Nutritional support is one of the key elements of care in critically ill patients. Providing adequate nutrition to patients with multiorgan failure can pose several challenges. Many new concepts have emerged over the years that have enabled optimization of the nutritional strategy. I will address key issues related to feeding the critically ill in this brief review.
What is the preferred route for nutritional support?
Although the enteral route is generally preferred in most critically ill patients, parenteral nutrition may be equally efficacious and may not be associated with worse outcomes. In a multicenter study in the UK, enteral nutrition was compared with parenteral nutrition administered within 36 hours of ICU admission and continued for 5 days. (1) The 30-day mortality, which was the primary outcome, was not significantly different between the enteral and parenteral routes of administration. Unlike older studies, no increase in infective complications was observed with parenteral nutrition. The 90-day mortality, one of the secondary outcomes, was also similar between groups. However, considering the ease of administration and the lower cost of care, the enteral route would still be preferred in most clinical situations.
How early should nutritional support be initiated?
Initiation of enteral nutrition within 24–48 hours of initiation of mechanical ventilation is appropriate in critically ill patients. Early commencement of enteral nutrition may preserve enterocyte function, reduce the incidence of infective complications, and may prevent stress ulcers. In a retrospective observational study, initiation of enteral nutrition within 48 hours of commencement of mechanical ventilation was associated with a significantly lower ICU and hospital mortality. (2) The mortality was lowest in the sickest quartiles of patients. Lewis et al. performed a meta-analysis of 11 randomized controlled trials that compared enteral feeding within 24 hours with a variable period of nil by mouth management after gastrointestinal surgery. In six studies, feeding was by the oral route, while it was directly into the small bowel in five studies. Early enteral feeding significantly reduced the incidence of infectious complications. Furthermore, there was a reduced risk of anastomotic leak, surgical site infections, pneumonia, intra-abdominal infections, and mortality with early enteral feeding. These studies offer strong evidence that early enteral nutrition is feasible and may be associated with improved clinical outcomes in critically ill patients, especially in the more severely ill.
What is an appropriate nutritional dose?
Contrary to widely held belief, an early, full nutritional dose compared to a low-calorie restrictive feeding strategy may be associated with adverse outcomes. During critical illness, extensive damage occurs to cellular organelles and protein aggregates, leading to organ failure. Recovery involves the process of autophagy to clear and repair the damage. Early full nutritional support may inhibit autophagy and worsen clinical outcomes. (3) Administration of calories of up to 70% of the resting energy expenditure has been shown to reduce mortality. A higher calorie dose was associated with increased mortality, longer ICU stay, and duration of mechanical ventilation. (4) Even small volumes of enteral feed may exert beneficial effects including preservation of gut epithelium, prevention of translocation of bacteria from the gut and enhanced immune function. In a randomized controlled study of trophic compared to full nutrition in patients with acute lung injury, no difference was observed in the number of ventilator-free days to day 28, or the 90-day mortality. (5)
What route for enteral nutrition?
There is a largely theoretical, increased risk of aspiration and pneumonia with the gastric delivery of enteral nutrition. Post-pyloric feeding may reduce the gastric residual volume; however, no clear advantage has been shown in clinical outcomes, including duration of ventilation, ICU stay, or mortality. Besides, it is also unclear whether post-pyloric feeding reduces the incidence of ventilator-associated pneumonia. Post-pyloric feeds may be appropriate in patients with intolerance to gastric feeds with a high risk of aspiration.
Supplemental parenteral nutrition
If enteral nutrition alone cannot provide caloric requirement, would supplementation with parenteral nutrition help? In the EPANIC study, patients were randomized to receive early supplementation within the first 48 hours of ICU admission to later initiation of parenteral nutrition, after 8 days. (6) Clinical outcomes were more favorable with late supplementation, including reduced ICU and hospital stay, fewer infective complications, reduced duration of renal replacement therapy, and lower health care costs. In a later study, parenteral nutrition was supplemented to meet calorie requirements within the first 4–8 days of ICU, compared to continued enteral nutrition. (7) Nosocomial infections were significantly lower with parenteral nutritional supplementation. Based on overall evidence, it may be inappropriate to commence supplemental parenteral nutrition within the first 5–8 days on ICU.(8)
Should we withhold enteral nutrition in shock?
In patients who are hemodynamically unstable and need support with vaso-active gastrointestinal hypoperfusion may occur. Arterial and venous flow are in opposite directions in the intestinal villi. This results in the transfer of oxygen from the artery to the vein in a countercurrent fashion, with a progressively lower oxygen content from the base to the apex of the villi. The apices of the villi may thus be prone to ischemia in low-flow states. Furthermore, a splanchnic “steal” phenomenon may occur in shocked patients, compromising oxygen delivery to vital organs. Non-occlusive bowel necrosis has also been reported in critically ill patients who were administered post-pyloric feeds. Presumably, direct feeding distal to the stomach may lead to distension of the small intestine and increased intraluminal pressure, predisposing to ischemia. Most guidelines recommend primary focus on resuscitative measures in unstable patients and commencement of low-volume, trophic feeds once reasonable hemodynamic stability has been achieved. (9)
Do we need to diligently measure gastric residual volumes and titrate feeds accordingly?
Contrary to conventional wisdom, gastric residual volumes are poor indicators of feeding tolerance. Intolerance to feeds is more clearly discernible by the presence of gastric distension, vomiting, or passive regurgitation. There is no evidence to support a threshold for gastric residual volume that may indicate inadequate absorption of feeds. In a randomized controlled study, continued administration of feeds without measurement of residual volumes did not increase the incidence of ventilator-associated pneumonia; besides, it enabled better achievement of nutritional targets. There was no significant difference in the incidence of other infectious complications, duration of ventilation, ICU stay, or mortality. (10)
Is a mandatory period of fasting required for intubated patients who undergo specific interventions?
In many critically ill patients, multiple interventions may be required that mandate fasting based on conventional wisdom. As a result, a substantial number of patients may fail to achieve adequate nutrition due to frequent interruption of enteral nutrition. In many clinical situations, it may not make intuitive sense to withhold feeds, when the planned procedure is unlikely to require airway manipulation that may pose a risk of aspiration. A shortened duration of 45 minutes of fasting did not lead to complications during bedside tracheostomy. (11) Uninterrupted delivery of enteral nutrition throughout the perioperative period has also been shown to be safe in burns patients who undergo serial debridement. (12)
- Early initiation of enteral nutrition is preferred in most critically ill patients. Commencement of hypocaloric feeds may be appropriate in most situations. Trophic feeds of 20 ml/h is generally well tolerated and may carry non-nutritional benefits.
- Supplemental parenteral nutrition may be considered when nutritional targets are not achieved after 5–8 days.
- Enteral nutrition may be commenced in patients who are in shock, once the dose of vaso-active drugs has stabilized.
- Titration of feeds based on measurement of gastric residual volumes may be unnecessary in most patients.
- Mandatory duration of fasting recommended in anesthetic guidelines may need modification in patients who are intubated and mechanically ventilated.
- Harvey SE, Parrott F, Harrison DA, Bear DE, Segaran E, Beale R, et al. Trial of the Route of Early Nutritional Support in Critically Ill Adults. N Engl J Med. 2014 Oct 30;371(18):1673–84.
- Artinian V, Krayem H, DiGiovine B. Effects of Early Enteral Feeding on the Outcome of Critically Ill Mechanically Ventilated Medical Patients. Chest. 2006 Apr;129(4):960–7.
- Van Dyck L, Casaer MP, Gunst J. Autophagy and Its Implications Against Early Full Nutrition Support in Critical Illness. Nutr Clin Pract. 2018 Jun;33(3):339–47.
- Zusman O, Theilla M, Cohen J, Kagan I, Bendavid I, Singer P. Resting energy expenditure, calorie and protein consumption in critically ill patients: a retrospective cohort study. Crit Care [Internet]. 2016 Dec [cited 2019 Jan 9];20(1). Available from: http://ccforum.biomedcentral.com/articles/10.1186/s13054-016-1538-4
- The National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network, Rice TW, Wheeler AP, Thompson BT, Steingrub J, Hite RD, et al. Initial Trophic vs Full Enteral Feeding in Patients With Acute Lung Injury: The EDEN Randomized Trial. JAMA J Am Med Assoc. 2012 Feb 22;307(8):795–803.
- Casaer MP, Mesotten D, Hermans G, Wouters PJ, Schetz M, Meyfroidt G, et al. Early versus Late Parenteral Nutrition in Critically Ill Adults. N Engl J Med. 2011 Aug 11;365(6):506–17.
- Heidegger CP, Berger MM, Graf S, Zingg W, Darmon P, Costanza MC, et al. Optimisation of energy provision with supplemental parenteral nutrition in critically ill patients: a randomised controlled clinical trial. The Lancet. 2013 Feb;381(9864):385–93.
- Bost RB, Tjan DH, van Zanten AR. Timing of (supplemental) parenteral nutrition in critically ill patients: a systematic review. Ann Intensive Care [Internet]. 2014 Dec [cited 2019 Jan 9];4(1). Available from: http://www.annalsofintensivecare.com/content/4/1/31
- Dhaliwal R, Cahill N, Lemieux M, Heyland DK. The Canadian Critical Care Nutrition Guidelines in 2013. Nutr Clin Pract. 2014 Feb 1;29(1):29–43.
- Reignier J, Mercier E, Le Gouge A, Boulain T, Desachy A, Bellec F, et al. Effect of not monitoring residual gastric volume on risk of ventilator-associated pneumonia in adults receiving mechanical ventilation and early enteral feeding: a randomized controlled trial. JAMA. 2013 Jan 16;309(3):249–56.
- Gonik N, Tassler A, Ow TJ, Smith RV, Shuaib S, Cohen HW, et al. Randomized Controlled Trial Assessing the Feasibility of Shortened Fasts in Intubated ICU Patients Undergoing Tracheotomy. Otolaryngol-Head Neck Surg. 2016 Jan;154(1):87–93.
- McElroy LM, Codner PA, Brasel KJ. A Pilot Study to Explore the Safety of Perioperative Postpyloric Enteral Nutrition. Nutr Clin Pract. 2012 Dec;27(6):777–80.