Enteral Routes of Nutritional Supplementation
The choice whether to use the enteral or parenteral route of feeding can be summarized by the simple statement, “if the gut works, use it.” While there are conflicting data regarding the pros and cons of parenteral feeding versus enteral feeding, it is clear that enteral feeding has some distinct benefits.
Enteral nutrients provide the majority of nutrition to the gut, which is responsible for 15% to 35% of the total body oxygen consumption and protein turnover.34 Enteral feeding offers the advantage of maintaining the gastrointestinal tract and is generally less expensive. Enteral feeding has been shown to improve gut barrier integrity, gut mass, protein content, motility, and function in piglets.35 The complete absence of enteral nutrition results in mucosal atrophy, increased gut permeability, and enzymatic dysfunction in critically ill human patients.36 Even small amounts of enteral feeding may provide benefits. In a neonatal piglet model, provision of 5% to 10% of nutritional needs by enteral feeding resulted in improved intestinal motility and lactose digestion and decreased mucosal permeability. Enteral provision of 20% of energy and nutrient needs for normal growth prevented loss of gut protein mass, whereas 40% to 60% of nutritional needs were needed to maintain normal gastrointestinal growth.35The enteral route of nutritional support is simpler as there is less concern of fluid and electrolyte overload, and this route allows fiber feeding, which cannot be achieved parenterally. That said, clinicians are often hesitant to use the enteral route in patients with gastrointestinal disorders. In the critically ill patient with poor perfusion and decreased oxygen delivery to the tissues, the gastrointestinal tract is one of the most vulnerable organs to ischemia. Decreased oxygen delivery has been shown to increase mucosal permeability, resulting in increased translocation of bacteria and absorption of bacterial toxins.37,38 Inflammatory mediators, produced in the gut as a result of ischemia, are absorbed across the damaged mucosa and enter the portal and systemic circulations; this absorption has been
■ TABLE 50.2
Equine Feeds Suitable for Use in Liquid Enteral Diet
| Feed | Digestible Energy (kcal/kg) | Crude Protein (%) | Crude Fat (%) | Crude Fiber (%) | Nonstructural Carbohydrate (%) | Ethanol- Soluble Carbohydrate (%) | Starch (%) |
| Equine Seniora (Purina Mills) | 2695 | 14.0 | 4.0 | 13.0 | 20 | 8 | bgcolor=white>9|
| Strategy Healthy Edgea (Purina Mills) | 2860 | 12.5 | 8.0 | 18.0 | 18 | 5 | 12 |
| Seniora (LMF) | 2341 | 14.0 | 4.0 | 20.0 | 5.9 | 22 | |
| Seniora (Triple Crown) | 3401 | 14.0 | 10.0 | 17.0 | 11.7 | 5.3 | 6.4 |
| Low Starcha (Triple Crown) | 3142 | 13.0 | 6.0 | 18.0 | 13.5 | 3.1 | 10.4 |
| Alfalfa pelletsb | 2190 | 16.7 | 2.3 | 24.7 | 9.3 | 7.0 | 2.1 |
| Grass pelletsb | 2050 | 13.1 | 2.6 | 22.1 | 12.1 | 6.8 | 3.3 |
| Oat hay pelletsb | 1790 | 7.74 | 2.1 | 26.2 | 20.1 | 9.9 | 4.4 |
aAs fed, manufacturer analysis.
bAs fed, average values, Equi-Analytical Laboratories, 2013.
■ TABLE 50.3
Composition of and Feeding Schedule for Naylor Diet
| Constituents | Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 |
| Electrolyte mixture | 230 | 230 | 230 | 230 | 230 | 230 | 230 |
| Water (liters) | 21 | 21 | 21 | 21 | 21 | 21 | 21 |
| Dextrose (grams) | 300 | 400 | 500 | 600 | 800 | 800 | 900 |
| Dehydrated cottage cheese (grams) | 300 | 450 | 600 | 750 | 900 | 900 | 900 |
| Dehydrated alfalfa meal (grams) | 2000 | 2000 | 2000 | 2000 | 2000 | 2000 | 2000 |
| Energy (nonprotein calories), kCal | 7400 | 8400 | 9400 | 10,400 | 11,800 | 11,800 | 12,200 |
From Naylor JM, Freeman DE, Kronfield DS: Alimentation of hypophagic horses. Comp ContEducPract Vet 6:S93, 1984.
implicated in the onset of septic shock or multiorgan failure.39 Inflammation and enterocyte injury can result in decreased motility and nutrient absorption.
In this situation, institution of forced enteral feeding may result in colic, bloat, bacterial overgrowth, diarrhea, and other complications. Because digestion increases the metabolic activity of the enterocytes, enteral feeding during states of poor oxygen delivery may actually worsen the oxygen debt and ischemic injury. In contrast, enteral nutrition has been shown to increase total hepatosplanchnic blood flow in healthy patients, resulting in greater oxygen delivery to the mucosa, suggesting that enteral feeding may be beneficial in the poorly perfused gut.39 In a rat Escherichia coli sepsis model, enteral feeding of glucose resulted in improved intestinal perfusion rates.40 Given this conflicting information, the decision on the route of administration of supplemental nutrition must be determined on a case-by-case basis, with consideration of the primary disease condition, the status of the gastrointestinal tract, and individual clinician experience. The enteral route is always preferred when the gastrointestinal tract is functional. However, patients with overwhelming bowel ischemia, inflammation, and high risk of ileus or intestinal resection may not always be the best candidates for EN and may be better off started on PN while they are gradually reintroduced to enteral nutrition.