Tube Feedings With Nasogastric and Nasoenteric Devices
Tube feedings are given to meet nutritional requirements when oral intake is inadequate or not possible and the GI tract is func-tioning normally. Tube feedings have several advantages over par-enteral nutrition: they are low in cost, safe, well tolerated by the patient, and easy to use both in extended care facilities and in the patient’s home. Tube feedings have other advantages:
• They preserve GI integrity by delivery of nutrients and medications (antacids, simethicone, and metoclopramide) intraluminally
• They preserve the normal sequence of intestinal and hepatic metabolism
• They maintain fat metabolism and lipoprotein synthesis
• They maintain normal insulin/glucagon ratios
Tube feedings are delivered to the stomach (in the case of NG intubation or gastrostomy) or to the distal duodenum or proximal jejunum (in the case of nasoduodenal or nasojejunaltube feeding). Nasoduodenal or nasojejunal feeding is indicatedwhen the esophagus and stomach need to be bypassed or when the patient is at risk for aspiration (breathing fluids or foods into the trachea and lungs). For long-term feedings (longer than 4 weeks), nasoduodenal, gastrostomy, or jejunostomy tubes are preferred for administration of medications or food. The nu-merous conditions requiring enteral nutrition are summarized in Table 36-2.
Osmolality is an important consideration for patients receiving tube feedings through the duodenum or jejunum, because feed-ing formulas with a high osmolality may lead to undesirable ef-fects, such as dumping syndrome (described below).
Fluid balance is maintained by osmosis, the process by which water moves through membranes from a dilute solution of lower osmolality (ionic concentration) to a more concentrated solutionof higher osmolality until both solutions are of nearly equal os-molality. The osmolality of normal body fluids is approximately 300 mOsm/kg. The body attempts to keep the osmolality of the contents of the stomach and intestines at approximately this level.
Highly concentrated solutions and certain foods can upset the normal fluid balance in the body. Individual amino acids and carbohydrates are small particles that have great osmotic effect. Proteins are extremely large particles and therefore have less os-motic effect. Fats are not water-soluble and do not enter into a solution in water; thus, they have no osmotic effect. Electrolytes, such as sodium and potassium, are comparatively small particles; they have a great effect on osmolality and consequently on the pa-tient’s ability to tolerate a given solution.
When a concentrated solution of high osmolality is taken in large amounts, water will move to the stomach and intestines from fluid surrounding the organs and the vascular compartment. The patient has a feeling of fullness, nausea, and diarrhea; this causes dehydration, hypotension, and tachycardia, collectively termed the dumping syndrome. Starting with a more dilute solution and increasing the concentration over several days can generally alleviate this problem. Patients vary in the degree to which they tolerate the effects of high osmolality; usually debilitated patients are more sensitive. The nurse needs to be knowledgeable about the osmolality of the patient’s formula and needs to observe for and take steps to prevent undesired effects.
The choice of formula to be delivered by tube feeding is influ-enced by the status of the GI tract and the nutritional needs of the patient. The formula characteristics evaluated include chem-ical composition of the nutrient source (protein, carbohydrates, fat), caloric density, osmolality, residue, bacteriologic safety, vita-mins, minerals, and cost.
Various major formula types for tube feedings are available commercially. Blenderized formulas can be made by the patient’s family or obtained in a ready-to-use form that is carefully prepared according to directions. Commercially prepared polymeric for-mulas (formulas with high molecular weight) are composed of protein, carbohydrates, and fats in a high-molecular-weight form (Boost Plus, TwoCal HN, Isosource). Chemically defined for-mulas contain predigested and easy-to-absorb nutrients (Osmo-lite HN). Modular products contain only one major nutrient, such as protein (Promote). Disease-specific formulas are available for various conditions, such as renal failure (Nepro), severe chronic obstructive pulmonary disease (Pulmocare). Nepro is high in calories and low in electrolytes. It is ideal for patients who re-quire electrolyte and fluid restriction. Pulmocare is high in fat and low in carbohydrates. Its high density (1.5 calories/mL) is ideal for patients who require fluid restriction, and it is also de-signed to reduce carbon dioxide production. Fiber has also been added to formulas (Jevity) in an attempt to decrease the occur-rence of diarrhea. Some feedings are given as supplements, and others are designed to meet the patient’s total nutritional needs. Dietitians collaborate with physicians and nurses in determining the best formula for the individual patient.
Many patients do not tolerate NG and nasoenteric tube feedings well. Often a medium- or fine-bore Silastic nasoenteric tube is tolerated better than a plastic or rubber tube. The finer-bore tube requires a finely dispersed formula to ensure that the patency of the tube is maintained. For long-term tube feeding therapy, a gas-trostomy or jejunostomy tube is used (see later discussion).
The tube feeding method chosen depends on the location of the tube, patient tolerance, convenience, and cost. Intermittent bolus feedings are administered into the stomach (usually by gas-trostomy tube) in large amounts at designated intervals and may be given 4 to 8 times per day. The intermittent gravity drip is another method for administering tube feedings into the stomach and is commonly used when the patient is at home. In this in-stance, the tube feeding is administered over 30 minutes at desig-nated intervals. Both of these tube-feeding methods are practical and inexpensive. However, the feedings delivered at variable rates may be poorly tolerated and time-consuming.
The continuous infusion method is used when feedings are administered into the small intestine. This method is preferred for patients who are at risk for aspiration or who tolerate the tube feedings poorly. The feedings are given continuously at a con-stant rate by means of a pump. The continuous tube feeding method, which requires a pump device, decreases abdominal distention, gastric residuals, and the risk of aspiration. However, pumps are expensive, and they permit the patient less flexibility than intermittent feedings do.
An alternative to the continuous infusion method is cyclicfeeding. The infusion is given at a faster rate over a shorter time(usually 8 to 12 hours). Feeding may be infused at night to avoid interrupting the patient’s lifestyle. Cyclic continuous infusions may be appropriate for patients who are being weaned from tube feedings to an oral diet, as a supplement for a patient who cannot eat enough, and for patients at home who need daytime hours free from the pump.
Tube feeding solutions vary in terms of required preparation, consistency, and the number of calories and supplemental vita-mins they contain. The choice of solution depends on the size and location of the tube, the patient’s nutrient needs, the type of nu-tritional supplement, the method of delivery, and the convenience for the patient at home. A wide variety of containers, feeding tubes and catheters, delivery systems, and pumps are available for use with tube feedings.