Clinical Review

Current Controversies Regarding Nutrition Therapy in the ICU



From the Center for Nursing Science & Clinical Inquiry (Dr. McCarthy), and Nutrition Care Division, (Ms. Phipps), Madigan Army Medical Center, Tacoma, WA.


  • Background: Many controversies exist in the field of nutrition support today, particularly in the critical care environment where nutrition plays a more primary rather than adjunctive role.
  • Objective: To provide a brief review of current controversies regarding nutrition therapy in the ICU focusing on the choices regarding the nutrition regimen and the safe, consistent delivery of nutrition as measured by clinical outcomes.
  • Methods: Selected areas of controversy are discussed detailing the strengths and weaknesses of the research behind opposing opinions.
  • Results: ICU nutrition support controversies include enteral vs parenteral nutrition, use of supplmental parenteral nutrition, protein quantity and quality, and polymeric vs immune-modulating nutrients. Issues surrounding the safety of nutrition support therapy include gastric vs small bowel feeding and trophic vs full feeding. Evidence-based recommendations published by professional societies are presented.
  • Conclusion: Understanding a patient’s risk for disease and predicting their response to treatment will assist clinicians with selecting those nutrition interventions that will achieve the best possible outcomes.

According to the National Library of Medicine’s translation of the Hippocratic oath, nowhere does it explicitly say “First, do no harm.” What is written is this: “I will use those dietary regimens which will benefit my patients according to my greatest ability and judgement, and I will do no harm or injustice to them” [1]. In another renowned text, one can find this observation regarding diet by a noted scholar, clinician, and the founder of modern nursing, Florence Nightingale: “Every careful observer of the sick will agree in this that thousands of patients are annually starved in the midst of plenty, from want of attention to the ways which alone make it possible for them to take food” [2,]. While Nightingale was alluding to malnutrition of hospitalized patients, it seems that her real concern may have been the iatrogenic malnutrition that inevitably accompanies hospitalization, even today [3].

From these philosophic texts, we have two ongoing controversies in modern day nutrition therapy identified: (1) what evidence do we have to support the choice of dietary regimens (ie, enteral vs parenteral therapy, timing of supplemental parenteral nutrition, standard vs high protein formula, polymeric vs immune-modulating nutrients) that best serve critically ill patients, and (2) how do we ensure that ICU patients are fed in a safe, consistent, and effective manner (gastric vs small bowel tube placement, gastric residual monitoring or not, trophic vs full feeding) as measured by clinically relevant outcomes? Many controversies exist in the field of nutrition support today [4–7] and a comprehensive discussion of all of them is beyond the scope of this paper. In this paper we will provide a brief review of current controversies focusing on those mentioned above which have only recently been challenged by new rigorous randomized clinical trials (RCTs), and in some cases, subsequent systematic reviews and meta-analyses [8–11].

The Path to Modern Day Nutrition Support Therapy

The field of nutrition support, in general, has expanded greatly over the last 4 decades, but perhaps the most notable advancements have occurred in the critical care environment where efforts have been directed at advancing our understanding of the molecular and biological effects of nutrients in maintaining homeostasis in the critically ill [6]. In recent years, specialized nutrition, delivered by the enteral or parenteral route, was finally recognized for its contribution to important clinical outcomes in the critically ill population [12]. Critical care clinicians have been educated about the advances in nutrition therapy designed to address the unique needs of a vulnerable population where survival is threatened by poor nutritional status upon admission, compromised immune function, weakened respiratory muscles with decreased ventilation capacity, and gastrointestinal (GI) dysfunction [6]. The rapid deterioration seen in these patients is exaggerated by the all too common ICU conditions of systemic inflammatory response syndrome (SIRS), sepsis, hemodynamic instability, respiratory failure, coagulation disorders, and acute kidney injury [13,14].

Beginning in the early 1990s, formulations of enteral nutrition (EN) contained active nutrients that reportedly reduced oxidative damage to cells and tissues, modulated inflammation, and improved feeding tolerance. These benefits are now referred to as the non-nutritive benefits of enteral feeding [15]. For the next 20 years, scientific publications released new results from studies examining the role of omega-3 fatty acids, antioxidant vitamins, minerals such as selenium and zinc, ribonucleotides, and conditionally essential amino acids like glutamine and arginine, in healing and recovery from critical illness. The excitement was summarized succinctly by Hegazi and Wischmeyer in 2011 when they remarked that the modern ICU clinician now has scientific data to guide specialized nutrition therapy, for example, choosing formulas supplemented with anti-inflammatory, immune-modulating, or tolerance-promoting nutrients that have the potential to enhance natural recovery processes and prevent complications [16].

The improvements in nutritional formulas were accompanied by numerous technological advances including bedside devices (electromagnetic enteral access system, real-time image-guided disposable feeding tube, smart feeding pumps with water flush technology) that quickly and safely establish access for small bowel feedings, which help minimize risk of gastric aspiration and ventilator-associated pneumonia, promote tolerance, decrease radiologic exposure, and may reduce nursing time consumed by tube placements, GI dysfunction, and patient discomfort [17–20]. Nasogastric feeding remains the most common first approach, with local practices, contraindications, and ease of placement usually determining the location of the feeding tube [5]. The advancements helped to overcome the many barriers to initiating and maintaining feedings and thus, efforts to feed critically ill patients early and effectively became more routine, along with nurse, patient, and family satisfaction. In conjunction with the innovative approaches to establishing nutrition therapy, practice guidelines published by United States, European, and Canadian nutrition societies became widely available in the past decade with graded evidence-based recommendations for who, when, what, and how to feed, and unique considerations for various critically ill populations [12,21,22]. The tireless efforts by the nutrition societies to provide much needed guidelines for clinicians were appreciated, yet there was a wide range in the grade of the recommendations, with many based on expert opinion alone. In some cases, the research conducted lacked rigor or had missing data with obvious limits to the generalizability of results. Nevertheless, for the 7 years between the publication of the old and newly revised Society of Critical Care Medicine (SCCM)/ American Society of Parenteral and Enteral Nutrition (ASPEN) Guidelines (2016), [12,23] nutrition therapy was a high-priority intervention in most ICUs. The goal was to initiate feeding within 48 hours, select an immune-modulating or other metabolic support formula, and aggressively advance the rate to 80% to 100% of goal to avoid caloric deficit, impaired intestinal integrity, nitrogen losses, and functional impairments [9,24,25]. Nutrition support evolved from adjunctive care to its rightful place in the ABCD mnemonic of early priorities of ICU care: Airway, Breathing, Circulation, Diet.

The 2016 joint publication of the SCCM/ASPEN guidelines includes primarily randomized controlled trial (RCT) data, along with some observational trial data, indexed in any major publication database through December 2013. In these guidelines there were 98 recommendations, of which only 5 were a Level 1A; most of the recommendations were categorized as “expert consensus” [12]. The results of several important clinical trials in the United States and Europe that were underway at the time have since been published and compared to the SCCM/ASPEN relevant recommendations [7]. The results have forced nutrition support clinicians to take a step back and re-examine their practice. For many seasoned clinicians who comprised the nutrition support teams of the 1980s and 1990s, it feels like a return to the basics. Until biology-driven personalized medicine is commonplace and genotype data is readily available to guide nutrition therapy for each critically ill patient, standard enteral feeding that begins slow and proceeds carefully over 5 to 7 days towards 80% of goal caloric intake under judicious monitoring of biochemical and metabolic indices may be the “best practice” today, without risk of harm [15,26]. As in all aspects of clinical care, this practice is not without controversy.


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