Presentation Summary

Written by Jasna Trbojevic-Stankovic
Reviewed by Enrico Fiaccadori

Epidemiology and prognostic impact of nutrition in ICU patients with AKI
Despite the major advances in the diagnosis and treatment of acute kidney injury (AKI), the prognosis remains poor for these patients. The population developing AKI is increasingly older, with multiple comorbidities and conditions contributing to AKI development and aggravating its course. Malnutrition is a frequent finding in patients with AKI and as many as 40% of them are severely malnourished according to the Subjective Global Assessment method. Malnourished AKI patients exhibit a higher risk for sepsis, septic shock, hemorrhage, cardiac dysrhythmia, acute respiratory failure, and in-hospital mortality (1). In critically ill AKI patients treated with continuous renal replacement therapies (CRRT), dietary protein intake is a good predictor of survival, while serum albumin predicts renal outcome (2).

The complex underlying pathogenetic mechanisms of malnutrition in AKI are presented in Figure 1. Several factors, such as prolonged critical illness, chronic comorbidities, and hospital-associated protein-energy wasting predispose to malnutrition, while delayed start and/or insufficient nutritional support combined with high catabolism rate in AKI further aggravate it (4).

Figure 1. Pathogenesis of malnutrition in AKI (3, 4)

Energy and protein intake in ICU patients with AKI: What are the numbers?
Most current guidelines agree that the recommended daily energy intake for AKI patients, either treated conservatively or with renal replacement therapy, should be 20-30 Kcal/kg (5-11). Protein requirements, on the other hand, differ substantially for patients treated conservatively and those requiring renal replacement therapy, since dialyzed patients require nearly double protein intake compared to non-dialyzed ones (5-11). The current recommendations for protein intake in AKI are summarized in Figure 2. It is important to note that nutritional prescription should rely on pre-hospitalization or usual body weight, and not on current measurement, as emphasized in the newest, yet unpublished European Society for Clinical Nutrition and Metabolism guidelines. This is especially important since AKI patients often exhibit fluid overload which may obscure the actual nutrition status and conceal malnutrition.

Figure 2. Current recommendations for protein intake in AKI (3, 5-11)

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.


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