Metabolic aspects of muscle wasting during critical illness

Abstract

Purpose of review: Skeletal muscle wasting during critical illness is the result of disturbed metabolism. No proven effective interventions targeting skeletal muscle mass and function during critical illness currently exist. This review summarizes recent advances regarding the complexity of metabolic factors involved and the challenge of establishing the clinical effects of metabolic interventions targeting the muscle.

Recent findings: Although the catabolic state is limited to the acute phase of critical illness, its subsequent impact on muscle mass and function persists long after ICU discharge. Immobilization, inflammation and disturbed muscle energy and nutrient metabolism are key drivers of muscle protein loss. Current research focuses on the effects of enhanced protein provision, specific substrate delivery and physical exercise. Whilst some interventions have been successful at improving muscle mass, these effects do not always carry over into muscle function or strength.

Summary: Increased understanding of metabolic derangements during critical illness provides new potential targets for treatment. The potential of dietary protein to attenuate the muscle protein catabolic state has yet to be established in clinical trials. Basic research should focus on ways to further improve the anabolic potential of nutrition by unravelling mechanisms that regulate anabolic and catabolic pathways and energy metabolism.

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FIGURE 1

Protein metabolism in critical illness and impact on muscle mass and function. Changes over time in muscle protein metabolism, mass and function, distinguishes a short catabolic phase during ICU stay with subsequent persistent impact on muscle mass and function. Put together, this timeline further emphasizes the long-lasting impact of the relative short period of disturbed protein metabolism.