Nutrients and micronutrients at risk during renal replacement therapy: a scoping review.

The increased risk of both mortality and morbidity is well recognized in hospitalized patients who develop acute kidney injury (AKI) [1]. The pathophysiological causes are complex, but one aspect that is often overlooked is the profound effect of AKI on nutritional status resulting in significant depletion of lean body mass. Indeed, low caloric and protein intake, a negative nitrogen balance and low serum albumin are all associated with increased hospital mortality [2]. To date, there is no specific treatment for AKI, instead management is aimed at correcting the resulting metabolic and volume disturbances, which may result in the use of renal replacement therapy (RRT) [3]. However, exposure to an extracorporeal circuit has potential drawbacks, not least in terms of nutritional status, wherein removal of essential dietary components may not be replenished adequately. This is particularly relevant to micronutrients, which play a central role in metabolism and maintenance of cellular function [4]. The term ‘micronutrient’ includes essential trace elements (inorganic metals and metalloids) and organic vitamins (fat-soluble and water-soluble molecule). Daily recommended intakes (DRIs) have been validated [5]. Their key functions are summarized in Table ​Table1.1. However, the latter are based on the observed intakes in healthy individuals where ‘normal’ defines ranges below which a clinical deficiency state is increasingly likely, and intakes above upper tolerable limits are those where toxicity state is likely to develop [6]. Such levels are relevant at a population level but translate less well to the individual, particularly if exposed to critical illness and its management, including continuous renal replacement therapy (CRRT), prolonged intermittent therapies as well as intermittent haemodialysis (IHD). Independent of RRT modality, micronutrients may be removed through convection or diffusive techniques potentially leading to a deficiency state in at-risk individuals.  Table 1 Key functions of the vitamins, and trace elements reported in CRRT studies