Despite the available recommendations, the real-world clinical data from a secondary analysis of the Randomized Evaluation of Normal versus Augmented Level of Replacement Therapy, conducted on 14,456 patients with AKI treated with CRRT, revealed that the average daily calorie delivery was 10.9 Kcal/kg and average overall protein delivery 34.8 g/day (12). These numbers, which are well below those recommended in the current guidelines, suggest that underfeeding is quite frequent among AKI patients treated in intensive care units. On the other hand, more doesn’t necessarily seem to be better, as no advantages have been noted on nitrogen balance with increased calorie intake in AKI patients (13). Even more so, high-calorie regimens were associated with increased fluid administration and risk of fluid overload, higher serum glucose levels, and increased insulin requirement (13).
Unlike energy needs, which are similar in critically ill patients whether they have AKI or not, protein requirements may be different (15). The catabolic rate in AKI patients treated with different renal replacement therapies can be as high as 1.5g/kg/day, corresponding to a weekly loss of 3kg of lean body mass if not compensated (14-18).
An individualized approach to nutrition needs in AKI
It seems that better tools are still needed for evaluation and monitoring of nutritional status in order to provide more personalized nutrition prescription for AKI patients. These need to be practical and easy to apply, but accurate in determining energy expenditure and protein needs. Promising results have been reported with bedside ultrasound measurement of quadriceps muscle thickness. This simple, widely available, inexpensive, non-invasive method proved to be reliable and reproducible in assessing skeletal muscle mass, independent of acute body weight changes due to fluid removal (19). A very recent study evaluated this method by comparing it to the gold standard of muscle CT scan and found an excellent agreement between these two modalities, with insignificant loss of precision of ultrasound measurement compared to CT (20).
The most accurate method for quantifying the metabolic rate is direct calorimetry. Nevertheless, its use is limited by the high cost. Indirect calorimetry also provides an exact measure of calorie needs by quantifying energy expenditure. It relies on the measurement of inspired and expired gas volume, and the concentrations of oxygen and carbon dioxide. The procedure is non-invasive and more accurate than conventional predictive formulas which are used to calculate energy expenditure, micro and macronutrient needs in critically ill patients with AKI (21). Thus, to provide optimal individualized nutrition prescription for AKI patients, nutrient needs should be measured and energy expenditure closely monitored for each patient.