grow. Accordingly, intensivists must have familiarity with and mechanical ventilation in the elderly. To determine the impact of a
the presentation of ICUAW, recognize when to conduct advanced test- hospitalization for severe sepsis, Iwashyna and colleagues utilized The
ing, and understand the diagnostic tests involved. Although currently Health and Retirement Study, a cohort of Americans over age 50 under-
limited in scope, measures designed to prevent or attenuate ICUAW going biennial surveys of physical and cognitive function. Participants
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must be considered and implemented. were stratified into those surviving a hospitalization for severe sepsis
(n = 516) versus controls (survivors of a nonsepsis hospitalization,
CRITICAL CARE SURVIVORSHIP AND ICUAW n = 4517). Among patients with no functional limitations at baseline,
severe sepsis was associated with the development of 1.57 new limita-
Critical care outcomes research has demonstrated substantial morbidity tions (95% CI: 0.99-2.15), as well as a more rapid rate of development
in survivors. Injuries include general deconditioning, muscle weakness, of functional limitations after hospitalization (0.51 new limitations per
dyspnea, depression, anxiety, and reduced health-related quality of life. year, p = 0.007 compared with baseline). The study also found that the
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incidence of severe sepsis was highly associated with progression to
moderate to severe cognitive impairment.
ICU-acquired weakness In a similar design, Barnato et al used a longitudinal cohort study
of Medicare recipients to investigate the association of mechanical
ventilation and disability. Community dwelling patients over age 65
17
completed quarterly interviews of physical function for four years.
Prolonged Survivors of hospitalization with or without mechanical ventilation had
CIM CIPNM CIP NMJ similar levels of disability from each other, but significantly more than
blockade those who were never hospitalized. There was a substantial increase in
disability in both groups after hospitalization, greater among survivors
of mechanical ventilation than in those hospitalized without mechanical
FIGURE 83-1. Classification of intensive care unit-acquired weakness. CIM, critical illness ventilation. In adjusted analyses, mechanical ventilation was associated
myopathy; CINM, critical illness polyneuromyopathy; CIP, critical illness polyneuropathy; NMJ, with a 30% greater disability in activities of daily living (ADLs) and a
neuromuscular junction. 14% greater disability in mobility.

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