Nutrition in Critically ill Patients

1 Why is nutrition therapy in critical illness important?

Critical illness is most often accompanied by a catabolic stress state in which patients demonstrate a systemic inflammatory response, hypermetabolism, multiple organ dysfunction, infectious complications, and malnutrition. Malnutrition is associated with impaired immunologic function and increased morbidity and mortality in acutely ill patients. Therefore nutrition therapy is important to attempt to improve patient outcomes.

2 What are the goals of nutritional therapy in critically ill patients?

Over the past decade, there has been a shift away from the concept of nutrition support, where nutrition was provided as a fuel to support patients during a time of critical illness, toward the concept of nutrition therapy, where nutritional interventions are focused on modulating the immunologic and inflammatory response of critical illness. Therefore the generally accepted goals of nutritional delivery in critically ill patients are to

3 How should the nutritional status of critically ill patients be assessed?

Nutritional status assessment in critically ill patients is difficult. Traditionally, albumin, prealbumin, and anthropometric measurements have been used to assess nutritional status. However, these are inaccurate in critical illness because of fluid resuscitation and the acute phase response. Therefore one must rely on information such as recent weight loss, comorbid illnesses, and recent gastrointestinal (GI) dysfunction.

4 What mode of feeding (enteral or parenteral) should be initiated in critically ill patients?

Unless an absolute contraindication to enteral nutrition (EN) exists (such as ischemic bowel or bowel obstruction), EN should be initiated preferentially over parenteral nutrition (PN). Several randomized controlled trials (RCTs) have compared EN with PN in critically ill patients with an intact GI tract. When these studies were aggregated in a meta-analysis, no difference in survival was seen. However, EN is associated with a significant reduction in infectious complications, and it is less expensive than PN. Evidence also suggests that lack of use of the GI tract rapidly results in atrophy of gut luminal mucosa, which may lead to bacterial translocation across the gut wall and into the systemic circulation. Even small amounts of, or trophic, EN increase blood flow to the gut, preserve GI epithelial structures, and maintain villous height. EN also improves immune function by supporting gut-associated lymphoid tissue. EN is therefore recommended over PN unless the patient has an absolute contraindication to enteral feeding (discussed later).

5 When should EN be initiated in critically ill patients?

Early EN is usually defined as initiating enteral feedings within 48 hours of intensive care unit (ICU) admission. Many RCTs have compared early EN versus delayed nutrient intake in critically ill patients receiving mechanical ventilation, and, when these results were aggregated, early EN was associated with a trend toward mortality reduction and a significant reduction in infectious complications. Starting EN early does not seem to affect the duration of mechanical ventilation or ICU length of stay. The presence of bowel sounds and the passage of flatus are not necessary before the institution of EN.

6 How many calories should critically ill patients receive?

Energy expenditure varies with age, sex, body mass, and type and severity of illness. During critical illness, total energy expenditure (TEE) can be measured with indirect calorimetry. However, in clinical practice, resting energy expenditure (REE) is usually estimated by using a variety of available equations and is then multiplied by a stress factor of 1.0 to 2.0 to estimate TEE (and therefore caloric requirements). Roughly 25 kcal/kg ideal body weight is often the standard practice, and other equations, such as Harris-Benedict, Ireton-Jones, and Weir, are commonly used (Table 8-1). Unfortunately, predictive equations tend to be inaccurate. The optimal amount of calories to provide critically ill patients is unclear given the paucity of existing data, but studies do suggest that providing an amount of calories closer to goal calories is associated with improved clinical outcomes.

^{Table 8-1} Examples of Predictive Equations for Ree in Critical Illness

ActBW, Actual body weight = weight on admission (kilograms); AdjBW, adjusted body weight = ideal body weight + 0.4 (actual body weight − ideal body weight); BMI, body mass index; Ht, height (centimeters); IBW, ideal body weight = 50 + 2.3 per inch > 60 inches (men), 45.5 + 2.3 per inch > 60 inches (women).

7 What should be the composition of EN in critically ill patients?

Few data are available to inform the macronutrient composition of enteral feedings. In general, critically ill patients should receive an amount of protein daily between 1.5 and 2.0 g/kg of ideal body weight. The use of whole protein, or polymeric, formulas is recommended because insufficient data exist to support the routine use of peptide-based formulas in most patients. In most enteral formulas, approximately 25% to 30% of calories are from fat. Similar to the situation with protein, evidence in the literature is insufficient to support the routine use of high-fat or low-fat enteral formulas. In some ICU populations, specific enteral formulas are recommended (discussed later). For example, formulas containing arginine are often considered in patients who have had elective surgery, trauma, or burns but should generally not be used in patients with sepsis. Specific formulas designed for patients with renal failure are also available.

8 Should critically ill patients in shock and/or receiving vasopressors receive EN?

Ischemic bowel is a very rare complication of EN but has been reported in critically ill patients and can be fatal. Therefore the general recommendation is that EN be avoided in patients who are in shock and in those patients in whom resuscitation is active, vasopressors are being initiated, or vasopressor doses are increasing. Once patients are resuscitated and hemodynamically stable, EN may be initiated, even if they are receiving stable lower doses of vasopressors. However, special attention should be paid to signs of enteral feeding intolerance such as abdominal distention or increasing gastric residual volumes (GRVs).

9 Should gastric or small-bowel EN be used?

EN can be delivered through an intragastric gastric (nasogastric or orogastric) or postpyloric (either in the duodenum or jejunum) feeding tube. Enteral tubes may also be surgically placed. Each option has risks and benefits. In patients who have endotracheal tubes in place, nasal tubes can increase the risk of sinusitis. Intragastric feeding tubes can be placed at the bedside, and their position can be immediately confirmed radiographically (it is not sufficient to assess placement with auscultation alone). However, successful placement of a small-bowel feeding tube at the bedside varies from 11% to 93% depending on technique and operator experience. The use of endoscopy or fluoroscopy for postpyloric feeding tube placement can cause delays in initiating enteral feeding. In a meta-analysis of gastric versus small-bowel feeding in ICU patients, small-bowel feeding was not found to be associated with any improvement in survival but was associated with a reduction in infections, particularly pneumonia. Therefore the routine use of small-bowel enteral feeding is recommended when possible. However, in many ICUs, obtaining access to the small bowel may be logistically difficult and expensive if fluoroscopy or endoscopy is needed. In ICUs where obtaining small-bowel access is less feasible, small-bowel feedings should be considered for patients showing signs of intolerance to intragastric feeding (see later) or at high risk for aspiration (e.g., must remain in supine position).

10 Should EN be delivered continuously or in boluses?

Continuous feeding delivers a small amount of feeding formula continuously over a 24-hour period, whereas bolus feeding delivers a large volume of formula over a short period of time. Because one pseudorandomized study found that aggressive early EN via bolus feeding was harmful, it is generally thought that bolus feeding is less safe than continuous feeding. However, a paucity of evidence is available on this topic.

11 How should enteral feeding tolerance be monitored?

Patients should be monitored frequently (e.g., every 4 to 6 hours) for tolerance of EN, especially in the first few days after initiating enteral feedings. This monitoring should include an assessment of pain (often difficult in critically ill patients), abdominal distention, and stooling. GRVs should also be measured frequently. However, evidence suggests that higher GRVs as high as 250 to 500 mL are not associated with an increased risk for pneumonia or aspiration. Thus the recently published American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) and Society of Critical Care Medicine (SCCM) Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient recommend that GRVs between 250 and 500 mL should prompt clinicians to take measures to reduce the risk of aspiration (e.g., elevate the head of the patient’s bed) but that automatic cessation of enteral feeding should not occur for GRVs < 500 mL unless other signs of intolerance are present.

McClave SA, Martindale RG, 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 (SCCM) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.). JPEN J Parenter Enteral Nutr 33:277-316, 2009.

12 How should critically ill patients be positioned during enteral feeding?

Two prior randomized trials have compared semirecumbent with supine positioning in ICU patients. In one study (Drakulovic, 1999), the incidence of pneumonia was significantly reduced in patients in the semirecumbent position. The other study (van Nieuwenhoven, 2006) did not achieve the target positioning and did not find a reduction in infections. On the basis of these limited data, it is recommended that critically ill patients have the head of their beds raised to as close to 45 degrees as possible.

Drakulovic MB, Torres A, Bauer TT, et al: Supine body position as a risk factor for nosocomial pneumonia in mechanically ventilated patients: a randomised trial. Lancet 354:1851-1858, 1999.

van Nieuwenhoven CA, Vandenbroucke-Grauls C, van Tiel FH, et al: Feasibility and effects of the semirecumbent position to prevent ventilator-associated pneumonia: a randomized study. Crit Care Med 34:396-402, 2006.

13 Should motility agents be used in critically ill patients?

The use of motility agents is recommended when clinically feasible, especially in patients with signs of enteral feeding intolerance. Motility agents including erythromycin or metoclopramide have been found to improve gastric emptying and tolerance of EN but do not seem to change outcomes in critically ill patients. In one study, administration of enteral naloxone (to reverse the side effects of opioid narcotics on the GI tract) resulted in an increased volume of EN infused, decreased GRVs, and decreased incidence of ventilator-associated pneumonia.

14 Should feeding protocols be used in ICUs?

Nurse-driven feeding protocols that include rapid startup of enteral feeding, goal infusion rate, orders for GRVs, and directions for when to stop and start feedings increase the percentage of goal calories administered. In an effort both to start enteral feedings in the critically ill patient early and to provide an amount of calories close to goal, feeding protocols should be implemented.

15 When is EN contraindicated?

Contraindications to EN include conditions that lead to a nonfunctioning GI tract such as ischemic bowel, intestinal obstruction, severe malabsorption, and severe short gut syndrome. In general, pancreatitis, enterocutaneous fistulae, and recent GI surgery are not contraindications to enteral feeding.

16 What are some complications of enteral feeding, and how can they be minimized?

EN is not without risks, and complications can be categorized as GI, mechanical, or metabolic.

17 When should PN be used in critically ill patients?

EN is the preferred method of delivering nutrition therapy in critically ill patients, and measures such as placing a small-bowel feeding tube and starting motility agents should be used in patients who have signs of intolerance to enteral feedings before considering initiating PN. However, PN is appropriate in some ICU patients, including those in whom EN is not feasible (e.g., ongoing intolerance or contraindication to enteral feeding) and those who are obviously malnourished at admission. Data answering this question are sparse, but the recent A.S.P.E.N.-SCCM Guidelines recommend that PN be considered in the following three circumstances:

Given these recommendations, very few patients in a medical ICU should need PN.

18 What are some complications of PN?

19 Which pharmaconutrients or specialized formulas should critically ill patients receive?

20 What nutrition therapy should patients with acute kidney injury (AKI) receive?

Like most other critically ill patients, patients with AKI should receive early EN with standard amounts of protein and calories. Protein restriction should not be used to delay the initiation of dialysis. Specific enteral formulas designed for renal failure that have varying electrolyte compositions (e.g., lower phosphate or potassium) or are calorie dense (i.e., fluid restricted) can be used if needed.

21 What nutrition therapy should patients with acute pancreatitis receive?

Early EN is now standard of care in patients with acute pancreatitis. In past decades, patients with acute pancreatitis were not allowed any enteral intake and were fed parenterally. In recent times, however, research has found that these patients have improved outcomes if they receive early EN started within 48 hours of admission, even in cases of severe acute pancreatitis. Two trials have also found that outcomes in these patients are not different when they are fed gastrically versus jejunally.

22 How might propofol influence the nutritional support provided to critically ill patients?

Propofol is a sedative commonly used in an ICU setting that is delivered as a 10% lipid emulsion and provides 1.1 kcal/mL. When patients are receiving propofol for longer periods of time (i.e., more than 3-4 days) or in large doses, the calories received from propofol should be taken into account in relation to the overall caloric prescription to avoid excess delivery of calories. Because propofol can also cause hypertriglyceridemia, which can lead to acute pancreatitis, serum triglyceride levels should be measured in patients receiving larger doses of propofol.