Enteral nutrition (EN) is a way of providing nutrition for patients who are unable to consume an adequate oral intake but have at least a partially functional GI tract that is accessible and safe to use. EN may augment an oral diet or may be the sole source of nutrition. Patients who have problems chewing and swallowing; have prolonged lack of appetite; have an obstruction, fistula, or altered motility in the upper gastrointestinal tract; are in a coma; or have very high nutrient requirements are candidates for a tube feeding. Although they are not routinely prescribed, tube feedings may be beneficial in cases of major trauma, acute or chronic liver failure, malabsorption syndromes, chemotherapy, or radiotherapy
and as a transition between parenteral nutrition and an oral diet. Tube feedings are contraindicated when the gastrointestinal tract is nonfunctional as in gastric or intestinal obstruction, paralytic ileus, intractable vomiting, and severe diarrhea.
Tube feedings are significantly less costly than parenteral nutrition and provide the psychological benefit of a more “normal” intake than feeding by vein. Other long-held beliefs, such as that EN has fewer complication and better outcomes than parenteral nutrition, are being challenged. Recent comparative studies suggest that there is no significant difference in outcome between the two nutritional support methods and that it is more difficult to achieve full feeding rates with EN than with PN. Also, procedure-related complications may be slightly higher with EN than with PN.
Types of Formulas
There is a vast array of EN formulas available in ready-to-use or powdered mixes specially designed to meet the needs of virtually any patient. The most common way to categorize formulas is by the complexity of protein they contain. The two major types of formulas available are standard and hydrolyzed (Table 15.2
TABLE 15.2 A COMPARISON BETWEEN STANDARD AND HYDROLYZED ENTERAL FORMULAS
||Most are 1.0–1.2
|Sources of: Protein
||Hydrolyzed casein, whey, or soy protein; amino acids
||Maltodextrin, sucrose, corn syrup solids
||Maltodextrin, modified corn starch
||Vegetable oil, MCT, fish oil
||Similar to oral diet
||Many are higher in CHO and much lower in fat than usual mixed diet
||Many are isotonic
||Most are hypertonic
||Most are low
||Fiber-enriched formulas are available
Standard formulas, also known as polymeric or intact formulas, are made from whole proteins as found in foods. (e.g., milk, meat, eggs) or protein isolates. Because they contain complex molecules of protein, carbohydrate, and fat, standard formulas are intended for patients who have normal digestive and absorptive capacity. They are complete with regard to vitamins, minerals, and trace elements. Like oral supplements, standard tube feedings come in a wide variety such as standard, high protein, high calorie, and disease specific.
Partially hydrolyzed formulas contain proteins that are partially digested into small peptides. The protein in completely hydrolyzed formulas, frequently referred to as elemental formulas, is in its simplest form: free amino acids. Hydrolyzed formulas also provide other nutrients in simpler forms that require little or no digestion. For instance, the fat content is very low and in the form of medium-chain triglycerides (MCT). Hydrolyzed formulas are intended for patients with impaired digestion or absorption such as people with inflammatory bowel disease, short-gut syndrome, cystic fibrosis, and pancreatic disorders.
Additional Factors to Consider When Choosing a Formula
The first step in choosing a formula is to select either a standard or hydrolyzed formula based on the patient’s ability to digest and absorb foodstuffs. Other characteristics of the formula to evaluate when choosing a formula are the nutrient density, osmolality, fiber and residue content, and the feeding equipment available.
Routine formulas provide 1.0 to 1.2 cal/mL, whereas high calorie formulas provide 1.5 to 2.0 cal/mL. The calorie density of a product determines the volume of formula needed to meet the patient’s estimated needs. For instance, a patient who needs 2000 calories can meet her or his calorie needs with 2000 mL of a 1.0 cal/mL formula. However, if that patient is volume- or fluid-restricted, a better option is 1000 mL of a 2.0 cal/mL formula. The following guidelines are useful for evaluating calorie density:
||Elevated fluid need
||Strict volume limitations
Although the Harris-Benedict equation is commonly used to calculate calorie requirements based on the patient’s age, gender, height, weight, level of physiologic stress, and activity level, a short-cut method often yielding similar results with fewer calculations is to simply multiply the patient’s weight in kilograms by
25 to 35 cal/kg for most adults
21 cal/kg for critically ill obese adults
The water content of tube feedings varies with the caloric concentration and is generally as follows:
||mL of Water/Liter
Adults in general need approximately 1 mL/cal consumed daily, or urine output + 500 mL/day. Patients with fever, vomiting, diarrhea, blood loss, draining fistulas, or burns have higher fluid requirements. Whether or not the patient needs additional water to meet fluid requirements depends on his or her medical status and how much fluid is given through the tube feeding and flushing.
When calculating volume, it is important to note the volume of formula required to obtain 100% of the recommended intake for vitamins and minerals. If the tube feeding is the patient’s sole source of nutrition, the volume provided must furnish adequate levels of essential nutrients.
Protein density ranges from low to high. Low-protein formulas designed for patients with chronic renal failure may provide as little as 30 g protein/liter of formula. Conversely, the protein content of high nitrogen formulas ranges from 44 to 63 g protein/liter. “Routine” standard formulas provide 34 to 43 g protein/liter. Adding a protein module to a tube feeding can increase protein density without significantly impacting the volume of formula needed.
Healthy adults need 0.8 gm/kg of protein daily. Protein needs increase in response to surgery, stress, trauma, burns, and catabolic states. Patients with renal impairments need to restrict protein intake.
Although the concentrations of fat and carbohydrate also vary among formulas, they are usually not considered unless they are important because of disease. For instance, high-fat formulas are available for patients with respiratory disease and modified-fat formulas are designed for patients with malabsorption. A number of diabetic formulas are available, as are electrolyte-modified formulas for renal disease.
In enteral formulas, osmolality is determined by the concentration of sugars, amino acids, and electrolytes. Isotonic formulas have approximately the same osmolality as blood and are well tolerated. Generally, the more digested the protein, the greater the osmolality; thus, hydrolyzed formulas are higher in osmolality than standard formulas. For most people, osmolality does not impact tolerance. However, some patients develop diarrhea when a hypertonic formula is infused into the small intestines. Initiating the formula at a slow rate and advancing the rate gradually and slowly improves tolerance.
Fiber and Residue Content
Although they are not synonymous, the terms fiber and residue are frequently used interchangeably. Fiber stimulates peristalsis, increases stool bulk, and is degraded by gastrointestinal bacteria to short-chain fatty acids that promote repair and maintenance of the intestinal lining. Fiber combines with undigested food, intestinal secretions, and other cells to make residue. Fiber is one component of residue, but residue encompasses other substances as well.
The residue content of enteral formulas varies greatly. Hydrolyzed formulas are essentially residue free because they are completely absorbed. Most standard formulas are low in
residue; because low-residue formulas are not likely to cause gas or abdominal distention, they are most suited as an initial feeding in patients who have been on bowel rest, in patients with certain gastrointestinal disorders, or in patients who have had gastrointestinal surgery.
Some standard formulas contain fiber. Blenderized formulas, a source of natural fiber, have approximately 4 g of fiber/L. The fiber content of fiber-enriched formulas is generally 10 to 14 g/L. Fiber-enriched formulas may help to normalize bowel function in people with constipation or diarrhea but may cause gas and bloating. Because fiber helps to maintain GI integrity, formulas with added fiber should be considered when EN is to be used for a long period.
Tubing size and pump availability may impact formula selection. Generally, high-fiber formulas have a high viscosity and require a large bore tube (8F or greater) to prevent clogging. Adding a modular product to a formula to increase the nutrient or calorie density may also necessitate the use of a larger tube. Hydrolyzed formulas have very low viscosity but should be delivered by pump to ensure controlled administration.
The feeding route, or placement of the feeding tube, depends on the patient’s medical status and the anticipated length of time the tube feeding will be used. Transnasal tubes, of which the nasogastric (NG) tube is the most common, are generally used for tube feedings of relatively short duration (i.e., less than 3 to 4 weeks). Ostomy feedings are preferred for permanent or long-term feedings because they can be hidden under clothing and eliminate irritation to the mucous membranes. Percutaneous endoscopic gastrostomy (PEG) tubes are placed with the aid of an endoscope. The correct placement of any feeding tube should be determined by radiographs of the chest taken before the first feeding is initiated. Table 15.3
summarizes the advantages and disadvantages of various feeding routes.
TABLE 15.3 ADVANTAGES AND DISADVANTAGES OF VARIOUS FEEDING ROUTES
||Inability to safely and adequately consume oral intake
Short-term feeding (<6 wk) with functional gastrointestinal tract
|Easy to place and remove tube
Uses stomach as reservoir
Can use intermittent feedings
Dumping syndrome less likely than with NI feedings
|Contraindicated for clients at high risk for aspiration
Potentially irritating to the nose and esophagus
May be removed by uncooperative or confused patients
Not appropriate for long-term use
Unaesthetic for patient
||Short-term feeding for patients at high risk of aspiration, delayed gastric emptying, or gastroesophageal reflux disease (GERD)
||Less risk of aspiration, especially important for patients who have impaired gag or cough reflex, decreased consciousness, ventilator dependence, or a history of aspiration pneumonia
||Increased risk of dumping syndrome
Not appropriate for intermittent or bolus feedings
Not appropriate for long-term use
Unaesthetic for patient
||For long-term use in patients with a functional gastrointestinal tract
Frequently used for patients with impaired ability to swallow
|Same advantages as NG, but more comfortable and aesthetic for patient
Confirmation of tube placement easier
Cannot be misplaced into the trachea
|PEG insertion contraindicated for clients who cannot have an endoscopy
Risk of aspiration pneumonia in clients with GERD
Stoma care required
Danger of peritonitis
Potential for tube dislodgment
||For long-term use in patients at high risk for aspiration pneumonia and in clients with altered gastrointestinal integrity above the jejunum
For short-term use after gastrointestinal surgery
|Low risk of aspiration
No risk of misplacing tube into the trachea
More comfortable and aesthetic for clients than transnasal tubes
Because motility resumes more quickly in the intestines than in the stomach after gastrointestinal surgery, feedings can begin sooner than other feedings
|Small-diameter tubes easily become clogged
Peritonitis can occur from tube dislodgment
Cannot be used for intermittent or bolus feedings
Stoma care required
Formulas may be given intermittently or continuously over a period of 8 to 24 hours. The rates may be regulated either by a pump or by gravity drip. The type of delivery method to be used depends on the type and location of the feeding tube, the type of formula being administered, and the patient’s tolerance.
Intermittent Tube Feedings
Intermittent feedings are administered throughout the day in equal portions of 200 mL to 300 mL of formula over 30 to 60 minutes every 4 to 6 hours, usually by gravity drip. The number of feedings given per day depends on the total volume of feeding needed. Feedings may be spaced throughout an entire 24-hour period or may be scheduled only during waking hours to give patients time for uninterrupted sleep. Intermittent feedings are generally used for noncritical patients, home-tube feedings, and patients in rehabilitation. They offer the advantage of resembling a more normal pattern of intake and they allow the client more freedom of movement between feedings. Tolerance of intermittent feedings is optimized by infusing the formula at room temperature. To decrease the risk of aspiration, gastric residuals are checked before each feeding until tolerance is clearly established. Residuals should be less than 150 mL before each intermittent feeding; replace aspirate to reduce the loss of electrolytes and gastric juices.
Bolus feedings are a variation of intermittent feedings. The formula is poured into the barrel of a large syringe attached to the feeding tube. A large volume of formula (500 mL maximum; usual volume is 250 to 400 mL) is delivered relatively quickly, usually in less than 15 minutes. These rapid feedings are given four to six times per day. They are used only for feedings into the stomach. Bolus feedings may be poorly tolerated and often cause dumping syndrome: nausea, diarrhea, glucosuria, distention, cramps, vomiting, and increased risk of aspiration.
Continuous Drip Method
Continuous drip feedings are given at a constant rate over a 16- to 24-hour period to maximize tolerance and nutrient absorption. Infusion pumps are used to ensure consistent flow rates. This method is recommended for feeding of critically ill clients because it is associated with smaller residual volumes, lower risk for aspiration, a decrease in the severity of diarrhea, and a decrease in the hypermetabolic response to stress when compared to other delivery methods. Continuous feeding is also preferred for feedings delivered into the jejunum; it is frequently used to begin a feeding into the stomach (i.e., NG, gastrostomy, or PEG).
Continuous feedings should be interrupted every 4 hours so that water can be infused into the line to clear the tubing and hydrate the client. Gastric residuals are measured every 4 to 6 hours. If the volume of gastric residual exceeds the volume of formula given over the previous 2 hours, it may be necessary to reduce the rate of feeding.
A variation of continuous drip feedings, cyclic feedings deliver a constant rate of formula over 8 to 16 hours often during sleeping hours although extra care must be taken to keep the head of the bed continuously elevated more than 30° to avoid aspiration. Because there is “time off,” the rate of infusion tends to be higher than for continuous
feedings. Cyclic feedings are usually well tolerated and are often used to maintain a reliable source of nutrition while transitioning from total EN to an oral intake or in noncritical, undernourished patients unable to meet their nutritional needs orally.
Initiating and Advancing the Feeding
Before initiating a feeding, tube placement is verified ideally by radiography and bowel sounds are confirmed to be present. Other common verification methods, such as aspirating gastric contents and pH testing, are less reliable. Elevate the patient’s upper body to at least a 30° angle during the feeding and for at least 30 minutes afterward to reduce the risk of aspiration.
Regardless of the access route, tube feeding formulas are initiated at full strength. The previous practice of diluting hypertonic feedings has not been shown to improve tolerance, prolongs the period of inadequate nutrition support, and may increase the risk of bacterial contamination. Initiating feedings at full strength has not been found to cause tube feeding intolerance or diarrhea.
Although facility policies vary, initial feedings may begin at 10 to 40 mL/hour and advance by 10 to 20 mL/hour every 8 to 12 hours as tolerated until the desired rate is achieved. The commonly recommended maximum flow rate for gastric feedings is 125 mL/hr; higher volumes may increase the risk of aspiration. The maximum flow rate for small bowel feedings is determined by individual tolerance. Usually, rates of 140 to 160 mL/hr are well tolerated. Using a standard feeding progression schedule helps to ensure timely progression of feedings to the goal rate: the sooner the goal rate is achieved, the sooner the patient’s nutritional needs are met.
Tolerance may be a problem for patients who are malnourished, who are under severe stress, who have not eaten in a long time, or who are given hypertonic formulas. Starting the feeding at the lower end of the recommended range and progressing slowly generally improves tolerance.
Tolerance and Safety Issues
Tolerance and safety can be maximized by careful attention to details.
Avoiding Bacterial Contamination
Improper handling of formulas increases the risk of bacterial contamination, which causes what is commonly known as food poisoning. In a population of patients who are malnourished and, therefore, immunologically compromised, food poisoning is a serious tube feeding complication. To reduce the risk of bacterial contamination, closed feeding systems are recommended. Precautions to take when open feeding systems are used include
Use clean equipment.
Wash hands thoroughly before handling the formula.
Clean the top of the formula can before opening.
Label unemptied cans with the date and time of opening.
Cover opened cans; store mixed or diluted formulas in clean containers.
Refrigerate unused formula promptly.
Discard unlabeled formula and all opened cans within 24 hours.
Rinse the feeding container and extension tubing with water before adding new formula.
Never add a supply of new formula to old formula.
Flush the tube with water before and after each use.
Hang feeding solutions for less than 6 hours.
Change the feeding container and extension tubing every 24 hours.
Aspiration is one of the most dangerous complications of EN. Patients with inhibited cough reflex related to debilitation, unconsciousness, or pulmonary complications are at high risk for aspiration as are those with delayed gastric emptying or gastroesophageal reflux. Preventative measures to avoid aspiration are to
Confirm proper placement of the feeding tube by radiograph prior to initiating a feeding so that formula is not mistakenly infused into the lungs.
Elevate the head of the bed 30 to 45° during the feeding and for approximately 1 hour afterwards to help maintain normal functioning of the lower esophageal sphincter.
Monitor gastric residuals to identify delayed gastric emptying, which places the patient at risk for aspiration. A continuous drip method of deliver may be necessary to control gastric residuals.
Use the smallest diameter feeding tube possible.
Consider a nasointestinal or jejunostomy feeding for patients with impaired cough reflex.
Maintaining Tube Patency
Periodic flushing of the tube with water helps to ensure patency. The often cited standard for maintaining patency is to flush with
15 to 30 mL of water before and after medications
20 to 60 mL of water every 4 hours during continuous feedings
20 to 60 mL of water after each intermittent feeding
20 to 60 mL of water any time the feeding is interrupted
If the tube becomes clogged, a 60 mL syringe containing 30 to 60 mL of warm water is recommended.
Giving Medications by Tube
Although many medications are frequently given through feeding tubes to patients who are unable to swallow, they should never be given while a feeding is being infused. Some drugs become ineffective if added directly to the enteral formula; also, adding drugs to the formula may result in a clogged tube. It is important to stop the feeding
before administering drugs and to make sure the tube is flushed with 15 to 30 mL of water before and after the drug is given. If more than one drug is given, flush the tube between doses with 5 mL of water.
Other drug considerations include the following:
Drugs absorbed from the stomach should never be given through a nasointestinal tube.
The liquid form of a medication diluted with 30 mL of water should be used for feeding tube administration. If there is no alternative, a drug can be crushed to a fine powder and mixed with water before it is administered. Slow-release drugs should never be crushed.
Dilute highly viscous and hyperosmolar liquid medications with 10 to 30 mL of water before administering.
Drugs should be given orally whenever possible.
Tube feeding may need to be temporarily stopped to permit drug administration on an empty stomach or to avoid drug-nutrient interaction. Some experts recommend stopping a continuous feeding for 15 minutes before and after the delivery of the medication.
Close monitoring is essential to ensure that the patient is tolerating the EN regimen and that it is adequately meeting the patient’s needs. In the hospitalized patient, monitor
Daily weight to detect fluid shifts.
Daily intake and output.
Gastric residuals every 4 hours. Return all aspiration secretions to the stomach because they contain nutrients, electrolytes, and digestive enzymes.
The character and frequency of bowel movements.
For signs and symptoms of intolerance: vomiting, nausea, diarrhea, constipation.
Daily electrolyte levels, BUN, and creatinine until goal rate is achieved; thereafter 2 to 3 times/week. Minerals and a weekly blood count may be ordered.
Tube site for placement, infection.