Enteral Nutrition Support

Enteral Nutrition Support

Ezra Steiger

Laura E. Matarese


Stressful conditions such as surgery are often characterized by hypermetabolism, depletion of protein stores, impaired immune function, and delayed recovery. Provision of adequate nutrition to the surgical patient is vital in order to ensure optimal outcomes. Traditionally, nutrition was regarded as adjunctive care designed to provide nutrients to support the patient during the perioperative state. Recently, nutrition has evolved to become a medical intervention, specifically designed to attenuate the metabolic response to stress, to prevent oxidative cellular injury, and to modulate the immune response. Enteral nutrition (EN), the provision of nutrients via the gastrointestinal (GI) tact, nonvolitionally through a feeding tube or catheter is recommended for patients who cannot meet their nutrient needs through voluntary oral intake. The surgeon is often faced with serious decisions about what, how, and when to feed these patients. Recent technological advancements in enteral formulations and equipments have made it possible to provide EN to a variety of patients in many different settings. This chapter reviews the evidence for the use of EN, timing of feedings, specific nutrients, and the various aspects that are important to consider with this intervention.

Role of the Gastrointestinal Tract

Historically, it was thought that the GI tract was quiescent following surgical intervention and that the primary role of the gut was digestion, absorption, and secretion. It is now evident that the gut is an important metabolically active organ and plays a vital role in nutrient transport, exposure of nutrients to absorptive mucosa, prevention of stasis and bacterial overgrowth, as well as immune regulation. As a result, efforts have been focused on using the GI tract whenever possible.

Route of Feeding: Enteral Versus Parenteral

The question of route of feeding, that is, the use of enteral versus parenteral feedings is largely academic primarily due to the physiological benefit associated with using normal digestive and absorptive pathways. In practice, if the GI tract is functional, accessible, and safe to use, EN is preferred over parenteral nutrition (PN).  PN can be used in conjunction with EN. The two are not mutually exclusive. However, enterally supplied nutrients experience first-pass metabolism in the liver, which promotes their efficient utilization. The presence of
nutrients in the small intestine supports the functional integrity of the gut by maintaining tight junctions between the intraepithelial cells, stimulating blood flow, and inducing the release of trophic endogenous agents (e.g., cholecystokinin, gastrin, bombesin, and bile salts). Luminal nutrients also help to maintain normal intestinal pH and microbial flora, while specific nutrients contained in enteral formulas, such as glutamine and short-chain fatty acids, serve as a fuel source for the intestine. Luminal nutrients are potent stimulators of enterocyte growth and intestinal adaptation. From a practical standpoint, enteral formulas can mimic the normal diet and supply intact nutrients such as fiber, whole proteins, dipeptides, and specialized fatty acids, which cannot be supplied parenterally.

The beneficial effects of EN when compared to PN are well documented in numerous prospective randomized controlled trials involving a variety of patient populations, including major surgery, trauma, burns, head injury, and acute pancreatitis (Table 1). The most consistent beneficial outcome from the use of EN compared with PN is a reduction in infectious morbidity. A reduction in mortality has not been clearly demonstrated. Other outcome variables include significant reductions in hospital length of stay and cost of nutrition intervention.

Table 1 Benefits of Enteral Nutrition


  • Preservation of GI mucosal integrity
  • Support of gut-associated lymphoid tissue (GALT) and mucosa-associated lymphoid tissue (MALT) for preservation of mucosal immunologic functions
  • Preservation of gut barrier function
  • First-pass metabolism in the liver
  • Stimulates release of cholecystokinin
  • Attenuation of the catabolic response
  • Maintenance of digestive and absorptive capabilities of the GI tract
  • Augmentation of cellular antioxidant systems
  • Decreased incidence of hyperglycemia when compared with PN
  • Formulas contain nutrients not available in PN form (i.e. fiber)

  • Significantly lowered risk of infectious morbidity
  • Improved wound healing

  • Shorter length of hospital stay than with PN
  • Less expensive than PN
  • Less complicated procedures and equipment


EN should be considered after assessment of nutritional risk (see Chapter 2) and the ability of the patient to consume adequate nutrition. The presence and degree of malnutrition should be established since malnourished patients tend to have higher rates of morbidity and mortality and longer hospitalizations than adequately nourished patients.

EN provided orally or delivered via a feeding tube is the method of choice for those individuals with adequate digestive and absorptive capacity of the GI tract, but have clinical conditions in which oral intake is impossible, inadequate, or unsafe to use. Specific indications for EN include psychiatric disorders, severe dysphagia or esophageal obstruction, neurologic impairment, major burns or trauma, organ system failure, ration or chemotherapy, acquired immunodeficiency syndrome, and low output enterocutaneous fistulas. However, determining which patients should receive a feeding tube is more complex and requires consideration of several factors including the patient’s clinical status, diagnosis, prognosis, risk–benefit ratio, discharge plans, quality of life, ethical considerations, and the patient/family wishes.

Although few, there are some contraindications to enteral feeding, which relate primarily to the presence and degree of malnutrition, the patient’s ability to consume adequate nutrition by mouth, and the integrity and functional capacity of the GI tract. These can be considered as relative or absolute contraindications. EN, either supplementation via mouth or via enteral feeding tube, is not indicated in those individuals who are well nourished, are able to eat by mouth, or do not have a functional GI tract that can be safely accessed (Table 2). However, some of the potential barriers to EN can be circumvented with careful selection of enteral access device, formula, and route of administration.

Table 2 Contraindications to Enteral Nutrition

  • Nonoperative mechanical GI obstruction, which cannot be bypassed with a feeding tube
  • Intractable vomiting or diarrhea refractory to medical management
  • Severe GI malabsorption
  • Adynamic ileus
  • Distal high-output fistulas, which cannot be bypassed with a feeding tube
  • Severe GI bleed
  • Inability to gain access to the GI tract
  • Need is expect for <5 to 7 days for malnourished patients or 7 to 10 days if adequately nourished
  • Aggressive nutrition intervention is not consistent with prognosis or patient wishes

Special Clinical Circumstances

Reperfusion Injury and Low Flow States

Reperfusion injury and low flow states in which hypoperfusion of the GI tract is suspected must be considered when initiating enteral feedings. Certain clinical conditions frequently observed in critically ill patients such as hypovolemia, hypotension, and hemorrhagic and septic shock pose a risk for low splanchnic blood flow that can lead to GI dysmotility, increased mucosal permeability, endotoxemia, and multiple system organ failure. Preservation and reperfusion injury may also occur following intestinal and multivisceral transplantation potentially delaying the return of bowel function and initiation of enteral feeding. Unfortunately, a disproportionate vasoconstriction occurs in response to the insult sustained during critical illness. A 3% to 5% reduction of blood volume can result in a 50% to 70% shunt of visceral blood flow. This raises concern that initiation of EN would be poorly tolerated by an underperfused intestine or may result in intestinal ischemia. Intestinal ischemia is a potential but rare complication of EN, occurring in <1% of cases. It appears to be more common with surgical jejunostomies, but has been reported with the use of nasojejunal tubes.

Despite these concerns, there is evidence that with appropriate patient selection, careful initiation, and close monitoring, EN can be used successfully in these patients. Continuous infusion of enteral feedings at a very low rate can be employed while receiving nutrition support parenterally until full volume of tube feeding can be achieved. EN may be provided guardedly to patients who are receiving low doses of pressor agents, while observing for signs of intolerance or gut ischemia. There are certain situations in which EN should be withheld until the patient is stabilized. For those patients requiring significant hemodynamic support including high-dose catecholamine agents, alone or in combination with large volume fluid or blood product resuscitation to maintain cellular perfusion, EN should be withheld until the patient is fully resuscitated and/or stable. EN intended to be infused into the small bowel
should be withheld in patients who are hypotensive (mean arterial blood pressure <60 mm Hg), particularly if catecholamine agents (e.g., norepinephrine, phenylephrine, epinephrine, and dopamine) are being used to maintain hemodynamic stability.

Enteral Nutrition in Altered Intestinal Anatomy

Patients who have had intestinal anatomy altered by surgical resection, reconstruction, or replacement with intestinal or multivisceral allografts can be fed enterally. This often represents the first step toward obtaining nutritional autonomy from PN. In patients with short-bowel syndrome, EN provided as the sole source of nutrition or in conjunction with oral feeding has been shown to result in increased net absorption of lipids, proteins, and energy compared with oral feeding. For the patient with short-bowel syndrome a number of factors will influence tolerance to EN. The length of the remnant bowel is the most important factor in determining whether a patient can be transitioned to EN. Adults with >100 cm of small bowel ending in stoma or >60 cm of small bowel anastomosed to the colon can generally be weaned from PN onto EN and eventually to oral diet. The site and extent of the surgical resection will also impact the patient’s ability to digest and absorb. Digestion and absorption of most nutrients occurs in the duodenum and proximal jejunum, while the distal 100 cm of ileum is responsible for absorption of vitamin B12 and bile salts. With jejunal resections, adequate absorption generally occurs unless there is >75% resected largely due to adaptation occurring in the ileum. There is preserved absorption of vitamin B12 and bile salts. Gastrin levels increase resulting in gastric hypersecretion with ensuing low intraluminal pH, inactivating pancreatic enzymes. These patients generally have normal transit through the gut and most will be able to tolerate EN. The consequences of an ileal resection are more severe. There is adequate calorie and fluid absorption if there is ≥60 cm jejunum anastomosed to the colon. Malabsorption of bile salts and vitamin B12 also occurs. The loss of bile salts will result in fat malabsorption, steatorrhea, and loss of fat-soluble vitamins. In addition, there is poor jejunal adaptation, rapid intestinal transit, and small-bowel bacterial overgrowth. Peptide YY, released from L cells in distal ileum and colon, slows gastric emptying and intestinal transit. With distal ileal and colonic resections, this feedback inhibition is lost.

Retention of the ileocecal valve may play a role in absorption and transit time following massive small-bowel resections. The ileocecal valve is thought to control the release of fluid, electrolytes, and nutrients into the colon and to prevent the reflux of colonic material back into the small bowel. If the ileocecal valve is lost, transit time through the proximal gut may be increased, and loss of fluid and nutrients may be greater. Nutrients contained in the enteral formula must have adequate contact time with the intestinal mucosa. In addition, colonic bacteria can reflux and colonize the small bowel worsening diarrhea and nutrient loss.

Preservation of the colon is extremely important for fluid and electrolyte absorption. In addition, bacteria in the colon metabolize carbohydrate and soluble fiber into short-chain fatty acids. These aid in fluid and electrolyte absorption, provide a source of energy, and stimulate intestinal adaptation. Likewise, an intact stomach, pancreas, and liver will play a role in digestion and absorption.

Although the length of the remnant bowel is critical for successful EN, the health of the remaining intestine is also an important consideration. If the mucosa of the remaining bowel is diseased (i.e., Crohn’s disease and radiation enteritis) absorption will be impaired.

Following surgical resection, the bowel adapts. This is both an anatomical and a functional adaptation. The adaptive period is thought to continue for 2 to 3 years. Thus, the extent of intestinal adaptation will also affect the patient’s ability to tolerate EN.

Medications are essential for patients with altered GI anatomy during EN therapy. Antidiarrheal agents can be used to prolong transit time. Pancreatic enzymes and bile acid sequestrates can be used to enhance absorption. Bacterial overgrowth, common in short-bowel syndrome, can be treated with antibiotics or probiotics.

A standard isotonic polymeric formula containing intact proteins, glucose polymers, and a mixture of LCT (long chain triglycerides) and MCT (medium chain triglycerides) should be utilized for most patients with compromised gut. Formulas that also contain soluble fiber are especially useful in patients with an intact colon in order to improve absorptive function and to serve as a source of energy.

Intestinal and multivisceral transplantation has become a therapeutic option for those individuals with permanent intestinal failure who fail PN or intestinal rehabilitation efforts. A jejunostomy tube is placed directly into the allograft at the time of surgery and EN commences within the first 1 to 2 weeks. As the EN is advanced, PN is reduced and oral nutrition is initiated. A polymeric formula, which is high in protein and low in potassium, is utilized as there is no data to suggest significant malabsorption of the intestinal allograft. A fiber-containing formula is used if the patient develops diarrhea. The low potassium content is necessary because tacrolimus can cause hyperkalemia.

Enteral Nutrition in the Intensive Care Unit

The underlying metabolic responses to early enteral feeding and the derived clinical beneficial outcomes have been well described for the intensive care unit (ICU) patient. Secretory IgA, gut-associated lymphoid tissue (GALT), and mucosal-associated lymphoid tissue (MALT) are stimulated by enteral feeds and help fight infection locally in the gut and at distant sites as well. In a systematic review and analysis of 12 randomized prospective controlled trials, Lewis et al. showed a significant reduction in infections and hospital length of stay with the use of immediate postoperative tube feeding or aggressive early oral nutrition versus standard therapy. EN has even been successfully used in trauma patients with an open abdomen. Although GI motility is impaired in critically ill postoperative patients, the use of prokinetic agents alone or in combination and opiate antagonists and a multifaceted change in clinical practice aided the delivery of adequate EN support to critically ill and postoperative patients. Recent EN and PN clinical guidelines for critically ill patients were published by the European Society of Parenteral and Enteral Nutrition (ESPEN) and the American Society of Parenteral and Enteral Nutrition (ASPEN) jointly with the Society of Critical Care Medicine (SCCM). The guideline publications have extensive bibliographies containing all the studies that were analyzed and graded for levels of evidence by a multidisciplinary group of clinical experts in the field. Grades of recommendations were made based on levels of evidence with Grade A recommendations in the ESPEN guidelines based on either a meta-analysis of randomized controlled trials or at least one randomized controlled trial and Grade B recommendations were based on either a well-designed controlled trial without randomization or a well-designed nonexperimental descriptive study. The lowest grade was C while Grade A recommendations for the ASPEN/CCM guidelines were supported by at least two large randomized trials with clear-cut results and a low risk of false-positive and/or false-negative error and Grade B recommendations were supported by just
one such large randomized trial. The lowest possible recommendation grade was E, which was similar to the ESPEN Grade C. In the ESPEN surgery enteral nutrition publication, there were 36 guidelines developed of which 12 were category A. In the ESPEN intensive care enteral nutrition publication, there were 21 guidelines of which 6 were category A. The ASPEN/CCM guidelines were developed for both EN and PN in the adult ICU patient for whom there were 72 guidelines 11 of which were graded A or B. Only those recommendations with strong levels of supportive evidence are reviewed in this section. For those patients with severe malnutrition (weight loss >10% in the preceding 6 months, BMI <18.5 kg/m2, and Subjective Global Assessment of C or serum albumin <3.0 mg%) consideration should be given to providing nutrition support for 10 to 14 days prior to major surgery. Both sets of guidelines made strong well-supported recommendations to initiate normal food intake or enteral feeding early after GI surgery and that EN is the preferred route of nutrition support over PN. Tube feedings should be started within 24 hours after surgery for patients undergoing major head and neck surgery or major GI surgery for cancer. In addition, it should be initiated early in patients with severe trauma and in those patients who came to surgery malnourished. Strong consideration should be given to inserting a jejunostomy or nasojejunal feeding tube at the time of major abdominal surgery to facilitate postoperative EN. The presence of bowel sounds, passage of flatus, or passage of stool is not required to start EN. Immune-modulating enteral solutions containing arginine, nucleotides, and omega-3 fatty acids are superior to standard enteral formulas in significantly reducing duration of mechanical ventilation, infectious morbidity, and hospital length of stay for patients having major elective surgery, trauma patients, and surgical ICU patients. Glutamine should be added to enteral formulas given to burn and trauma patients. These guidelines and the supporting literature favor the early institution of postoperative EN for surgical patients in the ICU setting; however, there is no uniformity of agreement and no clear definition of “early.” Ultimately, the surgeon has to make a clinical decision to start early EN based not only on these recommendations, but also on each patient’s condition and special circumstances. Relative contraindications to EN include expectation of early resumption of oral intake in a previously well-nourished patient, mechanical intestinal obstruction, irresolvable severe diarrhea, severe short-bowel syndrome (<100 cm of small intestine), and severe GI bleeding. Hypoperfusion associated with low flow states had previously led to the belief that an underperfused intestine would not be able to tolerate enteral feedings. However, more recently, it has been proposed that EN is possible in some patients with low flow states and may even be beneficial. In both of these publications, however, it is noted that the patient must be carefully and frequently monitored for signs of ischemic bowel clinically, radiologically, and by laboratory studies. However, the early diagnosis of ischemic bowel is very difficult and EN should be withheld until the patient is stable. Despite the advantages of EN over PN, parenteral nutrition should not be avoided when EN support cannot be given or when EN cannot meet energy and protein requirements. When energy and protein requirements cannot be met by enteral feeding alone a combined EN and PN support program should be considered to prevent the negative outcomes of prolonged cumulative negative energy balance.

Enteral Access Devices

Access to the GI tract can be obtained at the patient’s bedside, in the radiology department, in the endoscopy suite, or in the operating room. The anticipated length of time that EN is required and the potential risk of aspiration will determine the type of feeding device needed and its modality of placement. Short-term feeding can be accomplished with nasogastric or nasoenteral feeding tubes that are usually made of polyurethane and are 8 to 12 French in diameter; long-term feeding tubes such as those placed percutaneously are made of silastic and are 18 to 28 French in diameter (gastrostomy tubes) or 8 to 12 French in diameter (jejunostomy tubes). Silicone material is generally preferred for long-term feeding tubes, because it resists irritation and does stiffen.

The tip of the feeding tube should be positioned in the stomach, duodenum, or proximal small intestine. Despite several techniques described to correctly place feeding tubes, nasogastric or nasoenteral feeding tube position should be confirmed radiologically prior to starting tube feeding.

In the critically ill patient needing temporary enteral feeding, concerns over risk of aspiration have encouraged the use of post-pyloric feeding tube placement.

In addition, post-pyloric feeding has been shown to allow for the delivery of more kilocalories and protein with less vomiting compared to nasogastric tube feeding. Main-taining nasoenteral tube position without accidental displacement is helped with the use of a nasal bridle and the risk of nasal necrosis is minimized by using umbilical tape instead of a red rubber catheter.

Nasogastric tube feedings in the postoperative patient are of concern if there is impaired gastric emptying and high gastric residuals that could lead to vomiting and aspiration. Although there is poor correlation between gastric residual volumes and the risk of aspiration, gastric residual volumes >200 to 500 mL should alert the clinician to institute measures to minimize the risk of aspiration such as elevating the head of the bed, avoiding bolus infusion, consider the use of a promotility agent such as erythromycin or a narcotic antagonist such as naloxone and alvimopan, and consider the use of post-pyloric feeding. In addition, the use of chlorhexidine mouthwash could reduce the risk of ventilator-associated pneumonia.

Diarrhea associated with tube EN is common and is multifactorial. It is commonly associated with magnesium or sorbitol-containing medication, antibiotics, infections such as Clostridium difficile, and intolerance of the formula. Infectious and inflammatory etiologies, fecal impaction, and medications should be ruled out before starting antidiarrheals. Changing to an isotonic, lactose-free solution with soluble fiber may be of help, but some authors suggest limiting soluble fiber. If diarrhea persists, the volume of enteral feeding should be reduced until it is tolerated and the unmet kilocalories and protein needs are provided by PN.

When enteral access is required for 4 or more weeks feeding tubes can be placed endoscopically, laparoscopically, fluoroscopically, or by open abdominal surgery. The morbidity and mortality of feeding tubes placed by open surgery as the sole reason for the operation is high primarily due to the patient’s underlying medical conditions.

A number of techniques for surgical gastrostomies have been described. At the time of laparotomy, for other reasons, the most common approach to gastrostomy tube placement is the Stamm procedure. The introduction of percutaneous endoscopic gastrostomy (PEG) revolutionized the technique of obtaining long-term enteral access and greatly reduced the associated morbidity and mortality in properly selected patients. Beneficial outcomes with the use of PEGs have been reported for head and neck cancer patients and stroke and head trauma patients, while its use in patients with dementia is controversial.

There have been many techniques described to gain access to the jejunum for EN. At the time of surgery, for other reasons, the
Witzel jejunostomy or a modification thereof is the most commonly used technique.

Gastrojejunal tubes are used when gastric decompression is needed as well as jejunal feeding occurs in patients with impaired gastric motility with normal small-bowel motility and absorption. These tubes can be placed at the time of surgery or laparoscopically.

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Aug 2, 2016 | Posted by in GENERAL SURGERY | Comments Off on Enteral Nutrition Support

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