Nutrition in Critical Illness and Organ Failure
Nutrition in critical illness and organ failure is the area of clinical nutrition concerned with how acutely and severely ill patients are nourished when metabolism, organ function, and the route of feeding are all disrupted. It spans the intensive care unit and the dysfunction of specific organ systems, where the stress response, inflammation, and altered substrate handling change what the body can use and tolerate.
Definition
The study of nutritional assessment and support in patients whose critical illness or failure of one or more organ systems alters energy and protein requirements, substrate metabolism, and the safe delivery of nutrition.
Scope
This area orients the reader to nutritional support across the critically ill and organ-failure population: the acute critically ill patient in general, and the organ-specific contexts of renal disease, respiratory disease, sepsis with immune modulation, and trauma and burns. It frames the shared physiology of catabolic stress and the controversies over timing, route, and dose of nutrition support, and links to the detailed topic entries beneath it. It is a reference overview, not a protocol.
Sub-topics
Core questions
- How does the metabolic stress response of critical illness change energy and protein requirements?
- When should nutrition support be started, and should early feeding meet full targets or be deliberately limited?
- How do the enteral and parenteral routes differ in benefit and risk for the critically ill?
- How does failure of a specific organ system (kidney, lung, in sepsis, or after trauma and burns) modify nutritional needs?
Key concepts
- Metabolic stress response and catabolism
- Hypermetabolism and hypercatabolism
- Energy and protein requirements in illness
- Enteral versus parenteral nutrition
- Timing of nutrition support (early versus delayed)
- Permissive underfeeding and caloric targets
- Refeeding syndrome
- Organ-specific nutritional modification
Mechanisms
Critical illness and organ failure provoke a neuroendocrine and inflammatory stress response that shifts the body toward catabolism: counter-regulatory hormones and cytokines drive the breakdown of muscle protein, alter glucose and lipid handling, and produce insulin resistance. Provision of nutrition interacts with endogenous substrate mobilization, so the relationship between calories delivered and calories used is not simple, and overfeeding can be as harmful as underfeeding. Failure of individual organs then constrains delivery further: the kidney governs fluid, electrolyte, and nitrogenous-waste tolerance; the lung links nutrition to carbon-dioxide load and respiratory work; sepsis amplifies the inflammatory and catabolic state; and trauma and burns add wound-driven losses and extreme hypermetabolism.
Clinical relevance
Nutrition support is a routine part of critical care and of managing organ failure, and the evidence base shapes how guidelines describe assessment, route, and timing of feeding. This area explains the physiology and the principal trials and recommendations so the reader can interpret that literature; it describes how nutritional care is reasoned about at the population and guideline level and is not a source of individualized prescriptions.
Epidemiology
Malnutrition and loss of lean body mass are common among critically ill and organ-failure patients and are associated with worse outcomes, which is why nutritional assessment is embedded in critical-care practice. Large randomized trials such as Casaer and colleagues' comparison of early versus late parenteral nutrition have reshaped expectations about how aggressively to feed in the acute phase.
Evidence & guidelines
Two major guideline streams orient this area: the ESPEN guideline on clinical nutrition in the intensive care unit (Singer et al., 2019) and the joint SCCM/ASPEN guidelines (McClave et al., 2016). Both synthesize randomized trials and observational data on route, timing, and dose, and both emphasize that recommendations are framed for populations and refined for specific organ-failure contexts in the topic entries below.
History
Modern critical-care nutrition grew from the development of parenteral and enteral feeding techniques in the twentieth century, followed by a shift from a 'feed as much as possible' stance toward more cautious, evidence-driven targets. Trials in the 2010s, including Casaer and colleagues (2011), challenged early aggressive parenteral feeding and contributed to today's emphasis on timing and dose.
Debates
- How aggressively should critically ill patients be fed early in their illness?
- Randomized evidence suggests that early full-target feeding, especially by the parenteral route, may not improve and can worsen outcomes compared with more permissive early feeding, but the optimal early caloric and protein dose remains contested.
Related topics
Seminal works
- singer-2019
- mcclave-2016
- casaer-2011
Frequently asked questions
- Why is nutrition different in critical illness than in health?
- Severe illness triggers a stress response that drives muscle breakdown and changes how the body handles glucose, fat, and protein, so the amount and route of nutrition that is beneficial differ from those in a stable, healthy person.
- What does this area cover?
- It is an overview of nutrition in the critically ill and in organ failure, linking to detailed topics on acute critical illness, renal disease, respiratory disease, sepsis and immune modulation, and trauma and burns.