Can the critically ill patient generate sufficient energy to facilitate exercise in the ICU?

Trials of physical rehabilitation post critical illness have yet to deliver improved health-related quality of life in critical illness survivors. Muscle mass and strength are lost rapidly in critical illness and a proportion of patients continue to do so resulting in increased mortality and functional disability. Addressing this issue is therefore fundamental for recovery from critical illness.

Altered mitochondrial function occurs in the critically ill and is likely to result in decreased adenosine tri-phosphate (ATP) production. Muscle contraction is a process that requires ATP. The metabolic demands of exercise are poorly understood in the ICU setting. Recent research has highlighted that there is significant heterogeneity in energy requirements between critically ill individuals undertaking the same functional activities, such as sit-to-stand. Nutrition in the critically ill is currently thought of in terms of carbohydrates, fat and protein. It may be that we need to consider nutrition in a more contextual manner such as energy generation or management of protein homeostasis.

Current nutritional support practices in critically ill patients do not lead to improvements in physical and functional outcomes, and it may be that alternative methods of delivery or substrates are needed.