Mechanisms of Neuromuscular Dysfunction in Critical Illness
Section snippets
Incidence of acquired neuromuscular dysfunction in the ICU
Acquired NMD is a comprehensive designation incorporating both CIM and CIP. Alternate terms include ICU-acquired paresis, critical illness neuromyopathy, and critical illness neuromuscular abnormalities. CIM has been reported in at least one third of ICU patients treated for status asthmaticus [7], and studies of critically ill patients suggest incidence rates between 12% and 35% [8], [9], [10], [11]. Prospective studies suggest that CIP may occur in up to 50% to 70% of patients admitted to the
Bedside examination
NMD is typically heralded by difficulty in weaning from mechanical ventilation or by the presence of diffuse weakness in a cooperative patient. Early signs of development of NMD are nonspecific and may simply include a reduction in spontaneous movement of the limbs. In many cases, establishing the presence of NMD in critically ill patients and then distinguishing CIM from CIP are limited by the ability of the clinician to obtain an adequate history and physical examination owing to factors such
Prognosis of ICU-acquired neuromuscular dysfunction
Prospective studies in patients ventilated for more than 7 days have reported increased hospital mortality associated with NMD [12], [14], [24]. In fact, the development of NMD early in the course of critical illness may predict mortality. In a prospective cohort of 48 patients with severe sepsis, it was found that abnormal nerve conduction studies obtained within 72 hours of ICU admission predicted hospital mortality (55% versus 0%, P<.001) [19]. The presence of NMD is also associated with
Mechanisms underlying acquired paresis in critical illness myopathy
There are at least three factors that contribute to weakness in patients with CIM: atrophy of muscle fibers, loss of myosin, and muscle inexcitability [3], [38]. Atrophy and loss of myosin both cause weakness due to loss of force generation following muscle fiber action potentials. The causes of muscle atrophy and loss of myosin are complex and are still poorly understood [5], [39] and, although important, will not be discussed further. The third factor is loss of the ability of muscle fibers
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This work was supported by NIH R01 NS040826 (MMR).