Clinical review: peripheral muscular ultrasound in the ICU

Abstract

Muscular weakness developing from critical illness neuropathy, myopathy and muscle atrophy has been characterized as intensive care unit-acquired weakness (ICUAW). This entity occurs commonly during and after critical care stay. Various causal factors for functional incapacity have been proposed. Among these, individual patient characteristics (such as age, comorbidities and nutritional status), acting in association with sustained bed rest and pharmacological interventions (included the metabolic support approach), seem influential in reducing muscular mass. Long-term outcomes in heterogeneous ICUAW populations include transient disability in 30% of patients and persistent disabilities that may occur even in patients with nearly complete functional recovery. Currently available tools for the assessment of skeletal muscle mass are imprecise and difficult to perform in the ICU setting. A valid alternative to these imaging modalities is muscular ultrasonography, which allows visualization and classification of muscle characteristics by cross-sectional area, muscle layer thickness, echointensity by grayscale and the pennation angle). The aim of this narrative review is to describe the current literature addressing muscular ultrasound for the detection of muscle weakness and its potential impact on treatment and prognosis of critically ill patients when combined with biomarkers of muscle catabolism/anabolism and bioenergetic state. In addition, we suggest a practical flowchart for establishing an early diagnosis.

ICU-acquired weakness

“…Electrophysiological assessments are also used to diagnose ICU-acquired weakness and can be applied to unconscious/uncooperative patients. Although CIP and CIM share many features on nerve conduction studies and electromyography, differentiation is possible in ideal circumstances, particularly when the patient is cooperative and voluntary muscle activation is possible (Table 3) [2,5,6,22,30,42]. Single nerve conduction studies have shown promise as alternative for time-consuming full electrophysiological studies [22,31,32].…”

“…A variety of imaging techniques have been evaluated to assess muscle mass, as a surrogate of muscle strength, some of which also can visualize muscle quality. Of these, ultrasonography is considered most promising [30,33]. Although ultrasonography allows quick and repeated bedside evaluation of measures of muscle quantity and quality, it may underestimate muscle and protein loss [4,30,33,34].…”

“…Although ultrasonography allows quick and repeated bedside evaluation of measures of muscle quantity and quality, it may underestimate muscle and protein loss [4,30,33,34]. Furthermore, interpretation of the available studies is complicated by significant methodological defects, small sample sizes, and lack of standardization to control for operator dependency [30,33]. The clinical relevance also remains to be determined [22,35].…”

Diagnostic Value of Muscle Ultrasound for Myopathies and Myositis

“…In addition, US can be combined with EMG and muscle biopsies to provide more targeted acquisition of tissue [61]. Muscle skeletal architecture can be assessed non-invasively even in patients where weakness or pain precludes their cooperation [62]. As the technique is well-tolerated even in children and has no contraindications, it allows for repeated measurements of any muscle accessible on US including facial muscles [63,64].…”

Approach to critical illness myopathy and polyneuropathy in the older SARS-CoV-2 patients

“…This technique has gained favor because it is speedy, easily reproducible and it does not require patient cooperation. Note, however, that the CRIMYNE-2 study excluded diabetic patients [37].…”