Enteral Nutrition

Enteral Nutrition is a topic covered in the Washington Manual of Medical Therapeutics.

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General Principles

Whenever possible, oral/enteral feeding is preferred to parenteral feeding because it limits mucosal atrophy, maintains IgA secretion, and prevents cholelithiasis. Additionally, oral/enteral feeds are less expensive than parenteral nutrition and have a lower likelihood of infectious complications.

Types of Feedings

Hospital diets include a regular diet and those modified in either nutrient content (amount of fiber, fat, protein, or sodium) or consistency (liquid, puréed, soft). There are ways that food intake can often be increased:

  • Aid at mealtime.
  • Allow relatives and friends to supply food.
  • Limit missed meals for medical tests and procedures.
  • Avoid unpalatable diets. Milk-based formulas (e.g., Carnation Instant Breakfast™) contain milk as a source of protein and fat and are more palatable than many other formula diets.
  • Use of calorically dense supplements (e.g., Ensure™, Boost™).

Defined Liquid Formulas

Table 2-6
Table 2-6: Enteral Feeding Formulas: Comparing Composition
Formulakcal/mL% Protein% Lipid% CarbohydrateK+ (mEq/L)PO43- (mg/L)Purpose/Niche
Osmolite1.016.72954.340.2760Standard polymeric
Jevity1.5172953.640.21200Standard polymeric
TwoCal HN216.740.143.262.61050Volume restricted
Nepro with Carb Steady1.818483427.2700ESRD
Glucerna1.522453364.61000Glucose intolerance/diabetes
Promote1.025235250.81200High protein
Vital AF1.225393643.2844Short gut, exocrine pancreatic insufficiency
Vivonex RTF1.020107031668Fat malabsorption
Pivot 1.51.525304551.31000SIRS, ARDS, sepsis

ARDS, acute respiratory distress syndrome; ESRD, end-stage renal disease; SIRS, systemic inflammatory response syndrome.

Adapted from Barnes-Jewish Hospital Enteral Nutrition Formulary (2019).

  • Polymeric formulas (e.g., Osmolite™, Jevity™) are appropriate for most patients. They contain nitrogen in the form of whole proteins and include blenderized food, milk-based, and lactose-free formulas. Other formulas are available with modified content including high-nitrogen, high-calorie, fiber-enriched, and low-potassium/phosphorus/magnesium.
  • Semielemental oligomeric formulas (e.g., Peptamen™) contain hydrolyzed protein in the form of small peptides and free amino acids. Although these formulas may have benefit in those with exocrine pancreatic insufficiency or short gut, pancreatic enzyme replacement is a less expensive and an equally effective intervention in most patients.
  • Elemental monomeric formulas (e.g., Vivonex™, Glutasorb™) contain nitrogen in the form of free amino acids and small amounts of fat (<5% of total calories) and are hyperosmolar (550–650 mOsm/kg). These formulas are not palatable and therefore require either tube feeding or mixing with other foods or flavorings for oral ingestion. Furthermore, these formulas have not been shown to be clinically superior to oligomeric or polymeric formulas in patients with adequate pancreatic digestive function and are much more expensive than polymeric formulas.
  • Oral rehydration solutions stimulate sodium and water absorption via the sodium–glucose cotransporter present in the brush border of intestinal epithelium. Oral rehydration therapy (using 90–120 mEq/L solutions to avoid intestinal sodium secretion and negative sodium and water balance) can be especially useful in patients with short bowel syndrome.1 The characteristics of several oral rehydration solutions are listed in Table 2-6.

Tube Feeding

  • Tube feeding is useful in patients who have a functional GI tract but cannot ingest adequate nutrients.
  • The type of feeding tube selected (nasogastric, nasoduodenal, nasojejunal, gastrostomy, jejunostomy, pharyngostomy, and esophagostomy tubes) depends on physician experience, clinical prognosis, gut patency and motility, risk of aspirating gastric contents, patient preference, and anticipated duration of feeding.
  • Short-term (<6 weeks) tube feeding can be achieved using a soft, small-bore nasogastric or nasoenteric feeding tube. Although nasogastric feeding is usually the most appropriate route, orogastric feeding may be needed in those who are intubated or those with nasal injury or deformity. Nasoduodenal and nasojejunal feeding tubes can be placed at the bedside; however, ∼2% of tubes can be misplaced and the use of electromagnetic, carbon dioxide sensing (capnography), or direct camera visualization devices is recommended. Confirmation of placement, usually by using radiography, is mandatory prior to use. Auscultation should not be used to confirm placement.
  • Long-term (>6 weeks) tube feeding usually requires a gastrostomy or jejunostomy tube that can be placed percutaneously by endoscopic or radiographic assistance. Alternatively, they can be placed surgically, depending on the clinical situation and local expertise.

Feeding Schedules

Patients who have feeding tubes in the stomach can often tolerate intermittent bolus or gravity feedings, in which the total amount of daily formula is divided into four to six equal portions.

  • Bolus feedings are given by syringe as rapidly as tolerated.
  • Gravity feedings are infused over 30–60 minutes.
  • The patient’s upper body should be elevated by 30–45 degrees during feeding and for at least 2 hours afterward. Tubes should be flushed with water after each feeding. Intermittent feedings are useful for patients who cannot be positioned with continuous head-of-the-bed elevation or who require greater freedom from feeding. Patients who experience nausea and early satiety with bolus gravity feedings may require continuous infusion at a slower rate.
  • Continuous feeding can often be started at 20–30 mL/h and advanced by 10 mL/h every 6 hours until the feeding goal is reached. Patients who have gastroparesis often tolerate gastric tube feedings when they are started at a slow rate (e.g., 10 mL/h) and advanced by small increments (e.g., 10 mL/h every 8–12 hours). Patients with severe gastroparesis may require passage of the feeding tube tip past the ligament of Treitz. Continuous feeding should always be used when feeding directly into the duodenum or jejunum to avoid distention, abdominal pain, and dumping syndrome.
  • Jejunal feeding may be possible in closely monitored patients with mild to moderate acute pancreatitis.2 RCTs comparing jejunal and gastric feeding in severe acute pancreatitis showed no differences in tolerance, complication rates, and mortality rates. Early initiation of enteral nutrition within 24–72 hours of admission is associated with decreased mortality, organ failure, and infectious complications compared with delayed enteral nutrition.3

Contraindications to Enteral Feeding

The intestinal tract cannot be used effectively in some patients because of the following:

  • Persistent nausea or vomiting
  • Postprandial abdominal pain or diarrhea
  • Mechanical obstruction or severe hypomotility
  • Malabsorption
  • Presence of high-output fistula

Complications

  • Mechanical complications
    • Nasogastric feeding tube misplacement, including intubation of the tracheobronchial tree, occurs more often in unconscious patients. Intracranial placement can occur in patients with skull fractures.
    • Erosive tissue damage can lead to nasopharyngeal erosions, pharyngitis, sinusitis, otitis media, pneumothorax, and GI tract perforation.
    • Tube occlusion is often caused by inspissated feedings or pulverized medications given through small-diameter (<#10 French) tubes. Frequent flushing of the tube with 30–60 mL of water and avoiding administration of pill fragments or viscous medications help to prevent occlusion. The techniques used to unclog tubes include the use of a small-volume syringe (10 mL) to flush warm water or pancreatic enzymes (Viokase™ dissolved in water) through the tube.
  • Hyperglycemia
    • ADA/AACE guidelines recommend a blood glucose target between 140 and 180 mg/dL for most hospitalized patients. In patients with severe comorbidities and terminal illness, less stringent targets are appropriate.4,5
    • The majority of non–critically ill inpatients will require basal insulin while receiving enteral nutrition to achieve and maintain reasonable glucose control.6
    • Long-duration insulin (e.g., detemir, glargine) can be used for basal coverage, while short-acting (e.g., lispro™) can be used to cover prandial and correctional needs.
    • Patients receiving bolus feeds should be given short-acting insulin at the time of each feed with an approximate dose of 1 unit of short-acting insulin per 10–15 g carbohydrate, plus a correctional dose if needed.
    • Patients receiving continuous (24 hours per day) feeding should receive basal and bolus insulin when clinically stable.
    • For patients receiving nocturnal tube feeding, intermediate-duration insulin (e.g., NPH) administered with initiation of feeding is a reasonable approach; however, care should be taken to avoid nocturnal hypoglycemia.
    • If tube feeds are interrupted and insulin has been given, an infusion of dextrose-containing fluid should be started at a rate to match the infusion rate of the scheduled tube feeds until the insulin has worn off.
  • Pulmonary complications
    • The etiology of pulmonary aspiration is often difficult to discern in tube-fed patients as it can occur both from refluxed tube feedings or oropharyngeal secretions unrelated to feedings. Recent evidence suggests that oral secretions play a far greater role in the development of ventilator-associated pneumonia than aspiration of tube feedings.7
    • Gastric residuals are poorly predictive of aspiration risk.8
    • Prevention of reflux: Decrease gastric acid secretion with H2 blockers or proton pump inhibitors, elevate head of bed during feeds, and avoid gastric feeding in high-risk patients (e.g., those with gastroparesis, frequent vomiting, gastric outlet obstruction).
  • GI complications
    • Nausea, vomiting, and abdominal pain are common.
    • Diarrhea is often associated with antibiotic therapy and the use of liquid medications that contain nonabsorbable carbohydrates, such as sorbitol. If diarrhea from tube feeding persists after proper evaluation of possible causes, a trial of antidiarrheal agents or fiber is warranted. Diarrhea is common in patients who receive tube feeding and occurs in up to 50% of critically ill patients. Supplementation with fiber or switching to a fiber-enriched feed has not yielded consistent results. A change to an elemental feeding formula is rarely needed and likely will not resolve the issue unless significant impairment in absorption is well-documented.9
    • Diarrhea in patients with short gut, who do not have other causes such as Clostridioides difficile infection, may be minimized using small, frequent meals that do not contain concentrated sweets (e.g., soda). Intestinal transit time should be maximized to optimize nutrient absorption using a tincture of opium, loperamide, or diphenoxylate. Low-dose clonidine (0.025–0.05 mg orally bid) may be used to reduce diarrhea in hemodynamically stable patients with short bowel syndrome.10 Intestinal ischemia/necrosis has been reported in patients receiving tube feeds. These cases have occurred predominantly in critically ill patients receiving vasopressors for blood pressure support in conjunction with enteral feeding. There are no reliable clinical signs for diagnosis, and the mortality rate is high. Caution should be used when enterally feeding critically ill patients requiring vasopressors.

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General Principles

Whenever possible, oral/enteral feeding is preferred to parenteral feeding because it limits mucosal atrophy, maintains IgA secretion, and prevents cholelithiasis. Additionally, oral/enteral feeds are less expensive than parenteral nutrition and have a lower likelihood of infectious complications.

Types of Feedings

Hospital diets include a regular diet and those modified in either nutrient content (amount of fiber, fat, protein, or sodium) or consistency (liquid, puréed, soft). There are ways that food intake can often be increased:

  • Aid at mealtime.
  • Allow relatives and friends to supply food.
  • Limit missed meals for medical tests and procedures.
  • Avoid unpalatable diets. Milk-based formulas (e.g., Carnation Instant Breakfast™) contain milk as a source of protein and fat and are more palatable than many other formula diets.
  • Use of calorically dense supplements (e.g., Ensure™, Boost™).

Defined Liquid Formulas

Table 2-6
Table 2-6: Enteral Feeding Formulas: Comparing Composition
Formulakcal/mL% Protein% Lipid% CarbohydrateK+ (mEq/L)PO43- (mg/L)Purpose/Niche
Osmolite1.016.72954.340.2760Standard polymeric
Jevity1.5172953.640.21200Standard polymeric
TwoCal HN216.740.143.262.61050Volume restricted
Nepro with Carb Steady1.818483427.2700ESRD
Glucerna1.522453364.61000Glucose intolerance/diabetes
Promote1.025235250.81200High protein
Vital AF1.225393643.2844Short gut, exocrine pancreatic insufficiency
Vivonex RTF1.020107031668Fat malabsorption
Pivot 1.51.525304551.31000SIRS, ARDS, sepsis

ARDS, acute respiratory distress syndrome; ESRD, end-stage renal disease; SIRS, systemic inflammatory response syndrome.

Adapted from Barnes-Jewish Hospital Enteral Nutrition Formulary (2019).

  • Polymeric formulas (e.g., Osmolite™, Jevity™) are appropriate for most patients. They contain nitrogen in the form of whole proteins and include blenderized food, milk-based, and lactose-free formulas. Other formulas are available with modified content including high-nitrogen, high-calorie, fiber-enriched, and low-potassium/phosphorus/magnesium.
  • Semielemental oligomeric formulas (e.g., Peptamen™) contain hydrolyzed protein in the form of small peptides and free amino acids. Although these formulas may have benefit in those with exocrine pancreatic insufficiency or short gut, pancreatic enzyme replacement is a less expensive and an equally effective intervention in most patients.
  • Elemental monomeric formulas (e.g., Vivonex™, Glutasorb™) contain nitrogen in the form of free amino acids and small amounts of fat (<5% of total calories) and are hyperosmolar (550–650 mOsm/kg). These formulas are not palatable and therefore require either tube feeding or mixing with other foods or flavorings for oral ingestion. Furthermore, these formulas have not been shown to be clinically superior to oligomeric or polymeric formulas in patients with adequate pancreatic digestive function and are much more expensive than polymeric formulas.
  • Oral rehydration solutions stimulate sodium and water absorption via the sodium–glucose cotransporter present in the brush border of intestinal epithelium. Oral rehydration therapy (using 90–120 mEq/L solutions to avoid intestinal sodium secretion and negative sodium and water balance) can be especially useful in patients with short bowel syndrome.1 The characteristics of several oral rehydration solutions are listed in Table 2-6.

Tube Feeding

  • Tube feeding is useful in patients who have a functional GI tract but cannot ingest adequate nutrients.
  • The type of feeding tube selected (nasogastric, nasoduodenal, nasojejunal, gastrostomy, jejunostomy, pharyngostomy, and esophagostomy tubes) depends on physician experience, clinical prognosis, gut patency and motility, risk of aspirating gastric contents, patient preference, and anticipated duration of feeding.
  • Short-term (<6 weeks) tube feeding can be achieved using a soft, small-bore nasogastric or nasoenteric feeding tube. Although nasogastric feeding is usually the most appropriate route, orogastric feeding may be needed in those who are intubated or those with nasal injury or deformity. Nasoduodenal and nasojejunal feeding tubes can be placed at the bedside; however, ∼2% of tubes can be misplaced and the use of electromagnetic, carbon dioxide sensing (capnography), or direct camera visualization devices is recommended. Confirmation of placement, usually by using radiography, is mandatory prior to use. Auscultation should not be used to confirm placement.
  • Long-term (>6 weeks) tube feeding usually requires a gastrostomy or jejunostomy tube that can be placed percutaneously by endoscopic or radiographic assistance. Alternatively, they can be placed surgically, depending on the clinical situation and local expertise.

Feeding Schedules

Patients who have feeding tubes in the stomach can often tolerate intermittent bolus or gravity feedings, in which the total amount of daily formula is divided into four to six equal portions.

  • Bolus feedings are given by syringe as rapidly as tolerated.
  • Gravity feedings are infused over 30–60 minutes.
  • The patient’s upper body should be elevated by 30–45 degrees during feeding and for at least 2 hours afterward. Tubes should be flushed with water after each feeding. Intermittent feedings are useful for patients who cannot be positioned with continuous head-of-the-bed elevation or who require greater freedom from feeding. Patients who experience nausea and early satiety with bolus gravity feedings may require continuous infusion at a slower rate.
  • Continuous feeding can often be started at 20–30 mL/h and advanced by 10 mL/h every 6 hours until the feeding goal is reached. Patients who have gastroparesis often tolerate gastric tube feedings when they are started at a slow rate (e.g., 10 mL/h) and advanced by small increments (e.g., 10 mL/h every 8–12 hours). Patients with severe gastroparesis may require passage of the feeding tube tip past the ligament of Treitz. Continuous feeding should always be used when feeding directly into the duodenum or jejunum to avoid distention, abdominal pain, and dumping syndrome.
  • Jejunal feeding may be possible in closely monitored patients with mild to moderate acute pancreatitis.2 RCTs comparing jejunal and gastric feeding in severe acute pancreatitis showed no differences in tolerance, complication rates, and mortality rates. Early initiation of enteral nutrition within 24–72 hours of admission is associated with decreased mortality, organ failure, and infectious complications compared with delayed enteral nutrition.3

Contraindications to Enteral Feeding

The intestinal tract cannot be used effectively in some patients because of the following:

  • Persistent nausea or vomiting
  • Postprandial abdominal pain or diarrhea
  • Mechanical obstruction or severe hypomotility
  • Malabsorption
  • Presence of high-output fistula

Complications

  • Mechanical complications
    • Nasogastric feeding tube misplacement, including intubation of the tracheobronchial tree, occurs more often in unconscious patients. Intracranial placement can occur in patients with skull fractures.
    • Erosive tissue damage can lead to nasopharyngeal erosions, pharyngitis, sinusitis, otitis media, pneumothorax, and GI tract perforation.
    • Tube occlusion is often caused by inspissated feedings or pulverized medications given through small-diameter (<#10 French) tubes. Frequent flushing of the tube with 30–60 mL of water and avoiding administration of pill fragments or viscous medications help to prevent occlusion. The techniques used to unclog tubes include the use of a small-volume syringe (10 mL) to flush warm water or pancreatic enzymes (Viokase™ dissolved in water) through the tube.
  • Hyperglycemia
    • ADA/AACE guidelines recommend a blood glucose target between 140 and 180 mg/dL for most hospitalized patients. In patients with severe comorbidities and terminal illness, less stringent targets are appropriate.4,5
    • The majority of non–critically ill inpatients will require basal insulin while receiving enteral nutrition to achieve and maintain reasonable glucose control.6
    • Long-duration insulin (e.g., detemir, glargine) can be used for basal coverage, while short-acting (e.g., lispro™) can be used to cover prandial and correctional needs.
    • Patients receiving bolus feeds should be given short-acting insulin at the time of each feed with an approximate dose of 1 unit of short-acting insulin per 10–15 g carbohydrate, plus a correctional dose if needed.
    • Patients receiving continuous (24 hours per day) feeding should receive basal and bolus insulin when clinically stable.
    • For patients receiving nocturnal tube feeding, intermediate-duration insulin (e.g., NPH) administered with initiation of feeding is a reasonable approach; however, care should be taken to avoid nocturnal hypoglycemia.
    • If tube feeds are interrupted and insulin has been given, an infusion of dextrose-containing fluid should be started at a rate to match the infusion rate of the scheduled tube feeds until the insulin has worn off.
  • Pulmonary complications
    • The etiology of pulmonary aspiration is often difficult to discern in tube-fed patients as it can occur both from refluxed tube feedings or oropharyngeal secretions unrelated to feedings. Recent evidence suggests that oral secretions play a far greater role in the development of ventilator-associated pneumonia than aspiration of tube feedings.7
    • Gastric residuals are poorly predictive of aspiration risk.8
    • Prevention of reflux: Decrease gastric acid secretion with H2 blockers or proton pump inhibitors, elevate head of bed during feeds, and avoid gastric feeding in high-risk patients (e.g., those with gastroparesis, frequent vomiting, gastric outlet obstruction).
  • GI complications
    • Nausea, vomiting, and abdominal pain are common.
    • Diarrhea is often associated with antibiotic therapy and the use of liquid medications that contain nonabsorbable carbohydrates, such as sorbitol. If diarrhea from tube feeding persists after proper evaluation of possible causes, a trial of antidiarrheal agents or fiber is warranted. Diarrhea is common in patients who receive tube feeding and occurs in up to 50% of critically ill patients. Supplementation with fiber or switching to a fiber-enriched feed has not yielded consistent results. A change to an elemental feeding formula is rarely needed and likely will not resolve the issue unless significant impairment in absorption is well-documented.9
    • Diarrhea in patients with short gut, who do not have other causes such as Clostridioides difficile infection, may be minimized using small, frequent meals that do not contain concentrated sweets (e.g., soda). Intestinal transit time should be maximized to optimize nutrient absorption using a tincture of opium, loperamide, or diphenoxylate. Low-dose clonidine (0.025–0.05 mg orally bid) may be used to reduce diarrhea in hemodynamically stable patients with short bowel syndrome.10 Intestinal ischemia/necrosis has been reported in patients receiving tube feeds. These cases have occurred predominantly in critically ill patients receiving vasopressors for blood pressure support in conjunction with enteral feeding. There are no reliable clinical signs for diagnosis, and the mortality rate is high. Caution should be used when enterally feeding critically ill patients requiring vasopressors.

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