Permissive Underfeeding Versus Standard Enteral Feeding in the Intensive Care Setting

Mohammed Naveed Aijaz, Mercer University College of Pharmacy 2016

According to the Society of Critical Care Medicine and American Society for Parenteral and Enteral Nutrition (ASPEN), nutritional support is an essential component for the management of adult patients in the intensive care unit (ICU) setting.1 Based on expert opinion, enteral nutrition is generally preferred over parenteral because this allows for the functions of the gastrointestinal tract to be retained as well as its simplicity, safety, and low cost compared to the parenteral route.2,3

While ASPEN has established recommendations for standard doses of nutrition, uncertainty still exists regarding the dosages of enteral feeding;4 studies have provided conflicting results ranging from support for low dose enteral nutrition to support for the standard recommended dose.5-7 Specialized nutrition is not without risks and thus nutrition care plans must be highly personalized to meet each patient’s needs and goals. This personalized pharmacotherapy includes accounting for fluid, calorie, protein, and micronutrient requirements based on therapeutic goals and the patient’s condition. Nutrient composition for enteral formulas has been a target for improvement in past years resulting in varying degrees of complexity and patient specific proportions of macronutrients.8

Title: Permissive Underfeeding or Standard Enteral Feeding In Critically Ill Adults9
Design Randomized, unblinded; N = 894
Objective To determine if permissive underfeeding to restrict non-protein calories while preserving protein calories would reduce 90-day mortality among critically ill adults as compared with a standard feeding strategy
Study Groups Two groups:

–       Permissive-underfeeding group

–       Standard-feeding group

Methods The permissive-underfeeding group received 40-60% of caloric requirements; standard feeding group received 70-100% of caloric requirements. This treatment regimen was continued for up to 14 days or until discharge from ICU, initiation of oral feeding, withholding of nutrition altogether, or death. Daily caloric requirements were calculated by ICU dieticians based on “the Penn State equation” for mechanically ventilated patients who had a body mass index (BMI) of less than 30 or based on the 1992 Ireton-Jones equation for mechanically ventilated patients who had a BMI of 30 or higher or for spontaneously breathing patients.
Duration November 2009 to September 2014
Primary Outcome Measure Ninety-day all-cause mortality
Baseline Characteristics Both groups were similar in regards to demographic, physiological, and nutritional characteristics. Within the study population, average age was 50.6 (range 18-80), and percent female was 35.8%. All patients were admitted to an intensive care unit (ICU) and expected to remain admitted for ≥ 72 hours; 96.8% of patients were receiving mechanical ventilation. Patients were selected from sites in Saudi Arabia and Canada.
Results The 90-day mortality was 27.2% (121 of 445 patients) in the permissive-underfeeding group and 28.9% (127 of 440 patients) in the standard-feeding group (relative risk 0.94, 95% confidence interval [CI] 0.76 to 1.16; P = 0.58.
Adverse Events Common Adverse Events: Hypoglycemia (1.3% in permissive underfeeding group and 1.6% in standard-feeding group), hypokalemia (22.5% and 20.4%), hypomagnesaemia (28.3% and 29.4%), hypophosphatemia (59.6% and 58.5%), ICU-associated infection (35.9% and 37.9%), urinary tract infection (10.0% and 10.8%), catheter related infection (2.5% and 4.3%), ventilator-associated pneumonia (18.1% and 20.2%), ICU associated severe sepsis or septic shock (13.6% and 13.0), feeding intolerance (15% and 17.7%), diarrhea (21.7% and 26.2%)
Serious Adverse Events: None reported
Percentage that Discontinued due to Adverse Events: N/A
Study Author Conclusions In our study, a strategy of enteral feeding for critically ill adults in which patients received a moderate amount of non-protein calories (40 to 60% of estimated caloric requirements), along with the full recommended amount of protein, had no significant effect on mortality, as compared with a strategy in which patients received 70 to 100% of estimated caloric requirements.

This study sought to further delve into the issue of specialized nutrition administered in a ICU hospital setting to determine the effects of varying doses of enteral nutrition on patients. A limitation of this study was that only 14% of all screened ICU patients were included. This implies that the results cannot be extrapolated to other groups of patients, for example, those in whom enteral feeding was initiated later in their treatment process and not at the initial most point. Additional limitations included a lack of blinding, which was due to the need to make regular adjustments in patients’ treatments, as well as difficulty in reaching caloric goals in both groups due to feeding intolerance and interruptions in the ICU setting.


  1. Martindale RG, McClave SA, Vanek VW, et al. Guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient: Society of Critical Care Medicine and American Society for Parenteral and Enteral Nutrition: executive summary. Crit Care Med 2009;37:1757-1761
  2. Bistrian BR, Driscoll DF. Chapter 76. Enteral and Parenteral Nutrition Therapy. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison’s Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012. Accessed May 28, 2015
  3. Bistrian BR, Hoffer L, Driscoll DF. Enteral and Parenteral Nutrition Therapy. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. eds. Harrison’s Principles of Internal Medicine, 19e. New York, NY: McGraw-Hill; 2015. Accessed May 28, 2015
  4. Colaizzo-Anas T. Nutrient intake, digestion, absorption, and excretion. In: Mueller CM, ed. The A.S.P.E.N. Adult Nutrition Support Core Curriculum. Silver Spring, MD: American Society for Parenteral and Enteral Nutrition, 2012:3–21.
  5. Berger MM, Pichard C. Development and current use of parenteral nutrition in critical care – an opinion paper. Crit Care. 2014;18(4):478. 10.1186/s13054-014-0478-0.
  6. Heyland DK, Cahill N, Day AG. Optimal amount of calories for critically ill patients: depends on how you slice the cake! Crit Care Med 2011;39:2619-2626
  7. Dickerson RN. Optimal caloric intake for critically ill patients: first, do no harm. Nutr Clin Pract. 2011;26(1):48-54.
  8. Kumpf VJ, Chessman K. Chapter 120. Enteral Nutrition. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey L. eds. Pharmacotherapy: A Pathophysiologic Approach, 9e. New York, NY: McGraw-Hill; 2014. Accessed May 28, 2015.
  9. Arabi YM, Aldawood AS, Haddad SH, et al. Permissive Underfeeding or Standard Enteral Feeding in Critically Ill Adults. N Engl J Med. 2015; doi: 10.1056/NEJMoa1502826



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