JNEPHROL 2008; 21: 645-656 THOROUGH CRITICAL APPRAISAL 645 ABSTRACT Acute kidney injury (AKI), at least in critically ill patients, seldom occurs as isolated organ failure. Much more often it emerges as a component of the multiple organ failure syndrome, within the framework of the severe and pro- longed catabolic phase determined by critical illness, and intensified by specific derangements in substrate utiliza- tion due to the acute loss of kidney function. On these bases, patients with AKI often have protein-energy wast- ing (preexisting and/or hospital acquired), which repre- sents a major negative prognostic factor. Thus, nutritional support is frequently required, under the form of parenter- al and/or enteral nutrition, even though no formal demon- stration exists for its favorable effect on major outcomes. The primary goals of nutritional support in AKI are basical- ly the same as those suggested for critically ill patients with normal renal function: i.e., to ensure the delivery of adequate amounts of nutrients, to prevent protein-energy wasting with the attendant metabolic complications, to promote wound healing and tissue reparation, to support immune system function and to reduce mortality. Patients with AKI on renal replacement therapy (RRT) should re- ceive at least 1.5 g/kg per day of proteins, and no more than 30 kcal nonprotein calories or 1.3 x BEE (basal energy expenditure) calculated by the Harris-Benedict equation, with lipid supply representing about 30%-35% of energy. The enteral route should be the preferred route for nutrient delivery; however, parenteral nutrition is often required to target nutritional requirements. Due to the loss of the kid- ney’s homeostatic function, and the frequent need of RRT, patients with AKI are especially prone to complications of nutritional support, such as hyperglycemia, hypertriglyc- eridemia, fluid retention, electrolyte and acid-base de- rangements. Since AKI comprises a highly heterogeneous group of subjects with nutrient needs widely varying even along the clinical course in the same patient, nutritional re- quirements should be frequently reassessed, individual- ized and carefully integrated with RRT. Key words: Acute kidney injury, Enteral nutrition, Par- enteral nutrition INTRODUCTION Acute renal failure, now commonly referred to as acute kidney injury (AKI) (1), is a major clinical problem having an indepen- dent, major negative impact on patient outcomes, and is most often dealt with in the intensive care unit (ICU) (2-4). AKI is characterized by the sudden and rapid (i.e., within hours to days) impairment of kidney function that results from ischemic and/or nephrotoxic insults causing renal functional or structural changes (5). Diagnosis is based on a combination of serum creatinine level and urinary output changes. Recently, a simplified definition has been introduced, which takes into account the relevant prognostic impact of even relatively slight increases in serum creatinine levels (6); thus AKI can be defined as abrupt (within 48 hours) reduction in kidney func- tion with an absolute increase in serum creatinine of either ≥0.3 mg/dL (≥0.25 mmol/L) or a percentage increase of ≥50%, or a reduction urine output (≤0.5 ml/kg per hour for >6 hours) (7). A staging system (the RIFLE system) has recently been proposed for AKI classification and outcome evaluation (8). AKI represents a common complication among hospitalized patients, with an incidence of 3% to 10% (9), which can rise up to 10%-30% among patients admitted to the ICU (10). Up to 5% of patients with AKI in the ICU may require renal replacement therapy (RRT) (10); common indications include azotemia, hypercatabolism, volume overload refractory to diuretic therapy, electrolyte abnormalities (in particular hyper- kalemia), uremic complications (such as altered sensorium, pericarditis and bleeding diathesis), severe acidosis, severe acute intoxications etc. (11). In critically ill patients, AKI seldom occurs as an isolated organ failure. More often it represents a component of the multiple organ failure syndrome, which requires adequate nutritional intervention as a fundamental element of the com- plex treatment strategy (11-13). In the specific case of patients with AKI, a close integration between nutritional sup- port and RRT is required, especially when highly efficient RRTs are used, such as continuous venovenous hemofiltra- tion (CVVH), or daily prolonged intermittent RRT such as sus- tained low-efficiency dialysis (SLED). Moreover, nutritional Enrico Fiaccadori, Elisabetta Parenti, Umberto Maggiore Department of Clinical Medicine, Nephrology and Prevention Science, University of Parma, Parma - Italy Nutritional support in acute kidney injury www.sin-italy.org/jnonline – www.jnephrol.com