Bench-to-bedside review: Metabolism and nutrition

Critical Care, Aug 2008

Acute kidney injury (AKI) develops mostly in the context of critical illness and multiple organ failure, characterized by alterations in substrate use, insulin resistance, and hypercatabolism. Optimal nutritional support of intensive care unit patients remains a matter of debate, mainly because of a lack of adequately designed clinical trials. Most guidelines are based on expert opinion rather than on solid evidence and are not fundamentally different for critically ill patients with or without AKI. In patients with a functional gastrointestinal tract, enteral nutrition is preferred over parenteral nutrition. The optimal timing of parenteral nutrition in those patients who cannot be fed enterally remains controversial. All nutritional regimens should include tight glycemic control. The recommended energy intake is 20 to 30 kcal/kg per day with a protein intake of 1.2 to 1.5 g/kg per day. Higher protein intakes have been suggested in patients with AKI on continuous renal replacement therapy (CRRT). However, the inadequate design of the trials does not allow firm conclusions. Nutritional support during CRRT should take into account the extracorporeal losses of glucose, amino acids, and micronutrients. Immunonutrients are the subject of intensive investigation but have not been evaluated specifically in patients with AKI. We suggest a protocolized nutritional strategy delivering enteral nutrition whenever possible and providing at least the daily requirements of trace elements and vitamins.

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Bench-to-bedside review: Metabolism and nutrition

Critical Care Bench-to-bedside review: Metabolism and nutrition Michal P Casaer, Dieter Mesotten and Miet RC Schetz Corresponding author: Michal P Casaer 0 0 0 Department of Intensive Care Medicine, University Hospital Leuven, Catholic University of Leuven , Herestraat 49, B-3000 Leuven , Belgium Acute kidney injury (AKI) develops mostly in the context of critical illness and multiple organ failure, characterized by alterations in substrate use, insulin resistance, and hypercatabolism. Optimal nutritional support of intensive care unit patients remains a matter of debate, mainly because of a lack of adequately designed clinical trials. Most guidelines are based on expert opinion rather than on solid evidence and are not fundamentally different for critically ill patients with or without AKI. In patients with a functional gastrointestinal tract, enteral nutrition is preferred over parenteral nutrition. The optimal timing of parenteral nutrition in those patients who cannot be fed enterally remains controversial. All nutritional regimens should include tight glycemic control. The recommended energy intake is 20 to 30 kcal/kg per day with a protein intake of 1.2 to 1.5 g/kg per day. Higher protein intakes have been suggested in patients with AKI on continuous renal replacement therapy (CRRT). However, the inadequate design of the trials does not allow firm conclusions. Nutritional support during CRRT should take into account the extracorporeal losses of glucose, amino acids, and micronutrients. Immunonutrients are the subject of intensive investigation but have not been evaluated specifically in patients with AKI. We suggest a protocolized nutritional strategy delivering enteral nutrition whenever possible and providing at least the daily requirements of trace elements and vitamins. - Introduction Patients with acute kidney injury (AKI) have a high prevalence of malnutrition, a condition that is associated with morbidity and mortality [1]. AKI develops mostly in the context of critical illness and multiple organ failure, which are associated with major changes in substrate metabolism and body composition, overwhelming the alterations induced by AKI itself. Key effectors of these changes are inflammatory mediators and neuroendocrine alterations. The development of AKI further adds fluid overload, azotemia, acidosis, and electrolyte disturbances. In addition, AKI is associated with increased inflammation and oxidative stress [2]. The most severe cases of AKI require renal replacement therapy (RRT), with continuous treatments (continuous renal replacement therapy, CRRT) being the modality of choice in most intensive care units (ICUs) [3]. These extracorporeal treatments facilitate nutritional support but may, on the other hand, induce derangements of nutrient balances. The rationale for nutrition during critical illness is mainly to attenuate the catabolism and the loss of lean body mass in the hypermetabolic critically ill patient. However, the concept of improving clinical outcome by improving energy and nitrogen balance is still being challenged [4]. The purposes of this paper were to review the metabolic alterations underlying critical illness and AKI, to discuss nutritional and metabolic support in these patients, and to address the nutritional implications of CRRT. The reader is also referred to several other reviews on this subject [5-10]. Metabolic alterations in critical illness and acute kidney injury Critical illness is generally recognized as a hypermetabolic state, with energy expenditure (EE) being proportional to the amount of stress [11,12]. Although active solute transport in a functioning kidney is an energy-consuming process, the presence of AKI by itself (in the absence of critical illness) does not seem to affect resting EE (REE) [13]. EE in AKI patients is therefore determined mainly by the underlying condition. Studies in chronic kidney disease yield conflicting results varying between increased [14,15], normal [16], or even decreased REE [17]. A characteristic of critical illness is the so-called diabetes of stress with hyperglycemia and insulin resistance. Hepatic gluconeogenesis (from amino acids and lactate) increases mainly due to the action of catabolic hormones such as glucagon, epinephrine, and cortisol. In addition, the normal suppressive action of exogenous glucose and insulin on hepatic gluconeogenesis is decreased. Peripheral glucose utilization in insulin-dependent tissues (muscle and fat) is also decreased [18,19]. Since most patients with AKI also have an underlying critical illness, it is not surprising that the same AKI = acute kidney injury; CO2 = carbon dioxide; CRRT = continuous renal replacement therapy; EE = energy expenditure; EN = enteral nutrition; ESPEN = European Society for Enteral and Parenteral Nutrition; ICU = intensive care unit; MOD = multiple organ dysfunction; PN = parenteral nutrition; RCT = randomized controlled trial; REE = resting energy expendi (...truncated)


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Michaël P Casaer, Dieter Mesotten, Miet RC Schetz. Bench-to-bedside review: Metabolism and nutrition, Critical Care, 2008, pp. 222, 12, DOI: 10.1186/cc6945