Critical illness-associated limb and diaphragmatic weakness

Abstract

Purpose of review: In the current review, we aim to highlight the evolving evidence on the diagnosis, prevention and treatment of critical illness weakness (CIW) and critical illness associated diaphragmatic weakness (CIDW).

Recent findings: In the ICU, several risk factors can lead to CIW and CIDW. Recent evidence suggests that they have different pathophysiological mechanisms and impact on outcomes, although they share common risk factors and may overlap in several patients. Their diagnosis is challenging, because CIW diagnosis is primarily clinical and, therefore, difficult to obtain in the ICU population, and CIDW diagnosis is complex and not easily performed at the bedside. All of these issues lead to underdiagnosis of CIW and CIDW, which significantly increases the risk of complications and the impact on both short and long term outcomes. Moreover, recent studies have explored promising diagnostic techniques that are may be easily implemented in daily clinical practice. In addition, this review summarizes the latest research aimed at improving how to prevent and treat CIW and CIDW.

Summary: This review aims to clarify some uncertain aspects and provide helpful information on developing monitoring techniques and therapeutic interventions for managing CIW and CIDW.

Box 1

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FIGURE 1

Diagnostic algorithm for critical illness weakness, polyneuropathy and myopathy. (b1) Adapted from [27]. In critical illness polyneuropathy (CIP), nerve conduction studies show a reduction in the amplitude of both compound muscle action potential (CMAP) and sensory nerve action potential (SNAP, not shown). In critical illness myopathy (CIM), CMAP is reduced while SNAP remains normal. (b2, b3) At rest electromyography (EMG), various degrees of positive sharp waves (b2) and fibrillation potentials (b3) may be present in both CIP and CIM. (c) With cooperative patients, motor unit potentials at EMG are large in amplitude and have a long duration in CIP, whereas in CIM, they are low in amplitude and short; both are highly polyphasic. (a) Adapted from [96]. Direct muscle stimulation (DMS) can differentiate CIP and CIM in uncooperative patients: in CIM, CMAP reduction occurs after both conventional nerve stimulation and DMS, whereas in CIP CMAP reduction occurs only after conventional nerve stimulation. MRCss, medical research council sum score; PENT, peroneal nerve test. Reference [27,96].

FIGURE 2

Diagnostic features of critical illness-associated diaphragmatic weakness in intensive care patients. EMG, electromyography; P_di, transdiaphragmatic pressure; PEEP, positive-end expiratory pressure; P_es, esophageal pressure; P_ga, gastric pressure; TEE, end expiratory thickness; TEI, end inspiratory thickness; TF, thickening fraction.

FIGURE 3

Schematic presentation of critical illness-associated limb and diaphragm weakness. Eadi, diaphragmatic electromyography; ICU, intensive care unit; MRCss, Medical Research Council sum score; NMBA, neuromuscular blocking agents; P_di,tw, twitch trandiaphragmatic pressure; PENT, peroneal nerve test; SWE, shear wave elastography; Tdi, tissue Doppler imaging.