Predicative Valute of Muscular Ultrasound in the Diagnosta of ICUAW in Critically Ill Patients

Skeletal muscle weakness is a common complication of acute respiratory failure, shock and other manifestations of critical illness or injury. ICU acquired weakness (ICUAW) - an entity defined as a bundle of critically illness neuro-myopathy and disuse atrophy - is generally diagnosed on the basis of a volitional, clinical strength evaluation, which however requires patient cooperation and ability to comprehend the assessor's instructions. As patients are often unconscious or uncooperative, due to sedation or delirium, such clinical diagnosis is often not possible or is delayed. A further subclassification of critical illness neuromyopathy can be achieved using detailed nonvolitional electrophysiological investigations, which can be challenging in the ICU as they require skilled personnel for both assessment and interpretation. An average Medical Research Council strength score (MRC-SS) combined for 12 specified muscle groups lower than 48 has been widely used for diagnosing ICUAW. Recent studies reported the clinical applicability of the MRC-SS in a general ICU population, in particular its clinical usefulness in predicting ICU and in-hospital patient outcomes . Moreover, interobserver agreement and clinical predictive value have already been showed (8). However, ICU general population is less likely to be able to cooperate with volitional strength assessment and more likely to have limited access to their extremities because of trauma, burns and treatment involving medical devices. For these reasons, MRC-SS may be confined to the later stages of ICU stay. Skeletal muscle ultrasound is used for the evaluation of muscular, tendon and joint disorders. It allows the evaluation of normal and pathological skeletal muscles through the measure of parameters reflecting size, such as cross sectional area (CSA) , and architecture by calculating the pennation angle, and it allows quick and repeated bedside evaluations. Despite such promising features, to date, there are few published studies that have reported the clinical applicability of the muscle ultrasound in prediction of ICUAW during the ICU stay. The principal aim of this study is to evaluate the variation of peripheral muscle ultrasound characteristics (such as CSA and pennation angle) during the ICU stay and its possible early predictive value of ICUAW as compared to the MRC-SS performed when patients are able to cooperate.

Materials and methods

Study design and ethical approval

observational, single-center study in a mixed medical and surgical ICU in a university teaching hospital. We will investigate the variation of CSA and pennation angle of rectus femoris over the ICU stay. Moreover, we will examine the clinical predictive value of these two variables as compared with MRC-SS at awakening. Patients 18 years of age and older who had been invasively ventilated for 48 hours were eligible for inclusion. Exclusion criteria included preexisting neurological weakness, pregnancy, malignancy, and those admitted for routine overnight postoperative surgical recovery. A flow diagram of the study is showed in figure 1.

Study protocol