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Section 3 - TPN solution requirements

Introduction

The primary goal of parenteral nutrition (PN) is to provide patients with adequate calories and protein to prevent malnutrition and its associated complications. A normal diet provides individuals with an adequate mix of carbohydrates, fats and proteins for energy and tissue development. Parenteral nutrition therapy must provide patients with these same dietary components with: Please support this web site

  • Protein in the form of amino acids
  • Carbohydrates in the form of glucose
  • Fat as a lipid emulsion

In addition to protein, carbohydrates and fat, PN provides other dietary components, including:

  • Water
  • Electrolytes
  • Vitamins
  • Trace minerals

Because a number of factors can affect the amount of each of these components that the patient needs, each component of PN must be evaluated and ordered separately.


Patient selection

General indications
TPN therapy is indicated for patients:

  • Requiring long-term (>10 days) supplemental nutrition because they are unable to receive all daily requirements through oral or enteral feedings.
  • Requiring total nutrition because of severe gut dysfunction or inability to tolerate enteral feedings.

Specific indications
TPN therapy is part of routine care in:

  • Patients who cannot eat or absorb nutrients through the GI tract because of:
    • Massive bowel resection
    • Diseases of the small bowel
    • Radiation enteritis
  • Malnourished patients undergoing high-dose chemotherapy or radiation therapy.
  • Patients with severe necrotizing pancreatitis when enteral feeding is not possible.
  • Patients with severe malnutrition and nonfunctional gut.
  • Malnnourished patients with AIDS who have intractable diarrhea.
  • Severely catabolic patients whose gut cannot be used within 5 to 7 days.

When enteral feeding cannot be established, TPN is usually helpful:

  • After major surgery.
  • In patients with enterocutaneous fistulas, both high and low.
  • In patients with inflammatory bowel disease.
  • In patients with hyperemesis gravidarum.
  • In patients with small bowel obstruction secondary to adhesions.


Fluid requirements

Before TPN is initiated, and throughout the duration of TPN therapy, careful assessment of fluid status is imperative. Often, between meeting the caloric, protein, and electrolyte needs, sufficient, if not excessive, water is provided. However, in circumstances where water needs are elevated or reduced, or the patient's body size is abnormally large or small, fluid requirements become an extremely important consideration.

Fluid requirements
Increased in Decreased in
Fever Renal failure
Fistulas Congestive heart failure
Diarrhea Cirrhotic ascites
NG suction Pulmonary disease


Calorie and protein requirements

Since protein is needed for tissue synthesis and repair, amino acids are not routinely used for basic energy requirements. Dextrose and lipids are typically used to provide a patient's energy needs. The preferred mixture combines 70%-85% of calories from dextrose and 15%-30% from lipids. The inclusion of protein in the calculation of energy, called "total calories" versus "nonprotein calories", is controversial. However, in the hypermetabolic patient with excessive energy needs, protein may be utilized for energy.

Macronutrient requirements

Standard Range Maximum
Calories
kcal/kg/day
Infants = 90 - 100
Children = 70 - 100
Adolecents = 40 - 55
Adults = 28 - 30
Adults = 40
Protein
g/kg/day
Infants = 2.0 - 2.5
Children = 1.5 - 2.0
Adolecents = 0.8 - 2.0
Adults = 0.8 - 1.0
Adults = 2.0
Dextrose rate 4 - 5 mg/kg/min 7 mg/kg/min
Fat 15 - 30% kcal 60% kcal


Micronutrient requirements

Electrolytes

Initial electrolyte doses in a PN order must be individualized for each patient. Starting doses of electrolytes should be at maintenance levels and evaluated daily during initial startup of PN therapy. As the patient demonstrates tolerance and as electrolyte needs stabilize, less frequent monitoring may be performed.

Electrolyte requirements

Usual adult range Infants/children
Sodium 60 to 200 mEq/day 2 to 4 mEq/kg/day
Potassium 60 to 200 mEq/day 2 to 4 mEq/kg/day
Magnesium 8 to 40 mEq/day 0.25 to 0.5 mEq/kg/day
Calcium 10 to 30 mEq/day 0.5 to 3 mEq/kg/day
Phosphorus 10 to 40 mMol/day 0.5 to 2 mMol/kg/day
Chloride As needed to maintain acid-base balance Same as adults
Acetate As needed to maintain acid-base balance Same as adults

Vitamins

Vitamins are an essential component of a patient's daily PN regimen because they are necessary for normal metabolism and cellular function. Traditional "MVI-12" adult multivitamin preparations contain the daily requirements for all vitamins except Vitamin K. Therefore, patients receiving MVI-12 should receive supplemental Vitamin K. There are many methods used to meet Vitamin K requirements, for example, weekly administration of 5 to 10mg by subQ or IM injection. In 2001 FDA approved a new multivitamin formula, "MVI-13", which contains 150mcg of Vitamin K. This is a significantly lower dose of Vitamin K compared to traditional weekly supplementation. Patients who are on warfarin are best supplanted with a consistent daily dose of Vitamin K.

Pediatric multiple vitamin preparations have always contained Vitamin K, and are dosed according to weight:

Pediatric mulivitamin dosage
Manufacturer AMA
Weight (kg) Dose (ml) Weight (kg) Dose
< 1 1.5 < 2.5 2 ml/kg
1 - 3 3.25 >2.5 5 ml
> 3 5

Occasionally, a patient will need to be treated with a therapeutic dose of a vitamin. Since long term patients are susceptible to developing vitamin deficiencies, they are more like to require vitamin therapy.

Trace elements

Trace elements are metabolic cofactors essential for the proper functioning of several enzyme systems. Suggested daily intake for parenteral trace minerals is presented below. As with vitamins, long-term PN is more likely to be associated with deficiencies, therefore, additional trace mineral supplementation may be required in these patients.

Daily trace mineral requirements

Adults Peds < 5 years Peds 5 - 12 years
Copper 300 to 500 mcg 20 mcg/kg 200 to 500 mcg
Manganese 60 to 100 mcg 2 to 10 mcg/kg 50 to 100 mcg
Zinc 2.5 to 5 mg 0.1 mg/kg 2 to 5 mg
Chromium 10 to 15 mcg 0.14 to 0.2 mcg/kg 5 to 15 mcg
Selenium 60 mcg 2 to 3 mcg/kg 30 to 40 mcg
Molybdenum As needed 0.25 mcg/kg As needed
Iodine As needed 1 mcg/kg As needed
Iron As needed As needed As needed

Trace mineral administration should be decreased or withheld in patients with impaired ability to excrete them. In patients with renal impairment, selenium, chromium, and molybdenum may be omitted. In patients with severe hepatic disease, manganese and copper may be withheld.


Special populations

Diabetes

Diabetes is neither a relative nor an absolute contraindication to TPN, but careful monitoring of therapy to avoid hyperglycemia is obligatory. In both diabetic and nondiabetic patients, any benefit of TPN is compromised significantly by persistent hyperglycemia.

As with any other patient, in diabetic patients, vital energy substrates and protein should be administered in accordance with immediate metabolic needs. Insulin may be added to the parenteral admixture and combined with sliding-scale insulin administration to achieve an appropriate blood glucose level.

Reasonable glucose control should ensure a blood glucose level greater than 100 mg/dL (to minimize the risk of hypoglycemia) and less than 220 mg/dL (to reduce the harmful effects of hyperglycemia on metabolism, immunocompetence, and fluid balance). This guideline is applicable to any patient receiving TPN.

Acute renal failure

Patients with acute renal failure are hypercatabolic, hypermetabolic, and frequently afflicted by coexisting multiple-system organ failure. Therefore, nutritional substrates should be administered in accordance with metabolic needs.

Protein intake should not be limited arbitrarily. The presumption of impaired removal of nitrogenous waste does not mean that the patient has a reduced daily need for protein. Underfeeding of critically ill patients with renal failure perpetuates catabolism and exacerbates an already difficult, unstable situation.

Patients with acute renal failure must be assessed carefully for signs of fluid overload and electrolyte abnormalities, particularly hyperkalemia, hyperphosphatemia, and hypermagnesemia. TPN volume and composition may require modification.

Protein is provided at approximately 1- 1.2 g/kg/day, and dialysis is used as indicated to control uremia. Limitations should be guided by data gathered from careful assessment of nitrogen losses in urine, dialysate, and other sources.

Specialized formulations of amino acids (e.g., branched chain, essential and nonessential, and mixtures) are widely available. However, no reduction of mortality rates is seen with either mixtures or essential amino acids alone. Branched-chain amino acids (BCAAs; e.g., leucine, isoleucine, valine) may be combined with other amino acids to improve protein use.

Pulmonary disease

Patients with significant pulmonary dysfunction, and those who require ventilator support present therapeutic challenges for nutrition support. Increased catabolic needs, if unmet by feeding, pose threats to the pulmonary musculature and the ability to fuel the work of breathing. Overfeeding may increase CO2 production, complicate respiratory function, and impede weaning from ventilator support.

The amount of carbohydrate administered to patients with pulmonary disease should be carefully controlled. Carbohydrate metabolism is associated with a relatively greater production of CO2 than metabolism of other substrates. The delivery of excess carbohydrate energy also stimulates lipogenesis, which further increases CO2 production and may contribute to hypercapnia, increased work of breathing, and ongoing degradation of respiratory function.

The goal of nutritional therapy in these patients is to provide adequate carbohydrate calories to meet energy needs and (with fat) promote protein sparing, but not to produce unacceptably high levels of CO2. An acceptable strategy is to increase the proportion of calories supplied by fat and to restrict the administration of carbohydrate to 4 mg/kg/min. Protein needs should be estimated at 1.5 g/kg/day.

Hepatic disease

The liver performs a central role in metabolism, and impairment of this organ has profound consequences for nutrition support. Cirrhosis and alcoholism are associated with significant pre-existing malnutrition. This malnutrition is exacerbated by critical illness, surgery, and other stressors.

Lipid, carbohydrate, protein, and vitamin metabolism is sharply altered in patients with hepatic failure. Lipid clearance is defective, with decreased lipolytic activity, increased triglyceridemia, and decreased removal of free fatty acids. Glucose intolerance and insulin resistance, which are prevalent in this patient population, may occur in approximately 80% of patients with cirrhosis. Despite this background of broad dysfunction, intolerance to protein presents the greatest challenge to nutritional management.

Many patients with liver failure have fluid overload that may require restriction of TPN volume. Protein needs in patients with liver failure and mild or no encephalopathy should be calculated at 1.5 g/kg/day. These patients usually can tolerate a conventional parenteral amino acid formula with a full complement of essential amino acids.

Protein needs in patients with significant encephalopathy are reduced to 1.0 g/kg/day. BCAAs are useful sources of protein energy because they do not require hepatic metabolism. Their effect on the mortality rate is unclear; however, patients with pronounced encephalopathy should be given a modified amino acid formula containing a high percentage of BCAAs.

Cardiac disease

In addition to prolonged malnutrition, patients with long-standing cardiac disease are vulnerable to a typical wasting (cardiac cachexia). Impaired baseline cardiac function and pre-existing malnutrition, in conjunction with acute illness and other stressors, demand that patients with cardiac disease receive careful adjustment of TPN solutions and strict monitoring of infusions.

Calories should be provided to satisfy, not exceed, daily energy needs. The total volume of TPN solution is generally restricted to 1000 to 1500 mL/day in patients with severe congestive heart failure secondary to valvular dysfunction, coronary artery disease, or cardiomyopathy.


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Section 3 - TPN solution requirements

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