Enteral Nutrition

If tube feeding is needed for ≤ 4 to 6 weeks, a small-caliber, soft nasogastric or nasoenteric (eg, nasoduodenal, nasojejunal) tube made of silicone or polyurethane is usually used.

If a nasal injury or deformity makes nasal placement difficult or if tube feeding is needed for > 4 to 6 weeks, a gastrostomy or jejunostomy tube should be placed.

Jejunostomy tubes are useful for patients with contraindications to gastrostomy (eg, gastrectomy, bowel obstruction proximal to the jejunum). However, these tubes do not pose less risk of tracheobronchial aspiration than gastrostomy tubes, as is often thought. Jejunostomy tubes are easily dislodged and should be used for patients who must have jejunal access (eg, after esophagectomy or gastrectomy).

In patients who are ventilated mechanically, orogastric or other oroenteric tubes can be placed.

In alert patients, nasogastric or nasoenteric tubes may be placed blindly at the bedside; correct placement is confirmed with radiography. Otherwise, tubes may be placed endoscopically, surgically, or by using interventional radiology. Choice often depends on physician capabilities and patient preference; however, surgical placement is used if endoscopic and radiologic placement is unavailable, technically impossible, or unsafe (eg, because of overlying bowel). Open or laparoscopic techniques can be used.

(See also How To Insert a Nasogastric Tube.)

Liquid formulas for enteral nutrition may be polymeric, partially hydrolyzed, or completely hydrolyzed. Formulas for specific disorders are available. Modular products are available to adjust a feeding regimen to meet a patient's individual needs.

Polymeric formulas contain intact protein, carbohydrate, and fat, and some formulas contain added fiber. These products are designed to provide a complete, balanced diet and to meet needs for micronutrients. They are the most commonly used formulas. Most commercially available products are lactose free; products that contain milk are generally made with lactose-free milk and are intended for oral consumption and not for an enteral tube. Formulas made from blenderized foods are also available commercially or can be prepared at home.

Partially or completely hydrolyzed formulas have protein that is broken down into small peptides (partially hydrolyzed) or free amino acids (completely hydrolyzed, sometimes called elemental). These formulas are low in fat with a high percentage of fat as medium-chain triglyceride (MCT) oil. These formulas are designed for patients with malabsorption disorders. Partially or completely hydrolyzed formulas are commercially available.

Specialized formulas include partially hydrolyzed or completely hydrolyzed formulas but also include those designed for specific disorders such as renal disease or diabetes. Other disorder-specific formulas include those to support wound healing or to modify the immune response to trauma or metabolic stress. Some specialty formulas meet an important clinical need (for example, for patients with renal failure who require potassium, phosphorus, and fluid restriction), whereas other specialty formulas may not have strong evidence that clinical outcomes justify their expense. Specialized formulas are commercially available.

Modular products contain a single nutrient or occasionally 2 nutrients. Protein modular products can be used in addition to a commercially available polymeric formula to increase the total protein delivery to a patient with high protein demands. Combined products such as those with only carbohydrate and fat may be used for patients who require additional energy without additional protein; these are often mixed into food but may be used to supplement an enteral formula. Fiber modular products are available as soluble fiber or a blend of soluble and insoluble fiber for patients who may need additional fiber to help manage diarrhea or constipation. Modular products are commercially available.

Enteral nutrition administration depends on the type of feeding tube and tolerance to feeding.

Nasogastric or gastrostomy tube feeding may be provided as bolus feedings several times/day. Bolus feeding is more physiologic and may be preferred for stable patients with diabetes because it allows for insulin dosing tailored to the carbohydrate content of each bolus. The total daily volume of formula is divided into 4 to 6 separate feedings that are injected through the tube with a syringe or infused by gravity from an elevated bag. Patients should be sitting upright at 30 to 45° during tube feeding and for 1 to 2 hours afterward to minimize incidence of aspiration pneumonia and to allow gravity to help gastric emptying. If patients do not tolerate bolus feeding because of nausea or vomiting (and do not improve with a change in enteral formula), continuous feeding may be indicated.

Nasoduodenal, nasojejunal, or jejunostomy tube feeding requires an enteral feeding pump. Bolus feeding is not appropriate because the small intestine does not have the reservoir capacity to tolerate large volumes of formula over a short period of time. Feedings are typically started with a continuous infusion and then may be infused over a shorter period of time at a higher rate (ie, cycling) to allow the patient to have some time without feeding for activities of daily living. As with bolus feeding, patients should be sitting upright at 30 to 45° during tube feeding to reduce risk of aspiration pneumonia.

Pump-assisted feeding may be started at 20 to 30 mL/hour then advanced by 10 to 20 mL/hour every 4 to 8 hours until the goal rate required to provide the goal volume is achieved. The goal volume for formula is the patient's energy requirements divided by the kcal/mL of the formula (eg, for a daily energy requirement of 2400 kcal and a formula of 1 kcal/mL, 2400 mL/day or 100 mL/hour if flow is continuous). Post-pyloric feeding can be started at a lower rate and advanced slowly if the clinician is concerned that the patient may not tolerate the enteral formula (eg, develops abdominal discomfort, bloating, or diarrhea). The maximum rate of jejunal feedings is typically 125 mL/hour; however, some patients may tolerate a higher rate.

Bolus feeding is typically started with half of the desired goal volume and advanced with subsequent bolus feedings until the goal volume and frequency are achieved.

Water requirements must be met with additional water flushes via syringe through the enteral access device. Formulas range in caloric density from 1.0 to 2.0 kcal/mL; as the concentration increases, water content per kcal decreases. Clinicians should calculate the patient's water requirements (a common method for enteral nutrition is to use 1 mL water/kcal provided), subtract the amount of water provided from the formula (obtained from product information from the manufacturer), and then divide the remaining water into 4 to 6 water flushes/day. Patients with jejunal access may not tolerate large-volume water flushes (eg, > 150 to 200 mL) and may need more frequent small-volume flushes to meet hydration needs. The minimum recommended water flush is 30 mL every 4 hours to maintain tube patency. Water given with medications should also be added to the patient's total water delivery. For patients who are hospitalized, fluid deficits can be made up using IV fluids, particularly if fluid losses (eg, due to vomiting, diarrhea, sweating, or fever) exceed normal amounts.

Complications of enteral nutrition are common, and some can be serious (see table Complications of Enteral Nutrition).