Support Line December 2005 Volume 27 No. 6
`
`Parenteral Nutrition:
`Macronutrient Composition and Requirements
`Emily Gasser, RD, CNSD Neha Parekh, MS, RD, CNSD
`
`Abstract
`Parenteral nutrition (PN) is a complex
`formulation designed to deliver fluid
`and nutrients in the absence of a func-
`tional gastrointestinal (GI) tract. The
`determination of whether a patient
`should receive PN rests on a thorough
`assessment of his or her clinical and
`nutritional status, with consideration
`given to the potential risks and benefits
`of PN. PN solutions can be classified
`by either route of infusion or by macro-
`nutrient content reflected in the inclusion
`or exclusion of intravenous fat emulsion.
`The preparation of a stable and safe
`PN formulation requires a series of
`careful calculations. This article
`addresses the appropriate use of PN,
`with a focus on macronutrient
`composition and requirements.
`
`Introduction
`Parenteral nutrition allows for the
`provision of energy, vitamins, minerals,
`electrolytes, fluid, and various medica-
`tions via a peripheral or central vein.
`Since the introduction of PN in United
`States hospitals in the late 1960s, there
`has been a substantial increase in the
`demand for such specialized solutions.
`This has resulted in the diversification
`of health-care professionals prescribing
`PN, including physicians, pharmacists,
`nurse practitioners, and dietitians.
`Today, more registered dietitians are
`faced with the task of not only recom-
`mending macronutrient provisions, but
`also prescribing the entire PN solution
`based on each patient’s unique needs.
`Several publications provide evidence-
`based guidelines for the administration
`of PN (1–3). This article summarizes
`the standard practice guidelines and
`provides an overview of when to use
`PN, macronutrient composition and
`requirements, types of PN solutions,
`and calculations for designing the
`PN regimen.
`
`Patient Selection
`The determination of whether a
`patient should receive PN rests on
`a thorough assessment of his or her
`clinical condition and nutritional
`status. In cases of a nonfunctional GI
`tract, PN should be started within 7 to
`14 days. However, severely malnour-
`ished or highly catabolic patients with
`GI dysfunction need PN within 1 to
`3 days of hospital admission (2–4).
`Before initiating PN, the clinician
`should consider the risks and weigh
`them against the potential benefits of
`PN. The routine use of PN in the acute
`setting places the patient at higher risk
`for fluid, nutrient, and electrolyte
`abnormalities as well as infectious and
`noninfectious catheter-related compli-
`cations. Additional complications of
`PN extending to the long-term PN
`patient include metabolic bone disease
`and hepatobiliary dysfunction (5). The
`primary benefit of PN is the bypass of
`a nonfunctional GI tract via delivery of
`nutrients directly into the bloodstream.
`Of note, PN has not been shown to be
`superior to enteral nutrition (EN), and
`with careful administration, EN is safer,
`less expensive, and better tolerated
`than PN (6).
`Indications for the use of PN are
`listed in Table 1. Perioperative PN is
`generally of most benefit in patients
`with moderate-to-severe malnutrition
`and high levels of metabolic stress (7).
`Very limited benefit has been shown with
`the use of PN in end-stage, metastatic
`cancer (8–10). Patients with anorexia or
`the inability to ingest enough nutrients
`orally should not receive PN unless
`enteral access is refused or impossible
`to obtain (11).
`
`Macronutrient Composition
`Dextrose
`The primary energy source for the
`human body is carbohydrate. Brain
`and neural tissue, erythrocytes, leuko-
`cytes, the lens of the eye, and the renal
`
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`
`medulla exclusively require glucose or
`use glucose preferentially. Therefore,
`carbohydrates form the basis of all PN
`solutions. The most commonly used
`carbohydrate source in PN formulas is
`dextrose monohydrate. Dextrose pro-
`vides 3.4 kcal/g in its hydrated form
`and is available in a wide range of con-
`centrations from 5% to 70% (Table 2).
`Percent concentration refers to the
`grams of solute per 100 mL of solution.
`A 5% dextrose solution contains 5 g
`of dextrose per 100 mL of solution or
`50 g/L. Higher dextrose concentrations
`are used to decrease total volume for
`patients requiring fluid restriction.
`Amino Acids
`Protein is provided in PN for the
`maintenance of cell structure, tissue
`repair, immune defense, and skeletal
`muscle mass. Crystalline amino acids
`are used as the protein source for PN.
`These solutions are commonly available
`in concentrations ranging from 8.5%
`to 20% and provide 4 kcal/g (Table 2).
`Standard amino acid solutions are a
`physiologic mixture of both essential
`
`Table 1. Indications for the
`Use of Parenteral Nutrition
`• Intractable vomiting or diarrhea
`• Prolonged paralytic ileus
`• Lower gastrointestinal tract
`perforation or leak
`• High-output enterocutaneous
`fistula
`• Bowel ischemia
`• Short bowel syndrome with
`severe malabsorption
`• Complete lower intestinal
`obstruction
`• Diffuse peritonitis
`• Persistent gastrointestinal bleeding
`• Repeated failure of enteral
`feeding or inability to maintain
`enteral access
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`and nonessential amino acids and vary
`in composition among manufacturers.
`A 15% or 20% standard amino acid
`solution may be used to concentrate
`the PN formula for patients with
`marked fluid overload.
`Several disease-specific amino acid
`solutions are also available, primarily
`for use in renal or hepatic disease
`exacerbated by severe stress or critical
`illness (Table 3). Patients with declining
`renal function who are not undergoing
`dialysis may experience accumulation
`of urea nitrogen in the blood stream
`upon infusion of nonessential amino
`acids. In light of this, parenteral amino
`acid solutions containing only essential
`amino acids have been developed for
`this population. However, clinical trials
`have failed to show definitive improve-
`ment in renal function with these
`specialized solutions, and nonessential
`amino acids may become conditionally
`essential during periods of severe
`stress (12–14). See Table 4 for the
`categorization of amino acids.
`Patients with hepatic encephalopathy
`refractory to medical management may
`be candidates for the use of branched-
`chain amino acid (BCAA) parenteral
`solutions (Table 4). BCAAs are oxidized
`primarily in the muscle instead of the
`liver, which preserves appropriate
`metabolic pathways in cases of liver
`failure. This area of clinical therapy
`has been studied extensively, but few
`controlled trials have demonstrated
`a benefit over standard amino acid
`solutions (15,16). In general, disease-
`specific amino acid solutions should
`not be used for more than 2 weeks
`because they provide an incomplete
`amino acid profile (17). Additionally,
`routine use is not recommended due
`to lack of supporting research and
`substantial expense associated with
`these specialized amino acid solutions.
`Lipids
`Lipids are a concentrated, isotonic
`source of energy providing 9 kcal/g
`and are available for intravenous (IV)
`use as oil-in-water emulsions ranging
`in concentration from 10% to 30%
`(Table 2). Lipid emulsions currently
`available in the United States contain
`long-chain triglycerides (LCT) in the
`
`Support Line December 2005 Volume 27 No. 6
`
`form of soybean oil or safflower oil,
`egg phospholipids as an emulsifier, and
`water. Glycerol is added to create an
`isotonic solution.
`The primary role of IV lipid emulsion
`is to prevent essential fatty acid (EFA)
`
`deficiency. Daily EFA requirements
`can be met with 4% of total calories as
`linoleic acid or 10% of total calories as
`a safflower oil-based lipid emulsion.
`Patients with a documented egg
`(Continued on next page)
`
`Table 2. Macronutrient Solutions
`
`Nutrient
`Dextrose
`
`Amino Acids
`
`Lipid
`Emulsions
`
`Concentration
`5%
`10%
`20%
`50%
`70%
`8.5%
`10%
`15%
`20%
`
`Concentration
`10%
`20%
`30%
`
`Grams
`per Liter
`50
`100
`200
`500
`700
`85
`100
`150
`200
`Calories
`per Milliliter
`1.1
`2
`3
`
`Calories
`per Liter
`170
`340
`680
`1,700
`2,380
`340
`400
`600
`800
`Calories
`per Liter
`1,100
`2,000
`3,000
`
`Liver Disease
`
`Table 3. Disease-specific Amino Acid Solutions
`NephrAmine® 5.4% (B. Braun)
`Renal Failure
`RenAmin® 6.5% (Baxter)
`Aminosyn®-RF 5.2% (Hospira)
`HepatAmine® 8% (B. Braun)
`BranchAmin® 4% (Baxter)
`Aminosyn®-HBC 7% (Hospira)
`FreAmine® HBC 6.9% (B. Braun)
`B. Braun: Bethlehem, Pa.
`Baxter: Deerfield, Ill.
`Hospira: Lake Forest, Ill.
`
`Essential amino acid
`solutions
`
`Solutions high in
`branched-chain
`amino acids
`
`Table 4. Amino Acid Categorization
`
`Nonessential
`Essential
`Alanine
`Isoleucine
`Asparagine
`Leucine
`Aspartate
`Lysine
`Glutamate
`Methionine
`Glycine
`Phenylalanine
`Hydroxyproline*
`Threonine
`Ornithine*
`Tryptophan
`Serine
`Valine
`*Not routinely contained in parenteral nutrition amino acid formulations.
`
`Conditionally
`Essential
`Arginine
`Cysteine*
`Glutamine*
`Histidine
`Taurine
`Tyrosine
`
`Branched-
`chain
`Leucine
`Isoleucine
`Valine
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`Support Line December 2005 Volume 27 No. 6
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`allergy should not receive IV lipids
`because of the egg phospholipid content.
`Patients with egg allergy who require
`PN as the sole source of nutrition for
`more than 3 weeks should be closely
`monitored for clinical and biochemical
`evidence of EFA deficiency. A triene:
`tetraene ratio of more than 0.2, in
`addition to excessive hair loss; poor
`wound healing; dry, scaly skin unre-
`sponsive to water-miscible creams;
`and/or alterations in platelet function
`can signify EFA deficiency (18).
`In rare instances, cutaneous oil
`application may become necessary and
`is best used as a preventive measure in
`patients at risk for EFA deficiency.
`Miller and associates (18) reported
`successful prevention of EFA deficiency
`with 3 mg/kg/d safflower oil applied
`cutaneously over 4–6 weeks; Press and
`colleagues (19) reported correction
`of EFA deficiency with application of
`2 to 3 mg/kg/d sunflower seed oil for
`12 weeks.
`In addition to providing a source of
`EFA, lipids are also useful for replacing
`excessive dextrose calories manifested
`by uncontrolled blood glucose levels
`or hypercapnia with delayed weaning
`from mechanical ventilation. Lipid
`emulsions containing medium-chain
`triglycerides (MCT), fish oil, and olive
`
`oil have been used in Europe since
`1984, but are currently available in the
`United States for research purposes
`only. When compared with pure LCT
`emulsions, mixed MCT-LCT lipid
`emulsions have been shown to exert
`less stress on the liver, improve plasma
`antioxidant capacity, reduce generation
`of proinflammatory cytokines,
`improve neutrophil function, and
`enhance oxygenation in stressed
`patients (20–22).
`
`Types of Solutions
`PN solutions can be broadly classified
`as either total or peripheral PN based
`on route of administration and more
`specifically as “2-in-1” or “3-in-1”
`solutions based on macronutrient
`composition. A patient’s clinical and
`nutrition status, estimated duration of
`therapy, and type of IV access are impor-
`tant considerations when determining
`the most appropriate form of PN.
`Total Parenteral Nutrition
`Total parenteral nutrition (TPN)
`refers to the administration of PN
`through a large-diameter central vein.
`Central access allows for the use of a
`highly concentrated, hypertonic solu-
`tion, which can be tailored to meet the
`macronutrient and fluid requirements
`of individual patients. Patients requiring
`
`PN for longer than 2 weeks generally
`are candidates for PN via a central
`vein, using either a temporary central
`venous catheter (CVC) or a long-term
`CVC such as a tunneled catheter, an
`implanted port, or a peripherally inserted
`central catheter (PICC). Although TPN
`does offer greater freedom in formula
`preparation, CVCs can increase the
`risk of catheter-related blood stream
`infections, particularly when used for
`PN (23).
`Peripheral Parenteral Nutrition
`Peripheral parenteral nutrition (PPN)
`avoids the use of a central vein and
`associated complications. Because
`PPN is administered into a peripheral
`vein, the osmolarity of a PPN solution
`should not exceed 900 mOsm/L (Table
`5). Patients receiving PPN are at risk
`for vein damage and thrombophlebitis
`if this osmolarity level is exceeded (24).
`Generally, PPN solutions are lipid-
`based because lipids are a concentrated
`calorie source and contribute fewer
`mOsm/g. Due to the lower dextrose
`concentration of PPN, there is less
`risk of hyperglycemia. However, PPN
`solutions provide fewer total calories,
`protein, and electrolytes per liter than
`hypertonic TPN solutions. PPN is an
`acceptable form of parenteral support
`when a patient is not hypermetabolic,
`
`× 10
`= _____________ mOsm
`× 5
`= _____________ mOsm
`× 0.67 = _____________ mOsm
`× 2
`= _____________ mOsm
`= _____________ mOsm
`
`Table 5. Calculating the Osmolarity of PN Solutions
`A. Total grams of amino acids per liter of solution
`B. Total grams of dextrose per liter of solution
`C. Total grams of fat (using 30% emulsion) per liter of solution
`D. Total mEq of calcium, magnesium, potassium, and sodium per liter of solution
`Add A, B, C, and D to derive total osmolarity of the PN solution
`(For peripheral vein tolerance, total osmolarity per liter should be 900 mOsm/kg or less.)
`Example: PPN solution containing 1,800 kcal, 80 g amino acids (AA), 130 g dextrose, and 115 g lipid in 2,400 mL volume
`plus 200 total mEq of calcium, magnesium, potassium, and sodium.
`×
`330 mOsm
`33 g AA/L
`10
`=
`A. 80 g AA ÷ 2.4 L =
`55 g dextrose/L ×
`275 mOsm
`B. 130 g dextrose ÷ 2.4 L =
`5
`=
`×
`32 mOsm
`C. 115 g lipid ÷ 2.4 L =
`48 g lipid/L
`0.67
`=
`×
`167 mOsm
`D. 200 mEq electrolytes ÷ 2.4 L = 83 mEq/L
`2
`=
`804 mOsm
`Total Osmolarity
`=
`Reprinted with permission from Parekh NR, DeChicco RS, eds. Nutrition Support Handbook. Cleveland, Ohio: The Cleveland Clinic
`Foundation; 2004.
`
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`Support Line December 2005 Volume 27 No. 6
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`Table 6. Compatibility Ranges for Total Nutrient Admixtures
`Macronutrient
`Acceptable Range per Liter
`Standard amino acids
`20 to 60 g
`Dextrose
`35 to 253 g (119 to 860 kcal)
`Fat
`13 to 67 g (130 to 670 kcal)
`Reprinted with permission from Parekh NR, DeChicco RS, eds. Nutrition Support
`Handbook. Cleveland, Ohio: The Cleveland Clinic Foundation, 2004.
`
`requires therapy for fewer than 2
`weeks, has and can maintain adequate
`peripheral venous access, and does not
`require fluid restriction.
`“2-in-1” Versus “3-in-1” Solutions
`PN solutions are routinely comprised
`of carbohydrate, protein, electrolytes,
`vitamins, minerals, trace elements,
`medications, and sterile water. Such
`solutions are referred to as “2-in-1”
`solutions. Lipids can be infused sepa-
`rately or added to the PN solution to
`form a total nutrient admixture (TNA)
`or “3-in-1” solution. A 2-in-1 solution
`is favorable when patients have high
`protein or minimal fluid needs and can
`maintain euglycemia with the addition
`of a modest insulin dose.
`TNAs that include lipids are conve-
`nient and require less nursing time for
`administration. A TNA may be espe-
`cially advantageous in patients who
`have increased energy needs or who
`would benefit from reduced carbohy-
`drate provisions due to persistent
`hyperglycemia or hypercapnia (2). The
`phospholipid outer layer imparts sta-
`bility to intravenous lipids when pro-
`vided in a 3-in-1 admixture. However,
`macronutrient components must fall
`within acceptable ranges per liter for
`the 3-in-1 solution to remain stable
`(Table 6). If one component falls out-
`side of the acceptable range, the stabil-
`ity of the solution cannot be
`guaranteed for 24 hours. Disruption of
`stability can present as either distinc-
`tive creaming or “oiling out” in which
`the lipid portion separates from the
`aqueous phase of the solution contain-
`ing dextrose and protein. In this case,
`the TNA cannot be infused due to risk
`of fat embolus with unemulsified lipid.
`
`Macronutrient Requirements
`Daily macronutrient requirements
`are individualized based on age, sex,
`anthropometrics, body composition,
`activity level, medical diagnoses, degree
`of metabolic stress, and clinical circum-
`stances. Several techniques are available
`for the estimation and measurement of
`energy expenditure. The accuracy of
`predictive equations in hospitalized
`patients remains an area of debate due
`to physiologic differences among
`patients and the multitude of factors
`affecting the ability to obtain a valid
`body weight.
`A retrospective review by Barak and
`colleagues (25) used indirect calorimetry
`measurements to uncover disease-
`specific stress factors useful in estimating
`calorie needs for hospitalized patients.
`When multiplied by the Harris-Benedict
`equation, estimated energy expenditure
`using these stress factors closely approx-
`imated established literature values.
`The authors recommended using actual
`weight of normal and underweight patients
`and an adjusted body weight equal to
`ideal body weight plus 50% of excess
`body weight for estimating energy
`expenditure of obese patients requiring
`nutrition support.
`Indirect calorimetry is used to derive
`energy expenditure through measure-
`ments of O2 consumption, substrate
`oxidation, and CO2 production.
`Substrate utilization is reflected in the
`ratio of CO2 produced to O2 consumed
`or the respiratory quotient (RQ)
`(Table 7). In general, an RQ greater
`than 1.0 suggests administration of
`excess carbohydrate or total calories
`with ensuing lipogenesis. An ideal RQ
`is between 0.85 and 0.95, indicating
`protein sparing and mixed utilization
`of carbohydrate and fat (26). Despite
`
`– 9 –
`
`the need to use protein for wound
`healing and maintenance of muscle
`mass, when estimating total daily
`energy requirements and prescribing
`PN, calories from all three substrates
`should be included (27).
`Carbohydrate
`The average adult requires approx-
`imately 100 g/d carbohydrate or
`1 mg/kg/min to meet minimum daily
`requirements for central nervous system
`function. Without this daily requirement,
`protein is broken down to obtain the
`necessary fuel through gluconeogenesis.
`A minimum of 130 g/d carbohydrate is
`recommended for healthy adults and
`children as part of the Dietary Reference
`Intakes (DRI) (28). Prolonged under-
`feeding of carbohydrate and total
`calories via the enteral or parenteral
`route has been associated with poor
`wound healing, increased risk of
`infection, respiratory dysfunction,
`and an overall poor prognosis (29).
`In cases of chronic underfeeding,
`the body adapts by decreasing reliance
`on carbohydrate and gluconeogenesis
`pathways and increasing utilization of
`ketones and fatty acids for energy. An
`increase in ketone body formation puts
`the patient at risk for ketoacidosis, a
`disruption of acid-base balance within
`the body (30). The reintroduction of
`carbohydrate loads causes a rapid shift
`to glucose as the primary fuel, thereby
`increasing the demand for insulin, which
`may not be available in adequate amounts
`to meet the demand. Hyperglycemia,
`hypophosphatemia, hypokalemia,
`hypomagnesemia, hypotension,
`dehydration, fluid retention, and
`(Continued on next page)
`
`Table 7. Respiratory Quotients
`for Various Substrates
`Respiratory
`Quotient
`0.67
`0.71
`0.82
`0.85
`1.00
`1.01 to 1.20
`
`Substrate
`Alcohol
`Fat
`Protein
`Mixed substrate
`Carbohydrate
`Lipogenesis
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`metabolic acidosis can occur with
`rapid refeeding of carbohydrate after
`prolonged starvation, known as the
`refeeding syndrome. Any existing
`electrolyte deficiencies should be
`corrected before initiating PN at 50%
`of caloric requirements or approximately
`15 to 20 kcal/kg. PN can then be
`advanced over the next few days while
`closely monitoring electrolytes, blood
`glucose, and body weight.
`Overfeeding is also of concern because
`excess carbohydrate administration has
`been associated with hyperglycemia,
`hepatic steatosis, and increased CO2
`production, which may preclude wean-
`ing of the ventilator-dependent patient
`(31). Continuous dextrose infusion rates
`greater than 4 mg/kg/min led to an
`increased incidence of hyperglycemia
`in a study of 37 nondiabetic PN
`patients (32). Intravenous carbohydrate
`administration, therefore, should not
`exceed 4 mg/kg/min in critically ill
`patients and 7 mg/kg/min in stable
`hospitalized patients, unless they are
`undergoing cycling of PN with careful
`monitoring of blood glucose levels (33).
`Replacement of excess carbohydrate
`with lipid calories may aid in the main-
`tenance of euglycemia, the prevention
`of excess CO2 production, and the
`reduction of lipogenesis.
`Protein
`Daily protein needs are based on the
`patient’s age, weight, and nutritional
`and clinical status. Inadequate protein
`intake can result in negative nitrogen
`balance, depleted hepatic proteins, and
`delayed wound healing. The Recom-
`mended Dietary Allowance (RDA) for
`
`protein for healthy adults is 0.8 g/kg/d.
`In periods of acute illness, muscle
`breakdown is accelerated and exceeds
`protein synthesis, which results in a
`net negative nitrogen balance.
`Hospitalized patients requiring PN
`generally need 1.5 to 2.0 g/kg/d protein,
`with adjustments made according to
`tolerance, clinical course, nitrogen
`balance, and monitoring of hepatic
`protein status (34). Critically ill patients
`receiving continuous venovenous
`hemodialysis may require up to 2.5 g
`protein per kilogram of dry body weight
`daily to promote nitrogen balance (17).
`Prerenal azotemia may develop as a
`result of dehydration or excess protein
`intake, although a mild increase in
`blood urea nitrogen (BUN) values can
`be expected with moderate-to-high
`amounts of protein infusion via PN.
`IV protein provisions should be
`decreased when BUN levels exceed
`100 mg/dL (35).
`Fat
`Daily lipid requirements are met by
`providing adequate EFA in the form of
`linoleic acid. For healthy adults, the
`DRI for linoleic acid is 17 g/d for men
`and 12 g/d for women (28). This
`equates to about 10% of total calories
`as a commercial IV lipid emulsion of
`soybean or safflower oil. Lipid emul-
`sions currently available in the United
`States are composed principally of
`LCT, which may have an immunosup-
`pressive effect when administered in
`large amounts over short periods of
`time. Rapid infusion of IV lipids has
`been associated with the impairment of
`neutrophil production and the reduction
`
`of endotoxin clearance (36,37). An
`attempt should be made to limit IV
`lipid administration to 1 g/kg/d or
`25% to 30% of total calories to avoid
`adverse reactions such as respiratory
`insufficiency, fever, chills, headache, back
`or chest pain, nausea, and vomiting.
`PPN solutions are commonly lipid-
`based because of the low contribution
`of IV lipid to the osmolarity of the
`solution. Because PPN solutions have
`osmolarity restrictions and generally
`cannot meet total calorie requirements,
`patients receiving such solutions may
`be fed up to 50% of total calories as
`lipid safely. However, care must be
`taken to attempt to limit lipid adminis-
`tration to 1 g/kg/d. The overfeeding
`of lipids can also result in hypertriglyc-
`eridemia or reduced lipid clearance.
`In cases of suspected altered lipid
`metabolism, as in pancreatitis, sepsis,
`and moderate-to-severe liver disease,
`serum triglyceride levels should be
`monitored before and 6 hours after
`PN infusion (5). Lipid administration
`should be held when serum triglyceride
`levels exceed 400 mg/dL (2).
`
`Designing the PN Solution
`The route and nutrient composition
`of a PN solution governs the calcula-
`tions needed for preparation of a safe
`PN formula. Most institutions have a
`standardized order protocol used by all
`clinicians prescribing PN. In addition,
`an expert panel representing the
`American Society for Parenteral and
`Enteral Nutrition recently published
`updated guidelines on safe practices
`for PN formulations (3). The panel
`recommends standardized ordering
`
`Table 8. Guidelines for Dosing Macronutrients and Fluid in PN
`Normal Range
`Minimum Dose
`25 to 35
`10 (for morbid obesity)
`
`Total Calories (kcal/kg/d)
`
`Protein (g/kg/d)
`Dextrose (mg/kg/min)
`Fat (% total calories)
`
`Fluid (mL/kg/d)
`
`0.8 to 1.5
`2 to 3.5
`25 to 30
`
`30 to 40
`
`0.8
`1
`10% as commercial IV fat emulsion
`(4% as linoleic acid)
`As per compatibility/
`osmolarity guidelines
`
`Maximum Dose
`45 to 55
`(for severe malnutrition)
`2.5
`4 to 7
`
`30
`Variable, depending on fluid
`losses and need for repletion
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`and labeling of PN solutions to display
`dextrose, amino acids, and IV fat
`emulsion as grams per total daily
`volume to support the use of a 24-hour
`nutrient infusion system.
`Preparation of a stable and safe PN
`formulation requires a series of careful
`calculations. Once central venous access
`has been established, the process of
`designing the PN prescription begins.
`Table 8 provides an overview of dosage
`guidelines for macronutrient and fluid
`content of PN solutions. Protein is
`usually the first macronutrient to be
`addressed, and the first bag of TPN
`should provide full protein needs. The
`first bag of TPN also should deliver a
`reduced dextrose level (about 50% of
`total requirements or 150 to 200 g) to
`prevent complications such as hyper-
`glycemia or fluid and electrolyte
`abnormalities. Assuming that the first
`bag of TPN administers full fluid
`needs, lipids are generally excluded to
`avoid difficulties in maintaining com-
`patibility of the solution (Table 6).
`Once laboratory values are within
`normal limits, TPN calories can be
`advanced to full requirements, with
`lipids infused concurrently or separately,
`based on patient tolerance. The minimal
`volume required to maintain all nutrients
`in solution may be calculated for those
`patients in need of fluid restriction
`(Table 9). Given the osmolarity
`restrictions of PPN, nutrient provi-
`sions generally depend on the patient’s
`fluid allowance. Once this is determined,
`macronutrients can be calculated to
`maximize nutrient provisions for the
`given PPN volume (Table 5). Table 10
`provides sample TPN and PPN solu-
`tions for an average 70-kg patient. The
`level of macronutrients provided in
`PN solutions should be modified from
`the standard based on individual
`patient tolerance and requirements.
`
`Conclusion
`PN is a complex formulation of
`macronutrients, electrolytes, vitamins,
`trace elements, water, and medications
`used in the absence of a functioning
`GI tract. A thorough evaluation of
`each patient’s clinical and nutritional
`status forms the basis for deciding when
`to initiate PN, what form of PN to
`
`Support Line December 2005 Volume 27 No. 6
`
`Table 9. Calculating Minimum Volume for PN Solutions*
`×
`A. Total grams of amino acids
`10 = ______ mL
`B. Total dextrose calories
`÷ 2.38 = ______ mL
`C. Total lipid calories
`÷ 3.0 = ______ mL
`D. Estimate 200 mL for electrolytes and additives
`= ______ mL
`Add A, B, C, and D to derive total volume of the PN solution
`= ______ mL
`Example: PN solution containing 2,000 kcal, 100 g amino acids, 1,120 dextrose
`calories, and 480 lipid calories.
`×
`1000 mL
`10 =
`A. 100 g amino acids
`471 mL
`÷ 2.38 =
`B. 1,120 dextrose calories
`160 mL
`÷ 3.0 =
`C. 480 lipid calories
`200 mL
`=
`D. 200 mL electrolytes and additives
`1831 mL
`=
`Total Minimum Volume
`*Using a 10% amino acid solution, 70% dextrose solution, and 30% lipid emulsion.
`
`Table 10. Sample PN Solutions (for an Average 70-kg Patient)
`TPN
`PPN
`2,000
`2,000
`2,100
`1,400
`30
`20
`
`60
`30
`0.9
`
`137
`68.5
`1.36
`
`77
`38.5
`1.1
`50
`
`Total Volume (mL)
`Total Calories
`kcal/kg
`Protein
`g
`g/L
`g/kg/d
`Dextrose
`g
`g/L
`mg/kg/min
`Fat
`55
`g
`27.5
`g/L
`0.4
`g/kg/d
`24
`Percentage of total calories
`PN=parenteral nutrition, TPN=total parenteral nutrition,
`PPN=peripheral parenteral nutrition
`
`110
`55
`1.6
`
`342
`171
`3.4
`
`administer, and how to design the PN
`prescription. Adherence to evidence-
`based guidelines involving PN macro-
`nutrient composition can ensure
`provision of a safe and stable PN
`solution.
`Emily Gasser, RD, CNSD, is a metabolic
`support clinician in the Nutrition Support
`
`and Vascular Access Department of the
`Cleveland Clinic Foundation, Cleveland,
`Ohio.
`Neha Parekh, MS, RD, CNSD, is
`nutrition coordinator of the Intestinal
`Rehabilitation Program at the Cleveland
`Clinic Foundation, Cleveland, Ohio.
`(Continued on next page)
`
`– 11 –
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`Support Line December 2005 Volume 27 No. 6
`
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