Nutrition in the ICU

Nutrition support for intensive care unit (ICU) patients is a complex issue that involves several different factors. The most important aspect is nutritional management, which involves monitoring harmful changes in the metabolism of protein, fats (calories), and other micronutrients. Changes in metabolism, known as metabolic stress, is the body’s way of adapting to trauma in order to improve survival rates [1].

This response triggers the rapid breakdown of stored nutrients such as fats and muscle protein to supply vital organs with the energy they need to sustain life after a major event that lead to an emergency ICU admission. The nervous system is the first to respond to serious trauma and it subsequently increases the release of hormones that dramatically change the way the body produces and uses nutrients [1, 2].

Protein and Energy Requirements During Metabolic Stress

Metabolic stress can lead to serious complications if it is not quickly addressed. A major change in response to metabolic stress is an increased protein-energy requirement. For example, in order to promote survival by protecting vital organs, the body begins to break down muscle protein into amino acids that organs can use as energy. This can lead to the wasting away of muscle (loss of muscle mass) if the patient is not given a high protein supplement during the ICU stay [1, 2].

Similarly, the body breaks down stored fat and uses it for energy to combat inflammation, but this can lead to dramatic weight loss. Furthermore, the liver rapidly degrades various particles into glucose (sugar) that is also used for energy. This may cause dangerously high blood sugar levels that prevent healing and increase the risk of life-threatening complications [1-3]. Therefore, the body’s protein and caloric (energy) requirements dramatically increase in ICU patients.

Impact of Malnutrition and Muscle Mass Loss on ICU Outcomes

Malnutrition and muscle mass loss that develop in response to increased protein-energy requirements and poor nutrient intake are linked to prolonged use of ventilators, a lower body mass index (BMI), and an increased incidence of death [4]. Accordingly, increased protein and caloric intake during an ICU stay is associated with a higher number of ventilator-free days, BMI support, and lower rates of death [4].

The benefits of supplying nutrients through tube feeding, an intravenous injection (IV), or oral nutritional supplements (ONS) for those who can take them orally have repeatedly been demonstrated, with moderate to high protein supplements being administered based on a patient’s BMI [4-6]. Indeed, clinical studies show that providing ICU patients with IV-administered nutrients helps stop the inflammatory response, shortens the recovery period, and results in fewer complications [4, 6].

Continued Effect of Metabolic Stress After ICU Discharge

Another important factor that must be addressed after ICU discharge is re-feeding syndrome, which refers to complications such as electrolyte imbalances, fluid retention, respiratory problems, and heart issues that accompany the re-introduction of tube feeding or IV-based nutrition [1]. High protein supplementation shortly upon admission to the ICU, especially for patients with a low BMI, dramatically reduces the incidence of complications and improves survival rates [1, 4-6].

Furthermore, just as the healing process can be lengthy, protein and energy deficits often persist or even worsen for some individuals upon ICU discharge [7]. One particular study even showed that oral intake alone without oral nutritional supplements did not support the requirements for protein and energy after ICU discharge, while the addition of oral supplements, especially high protein and calorie-rich supplements dramatically improved the delivery of energy and protein [8]. Therefore, a proper diet that is fortified with nutrient-rich supplements is essential for the long-term health of ICU patients, including when they are discharged.


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  8. Ridley EJ, Parke RL, et al. What Happens to Nutrition Intake in the Post-Intensive Care Unit Hospitalization Period? An Observational Cohort Study in Critically Ill Adults. JPEN J Parenter Enteral Nutr. 2019;43(1):88-95.