Specialized formulas are designed for specific disease states or conditions; however,
clinical benefits are often controversial. Formulas generally have a good theoretic
basis for use, yet many lack conclusive clinical evidence of improved efficacy
compared with standard formulas. Well-designed studies showing a difference in
outcome between specialized and standard enteral formulas providing equal nitrogen
and equal calories are limited for most types of specialized formulas. As shown in
Table 37-2, there are several different types of specialized formulas; costs and
evidence for use vary greatly among them.
D.S. requires EN because he cannot adequately protect his airway when
swallowing. There is no evidence presented to suggest he has problems with
digestion or absorption. One of the polymeric formulas on the hospital EN formulary
should be selected for D.S. The choice of polymeric formula can be narrowed by
several factors, including requirements for calories, protein, fluid and fiber, as well
as potential nutrient intolerances.
special nutrient requirements?
D.S.’s nutrient requirements must be assessed before proceeding in the selection of
enteral formula. Based on his weight–height ratio, 10% weight loss over 6 months,
slightly elevated CRP, and mild muscle wasting D.S. has moderate malnutrition in the
context of chronic illness. Low serum albumin is a risk factor for morbidity and
mortality, but is not a reliable indicator of nutritional status.
ideal body weight ([IBW], 73 kg) most likely is due to chronic deficiency in total
energy intake, but may also be associated with significant loss of lean mass,
Because D.S. has an IBW less than the ideal for his height, his actual weight
should be used to estimate energy and protein requirements. Use of IBW to estimate
requirements for undernourished patients may result in fluid and electrolyte
imbalance. Once the patient is stabilized on nutrition support, calories can be
increased, if necessary, to achieve weight gain.
D.S.’s level of metabolic stress is relatively low. He has no surgical wounds,
fractures or skeletal trauma, burns, or major infections, although CRP indicates mild
inflammation. Caloric requirements are only slightly higher than basal needs.
Although the term calorie is used interchangeably with kilocalorie (kcal) in nutrition
literature, the large “Calorie” or kilocalorie technically is correct and energy
requirements generally are listed as kcal/day or kcal/kg body weight when specific
numbers are given for a patient. See Chapter 35, Basics of Nutrition and Patient
Assessment, for methods of determining nutrient requirements. An estimation of 20 to
25 kcal/kg actual weight can be used based on D.S.’s low level of metabolic stress,
but higher caloric intake (25–30 kcal/kg/day) may be needed for weight gain after he
Protein requirements for healthy elderly people are controversial but estimated to
be 1 to 1.2 g/kg/day, which is higher than the DRI of 0.8 g/kg/day.
needs are estimated to 1 to 1.2 g/kg actual weight per day, minimum, based on
inflammation and chronic malnutrition. Renal function appears adequate for D.S. to
tolerate 1.2 g/kg/day without experiencing azotemia. SCr, however, may provide a
poor estimate of renal function in underweight patients owing to less-than-normal
Daily fluid requirements for geriatric patients can be estimated at 30 mL/kg or 1
mL/kcal ingested, with a minimum of 1,500 mL daily, plus replacement of excess
losses from hyperthermia, vomiting, or diarrhea.
24 Baseline requirements of 1,500
mL for the first 20 kg plus 20 mL per each additional kilogram of body weight also
can be used to estimate fluid requirements. D.S. does not appear to have any excess
fluid losses at this time; therefore, calculation of baseline fluid requirements should
D.S.’s estimated daily requirements are approximately 1,240 to 1,550 total
calories, 62 to 74 g protein, and about 1,860 mL of fluid. These are estimated
requirements that should be adjusted based on frequent reassessment of D.S.’s
response to therapy and changes in his clinical situation. Additional calories and
protein may be needed for repletion of weight and protein status.
D.S.’s apparently suboptimal nutrition before hospitalization increases his risk for
vitamin deficiencies (see Chapter 35, Basics of Nutrition and Patient Assessment).
Medical, medication, and dietary histories should be evaluated to determine
nutritional risks associated with specific conditions. D.S.’s age, along with his acute
illness and chronic malnutrition, increases his risk of vitamin deficiencies, and he
may have at least some subclinical deficiencies. He should receive 100% of the DRI,
minimum, for vitamins and minerals daily.
If actual deficiencies are identified, D.S.
will require higher, therapeutic doses for the specific vitamins that are deficient.
D.S. may be at risk of refeeding syndrome. His weight is low (85% of IBW),
although his body mass index is acceptable at 19.5 kg/m2
lead to intracellular depletion of potassium, phosphorus, and magnesium, whereas
serum concentrations are maintained. When specialized nutrition support begins,
refeeding syndrome may develop as these electrolytes move from the extracellular
space into the cells, causing a decrease in serum concentrations during the first few
25 Failure to monitor the patient and replace electrolytes as necessary
can result in serious electrolyte abnormalities. Knowing D.S.’s weight history,
particularly recent weight loss, and his diet history could help assess his potential for
clinically significant electrolyte and fluid abnormalities associated with refeeding
CASE 37-2, QUESTION 4: Which category of polymeric formulas would be most appropriate for D.S.
based on his estimated nutritional requirements?
Polymeric formulas can be divided into several categories based on nutrient
sources, caloric density, and protein content. Each category should be evaluated
because formula characteristics overlap between the categories.
Polymeric formulas can be subdivided based on lactose content. Hospitalized
patients are presumed to be lactose intolerant due to reduced disaccharidase
production during fasting, malnutrition, and various GI tract diseases.
most ethnic groups, except northern Europeans, have reduced lactase production in
adulthood, leading to lactose intolerance. Lactose ingestion can cause bloating,
flatulence, abdominal cramps, and watery diarrhea in patients with permanent or
transient lactose intolerance. Lactose-free formulas are the standard for tube-fed
adults. Most enteral products are lactose-free, except the powdered products
reconstituted with milk and generally intended for oral consumption. Proteins, even
those derived from milk, do not contribute to lactose content because lactose is a
carbohydrate. The majority of enteral formulas are also gluten-free to avoid GI
symptoms associated with celiac disease.
General Descriptions of Macronutrient Quantity in Enteral Formulas
Low Standard Moderate High Very High
Caloric density (kcal/mL) <1 1–1.2 1.5 1.8–2 >2
Free water (%) 65%–75% 80%–85% 75%–80% >85%
>200:1 200:1–130:1 125:1–100:1 <100:1
Fiber content (g/1,000 kcal) 1–9 None >9–<14 ≥14
NPC:N, nonprotein calorie to nitrogen ratio.
Caloric density influences the volume of formula needed to meet nutrient
requirements. Standard caloric density is 1 to 1.2 kcal/mL. Table 37-3 lists the
general descriptions for caloric density and macronutrient quantities in enteral
formulas. Increased caloric density increases formula osmolality. Gastric emptying
can be reduced when osmolality exceeds 800 mOsm/kg and this may result in feeding
28 GI intolerance (e.g., nausea, flatulence, abdominal discomfort) also can
occur if the capacity of intestinal enzymes is overwhelmed by infusion of a
Caloric density reflects the free-water content of EN formulas. Risk of dehydration
increases with increasing caloric density; however, standard caloric density formulas
can result in fluid overload in patients with congestive heart failure, renal failure, or
other fluid-sensitive conditions. Calculation of water provided by EN helps
determine the volume of additional fluid needed to meet daily fluid requirements.
Free-water content is generally 80% to 85% (800–850 mL/L of formula) for
formulas with 1 to 1.2 kcal/mL. Table 37-3 lists free-water content associated with
other caloric densities. The available history for D.S. does not suggest a need for
fluid restriction; therefore, it would be reasonable to initiate feedings with a standard
caloric density product (1–1.2 kcal/mL).
Protein needs increase disproportionately to caloric needs during injury and critical
illness, whereas protein tolerance may limit protein provision in other conditions. To
meet the need for varying ratios between calories and protein, polymeric formulas
are available with a range from low- to very high protein content. Either percentage
of calories from protein or nonprotein calories to nitrogen (NPC:N) ratio can be used
to define protein content. Table 37-3 lists general descriptions for protein content.
High-nitrogen enteral formulas are designed for patients with an increased protein
requirement without a proportional increase in caloric needs. Very high nitrogen
formulas are generally intended for critically ill patients or those with large wounds
to heal. Low-nitrogen formulas are available for patients requiring protein
restriction. Some low-nitrogen formulas are designed for patients with reduced renal
function and can be classified as specialized formulas.
D.S. could obtain adequate protein from a formula with standard protein content. A
formula with slightly higher-protein content (17%–18% of calories) would also be
acceptable. A high-nitrogen formula that meets D.S.’s calorie needs will provide
protein at the upper end of the estimated requirement (1.2 g/kg/day), whereas a
standard-nitrogen formula will provide between 0.8 and 1 g/kg/day. A high-nitrogen
formula may replete D.S.’s somatic and visceral protein status sooner but it may not
provide adequate calories for weight gain. The decision to use a high-nitrogen versus
standard-nitrogen formula depends on the exact nutrient composition of products on
Fiber has potential physiologic benefits, including increased fecal bulk, decreased
bowel transit time in patients susceptible to constipation, increased transit time in
patients with diarrhea, reduction of serum cholesterol, and improved glycemic
control in patients with diabetes. Recommended daily fiber intake for healthy
Americans is 21 to 25 g for women and 30 to 38 g for men, with the lower end of
these amounts for people 51 years of age or older.
29 Adequate intake is determined
by calorie intake and fiber intake observed to protect against coronary artery disease
(14 g/1,000 calories). Optimal fiber intake for ill persons has not been determined.
Fiber-supplemented formulas vary considerably in fiber content. There is no
standardized terminology for low-fiber, moderate-fiber, and high-fiber content;
however, the amounts listed in Table 37-3 can serve as a general guideline.
Enteral formulas may contain either insoluble or soluble fiber, or both. Insoluble
fiber is associated with changes in fecal bulk and transit time, whereas soluble fiber
tends to be responsible for effects on cholesterol and glycemic control. Soluble
fibers, such as pectin, psyllium, and certain gums, tend to form gels and are used as a
single fiber source only for low-fiber formulas. Fructooligosaccharides (FOS) are
naturally occurring sugars that are added to some enteral formulas for soluble fiber
benefits with better formulation characteristics (i.e., less gelling). Soluble fibers and
FOS can be fermented to short-chain fatty acids by Bifidobacterium in the colon.
Short-chain fatty acids stimulate colonic blood flow, enhance fluid and electrolyte
absorption, and provide a trophic effect in the colon.
The most common fiber source for enteral formulas is soy polysaccharide, or soy
fiber. Although soy polysaccharide demonstrates beneficial effects associated with
both soluble and insoluble fibers in healthy subjects and non-critically ill patients,
studies do not provide clear evidence of improved bowel function in critically ill
31 Routine use of fiber is not supported by available data in critically ill
18–20 Given available data, stable patients on long-term EN appear most
likely to benefit from fiber-supplemented formulas. Some patients on short-term EN
without GI pathology who experience altered stool consistency may benefit from
Addition of fiber to enteral formulas creates some potential problems. Fiber
increases viscosity and fiber-containing formulas often require a pump for
administration through feeding tubes. GI symptoms from fiber can include increased
gas production and abdominal discomfort.
Improvement in constipation has been
noted with FOS administration; however, intake of greater than 45 g/day may cause
32 Flatulence and bloating can limit tolerance to FOS for some patients.
Gradual introduction of fiber may help reduce these symptoms. Bezoar formation
also has been reported in a patient receiving fiber-containing tube feedings and
medications that suppressed GI motility.
Insoluble fiber should be avoided in critically ill patients, and patients at high risk of
bowel ischemia or severe dysmotility should not receive either soluble or insoluble
Inadequate fluid intake may also contribute to the risk of bezoar formation and
intestinal blockage with fiber.
D.S. is not critically ill and does not appear to have bowel pathology precluding
use of a fiber-containing formula. He will require EN for a moderate duration of time
and potentially long term. It would be reasonable to provide a formula with at least
moderate fiber content. However, D.S. could experience GI symptoms from the fiber,
symptoms of bloating and gas improve.
CASE 37-2, QUESTION 6: What is an appropriate administration regimen for D.S.’s tube feeding?
The feeding route, formula selected, and anticipated duration of feeding influence
the administration regimen. Patient location (e.g., hospital, nursing facility, home)
and cost also are considered when developing the regimen, including the rate for
initiating and advancing feedings, and the administration method (i.e., syringe, gravity
Limited scientific data exist regarding EN administration regimens; thus, expert
opinion plays an important role and different regimens can be used in various
settings, all of which appear to meet the needs of the patients and personnel. The
administration regimen should be adjusted as necessary for feeding intolerance. Four
basic schedules for formula delivery are available: (a) continuous infusion, (b)
cyclic infusion, (c) intermittent infusion, and (d) bolus delivery of formula.
Continuous infusion provides formula at a continuous rate for 24 hours/day and can
be used with any route of feeding. Intragastric continuous infusion is most commonly
used for hospitalized patients, although small bowel feeding may be more
appropriate in certain settings (e.g., ICU).
18–20 Risks of gastric distension and
aspiration may decrease with continuous infusion compared with intermittent gastric
Comments
Post a Comment
اكتب تعليق حول الموضوع