Impact of Renal Replacement Therapy on Metabolism and Nutrient Requirements in the Critically Ill Patient

Abstract All types of renal replacement therapies (RRTs), intermittent and continuous treatment modalities, are associated with a broad spectrum of untoward side effects on metabolism and nutrient balances. One group of side effects affects nutrient balances. On the one hand, this represents the loss of various nutrients (e.g., amino acids, water-soluble vitamins) and of peptides and proteins. On the other hand, the modality of RRT and the type of anticoagulation, respectively, can be associated with the uptake of relevant amounts of energy substrates such as lactate and citrate or glucose. From a metabolic view, even more relevant is the induction of an inflammatory reaction caused by the extracorporeal circuit and the sustained contact of blood and artificial surfaces. This can contribute to protein catabolism and the generation of reactive oxygen species and potentially may promote distant organ injury and impair immunocompetence. Because of the prolonged treatment time and associated high fluid turnover, the evolution of electrolyte derangements is most pronounced during continuous RRT. Metabolically most important is the risk of inducing hypophosphatemia, which increases the evolution of complications and mortality. Knowledge of these additional effects of RRTs on metabolism and nutrient balances is relevant in the care of critically ill patients, because they can be associated with serious complications and have fundamental implications for designing nutritional programs. Nutrition therapy has to be coordinated with RRT and must take into consideration the losses of several nutrients and the uptake of energy substrates such as lactate or citrate.