Introduction

In a variety of patient populations, ranging from critical illness on mechanical ventilation and acute pancreatitis to trauma and burns, provision of early enteral feeding has been shown to improve outcome compared to the provision of parenteral therapy or standard therapy (in which no specialized nutritional support is provided) [1,2]. Compared to parenteral nutrition (PN), early enteral nutrition (EN) has been shown to maintain gut integrity and prevent gut permeability [3-5]. This reduces bacterial challenge to the immune system and results in a lower incidence of systemic endotoxemia [6]. Feeding through the gut helps set the tone for systemic immunity through stimulation of Th-2 pathways of CD4 helper lymphocyte proliferation (a process that opposes proliferation of Th-1 proinflammatory cellular pathways) [7-9]. Maintaining gut integrity and preventing increased permeability help attenuate oxidative stress and, in some cases, actually reduce disease severity such as seen in acute pancreatitis [10]. The effect of these physiologic changes is a dramatic favorable impact on patient outcome.

The most consistent outcome improved with use of EN is reduced infectious morbidity (specifically, pneumonia, abdominal abscess, and bacteremia), compared to use of PN [1]. Better gut integrity also correlates to reduced incidence of multiple organ failure syndrome [4,5,11]. In patients with head injury, early enteral feeding speeds recovery and return of cognitive function compared to PN [12]. In acute pancreatitis, enteral feeding compared to PN reduces the need for surgical intervention for associated complications of pancreatitis (such as bleeding or pancreatic gland infection) [13].

These positive outcomes associated with EN cannot be attributed to a deleterious effect of PN, as now improved outcome is seen with use of enteral feeding compared to standard therapy in which no nutritional support is provided [2]. In a large metanalyses, Lewis showed that early EN provided postoperatively in surgical critical care reduced infections, length of hospital stay, and anastomotic dehis-cence compared to standard therapy [2]. The innate benefits of early EN may be further enhanced by the addition of immune modulatory agents [14]. Adding arginine and nucleotides to an enteral formula, both of which are direct immune stimulants, may enhance proliferation of Th-2 lymphocyte cell populations. Substitution of omega-3 fatty acids from fish oil for the more routinely used omega-6 fatty acids helps modify the leukotrienes, thromboxanes, and prostaglandins produced by immune active cells and helps generate an anti-inflammatory effect. Agents such as glutamine, vitamin C, and selenium act as antioxidants, reducing the overall level of oxidative stress. A recent meta-analysis by Montejo of 26 studies in which immune active formulas were compared to standard enteral formulas showed that infections were reduced by 46-74%, organ failure was reduced by 79%, and length of stay in the ICU and hospital were reduced between 1.6 and 3.4 days with the use of immune-enhanced formulas (compared to standard formulas) [14] (Table 10.1).

These aforementioned studies highlight the role that the gut plays in critical illness and emphasizes the need for provision of early enteral feeding. At a time when the patient is at the height of critical illness with ileus, hypotension, and an active systemic inflammatory response syndrome, placement of an enteral feeding tube and initiation of EN are most important. Having the skills to place the feeding tube and the capability to monitor for complications and tolerance of EN are of utmost importance in optimizing patient outcome.

Enteral nutritional support is indicated for patients with poor volitional intake, neurological impairment, oropharyngeal dysfunction, short gut syndrome, and major trauma or burns [15]. Generally, the nutritional needs of patients who meet one or more of these criteria for less than 4 weeks are addressed with nasally or orally placed tubes; these include nasogastric tubes (NGT) or nasoenteric tubes (NET) [16]. These can be placed at the bedside, endoscopically, or fluoroscopi-cally [17]. Percutaneous tube enterostomies are placed into the stomach and/or small bowel when longer-term placement (>4 weeks) is needed.

Enteral access tube location (i.e., stomach versus small bowel) is determined by patient characteristics. Gastric feeding is preferred for most patients with normal gastric emptying and a low risk of gastric aspiration. However, in the certain clinical situations small bowel feedings may be preferred. Gastrojejunal tubes allow for simultaneous gastric decompression and small bowel feedings and are indicated when gastric outlet obstruction, gastroesophageal reflux/aspiration, and gastroparesis are present [18, 19]. Direct jejunal feeding may also be useful for patients with pancreatitis, previous gastric resection, after major abdominal surgery or an increased risk of gastric reflux and/or aspiration. Enteral access tubes may be placed by endoscopic, fluoroscopic, or surgical methods. The exact method utilized often depends on local expertise and available [20-26].

Table 10.1 Immune-enhancing Enteral Formulations

Omega-3 fish

Type of

Arginine per

oil/canola oil

Product

formula

1,000 calories

per liter

Borage oil

Manufacturer

Impact 1.5

Immune-enhancing

12.5 g

2.6 g combined

Novartis Medical Nutrition (St. Louis Park, MN)

Crucial

Immune-enhancing

10g

4.3 g combined

Nestle Nutrition (Glendale, CA)

Pivot 1.5

Immune-enhancing

8.6 g

3.9 g combined

2.86 gm/ 1000 cal

Ross Division, Abbott Labs (Columbus, Ohio)

Optimental

Immune-enhancing

«5g

Unspecified amount

Ross Division, Abbott Labs (Columbus, Ohio)

Perative

Immune-enhancing

«6g

Unspecified amount

Ross Division, Abbott Labs (Columbus, Ohio)

intlamatory

1.4 g

Unspecified amount

Ross Division, Abbott Labs (Columbus, Ohio)

intlamatory

0.0 g

9.3 g fish oil

Nestle Nutrition (Glendale, CA)

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