Characterising Changes in Muscle Quantity and Quality in Patients Requiring ECMO Oxygen During Critical Illness

Admission to the intensive care unit (ICU) with critical illness is typically associated with profound physical impairments including peripheral skeletal muscle wasting and dysfunction. These effects demonstrate a rapid onset from the point of ICU admission, affect those with higher illness acuity to greater levels, and contribute to the development of intensive care unit-acquired weakness (ICU-AW) defined as severe upper and lower limb muscle weakness.

Muscle structure has traditionally been evaluated using complex scanning approaches such as computed tomography or dual energy x-ray absorptiometry, however there are a number of caveats to their use in the clinical environment of critical care. Ionising radiation involved precludes their use in large populations, and especially for performance of sequential measurements. Whilst magnetic resonance imaging avoids this concern, practical limitations exist around scanning time and accessibility. In addition, all these imaging modalities require transfer out of the ICU environment, further restricting their application to acutely unwell, unstable patients. Finally, in addition to their expense, the nature of imaging using these approaches means that only a limited number of muscles may be assessed at any one time.

Ultrasound has emerged in recent years as a technique with significant clinical utility for assessing and monitoring the trajectory of change in muscle during acute critical illness. A range of parameters of muscle architecture and quality can be measured and data from the critical illness population is growing. Advantages of ultrasound include feasibility of bedside assessment, and that is it non-ionising, non-invasive and effort-independent with equipment is readily available in the critical care environment. Ultrasound imaging has robust clinimetric properties and predictive utility for morbidity and other clinical endpoints including mortality and hospital readmission.

A number of observational cohort studies have conducted sequential measurements of a range of respiratory and peripheral skeletal muscle groups during critical illness, characterising the decline in both muscle quantity and quality as a result of the acute insult. However no studies to date have included assessment of the abdominal muscles in critically ill patients necessary for core stability, trunk control and postural maintenance and therefore of significant clinical importance during the rehabilitation process.

In addition, whilst hypoxia has been found to be associated with greater muscle attenuation, no study has examined the relative changes in muscle in patients receiving extracorporeal membrane oxygenation (ECMO). ECMO is a ventilator support therapy primarily delivered to critically ill patients with severe respiratory failure where the hypoxic state is corrected.

The aim of this study is therefore to characterise sequential changes across respiratory, trunk and peripheral skeletal muscles in critically ill patients requiring ECMO.