Protein supplementation in critical illness: why, when and how?

Abstract

Purpose of reviewIn critically ill patients, optimal protein provision remains a challenge given the wide range in recommended protein delivery in international guidelines and the lack of robust, high quality evidence. As patients are confronted with poor functional outcomes after admission, often attributed to muscle wasting and persisting for multiple years, there is a pressing need for optimal nutritional strategies in the ICU, particularly including protein. This review will discuss the recent literature with regard to purpose, timing and mode of protein delivery.Recent findingsRecent studies on the effect of dose and timing of protein on clinical and functional outcomes are largely observational in nature and the protein delivery considered as “high” still often only nears the lower end of current recommendations. The majority of trials observed no effect of protein supplementation on mortality, muscle strength or function, though some report attenuation of muscle volume loss, especially when combined with muscle activation. There is no strong evidence that ICU patients should receive supplementation with any specific amino acids.SummaryThough adequate protein provision is likely important, it is difficult to come to a uniform conclusion regarding dosing and timing due to conflicting results in mostly observational studies as well as different cut-off values for high, moderate and low protein intake. This topic is currently subject to large clinical trials.

Nutritional strategies during gastrointestinal dysfunction

“…Although protein absorption rates were similar, postprandial increase in muscle protein synthesis was significantly blunted in critically ill patients. These data suggest that protein malabsorption might not be as severe during critical illness as previously thought, but it also raises the question of whether higher doses of dietary protein are beneficial to overcome the blunted response of muscle protein synthesis [25,26].…”

Amino acid kinetics in the critically ill

“…The increased glutamine production in the critically ill seems to be mainly caused by the increased protein breakdown in muscle. Hence, as previously suggested, providing additional glutamine or protein by enteral or parenteral nutrition is counterintuitive in critically ill patients from the viewpoint that plasma concentrations of several amino acids, including glutamine, are already elevated in these patients [25 ▪ ,26,32 ▪ ]. In our opinion, it makes more sense to provide anabolic stimulation using nutritional agents like HMB [33] to increase net protein synthesis and in this way stimulate the use of the available amino acids.…”

“…In ICU patients, the increase was 60 mmol/day, which is ∼10 g of phenylalanine or 250 g protein/day (about 3.3 g protein/kg body weight). The daily amount of proteins broken down and synthesized in the human body in ICU patients (∼900 g) is much larger than the ∼75 g of protein consumed per day [24,25 ▪ ,26]. Therefore, the 8% addition to the available amino acids for protein synthesis by daily protein intake in ICU patients represents, therefore, a relatively small stimulation of protein synthesis.…”

Editorial: The interaction between protein delivery and blood urea and ammonia during critical illness

“…Critically ill patients suffer from profound muscle loss, which is attributed to both increased protein catabolism and reduced protein anabolism [4]. While provision of dietary protein may attenuate muscle loss, the optimal dose and timing of delivery remain uncertain [5]. International clinical practice guidelines include recommendations that patients receive 1.2–2.0 g of protein per kilogram of bodyweight per day [6].…”

“…Studies evaluating the mechanisms underlying rapid muscle wasting and weakness during critical illness, population effects of augmenting dietary protein during the recovery phase and the interaction between protein and exercise are also warranted [19,20]. Finally, further work to understand whether the type of amino acid matters, with leucine (or its metabolite beta-hydroxy-betamethylbutyrate, HMB) or glycine, representing candidate amino acids that merit further evaluation [5,21,22].…”