Adult Enteral Formulations - The A.S.P.E.N. Nutrition Support Practice Manual, 2nd Edition

Introduction

II. Adult Enteral Formulations

A. General-purpose formulations

1. These formulations are generally palatable, easily absorbed, eco- nomical, and useful for most patients except those with special metabolic needs or intolerance. These formulations may be the sole source of nutrition, or they may be used to supplement in- adequate oral intake.

2. Formulation characteristics

a) The osmolality for oral formulations generally ranges from isotonic to hypertonic (ie, about 300–700 mOsm per kg of water).

b) Energy density ranges from 1 to 2 kcal/mL.

c) Protein content is between 35 and 62 g/L. The protein is high quality and is commonly provided as milk protein concentrate, casein, or soy protein. These intact proteins are readily broken down to peptides and amino acids in most clinical sce- narios, with the possible exception of conditions where the bowel absorptive surface is severely eroded.

d) To minimize osmolality, carbohydrates are provided in complex forms.

e) Fats are provided as MCTs and LCTs, usually providing 29%

to 38% of calories.

B. Nutrient-dense formulations

1. These formulations are designed for use in patients who require fluid restriction (eg, patients with cardiac, renal, pulmonary, or hepatic failure).

2. Formulation characteristics

a) These formulations are generally hypertonic, as the osmolality ranges from 640 to 950 mOsm per kg of water.

b) Energy density ranges from 2 to 2.25 kcal/mL.

c) Protein sources include sodium and calcium caseinates, soy and milk protein isolates, and milk protein concentrate at 57 to 84 g/L.

d) Carbohydrate is supplied by corn syrup, maltodextrin, hydrolyzed cornstarch, and/or sucrose as 39% to 45% of total calories.

e) Fat content includes various combinations of soy, corn, safflower, MCT, and canola oils in amounts ranging from 30% to 55% of total calories.

B. Cancer

1. Weight loss and loss of functional tissue (lean body mass) is a common problem in patients with advanced cancer despite aggressive nutritional interventions. Continued deterioration of nutritional status is thought to result from changes mediated by proinflam- matory cytokines, hormones, and other tumor-derived metabolites.

Enteral formulations enriched with fish oils (omega-3 fatty acids) and other immune-promoting substrates have been used in patients with GI cancers. The results of their use as revealed in clinical studies have been promising.^15–20

2. Formulation characteristics

a) Osmolality is 635 mOsm per kg of water.

b) Energy density is 1.27 kcal/mL.

c) The protein provided is approximately 64 g/L (21% of total energy).

d) Carbohydrate sources include corn syrup solids, maltodextrin, sugar, fructooligosaccharides, gum arabic, and soy fiber.

e) Omega-3 fatty acids are provided through a unique blend of sardine oil and canola oil. Additionally, MCT oil, soybean oil, and lecithin are included as fat sources (18% of total calories).

3. Clinical studies comparing the use of immune-enhancing formulations with standard formulations when enteral support is required for patients undergoing surgery for GI cancer have yielded mixed results.^14–18The contrasts in study results are likely due to differences in study design and the insufficient number of patients enrolled in each of the studies. Despite the flaws in study design, subanalysis of many of these studies sug- gests a role for immune-enhancing formulations for malnourished patients undergoing surgery for upper GI cancer (both pre- and postoperatively).¹⁸To obtain the maximal benefits associated with using these formulations, patients should be fed for at least 5 to 7 days.¹⁹

4. Consumption of a nutritional supplement enriched with fish oil (providing 2 g/day of eicosapentaenoic acid [EPA]) for at least 3 weeks was associated with gains in weight and lean body mass and reduced levels of several inflammatory biomarkers in severely cachectic patients with pancreatic cancer cachexia.²⁰However, further research is needed to determine specifically which patients with cancer cachexia are likely to benefit from consumption of this supplement.

D. Critical care/immunomodulating

1. Patients with trauma, sepsis, burns, or postsurgical stress are in a relative state of immunosuppression. When these patients must undergo surgical procedures, they have high rates of infectious complications such as pneumonia, intra-abdominal abscess, and wound infections. Commercially prepared enteral formulations have been developed through fortifying standard enteral formulations with omega-3 fatty acids, nucleotides, arginine, and glutamine. Unfortunately, it is still unclear which of these substrates is responsible for the immune-enhancing benefits associated with these formulations. The results from clinical studies and meta- analyses suggest that the use of immune-enhancing formulations for patients posttrauma and perioperative patients may reduce the number of overall infectious complications. Furthermore, clinical trials investigating immunomodulating formulations have demonstrated decreased antibiotic use, fewer days on mechanical ventilation, decreased length of hospitalization, and, ultimately, reduced health care costs.^21–25

2. Critically ill patients have been found to have reduced levels of antioxidants (vitamins C and E, retinol, beta-carotene, and sele- nium). Whether supplementation with therapeutic levels of these

S E C T I O N I Fundamentals of Nutrition Support Practice and Management

micronutrients results in positive clinical outcomes has yet to be determined. Excess supplementation may be undesirable.

3. Formulation characteristics

a) Osmolality is moderate, at a range of 375 to 630 mOsm per kg of water.

b) Energy density ranges from 1 to 1.5 kcal/mL.

c) The high protein content (55–84 g/L) is uniquely formulated to include the following:

(1) Arginine and glutamine, which, as previously discussed, may be conditionally essential during stress and are supplemented in some of the stress formulations

(2) BCAAs, which are essential amino acids mobilized from skeletal muscle during stress. Supplemental BCAAs may preserve muscle in metabolically stressed patients; however, studies have not consistently shown improved clinical outcomes.^26,27

(3) Nucleotides, which are required by rapidly proliferating tissues such as the intestinal epithelium. Nucleotides also enhance lymphocyte proliferation and responsiveness.

(4) Carbohydrate sources, which include maltodextrin or hydrolyzed cornstarch. Fiber may also be provided as hydrolyzed guar gum or soy fiber.

(5) Fat sources, which contribute between 20% and 55% of total calories. Long-chain omega-3 fatty acid content is one of the defining characteristics of this category of formulations. Inflammatory mediators normally produced during critical illness may be minimized with administration of omega-3 fatty acids because their metabolism produces prostaglandins and thromboxanes of a less inflammatory and less immunosuppressive nature than the products of omega-6 fatty acid metabolism. Supple- mentation with omega-3 fatty acids has been shown to attenuate the inflammatory response, stabilize the nuclear factor-Κ-B complex, possess antithrombotic properties, reduce platelet adhesion, enhance neutrophil function, and support membrane stability and microvasculature profusion.¹¹

(6) Structured lipids, which are also added to some of the immunomodulating formulations. Structured lipids are chemical combinations of long-, medium-, and short-chain fatty acids on a single glycerol backbone. The resultant product has improved absorption (compared with LCT), minimizes immune dysfunction,¹¹and can provide essential fatty acids.

d) A variety of commercially prepared formulations are available with various substrates added that may modulate the immune system. According to the recommendations of the US Summit on Immune-Enhancing Enteral Therapy²⁵held in 2000, immune-enhancing formulations may be beneficial for the following:

(1) Patients undergoing major elective GI surgery, especially malnourished patients

(2) Patients with blunt and penetrating torso trauma (3) Malnourished patients undergoing surgery for head and

neck cancer

(4) Patients with severe head injury (5) Burn patients

(6) Ventilator-dependent non-septic patients at risk for infection (7) Patients needing formulations for a minimum of 5 days (8) Patients with preexisting severe sepsis. Two studies suggest

that patients with preexisting severe sepsis may have an

increased mortality rate when fed an immune-enhancing diet. A third study reported a decreased incidence of mortality. Therefore, the use of immune-enhancing diets in this patient population requires further study.

E. Diabetes/glucose intolerance

1. Patients with diabetes mellitus or stress-induced glucose intolerance have difficulty tolerating the carbohydrate content of general- purpose enteral formulations. Hyperglycemia is associated with an increased risk for infectious complications, so promoting glycemic control is important when providing nutrition support.

In addition to pharmacotherapeutic interventions, a number of commercially prepared fiber-containing, reduced carbohydrate, modified fat formulations are now available for enteral feeding for patients with poor glucose control.²⁸

2. Formulation characteristics

a) These formulations are essentially isotonic.

b) Energy density is 1 to 1.2 kcal/mL.

c) An intact protein source provides 42 to 63 g/L.

d) Carbohydrate is primarily polysaccharide, with fructose for flavor, and provides 31% to 40% of total calories.

e) Fiber content ranges from 8 to 21 g/L. Fiber sources vary but generally are derived from hydrolyzed guar gum, soy fiber, acacia, cellulose, soy polysaccharides, pectin, gum arabic, or fruit and vegetable fiber.

f) Fat provides 40% to 50% of calories; the ratio of omega-6 to omega-3 fats is variable. There is generally a greater proportion of fat calories than is recommended by the American Diabetes Association for healthy patients with diabetes.^29,30

g) There is limited published evidence that the use of these spe- cialty formulations results in improved glucose control in hos- pitalized patients, especially the critically ill. Patients with glucose intolerance should be carefully evaluated for con- comitant morbidities (eg, gastroparesis, renal impairment) when selecting the appropriate formula. Improved glycemic control can reduce diabetic gastroparesis. Important goals of nutrition therapy should include avoiding overfeeding and controlling glucose through administration of insulin, if needed.

F. Hepatic disease

1. Patients with decompensated liver disease are typically malnourished and benefit from nutritional supplementation. Some patients who have worsening encephalopathy when they receive standard enteral formulations may improve when given a formulation containing a higher BCAA-to-AAA ratio. Hepatic disease formulations should not be used in patients with nonencephalopathic manifestations of liver disease.³¹

2. Formulation characteristics

a) These formulas are hypertonic, with osmolalities of >450 mOsm per kg of water.

b) Energy density ranges from 1.2 to 1.5 kcal/mL.

c) To minimize ammonia production, protein content is low (40–46 g/L). BCAAs are provided in greater amounts than AAAs because of the increased quantities of AAAs in patients with liver failure. This abnormal AAA-to-BCAA ratio, which results in AAAs acting as false neurotransmitters, is one of the theoretical etiologies of hepatic encephalopathy.³¹

d) Carbohydrate is supplied as maltodextrin and sucrose.

e) Hepatic formulations are low in fat because absorption can be impaired as a result of cholestasis.

3. Clinical studies have not demonstrated improved outcomes in patients who received formulations high in BCAAs.^31,32Use of

S E C T I O N I Fundamentals of Nutrition Support Practice and Management

these formulations should be restricted to patients who present with grade II or greater encephalopathy or whose grade of encephalopathy worsens as nutrition support with a standard enteral formulation is advanced.

G. Impaired GI digestion or absorption

1. In certain disease states, there may be impaired absorption of nutrients. Absorption may be enhanced with the use of a chemically defined formulation. Also, because they are less viscous, chemically defined formulations are commonly used in patients with needle catheter jejunostomies to minimize catheter clog- ging. Conditions that can benefit from the use of a chemically defined formulation include the following:

a) Diffuse diseases of the intestinal mucosa, such as celiac disease, inflammatory bowel disease, and enterokinase deficiency b) Critical illness, especially after shock, trauma, sepsis, or

surgery

c) Pancreatic or bile salt deficiencies

d) Intestinal atrophy or loss of absorptive surface, as with pro- longed nothing-by-mouth status, profound malnutrition, and short-bowel syndrome

2. Formulation characteristics

a) Semi-elemental or peptide-based formulations have a lower osmolality than elemental formulations but a higher osmolality than polymeric formulations.

b) Energy density ranges from 1 to 1.5 kcal/mL.

c) Protein is supplied as crystalline amino acids (elemental formulations) or as hydrolyzed whey, casein, wheat protein, soy, or lactalbumin or a mixture of free amino acids and hydrolyzed protein.

d) The fat content ranges from very low fat (1% of total calories) to 30% of total calories.

e) Peptides may be better absorbed than free amino acids by both healthy and diseased guts.³³Individual amino acids are absorbed by a less efficient, passive diffusion mechanism.

However, tolerance and clinical outcomes with peptide-based formulations have not been demonstrated to be superior to the outcomes of polymeric formulation use.^34,35Additional con- cerns of using these products include increased cost, evidence that less complex products are less trophic to the GI tract and may increase the risk of bacterial translocation, and deleterious effects on immunocompetence.^36,37To summarize, these products should be reserved for use in patients with disease states that lead to malabsorption of conventional polymeric formulations and in patients who have demonstrated intolerance to polymeric feedings.

H. Pancreatitis

1. Traditionally, parenteral nutrition was the preferred method of providing specialized nutrition support to patients with severe pancreatitis because it was thought that not using the GI tract would result in less stimulation of and more rest for the pancreas.

However, evidence has accumulated that favors the use of enteral nutrition support for patients with pancreatitis when specialized nutrition support is warranted. (See Chapter 15.)

2. Formulation characteristics

a) Elemental and peptide-based formulations generally range in osmolality from 270 to 650 mOsm per kg of water.

b) Energy density ranges from 1 to 1.5 kcal/mL.

c) Protein content ranges from 21 to 94 g/L.

d) Carbohydrate sources include maltodextrin, and hydrolyzed cornstarch, sucrose, and soy fiber; carbohydrates generally contribute 36% to 91% of total calories.

e) Fat content ranges from approximately 1% to 39% of total calories.

f) These products are nutritionally complete and provide 100%

of the RDI in approximately 950 mL to 2 L.

3. Studies show that jejunal administration of specialized enteral nutrition support not only is well tolerated but also attenuates the inflammatory response, reduces hyperglycemia and infectious complications, and hastens recovery from the pancreatic insult compared with parenteral nutrition.^38–40While the “ideal” enteral formulation for patients with pancreatitis has not been agreed upon, clinical studies where enteral nutrition has been successfully employed have generally used peptide-based formulations with good tolerance.

I. Pulmonary disease

1. Formulations for use in patients with long- or short-term pulmonary disease are designed based on the theory that, when more energy is provided from fat and less from carbohydrate, a patient’s carbon dioxide production will be lowered and thereby the amount of carbon dioxide retention will be reduced. Addi- tionally, some investigators have demonstrated significantly reduced time on mechanical ventilation for patients who receive these formulations.^41,42

2. Formulation characteristics

a) These formulas are moderately hypertonic (330–650 mOsm per kg of water).

b) Energy density is 1.5 kcal/mL.

c) Protein content ranges from 63 to 75 g/L.

d) Carbohydrate sources include sucrose, maltodextrin, and hydrolyzed cornstarch, which contribute between 28% and 40% of total calories. Some pulmonary formulations also contain fiber (8 g/L) from sources including hydrolyzed guar gum and soy fiber.

e) Fat content ranges from approximately 38% to 55% of total calories.

f) These products are nutritionally complete and provide 100%

of the RDI in ≤1 L.

g) Formulations designed for patients with Acute Respiratory Dis- tress Syndrome (ARDS) also contain borage and sardine oils.

3. In general, studies demonstrating the benefits of pulmonary formulations over general-purpose formulations have been criticized for having a small sample size.^41,42Recent studies suggest that avoiding overfeeding of energy is as effective in reducing PCO2, as is a low-carbohydrate feeding regimen.⁴³Thus, pulmonary formulations may not provide clinically significant benefits above those of a nutrition support regimen that provides adequate (instead of excessive) energy regardless of the carbohydrate-to- fat ratio.

4. Conversely, a recent clinical study reported positive clinical outcomes with the use of an enteral formulation specifically designed for patients with ARDS. Although this product provides a high fat content, the fat composition has been altered to provide greater amounts of EPA and gamma-linolenic acid. This combination has been shown to alter membrane phospholipid makeup, sub- sequently resulting in the synthesis of the less inflammation- producing eicosanoids.⁴⁴Improved clinical outcomes included decreased length of stay and fewer ventilator days.

5. Ambulatory patients with long-term pulmonary disease often need an oral supplement because these patients have high energy needs, fatigue easily, and often have trouble eating and breathing simul- taneously, which makes it difficult to consume adequate energy and protein from common foods. Energy-dense products allow

S E C T I O N I Fundamentals of Nutrition Support Practice and Management

such patients to consume a large amount of energy and protein in a small volume and with little effort.

J. Renal disease

1. Enteral formulations for patients with renal disease must provide adequate nutrients and minimize complications such as fluid over- load, uremia, and elevated serum electrolyte and mineral concen- trations. To achieve these goals, renal formulations typically are energy dense, low in electrolyte and mineral contents, and moderate in protein content.

2. Formulation characteristics

a) These formulations are very hypertonic, with osmolalities ranging from 570 to 700 mOsm per kg of water.

b) Energy density is 2 kcal/mL.

c) Protein content ranges from 30 to 75 g/L. Protein sources include sodium, calcium and magnesium caseinates, milk protein isolate, whey protein, and free amino acids.

d) Carbohydrate sources include maltodextrin, sucrose, fructose, corn syrup, and hydrolyzed cornstarch.

e) Fat sources include safflower, soy, canola, corn, and MCT oil and contribute 35% to 46% of calories.

f) Some formulations are not nutritionally complete; some are essentially vitamin- and mineral-free, and others contain some water-soluble vitamins and no fat-soluble vitamins or minerals 3. Historically, enteral renal formulations with protein sources derived chiefly from essential amino acids were used for patients with short-term renal failure who could not tolerate dialysis, or for whom dialysis was being postponed or avoided. However, today most patients with acute renal failure are dialyzed; therefore, the use of these formulations is rarely warranted. A variety of formulations designed for patients with impaired renal function are available with modified electrolyte and micronutrient compositions.

These formulations may be appropriate for patients whose serum electrolyte and mineral levels are difficult to control.

K. Wound healing

1. Obesity, poor oxygenation, infection, aging, impaired immune function, vascular insufficiency, and some medications can impair wound healing.⁴⁵Poor nutrition can also contribute to delayed and impaired wound healing. Reportedly, enteral nutrition is associated with improvements in wound healing when compared with parenteral support.⁴⁶The optimal provision of both macro- and micronutrients is required for cellular, collagen, and connective tissue synthesis. Of the micronutrients, vitamins A, E, K, and C, thiamine, riboflavin, and zinc have been identified with improved wound healing.⁴⁶The conditionally essential amino acid arginine may also enhance wound repair.⁴⁶

2. Formulation characteristics

a) Osmolality is moderate, at a range of 300 to 630 mOsm per kg of water.

b) Energy density ranges from 1 to 1.5 kcal/mL.

c) The high protein content (55–84 g/L) generally is provided by protein sources similar to those discussed in the immune- modulating formulation section; it typically includes sodium and calcium caseinates, L-arginine, whey and wheat protein hydrolysates, soy protein isolate, and free amino acids.

Some formulations are supplemented with L-arginine and L-glutamine.

d) L-arginine may be a conditionally essential amino acid to promote wound healing. Arginine supplementation has been found not only to improve nitrogen balance but also to enhance immune function and increase hydroxyproline accumulation in healthy people supplemented with arginine for 2 weeks.⁴⁶How-

ever, the optimal amount of arginine needed to promote wound healing is unknown. As previously discussed, several formulations are available that contain not only arginine but other substrates associated with wound healing.

e) Carbohydrate sources include hydrolyzed cornstarch, sucrose, maltodextrin, and corn syrup solids. Many formulations also offer fiber supplementation with hydrolyzed guar gum, soy fiber, or soy polysaccharides.

f) Fat generally comprises 25% to 40% of total calories. Sources include palm kernel, sunflower, canola, safflower, and MCT oil; soy lecithin; and menhaden fish oil.

g) Nutrition is one of many factors that influence wound healing.

A variety of commercially prepared enteral formulations are now available that contain greater levels of vitamins A, C, and E as well as zinc. While clinical studies have found these micronutrients to play an important role in wound healing, supplementation beyond the RDI has not been shown to improve wound healing when no clinical deficiency exists. In some cases, excess supplementation may be detrimental.

3. Poor nutritional status has been linked with the development of pressure ulcers. Provision of adequate nutrition is key in preven- tion and treatment. To promote positive patient outcomes as well as wound healing, the choice of the “optimal” enteral formulation should be dictated by both the patient’s clinical status and nutritional requirements.

4. Arginine, glutamine, omega-3 fatty acids, vitamins A and C, and zinc are specific substrates frequently associated with stimulating immunocompetence and enhanced wound healing postburn. The results of clinical trials using commercially prepared enteral formulations to alter clinical outcomes are mixed.^45,47In one study, burn patients receiving a formulation high in protein and low in fat but fortified with omega-3 fatty acids, arginine, cysteine, histidine, vitamins A and C, and zinc experienced fewer overall infections and had a shortened length of hospitalization.⁴⁷Another study found that an immune-enhancing formulation fortified with omega-3 fatty acids, nucleotides, and arginine provided no significant benefits.⁴⁵The A.S.P.E.N. Clinical Guidelines for the Use of Parenteral and Enteral Nutrition in Adult and Pediatric Patients state that “there is no current role for the routine use of specific nutrients in burn patients.”⁴⁸

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