determining factor for initiating tube feeding. EN should be used with caution in

patients with severe necrotizing or hemorrhagic pancreatitis, distal high-output

enterocutaneous fistulae, hypotension with significant inotropic support, GI ischemia,

and partial bowel obstruction.

3,4 Contraindications to EN generally include diffuse

peritonitis, complete bowel obstruction, severe paralytic ileus, intractable vomiting

or diarrhea, severe malabsorption, severe GI bleed, inability to access the GI tract,

and when aggressive intervention is not warranted or desired. Frequent reassessment

is recommended because patients may become candidates for EN as the condition

improves or resolves.

FEEDING TUBE PLACEMENT AND SITE OF

FORMULA DELIVERY

CASE 37-2

QUESTION 1: D.S., an 80-year-old man, was hospitalized 7 days ago after collapsing while grocery shopping.

He was diagnosed with ischemic stroke, and his condition has changed little since admission. D.S. is estimated

to be 5 feet 10 inches tall; his weight is 62 kg; clinic notes from 6 months ago show his weight at 69.3 kg. He

appears thin with mild wasting of arm and leg muscles. His maintenance IV drip is 5% dextrose/0.45% sodium

chloride with KCl 10 mEq/L at 80 mL/hour. Laboratory evaluation today shows the following:

Sodium, 141 mEq/L

Potassium, 3.7 mEq/L

Chloride, 106 mEq/L

Glucose, 88 mg/dL

SCr, 0.9 mg/dL

Serum albumin, 3.2 g/dL

D.S. failed his swallow study today and will remain NPO for 7 weeks prior to a repeat swallow study, which

he must pass before an oral diet is initiated. Nutrition support via tube feeding is ordered.

What is the most appropriate type of feeding tube placement and site for formula delivery?

The type of tube placement and site of formula delivery for EN are determined by

the anticipated duration of tube feeding, disrupted region or process in the GI tract,

and the risk of aspiration. Figure 37-1 illustrates the two basic types of tube

placement—nasal versus ostomy—and the sites available for formula delivery (i.e.,

gastric, duodenal, or jejunal). The name of the feeding route usually includes both the

type of tube placement and the site of formula delivery. For example, nasogastric

(NG) indicates nasal placement with gastric delivery of formula, whereas

gastrostomy indicates ostomy placement with gastric delivery of formula.

Nasal tube placement is preferred for short-term use in patients expected to resume

oral feeding and without obstruction of nasal, pharyngeal, or esophageal passages.

The tube is secured to the nose or cheek after placement to prevent the tube from

being displaced.

Clinically evident injury from nasal intubation is very low, but patients may suffer

mucosal trauma in the nasopharynx.

7–9 Pharyngitis, sinusitis, otitis media, and

incompetence of the lower esophageal sphincter are associated with nasal tubes,

especially large-bore tubes. The incidence of inadvertent pulmonary placement of

small-bore feeding tubes is 4% or less.

7 Radiographic confirmation of tube

placement is mandatory to rule out pleural perforation and pulmonary intubation in

unconscious patients and remains the standard to ensure correct tube placement in all

patients. Tube displacement is a potential complication occurring in 25% to 41% of

cases.

7

Feeding ostomies (tube enterostomies) generally are reserved for long-term EN,

interpreted as anywhere from 4 weeks to 6 months, depending on clinical

circumstances and the type of tube enterostomy placed. Access for enterostomies can

be achieved through open surgery, laparoscopy, or via percutaneous access.

Percutaneous access is usually performed under local anesthesia or conscious

sedation by endoscope (percutaneous endoscopic gastrostomy [PEG] or jejunostomy

[PEJ]) or by radiography (percutaneous radiologic gastrostomy [PRG] or

jejunostomy), including fluoroscopy, ultrasound, or computed tomography.

7,10,11 The

major advantage of radiologic compared with endoscopic placement is reduced

contamination of the puncture site by oral pharyngeal microorganisms, which are

implicated in the 5.4% to 30% incidence of site infections.

9 Most patients requiring

long-term EN receive either a PEG or a PRG. Less than 5% receive a combined

gastric and jejunal access (PEGJ or G-J) tube.

12

Figure 37-1 Nasoenteric and enterostomy feeding sites.

p. 770

p. 771

Endoscopic placement is contraindicated when obstruction prevents passage of the

endoscope, but radiographic placement may be possible in such cases. Relative

contraindications to percutaneous feeding tube placement include inability to see the

endoscopic light through the abdominal wall (e.g., morbid obesity, massive ascites),

peritoneal dialysis, coagulopathy, gastric varices, portal hypertension, hepatomegaly,

and neoplastic or infiltrative disease of the gastric or jejunal wall.

7–11

,

13 Prior total or

subtotal gastrectomy, including Roux-en-Y gastric bypass and gastric sleeve for

obesity reduction, prevents percutaneous gastrostomy placement, but percutaneous

jejunostomy may be possible. Major advantages of percutaneous access are shorter

procedure time and lower cost; morbidity and mortality appear to be similar to

surgical feeding tube access.

13 Major complications, such as aspiration, peritonitis,

hemorrhage, gastrocutaneous fistula formation, necrotizing fasciitis, gastric

perforation, and migration of the tube through the gastric wall, are generally low but

have been reported in up to 2.5% of patients.

7

Formula delivery into the stomach is preferred because it is the most

physiologically normal feeding site. Stimulation of normal digestive processes and

hormonal responses associated with eating occur. The stomach serves as a reservoir,

typically allowing tolerance of bolus, and intermittent or continuous feeding. Gastric

feeding requires adequate gastric motility to prevent accumulation of formula in the

stomach. Patients with gastric outlet obstruction, gastroparesis, gastric distension, or

gastroesophageal reflux are poor candidates for gastric feeding.

Postpyloric feeding into the duodenum or jejunum may be appropriate when gastric

dysfunction or disease is present, for early postoperative feeding when gastric

emptying may be impaired, when pancreatic stimulation is to be minimized, or when

risk of aspiration is high. Critically ill patients are at risk for aspiration and

ventilator-associated pneumonia, with a 25% to 40% incidence of aspiration in

patients with long-term nasoenteric feeding.

14 Evidence of reduced aspiration and

improved outcomes with postpyloric feeding remains controversial.

4 A study in 428

patients using pepsin as a marker of aspiration showed steady decline in the pepsin

positive samples moving from stomach (34.4%) to proximal, mid-, and distal

duodenum (20.8%, 17%, and 7.6%, respectively).

15 Conversely, a meta-analysis of

17 randomized, controlled trials failed to find a benefit of postpyloric feeding on

aspiration risk and ventilator-associated pneumonia.

16 Poor differentiation between

aspiration of oral secretions and aspiration from the GI tract occurs in many studies;

however, this is avoided by using pepsin as a marker. Tube placement beyond the

ligament of Treitz (into the jejunum) may be best for patients at risk of tube migration

and aspiration; however, studies are not conclusive, and either gastric or small

bowel feeding is considered acceptable in the intensive care unit (ICU) setting.

D.S. will require EN for at least 7 weeks and may require longer-term EN

depending on repeat swallow study results. A feeding ostomy is appropriate for him.

Because there does not appear to be a contraindication to feeding into the stomach, a

gastrostomy is appropriate. He will likely have a PEG or PRG placed to avoid the

need for surgery.

FORMULA SELECTION

CASE 37-2, QUESTION 2: What factors should be considered in selecting an enteral formula for D.S.?

Enteral formula selection is based on nutrient requirements, fluid restrictions, and

the extent of impaired digestion and absorption. Many enteral formulas are available,

but because of similarities between products, institutional formularies are generally

limited but still provide an adequate selection to meet a variety of patient needs.

Categorizing formulas as listed in Table 37-2 simplifies the formula selection

process. There are three major categories of enteral formulas: (a) polymeric

formulas, (b) oligomeric formulas, and (c) specialized formulas.

Polymeric Formulas

Polymeric formulas are designed for patients with full digestive capability and are

used most often. Osmolality is decreased and palatability increased in these formulas

by the use of relatively intact nutrients, including whole (i.e., intact) proteins.

Administration of approximately 1.5 to 2 L of most polymeric formulas provides

100% of dietary reference intakes (DRI) for vitamins and minerals; thus, these

formulas sometimes are called “complete” formulas.

17 As indicated in Table 37-2,

the relative cost for polymeric formulas tends to be less than that of oligomeric or

specialized formulas, although prices can vary considerably based on specific

nutrient content (e.g., omega-3 fatty acids [ω-3FAs], antioxidants).

Oligomeric Formulas

Oligomeric formulas, also called predigested, monomeric, or chemically defined

formulas, are designed for patients with reduced digestive function. Pancreatic

enzyme activity is required for digestion of oligosaccharides (carbohydrates) and

fats. Brush-border disaccharidase activity also is required. Minimal digestion is

required, however, for the hydrolyzed protein and medium-chain triglyceride (MCT)

components. These formulas can be used for patients with pancreatic insufficiency,

reduced mucosal absorption, or reduced hydrolytic capability. Although the Canadian

Clinical Practice (CCP) guidelines noted patients with GI complications, such as

short bowel syndrome and pancreatitis, may benefit from oligomeric formulas,

insufficient data were available to make recommendations regarding use of such

formulas.

18–20 Pancreatic enzyme supplementation combined with polymeric formulas

may be tried before oligomeric formulas for some patients with pancreatic

insufficiency (e.g., cystic fibrosis, chronic pancreatitis).

Two subgroups of oligomeric formulas can be differentiated based on the protein

source. True “elemental” formulas contain free amino acids, whereas “peptidebased” formulas contain oligopeptides plus dipeptides, tripeptides, and free amino

acids from hydrolysis of protein. Amino acids require no digestion, but the sodiumdependent active transport mechanism is somewhat slow and inefficient with only

about one-third of dietary protein absorbed as free amino acids; the remaining twothirds are absorbed as dipeptides and tripeptides.

21,22 Specific carriers for dipeptide

and tripeptide absorption, located in small bowel mucosa, do not compete with the

free amino acid transport system. Peptides longer than three amino acids require

further hydrolysis within the lumen of the small bowel before they are absorbed.

Most peptide-based formulas contain a significant portion of peptides requiring

hydrolysis before absorption. No well-designed, randomized, controlled trials have

clearly delineated clinical differences in elemental (free amino acid) versus peptidebased formulas. Elemental formulas generally have the lowest-fat content (10% or

less of calories from fat). Peptide formulas typically contain one-fourth to one-third

of calories from fat, but provide 20% to 70% of the fat as MCT to minimize the risk

of malabsorption.

Oligomeric formulas are typically hypertonic owing to their partially digested

nature; peptide-containing formulas are typically less hypertonic than free amino acid

products. Osmotic diarrhea can occur because of the hyperosmolality; however, the

CCP guidelines meta-analysis found no difference in diarrhea occurrence between

patients receiving intact protein and those receiving peptide-rich formulas.

18 Taste

and cost are disadvantages of oligomeric formulas. Flavoring packets are available

and newer formulas may be better accepted, but patients commonly complain of a

bitter taste when these formulas are taken orally. In general, patients do not tolerate

adequate oral consumption of an oligomeric formula. As shown in Table 37-2, the

cost of oligomeric formulas tends to be greater than 10 times the cost of polymeric

formulas.

p. 771

p. 772

Table 37-2

Generic Groups and Subgroups of Enteral Formulas with Relative Costs

Type of Formula Relative Cost

a

,

b Examples

Polymeric Formulas

c

Standard Caloric Density, Standard (or High Nitrogen) Content with Varied Fiber Content

Fiber free for oralsupplement or

tube feeding

$ Ensure; Nutren 1.0

Low fiber (from 1– g/1,000

kcal)

$ Nutren Probalance

d

Moderate fiber (>9–<14 g/1,000

kcal)

$ Ensure with fiber; Fibersource HN

d

High fiber (≥14 g/1,000 kcal) $ Glucerna; Jevity 1.2 Cal

d

; Nutren 1.0 with fiber

Standard-Nitrogen Content, Fiber-Free (or Low Fiber) with Varied Caloric Density

Standard caloric density (1–1.2

kcal/mL)

$ Ensure; Nutren 1.0

Moderate density (1.5 kcal/mL) $ Boost Plus; Ensure Plus; Isosource 1.5 Cal

e

; Nutren

1.5

Calorically dense (1.8–2

kcal/mL)

$ Nutren 2.0

Standard Caloric Density, Fiber-Free with Varied Nitrogen (Protein) Content

Low nitrogen (6%–10% of kcal

as protein)

$ Resource Breeze

Standard nitrogen (11%–16% of

kcal as protein)

$ Ensure; Nutren 1.0

High nitrogen (17%–20% of

kcal as protein)

$ Isosource HN; Osmolite 1.2 Cal

Very high nitrogen (>20% of

kcal as protein)

$$ Boost High Protein; Promote; Replete

Oligomeric Formulas

Elemental (free amino acids)

f && f.a.a.; Tolerex; Vivonex

T.E.N.

Peptide Based

Standard protein & Peptamen; Peptamen with

Prebio

High protein & Peptamen 1.5

Very high protein (NPC:N <100:1; >20% calories as

protein)

&& Crucial; Peptamen AF

Specialized Formulas

Renal Failure

Essential amino acid enriched

f &&&& Renalcal

Polymeric, low electrolyte (less than standard

potassium, phosphorus, and magnesium)

$$$$

Low nitrogen Suplena

Standard nitrogen Novasource Renal

High nitrogen (for dialysis) Nepro

Hepatic failure (high BCAA, low AAA

f

) &&&& Nutrihep

Stress or Critically Ill

Branched-chain enriched &&&

High nitrogen plus conditionally essential nutrients $$

Immune modulating && Oxepa

Pulmonary disease (standard; not IMP) $$ Nutren Pulmonary;

Pulmocare

Glucose control $$$ Diabetisource AC;

Glucerna; Nutren Glytrol

aBased on average cost per 1,000 calories for equivalent formulas on a University Health System contract from

2010 to 2013.

b

Index product is a standard caloric density, standard-nitrogen content, fiber-free formula. Cost is indicated relative

to an index product given a value of 1:

$ = same cost as index product, up to 1.5 times that cost per 1,000 calories.

$$ = cost is 1.6 to 2.5 times the cost of the index product per 1,000 calories.

$$$ = cost is 2.6 to 3.5 times the cost of the index product per 1,000 calories.

$$$$ = cost is 3.6 to 4.5 times the cost of the index product per 1,000 calories.

& = cost is 11 to 15 times the cost of the index product per 1,000 calories.

&& = cost is 16 to 20 times the cost of the index product per 1,000 calories.

&&& = cost is 20 to 24 times the cost of the index product per 1,000 calories.

&&&& = cost is 25 to 30 times the cost of the index product per 1,000 calories.

cAll products listed in the table are lactose-free.

dHigh nitrogen.

eLow fiber.

fSpecial order, not on formulary used for price calculations.

AAAs, aromatic amino acids; BCAAs, branched-chain amino acids; IMP, immune-modulating pulmonary; NPC:N,

nonprotein calorie to nitrogen ratio.

p. 772

p. 773