U.S. dietary guidelines (food pyramid)
• Maintain a healthy weight.
• Maintain a low-fat diet (< 30% of total calories).
• Eat plenty of fruits, vegetables, and grain products.
• Use salt, sugar, and alcohol in moderation.
• Causes of undernutrition (protein-calorie malnutrition):
• Depressed intake of nutrients (starvation, semistarvation)
• Alteration in nutrient metabolism (trauma, major infection)
• Causes of obesity:
• Excessive caloric intake (especially carbohydrate and fat)
• Alteration in nutrient metabolism (genetic predisposition)
• Sedentary lifestyle
Dietary reference intakes (DRIs) of selected nutrients
• Fiber: 20-35 g/d (many people find this goal unpalatable)
• Calcium: 1,200-1,500 mg/d in adolescents and young adults; 1,000 mg/d in men until age 65 and women until age 50; 1,200-1,500 mg/d for life thereafter (usually requires supplements)
• Multivitamins: Helpful to meet daily requirements of pregnant and lactating women, elderly persons, and those who eat vegetarian or low-calorie diets
Nutritional assessment components
History and physical examination
• Dietary intake (anorexia, bullemia, hyperphagia, taste alterations)
• Underlying pathology affecting nutrition (cancer, burns)
• End-organ effects (diarrhea, constipation)
• General appearance (edema, cachexia)
• Skin appearance (scaling skin, decubitus ulcers)
• Musculoskeletal effects (depressed muscle mass, growth retardation)
• Neurologic effects (depressed sensorium, encephalopathy)
• Hepatic effects (jaundice, hepatomegaly)
• Skinfold measurements for assessment of fat (triceps, calf)
• Arm muscle circumference for assessment of skeletal muscle
• Weight for height to determine undernutrition or obesity
• Head circumference in infants to document appropriate growth
• Percentage of ideal body weight (IBW) after calculation of IBW for patient:
• IBW of males (kg) = 50 + (2.3 × height in inches over 5 feet)
• IBW of females (kg) = 45.5 + (2.3 × height in inches over 5 feet)
• Body mass index (BMI) for assessment of undernutrition or obesity calculated from body weight (kg) and height (m): BMI = weight (kg)/height2 (m2)
Serum albumin concentration
• Good prognostic indicator and good for assessment of long-term nutritional status
• Poor for repletion marker because of long half-life (21 d) and large body pool
Serum prealbumin concentration
• Good for short-term assessment of nutrition support because of short half-life (2 d) and small body pool
Serum transferrin concentration
• Good for short-term assessment of nutrition support because of short half-life (7 d) and small body pool
• Elevated in iron-deficiency anemia
Creatinine height index
• Requires 24-hour urine collection to determine levels of creatinine
Other methods of nutritional assessment
• Muscle strength testing
• Bioelectrical impedance (i.e., a low-grade electrical current runs through the body to identify body protein stores and fat stores)
Types of malnutrition
• Marasmus: Features depleted fat and muscle stores, normal biochemical measurements, and intact immune status
• Kwashiorkor: Features normal or elevated fat and body weight with abnormally low biochemical measurements and depressed immune function
• Kwashiorkor-marasmus mix: All measurements depressed
• Obesity: Demonstrated as elevated body weight to at least 120% of IBW or BMI > 27.8 (male) or > 27.3 (female)
• Class I obesity: BMI > 30 and < 35
• Class II obesity: BMI > 35 and < 40
• Class III obesity: BMI > 40
• Hypermetabolism: An increase in energy expenditure above normal (usually > 10% above normal)
• Hypercatabolism: An increase in protein losses above normal (usually via urinary excretion of urea nitrogen)
• Specialized nutrition support: Parenteral nutrition (PN) or enteral nutrition (EN)
• Basal energy expenditure (BEE): A calculation of the normal energy needs of healthy adult men or women using sex, age, height, and weight
• Harris-Benedict equations for BEE:
• Male (kcal/d) = 66 + 13.7 (weight in kg) + 5 (height in cm) - 6.8 (age in years)
• Female (kcal/d) = 655 + 9.6 (weight in kg) + 1.8 (height in cm) - 4.7 (age in years)
• Mifflin equations for energy expenditure:
• Male (kcal/d) = 10 (weight in kg) + 6.25 (height in cm) - 4.9 (age in years) + 5
• Female (kcal/d) = 10 (weight in kg) + 6.25 (height in cm) - 4.9 (age in years) - 161
• Resting energy expenditure (REE): A measured value of energy expenditure (generally ~10% above BEE or Mifflin in health, but can be 100% above BEE in severe burns)
• Respiratory quotient (RQ): The value that results when carbon dioxide production (VCO2) is divided by oxygen consumption (VO2)
• RQ for carbohydrate oxidation = 1.0
• RQ for fat oxidation = 0.7
• RQ for protein oxidation = 0.8
• RQ for fat synthesis = 8.0
• Body cell mass: Lean, metabolically active tissue (skeletal muscle, body organs)
• Lean body mass: Body cell mass, extracelluar fluid, and extracellular solids (bone, serum proteins)
• RDI: Recommended daily intake
18-2. Nutritional Requirements
• Most clinicians dose specialized nutrition support in total calories (i.e., using carbohydrate, fat, and protein-calorie contributions to obtain the desired dose).
• 25 kcal/kg/d for adults with little stress (e.g., elective surgery)
• 30 kcal/kg/d for patients with infections, skeletal trauma
• 35 kcal/kg/d for patients with major trauma (head injury, long-bone fractures)
• 40 kcal/kg/d for patients with major thermal injury (> 50% total body surface area burn)
• Multiply BEE by the stress factor to determine calorie requirements:
• 1.0 × BEE for patients with little stress
• 1.3 × BEE for patients with minor trauma, infections
• 1.5 × BEE for patients with major trauma
• 2 × BEE for patients with severe thermal injury
• Measure the REE via indirect calorimetry for calorie requirements.
Caloric Contribution of the Major Macronutrients
• Glucose: 3.4 kcal/g because hydrated glucose is used in PN (glucose powder would be 4 kcal/g)
• Fat: 9 kcal/g
• Protein: 4 kcal/g
• Protein requirements are usually dosed in grams per kilogram per day.
• 0.8 g/kg/d is the adult recommended daily allowance (RDA) for protein in the United States.
• 1.0 g/kg/d is the adult RDA for patients with minor stress (elective operations).
• 1.5 g/kg/d is the adult RDA for patients with major trauma or infection.
• 2.0 g/kg/d is the adult RDA for patients with severe head injury, sepsis, or severe thermal injury.
Measurement of Nutritional Efficacy Using Nitrogen Balance (NB)
NB = nitrogen in - nitrogen out
• Nitrogen in (grams) is determined by dividing the grams of protein taken in on the day of balance by 6.25.
• Nitrogen out (grams) is determined by measuring the grams of urea nitrogen excreted during a 24-hour urine collection and then adding a factor of 2 or 4 g for insensible nitrogen loss or stool loss.
• Positive NB can be used to document adequacy of nutritional support:
• In undernourished patients, +4 to +6 g/d is desired.
• Nitrogen equilibrium (-2 to +2 g/d) is usually adequate in critically ill patients.
Other Requirements during Nutrition Support
• Up to 35 mL/kg/d for average-sized adults
• 40 mL/kg/d for smaller adults and adolescents
• > 40 mL/kg/d for patients with extrarenal losses (e.g., gastrointestinal drains)
• Sodium requirements:
• 60-100 mEq/d in adults
• 2-6 mEq/kg/d in children
• Chloride requirements:
• 60-100 mEq/d in adults
• 2-6 mEq/kg/d in children
• Potassium requirements:
• 60-100 mEq/d in adults
• 2-5 mEq/kg/d in children
• Calcium requirements:
• 5-15 mEq/d in adults
• 2-3 mEq/kg/d in children
• Phosphorus requirements:
• 20-45 mmol/d in adults
• 1-2 mmol/kg/d in children
• Magnesium requirements:
• 10-20 mEq/d in adults
• 0.25-1.00 mEq/kg/d in children
• Vitamins are provided daily in both PN (added) and EN (endogenous).
• Most enteral formulations provide the DRI for vitamins in a volume of 1,000-1,500 mL.
• For parenteral vitamin products:
• Adult products contain 12 (MVI-12) or 13 vitamins (Infuvite Adult, MVI-Adult); vitamin K is added separately when the product with 12 vitamins is used.
• Pediatric products (MVI-Pediatric, Infuvite Pediatric) contain all 13 vitamins.
• Zinc: 3-5 mg/d in adults with PN; 50-250 mcg/kg/d in children with PN
• Copper: 0.5-1.2 mg/d in adults with PN; 20 mcg/kg/d in children with PN (maximum of 300 mcg/d)
• Chromium: 10-15 mcg/d in adults with PN; monitored but not given to children
• Manganese: 50-100 mcg/d in adults with PN; monitored but not given to children
• Selenium: 40-80 mcg/d in adults with PN; 1.5-3.0 mcg/kg/d in children with PN
18-3. Specialized Nutrition Support
PN is generally used for patients who cannot be fed via the gastrointestinal tract.
Severe acute pancreatitis
• Oral or tube feeding will usually exacerbate this condition unless given via the jejunum (e.g., nasojejunal feeding tube or jejunostomy).
Short bowel syndrome
• This condition requires PN from a few weeks to lifelong, as needed.
• This condition is secondary to lack of bowel function (e.g., acute renal failure secondary to sepsis)
• Crohn's disease exacerbation with fistula or obstruction
• Neonates who cannot eat in the first day of life
• Preoperatively for undernourished patients who are undergoing an elective operation and for whom there is no direct access to the gastrointestinal tract (e.g., partial small bowel obstruction from cancer)
• Pregnancy with severe hyperemesis gravidarum (i.e., there is an inability to tolerate oral or enteral nutrition)
• Gastrointestinal fistulae where oral or enteral nutrition should be restricted
Components of parenteral nutrition
• Protein should be included in all PN formulations.
• Standard amino acids from 10%, 15%, or 20% stock solutions can be used for most patients.
• Final concentrations in the PN formulation vary from 2% to 7%.
• Doses > 2 g/kg/d are rarely needed.
• Fat is provided as intravenous fat emulsion either as a separate infusion or admixed with the rest of the PN formulation, making a total nutrient admixture (TNA).
• Products are manufactured as 10%, 20%, and 30% fat emulsions. (In the United States, 30% can be used only for TNAs, not for direct infusion.)
• Fat provides essential fatty acids to the patient who is most likely not eating by mouth.
• Fat provides nonprotein calories other than glucose.
• Common doses used in adults are ~1 g/kg/d (9-10 kcal/kg/d).
• Intravenous fat emulsions contain phospholipid to emulsify the product and glycerol to make the emulsion isotonic. (Both of these components provide modest calories.)
• Common doses of dextrose in critically ill patients are 3-4 mg/kg/min (~15-20 kcal/kg/d).
• Dextrose is in all PN formulations for obligate needs (central nervous system, renal medulla, white blood cells, red blood cells, and wound healing)
• PN formulations are usually made from 70% dextrose in water.
• Final concentrations in the PN formulation vary from D10W to D35W.
• Dextrose should never exceed a dose of 5 mg/kg/min (~25 kcal/kg/d).
• Sodium can be provided as chloride, acetate, or phosphate salts in PN.
• After phosphate addition, the remaining anions are added on the basis of acid-base status. They are split between chloride and acetate with a normal pH, predominantly acetate with metabolic acidosis, and predominantly chloride with metabolic alkalosis.
• Requirements can be increased when the patient has extrarenal losses from nasogastric suction, abdominal drains, or ostomy losses.
• Potassium can be provided as chloride, acetate, or phosphate salts in PN
• Requirements can be increased with administration of potassium-wasting drugs (diuretics, steroids) or in severe undernutrition.
• Like sodium, the remaining potassium can be added as acetate or chloride on the basis of acid-base status after the proper dose of phosphate is determined.
• Most practitioners add calcium as the gluconate salt.
• Higher doses of calcium (~20-25 mEq/d) are needed in patients receiving long-term PN to help prevent metabolic bone disease.
• Addition of calcium is limited in PN formulations because of the potential to precipitate with phosphate salts, which ultimately results in insoluble calcium phosphate.
• Phosphate is added as the sodium or potassium salt.
• Higher doses of phosphorus (e.g., 30 mmol/L) are needed to prevent refeeding syndrome in severely undernourished patients.
• Phosphorus should be decreased or removed in patients with renal failure.
• Most practitioners prefer sodium phosphate over potassium phosphate because of the higher concentration of aluminum in the latter product, especially in chronic use of PN.
• Addition of phosphorus is limited in PN formulations because of the potential to precipitate with calcium or magnesium salts to form an insoluble compound.
• Most practitioners add magnesium as the sulfate salt.
• Higher doses should be used in patients with alcoholism or large bowel losses or in patients receiving drugs causing renal wasting of magnesium (cisplatin, amphotericin B, aminoglycosides, loop diuretics).
• Magnesium should be restricted or deleted in patients with renal failure.
• Multivitamins are given daily as part of PN.
• Parenteral multivitamin preparations contain 12 or 13 vitamins. (Vitamin K should be administered separately if the 12-vitamin preparation is used.)
• Additional thiamine and folic acid are often given to alcoholic patients who are receiving PN.
• Additional folic acid (at least 600 mcg/d) should be given to pregnant patients receiving PN.
• Trace elements are given daily as a cocktail of four or five trace metals.
• Extra zinc should be given in patients with ostomy or diarrhea losses.
• Copper and manganese should be reduced or eliminated in patients with cholestasis.
• Extra selenium is usually needed in homebound PN patients.
Total nutrient admixtures versus two-in-one admixtures
Advantages of TNAs
• Decreased nursing time for administration
• Potentially decreased touch contamination
• Decreased pharmacy preparation time (assuming a 24-hour hang time)
• Financial savings (use of only one pump and one intravenous administration set)
Disadvantages of TNAs
• TNAs are better media for bacterial growth than are two-in-one admixtures.
• It is impossible to visualize particulate matter.
• Filter formulation with a 0.22-micron filter is not possible.
• Some additives like calcium and phosphorus are less compatible in TNAs.
Central vein PN versus peripheral vein PN
Advantages of central vein PN
• Central vein PN can maximize caloric intake.
• Volume restriction of patients is possible.
• Long-term catheter can be maintained.
Disadvantages of central vein PN
• Mechanical complications during catheter placement (e.g., pneumothorax)
• Potential hyperosmolar complications (e.g., from using hypertonic dextrose)
• Potential septic catheter complications
Advantages of peripheral vein PN
• It is easier to place the catheter (i.e., peripheral vein stick).
• Hyperosmolar complications are avoided because dilute formulations must be used.
Disadvantages of peripheral vein PN
• Incidence of thrombophlebitis is high.
• Frequent vein rotation is necessary.
• Energy intake is limited.
• Volume restriction is not possible (using dilute formulations).
• Cost is higher because more lipid calories are generally used. (Lipids are isotonic.)
Parenteral nutrition calculations
D20W (final concentration of PN formulation)
• D20W = 20% dextrose = 20 g/100 mL = 200 g/L × 3.4 kcal/g = 680 dextrose kcal/L
• 2 L/d of D20W (final concentration of PN formulation) = 1,360 dextrose kcal/d
Amino acids 5% (final concentration of PN formulation)
• 5% amino acids = 5 g/100 mL = 50 g/L × 4 kcal/g = 200 protein kcal/L
• 2 L/d of 5% amino acids = 100 g/d = 400 protein kcal/d
Lipid 2% (final concentration of TNA formulation)
• 2% lipid will deliver 200 kcal/L (includes calories from glycerol/phospholipid)
• 2 L/d of lipid 2% = 400 fat kcal/d
Lipid 20% infused at 20 m L/h × 24 h (separate infusion given with two-in-one PN formulations)
• 20% lipid = 2 kcal/mL
• 20 mL/h × 24 h = 480 mL/d
• 480 mL/d × 2 kcal/mL = 960 fat kcal/d
Example: D30W; amino acids 4%; lipid 3%, at 60 mL/h
• 60 mL/h × 24 h/d = 1,440 mL/d (1.44 L/d)
• D30W = 30% dextrose = 300 g/L × 3.4 kcal/g = 1,020 kcal/L × 1.44 L = 1,469 dextrose kcal
• 4% amino acids = 40 g/L = 160 kcal/L × 1.44 L = 230 protein kcal
• 3% lipid = 300 kcal/L × 1.44 L = 432 fat kcal
• 1,469 kcal + 230 kcal + 432 kcal = 2,131 total kcal/d from the above PN formulation
Example: dextrose 400 g; amino acids 100 g; lipids 40 g; at 85 mL/h
• Dextrose 400 g × 3.4 kcal/g = 1360 kcal/d
• Amino acids 100 g × 4 kcal/g = 400 kcal/d
• Lipids 40 g × 10 kcal/g (includes phospholipid and glycerol) = 400 kcal/d
General principles of compounding parenteral nutrition
• Each component of the PN prescription should be reviewed to ensure a balanced PN formulation is provided.
• Each component should be assessed for dose and potential compatibility programs.
• All compounded PN formulations should be visually inspected to ensure no gross contamination or precipitation is present.
• Manufacturers of automated compounders should provide the additive sequence to ensure safety in PN preparation.
General principles of stability and compatibility of parenteral nutrition
• Parenteral multivitamins should be added shortly before dispensing and administering the PN formulation because vitamins A and C degrade fairly quickly.
• Preparation of TNAs using dual-chambered bags (lipid is kept in a separate compartment until administration) can enhance the shelf life of a PN formulation.
• Dibasic calcium phosphate (CaHPO4) can precipitate in PN formulations if the amounts of calcium gluconate and sodium or potassium phosphate are excessive.
• Generally, phosphate should be added first to the PN formulation.
• Generally, calcium should be added last to the PN formulation.
• Calcium chloride should not be used in PN because it is highly reactive with phosphate.
• Iron dextran can be added to two-in-one PN formulations but should not be added to TNAs.
Parenteral nutrition filtration
• Filters are used to prevent administration of particulate matter, microorganisms, and air.
• Use a new 0.22-micron filter each day with two-in-one PN formulations (0.22-micron filters with positive charged nylon can be used for up to 96 hours in two-in-one PN formulations).
• Use a new 1.2-micron filter each day with TNAs.
Complications of parenteral nutrition
• Patients with stress of trauma or infection or those with diabetes often need regular human insulin added to the PN formulation to control hyperglycemia.
• Regular insulin continuous infusions are often needed to control hyperglycemia.
• Patients often require extra potassium in PN (e.g., 60 mEq/L).
• Patients often require extra phosphorus in PN (e.g., 30 mmol/L).
• Patients often require extra magnesium in PN (e.g., 16 mEq/L).
• Diagnosis of sodium disorders must include an assessment of extracellular fluid status (i.e., volume status).
• Volume depleted: Add sodium and water to PN, or increase intravenous fluid administration.
• Volume overloaded: Remove sodium from PN and concentrate the formulation.
• Euvolemic: Generally, water restriction is first-line therapy (concentrate the PN formula).
• Increase acetate and decrease chloride anions if the patient has metabolic acidosis.
• Increase chloride and decrease acetate anions if the patient has metabolic alkalosis.
Essential fatty acid deficiency
• During PN, at least 4% of total calories need to be provided as intravenous lipid (easily attained when lipid is used daily as a calorie source).
Trace element disorders
• Patients with increased ostomy output or chronic diarrhea need extra zinc.
• Hold copper and manganese in patients with cholestasis.
• Fatty infiltration of the liver has been reported with long-term PN.
• Hepatic steatosis is thought to be primarily caused by administration of excessive dextrose calories.
• The key to prevention is through administration of an appropriate dose of dextrose (e.g., < 5 mg/kg/min).
• Pneumothorax (punctured lung) can occur during central vein canulation.
• Subclavian artery injury can occur when the artery is cannulated instead of the vein.
• Subclavian vein thrombosis can occur with long-term central vein access. (Heparin is used in some PN patients to prevent this condition.)
• Such complications are usually due to catheter-related breakdown in sterile technique.
• They are rarely solution related.
Monitoring of parenteral nutrition
Frequency and intensity of monitoring is based on the patient's condition, as assessed by
• Electrolyte balance and glucose control
• Acid-base status via arterial blood gases
• Intake and output for assessment of fluid balance
• Serum prealbumin concentrations, nitrogen balance, or both to document efficacy
• EN is generally used in patients who cannot or will not eat but have a functional and accessible gastrointestinal tract.
• Neonates should begin EN as early as possible, even if receiving PN.
• EN is used in elderly patients who lack the ability to ingest food orally.
• Cardiac patients may need fluid-restricted EN with fluid overload.
• EN is used frequently in patients receiving mechanical ventilation.
• EN is used frequently in this population.
• In severe hepatic encephalopathy, use a formulation with high branched-chain amino acids and low aromatic amino acids.
• In the absence of encephalopathy or mild encephalopathy, use EN with standard protein.
• In short bowel syndrome, EN is used to enhance small bowel hypertrophy after major bowel resection.
• In inflammatory bowel syndrome, EN is the preferred method of nutrition support.
• EN is preferred because the patient may not be able to eat, but the gastrointestinal tract is functional and accessible.
Cancer or HIV infection
• Use EN (if possible) in these patients to prevent or treat undernutrition.
Types of enteral access
• Feeding enterostomy
• Feeding enterostomy is used for long-term EN.
• Gastrostomy requires a G-tube or PEG (percutaneous endoscopic gastrostomy).
• Jejunostomy requires an exploratory laparotomy to place.
• Oral route (by drinking supplements)
• Nasal tube feeding
• Nasal tube feeding is usual for short-term EN.
• Nasogastric, nasoduodenal, or nasojejunal tubes are used.
Products for enteral nutrition
• Polymeric, nutritionally complete tube feeding is used for patients with normal digestive processes (e.g., 1 kcal/mL).
• Concentrated, nutritionally complete tube feeding is used for patients who need severe fluid restriction (e.g., 2 kcal/mL).
• Polymeric, nutritionally complete, oral supplements are used to supplement an oral diet (e.g., 1.0 or 1.5 kcal/mL).
• Chemically defined, nutritionally complete tube feeding is used for patients with impaired digestive processes such as short bowel syndrome or pancreatic insufficiency (e.g., 1 kcal/mL).
• Fiber-containing, nutritionally complete tube feeding is beneficial in patients who receive long-term tube feeding (can prevent diarrhea and constipation; e.g., 1.0 or 1.2 kcal/mL).
• Concentrated, low-protein, low-electrolyte tube feeding is generally used for patients with renal failure.
• A high branched-chain amino acid, low aromatic amino acid EN formula is used for patients with liver failure and severe hepatic encephalopathy (e.g., 1.0 or 1.5 kcal/mL).
• High-fat, low-carbohydrate, nutritionally complete tube feeding is helpful in management of diabetic or other glucose-intolerant patients (e.g., 1.0 or 1.2 kcal/mL).
• Immune-enhancing formulas that contain arginine, glutamine, and omega-3 fatty acids are marketed and used in patients with high metabolic stress (e.g., severe trauma or infection; 1.0 or 1.3 kcal/mL).
Complications of enteral nutrition
Pulmonary (e.g., aspiration pneumonia)
• The most severe complications of EN are pulmonary.
• Pulmonary complications are caused by regurgitation of gastric contents into the lung (with or without tube feeding).
• Prevention is important.
• Elevate the head of the bed to 30° if possible.
• Frequently assess the patient's abdomen to ensure tolerance.
• Frequently assess the placement of the feeding tube (especially nasally placed tubes).
• Diarrhea is often associated with the administration of EN, but EN is not necessarily the cause of the diarrhea.
Increased frequency or volume of stools
• Pharmacotherapy is often the cause, because of sorbitol in liquid vehicles.
• Lack of fiber and excessive infusion rate advancements can also be causes.
• Decreasing (or at least not advancing) the infusion rate is appropriate.
• Change to a fiber-containing formulation if the patient is not receiving one.
• Pseudomembranous enterocolitis can occur from antibiotic therapy.
• Use pharmacotherapeutic treatment if the above factors are ruled out (bismuth subsalicylate, loperamide, diphenoxylate).
Constipation (decrease in stool frequency)
• Lack of fiber can be a cause.
• Lack of water can be a cause.
• Poor mobility and drugs with anticholinergic activity can contribute.
• Keep patient well hydrated and use a fiber-containing EN formulation.
• In the event of nasal necrosis, use a small-bore feeding tube and do not tape it too firmly to the nose.
• To prevent esophageal injury, use a small-bore feeding tube.
• To prevent it from clogging, frequently flush the feeding tube with warm water.
• In the event of tube displacement, discourage removing the tube; the tube may have to be anchored with a bridle.
• Use regular human insulin.
• Consider a high-fat, low-carbohydrate EN formulation.
• Regular insulin continuous infusions are sometimes necessary
• Provide additional potassium as an intravenous (IV) or per tube supplement.
• Some institutions allow the addition of potassium salts to the EN formulation.
• Provide additional phosphorus as an IV supplement (e.g., potassium phosphate).
• Some institutions allow the addition of phosphorus salts to the EN formulation (e.g., injectable sodium or potassium phosphate).
Monitoring of enteral nutrition
The intensity of monitoring will be dictated by the condition of the patient:
• Electrolyte balance and glucose control
• Acid-base status via arterial blood gases (critical care only)
• Intake and output for assessment of fluid balance
• Assessment of the patient's abdomen is required:
• Positive bowel sounds usually should be present.
• The abdomen should be soft, nontender, and nondistended in most cases.
• A profoundly distended abdomen usually requires the EN to be decreased or discontinued temporarily.
• Serum prealbumin concentrations, nitrogen balance, or both should be assessed to document efficacy.
Home Nutrition Support
• PN can be given from weeks to a lifetime (e.g., severe short bowel syndrome).
• PN is usually cycled at night over 10-16 hours.
• Patient must be monitored closely for iron deficiency because iron supplementation is not routinely added to PN.
• Regular assessment of hemoglobin, hematocrit, and mean corpuscular volume is required.
• Serum iron, total iron-binding capacity, and ferritin are commonly used in the diagnosis of iron deficiency.
• Metabolic bone disease is another long-term complication of home PN.
• Supplemental calcium in the PN formulation is usually required (15-25 mEq/d).
• Adequate vitamin K for osteocalcin is important on a long-term basis.
• EN can be given indefinitely as full nutrition support or as a supplement to an oral diet.
• Permanent feeding ostomies are used almost exclusively in home EN.
• Patients in nursing homes and extended care facilities usually receive EN as a continuous (24 hours) or intermittent (e.g., 12 hours) infusion.
• Patients who receive home EN via gastrostomy usually receive bolus feeding (e.g., two 240-mL cans tid via PEG).
• Patients who receive home EN as a supplement to oral intake are often cycled at night (e.g., 1,000 mL at 85 mL/h from 7:00 pm to 7:00 am each night).
18-4. Major Drug-Nutrient Interactions
Phenytoin and Enteral Tube Feeding
• It has been demonstrated that enteral feeding will bind to phenytoin, thus impairing the absorption dramatically, possibly because of the protein component of EN (caseinates).
Management of Phenytoin-Enteral Nutrition Interaction
• Hold the EN 2 hours before and after the daily dose of phenytoin capsules.
• Hold the EN 1 hour before and after each dose of phenytoin suspension (usually given bid or tid).
• Increase the EN infusion rate to allow the desired nutritional dose of EN to be given (i.e., to make up for the lost time while the EN is being held for drug administration).
Warfarin and Enteral Tube Feeding
• It has been reported that adequate anticoagulation with warfarin is very difficult to achieve with concurrent EN (low international normalized ratios).
Management of Warfarin-Enteral Nutrition Interaction
• Hold EN 1 hour before and after the daily warfarin dose. If this is done, the EN rate should be increased to attain the desired nutritional dose.
Management of Grapefruit Juice-Drug Interaction
• Grapefruit juice interacts with many drugs (e.g., amlodipine, carbamazepine, cyclosporine)
• Grapefruit juice from frozen concentrate has been reported to inhibit gastrointestinal cytochrome P450-3A4, resulting in enhancement of oral absorption of some drugs (toxicity).
• When taking drugs that are known to interact with grapefruit juice, patients should be advised to avoid these grapefruit products (i.e., substitute another fruit juice such as apple or orange juice).
18-5. Key Points
• Malnutrition can present as either undernutrition or obesity.
• The components of a nutritional assessment include a history and physical exam, anthropometric measurements, and biochemical tests.
• An increase in energy expenditure (energy needs) is defined as hypermetabolism, and an increase in nitrogen excretion (protein needs) is defined as hypercatabolism.
• Most patients receiving specialized nutrition support (parenteral or enteral nutrition) require 25-30 kcal/kg/d and 1-2 g protein/kg/d.
• The water requirement for most adult patients without substantial extrarenal losses is 30-40 mL/kg/d.
• PN should be reserved for patients whose gastrointestinal tracts are not functional or accessible (e.g., severe acute pancreatitis, severe short bowel syndrome).
• TNAs contain dextrose, amino acids, lipid emulsion, electrolytes, vitamins, and trace elements in one container.
• The advantages of TNAs include decreased nursing administration time, decreased potential for touch contamination, and reduced expense (the patient needs only one pump and one intravenous administration set).
• The advantages of central vein PN over peripheral vein PN include the ability to concentrate the formulation, administer adequate calories and protein, and use the catheter for long-term administration.
• For PN calculations: 1 g hydrated dextrose = 3.4 kcal, 1 g amino acids = 4 kcal, and 1 g lipid = 9 kcal. (Intravenous fat emulsion actually provides 10 kcal/g because it includes calories provided as glycerol and phospholipid.)
• All PN formulations should be filtered during administration (0.22-micron filter for two-in-one PN formulations and 1.2-micron filter for TNAs).
• Enteral nutrition support is generally used in patients who cannot or will not eat but have a functional and accessible gastrointestinal tract.
• Enteral tube feeding can be provided by one of the following methods: nasogastric, nasoduodenal, nasojejunal, gastrostomy, or jejunostomy.
• Diarrhea associated with enteral tube feeding is often caused by pharmacotherapy (e.g., sorbitol in liquid drug preparations as a vehicle).
• Patients receiving phenytoin or warfarin concurrently with enteral tube feeding should have the tube feeding held at least 1 hour before and after each dose.
What is the most appropriate calcium intake (mg/d) for adults over 65 years of age?
A. 600-800 mg
B. 800-1,000 mg
C. 1,000-1,200 mg
D. 1,200-1,500 mg
E. 1,500-1,800 mg
Case Study for Questions 2 and 3
A patient presents for a comprehensive nutritional assessment. She is 35 years old, is 5 feet 8 inches, and weighs 52 kg. She has a history of Crohn's disease involving both the small bowel and colon. She has had no surgeries but has intermittent diarrhea.
• Prednisone 5 mg qod
• Mesalamine 1 g tid
• Loperamide 2 mg q6h prn diarrhea
• Triceps skinfold = 3 mm (normal, 10-14 mm)
• Calf skinfold = 4 mm (normal, 10-15 mm)
• Serum albumin concentration = 2.5 g/dL
• Serum prealbumin concentration = 13 mg/dL (normal, 15-45 mg/dL)
The triceps skinfold measurement for this patient is an anthropometric measurement for assessment of
A. somatic protein stores.
B. fat stores.
C. visceral protein stores.
D. immune competence.
E. body cell mass.
What type of malnutrition does this patient have?
D. Kwashiorkor-marasmus mix
E. Fat overload syndrome
A patient with a bone fracture and gram-negative pneumonia excretes 15 g (normal, 6-8 g/d) of urea nitrogen during a 24-hour urine collection. On the basis of these data, the patient is
During nutritional assessment, the measurement of body cell mass includes
B. interstitial fluid.
C. skeletal muscle.
D. intravascular fluid.
E. extracellular fluid solids.
Case Study for Questions 6-9
Following major gastrointestinal resection, a patient with severe short bowel syndrome is started on parenteral nutrition (PN). It is anticipated that this patient may need this therapy for 6 months to 1 year. The PN prescription for this patient includes
• D20W amino acids 5% (final concentrations) at 105 mL/h (2,500 mL/d)
• Intravenous fat emulsion 20% at 10 mL/h × 24 h (240 mL/d)
• 0.45% sodium chloride injection at 50 mL/h × 24 h (1,200 mL/d)
How many calories from dextrose will this patient receive each day?
How many grams of protein will this patient receive each day?
How many calories from intravenous lipid will this patient receive each day?
Calculate the daily nitrogen balance (grams per day) in this patient if she excretes 12 g of urea nitrogen during the urine collection and 4 g are used as insensible and stool loss each day.
What would be an appropriate water or fluid requirement for a 60-kg patient with no extrarenal fluid losses?
A. 800 mL
B. 1,200 mL
C. 2,400 mL
D. 3,600 mL
E. 4,800 mL
Which of the following disease states or clinical conditions would usually require the administration of parenteral nutrition?
A. Severe acute pancreatitis
B. Motor vehicle crash resulting in femur fracture and head injury
C. 20% body surface area burn from a house fire
D. Laparoscopic cholecystectomy
E. Acute exacerbation of hepatic encephalopathy
What is the maximum dose (in kilocalories per kilogram per day) of dextrose in parenteral nutrition for adult patients?
In a patient with metabolic acidosis, what anion salt would you use to add the majority of sodium and potassium to a PN formulation?
If excessive amounts of calcium are added to a standard parenteral nutrition formulation, it will likely precipitate with
Which vitamin should be supplemented above standard amounts during nutrition support of a pregnant patient?
B. Folic acid
E. Pantothenic acid
Which of the following is an advantage of central vein parenteral nutrition over peripheral vein parenteral nutrition?
A. Allows easier catheter placement
B. Does not require a pump for administration
C. Allows for fluid restriction
D. Does not have to be filtered
E. Uses dilute formulations in most cases
Which component of a total nutrient admixture should be added last before storing it in a refrigerator?
C. Trace elements
E. Intravenous fat emulsion
Which of the following are advantages of using a 0.22-micron filter when administering a two-in-one parenteral nutrition formulation?
I. Traps particulate matter
II. Prevents precipitates from entering the patient
III. Filters most bacteria
A. I only
B. III only
C. I and II only
D. II and III only
E. I, II, and III
Which trace element should be reduced or removed in patients with cholestasis who are receiving parenteral nutrition?
A 70-year-old female who has mild congestive heart failure, gastroesophageal reflux disease (GERD), type II diabetes mellitus, and rheumatoid arthritis had a recent cerebral vascular accident. She will not regain her premorbid degree of mental status, so a decision is made to give her long-term nutritional support. Which method would be most appropriate for this patient?
A. Central parenteral nutrition
B. Nasogastric tube feeding
C. Peripheral parenteral nutrition
D. Jejunostomy tube feeding
E. Nasoduodenal tube feeding
A common cause of diarrhea in patients receiving enteral nutrition is from the
A. osmotic load of the enteral nutrition formulation.
B. sorbitol in drug vehicles.
C. addition of fiber to the enteral nutrition formulation.
D. solute load from the protein component of the enteral nutrition formulation.
E. improper placement of a nasogastric feeding tube.
What is the drug of choice for enhancing gastric emptying in a patient receiving enteral nutrition support?
A. Bismuth subsalicylate
A patient is receiving phenytoin capsules 300 mg each day for seizure control. She requires tube feeding with a 1 kcal/mL formulation at 85 mL/h (2,000 mL/d). What would be the most appropriate intervention to maintain a therapeutic drug concentration and maintain the required nutrition support?
I. Increase the dose of phenytoin to 600 mg/d.
II. Hold the enteral nutrition 2 hours before and after the dose.
III. Increase the enteral nutrition to 100 mL/h × 20 hours.
A. I only
B. III only
C. I and II only
D. II and III only
E. I, II, and III
What is the mechanism for grapefruit juice to inhibit the metabolism of some drugs that can result in drug toxicity?
A. Decreased renal excretion of drug
B. Inhibition of gastrointestinal cytochrome P450-3A4
C. Decreased systemic clearance of drug
D. Inhibition of hepatic cytochrome P450-3A4
E. Expanded apparent volume of distribution
D. Calcium requirements are 1,000 mg/d for male adults until age 65, when they increase to 1,200-1,500 mg/d. Calcium requirements are 1,000 mg/d for female adults until age 50, when they increase to 1,200-1,500 mg/d.
B. Skinfold measurements measure body fat stores, which assess the lipid component of the body. Visceral protein stores are serum proteins. Body cell mass and somatic protein stores assess skeletal muscle and visceral organs. Immune competence assessment requires a skin test with a common antigen.
D. All measurements of nutritional assessment are depressed (i.e., weight for height, anthropometric measurements, and biochemical serum markers of protein status).
A. Catabolism is related to loss of body protein. Because it is increased, the patient would be considered hypercatabolic in this case.
C. Lean body mass includes bone, skeletal muscle, visceral organs, and extracellular solids. Body cell mass includes only the lean, metabolically active tissue such as skeletal muscle and visceral organs (e.g., liver).
D. D20W = 20 g/100 mL = 200 g/L × 2.5 L/d = 500 g/d × 3.4 kcal/g = 1,700 kcal/d.
E. 5% amino acids = 5 g/100 mL = 50 g/L × 2.5 L/d = 125 g/d.
C. Intravenous lipid emulsion 20% = 2 kcal/mL × 240 mL/d = 480 kcal/d.
E. The nitrogen intake is calculated by dividing the protein intake (125 g) by 6.25, which results in 20 g. The nitrogen output would be the sum of the urinary urea nitrogen and insensible losses (12 g + 4 g = 16 g/d). Therefore, the nitrogen balance would be 20 g -16 g = 4 g. A nitrogen balance of +4 would be suggestive of nutritional adequacy with this PN formulation.
C. Water requirements are 30-40 mL/kg/d for patients without extrarenal fluid losses: 60 kg × 40 mL/kg/d = 2,400 mL/d.
A. It is difficult to feed patients with severe pancreatitis enterally unless there is access to the small bowel (e.g., jejunostomy). The other clinical conditions, such as trauma and burns, would occur in patients in whom the gastrointestinal tract could and should be used for nutrition support. A patient receiving laparoscopic cholecystectomy would not need nutrition support. Most patients with hepatic encephalopathy can be fed enterally if they require nutrition support.
E. The dose of dextrose in PN should never exceed 5 mg/kg/min in adult patients. This dose can be converted to 25 kcal/kg/d.
D. Acetate is converted to bicarbonate in the liver and would thus help or at least not exacerbate the metabolic acidosis.
A. Calcium phosphate is a relatively insoluble compound, so manufacturer guidelines for the concentrations of these two elements must be followed closely to prevent precipitation. The order of mixing these components in the PN formulation is also important.
B. Folic acid should be given at a dose of at least 600 mcg/d during pregnancy. Many practitioners administer 1 mg/d above what the patient is eating or receiving via nutrition support. This practice has been shown to prevent neural tube defects in the newborn.
C. Hyperosmolar nutrients (dextrose, amino acids) can be used to concentrate the PN formulation, but the PN would have to be administered via a central vein.
D. If calcium is added last, the PN formulation will contain the final volume, including all other nutrients. The chance of calcium causing a precipitate will be decreased because all other components (e.g., phosphorus) are diluted in the entire volume of the PN.
E. A 0.22-micron filter will do all three. In contrast, a 1.2-micron filter (used with TNAs) will not filter most bacteria.
D. Copper is excreted via the biliary tract. Patients with severe cholestasis should have copper removed during short-term parenteral nutrition. In long-term PN, copper may be required in reduced doses to prevent anemia. Serum copper concentrations should be monitored regularly in long-term patients who have cholestasis.
D. She is not a candidate for long-term PN because her gastrointestinal tract would be accessible and functional. Nasogastric and nasoduodenal methods are used only for short-term enteral nutrition. A jejunostomy would be ideal because she also has GERD and perhaps gastroparesis from her diabetes.
B. Several liquid preparations for drugs contain sorbitol as a pharmaceutical vehicle. These liquid preparations are commonly used in patients with tubes because the drugs can be given easily this way, especially if the patient cannot swallow. Most enteral nutrition formulations are close to being isotonic (i.e., the osmotic load or solute load is not a major factor causing diarrhea). Fiber will prevent or improve diarrhea in most cases.
C. Metoclopramide enhances gastric emptying and is commonly used in patients with gastrointestinal intolerance. This is true in both diabetics and nondiabetics.
D. Phenytoin absorption is markedly impaired when it is given concurrently with enteral tube feeding. The enteral tube feeding should be held 2 hours before and after the daily dose of phenytoin capsules. To maintain the current dose of enteral nutrition, the rate of feeding should be increased to 100 mL/h × 20 h (2,000 mL/d).
B. Drugs such as amlodipine, carbamazepine, and cyclosporine are profoundly metabolized in the gastrointestinal tract before absorption. Grapefruit juice from frozen concentrate has been shown to inhibit gastrointestinal cytochrome P 450-3A4 and thus allows more of the drug to be absorbed, thereby causing drug toxicity for drugs with a narrow therapeutic index.
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