Protein metabolism in critical illness

Purpose of review Critically ill patients experience skeletal muscle wasting that may contribute to the profound functional deficits in those that survive the initial injury. Augmented protein delivery has the potential to attenuate muscle loss, yet the ability for dietary protein to improve patient outcomes is reliant on effective protein metabolism. This review will discuss the recent literature on protein delivery and digestion, amino acid absorption, and muscle protein synthesis (MPS) in critically ill adults. Recent findings Critically ill patients are prescribed protein doses similar to international recommendations, yet actual delivery remains inadequate. The majority of trials that have achieved higher protein doses have observed no effect on muscle mass, strength or function. Critically ill patients have been observed to have minimal deficits in protein digestion and amino acid absorption when delivery bypasses the stomach, yet postprandial MPS is impaired. However, the literature is limited due to the complexities in the direct measurement of protein handling. Summary Postprandial MPS is impaired in critically ill patients and may exacerbate muscle wasting experienced by these patients. Studies in critically ill patients require assessment not only of protein delivery, but also utilization prior to implementation of augmented protein doses.