Polina Zmijewski, MD
Background
Malnutrition in the ICU is an unfortunately common occurrence that is underappreciated, undertreated and associated with poor outcomes. The reasons for this are multifactorial, including the patient being maintained NPO due to intestinal pathology, the inherent anorexia associated with inflammatory states, frequent feeding interruptions due to procedures and traveling for imaging, the holding of tube feeds due to pressor requirements, and provider reluctance to advance diet or tubefeeds after gastrointestinal surgery. The immediate postoperative state is catabolic, especially in those patients with severe traumatic injury and burns. Protein stores are depleted during times of critical illness and protein synthesis is shifted towards the proteins that maintain the inflammatory state, leading to deleterious effects such as muscle wasting, skin breakdown, and poor wound healing.
Malnutrition preoperatively portends poor postoperative outcomes, though in patients with diffuse inflammatory states, it is often difficult to assess pre-admission nutritional status. Serum markers such as albumin, prealbumin, and retinol binding protein are unhelpful in this context, as they are often deranged as a sequela of massive inflammatory states. In patients with high metabolic rates due to inflammation, indirect calorimetry is a valuable tool in evaluating the targeted daily caloric requirements of your patient, in order to optimize their nutritional therapy.
Nutritional delivery
For the majority of patients enteral feeding is the preferred route of administration unless there is a clear contraindication. Caloric goals should be calculated based on the patient’s ideal body weight, using 25 kcal/kg for the majority of patients, and increasing this up to 30 kcal/kg in states of severe stress/catabolism. The goal for all patients should be to establish enteral feeding within the first 48 hours of admission. If enteral nutrition is not being tolerated, or patient condition prohibits its administration, total parenteral nutrition (TPN) should be considered and initiated after a period of 5-7 days.
RCT of TPN in the ICU within 48h vs. not before 8 days:
If a patient is unable to swallow or limited in their ability to achieve their caloric targets, enteral access is preferentially obtained with a small NGT (14Fr). A percutaneous endoscopic gastrostomy tube may be considered if oral feeding/swallowing is likely to be inhibited for > 4 weeks. While enteral nutrition formulas come in a variety of offerings, it is always best to use a standard polymeric formula for the majority of patients (Jevity 1.2 kCal/mL, 1.5, etc.), as the designer formulas (Glucerna) tend to be more expensive, and the evidence behind them is often lacking. If the patient has acute/chronic/worsening kidney failure, a formula such as Nepro may be warranted, which is lower in phosphorus and potassium than most other formulas.
Minimize interruptions
Minimizing feeding interruptions is critical to achieving caloric goals. If a patient is in the ICU with a secure airway, and traveling to the operating room, tubefeeds should be discontinued immediately before leaving the ICU. The remainder of the feeds should be suctioned out of the stomach prior to leaving the unit. Feeding interruptions also often occur due to the pervasive myth that “high gastric residuals” are a sign of tube feed intolerance. In a RCT of 449 patients there was no difference in ventilator associated pneumonia incidence between patients who had residuals measured and those who did not. Better markers of tube feed intolerance include physical exam findings such as abdominal distension and/or abdominal pain or patient complaints of nausea. ASPEN/SCCM retracted the recommendation to check Gastric residuals in 2016.
Pulmcrit sums up the 2016 ASPEN/SCCM new recommendations for ICU nutrition.
Enteral vs. parenteral
Enteral nutrition is the preferred route of administration due to potential risks of hypertriglyceridemia, hyperglycemia, cholestasis, and central line associated bloodstream infection associated with parenteral nutrition. However, if patients have a persistently high pressor requirement, are not tolerating tube feeds, or have other contraindications to enteral nutrition, TPN should be considered. CALORIES, a RCT that compared enteral nutrition with TPN at 36 hours post ICU admission found no difference in mortality or infection rates between the groups, and hypoglycemia was shown to be more common in the enteral nutrition group. CALORIES Trial: https://www.nejm.org/doi/full/10.1056/nejmoa1409860
The risks of TPN may be overestimated. Current guidelines state that TPN should be started after 7 days of NPO status in adults who were previously well nourished before admission and immediately post-op in patients who have pre-existing weight loss, prolonged inadequate intake or obvious signs of malnutrition on physical exam.
Nutrition in the critically ill patient is highly individualized and care should be taken to establish a tailored plan for each patient early in their hospitalization. Nutrition should be revisited on daily rounds to ensure meeting of caloric needs, minimization of feeding interruptions, and timely advancement of diet.