Parental Nutrition
9 PARENTERAL NUTRITION
Margaret M. McQuiggan M.S., R.D., CNSD, Frederick A. Moore M.D.
1. What is parenteral nutrition?
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Parenteral nutrition is the provision of protein as amino acids (4 kcal/g), dextrose (3.4 kcal/g), and fat (lipid 20% solution delivers 2 kcal/mL), vitamins, minerals, trace elements, fluid, and sometimes insulin through an intravenous (IV) infusion. Acid-base status may be influenced by the amount of chloride and acetate used in providing sodium and potassium. The concentrations of calcium and phosphorus are limited to avoid precipitation of a calcium phosphate salt.
2. What are the indications for parenteral nutrition?
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Parenteral nutrition should be used when the gastrointestinal (GI) tract is totally nonfunctional, such as in major bowel resection, “short gut,” peritonitis, intestinal hemorrhage, paralytic ileus, high-volume enterocutaneous fistulas, ileus, and severe intractable diarrhea (> 1 L/day).
3. What types of access are available for the delivery of parenteral nutrition?
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Central parenteral solutions are highly concentrated hyperosmolar solutions with osmolarities up to 3000 mOsm/L. These should be delivered into a large lumen vein (e.g., subclavian) or, less commonly, a femoral vein. If a multiple-port catheter is used, a “virgin port” should be reserved exclusively for nutrient infusion. When long-term parenteral nutrition infusion is planned in the postacute setting, a long-term access device (e.g., Hickman or Broviac catheter) may be used. This may not be necessary, however, when the central venous catheter is placed under sterile conditions and the patient or family is taught meticulous care.
4. What is peripheral parenteral nutrition (PPN)?
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Although used infrequently, PPN may be used when the need for parenteral nutrition is < 7-10 days and central line placement is not desired. Solutions are low osmolarity (< 900 mOsm/L) to prevent thrombosis at the entry site. The inclusion of fat emulsion, which has a near-isotonic osmolarity, helps decrease the overall solution osmolarity while increasing total kilocalories. Because of the dilute nature of the solution, a large volume is required to provide ample nutrition to the patient. Thus, PPN may not be desirable in fluid-restricted individuals, such as patients with congestive heart failure (CHF).
5. Should patients with pancreatitis be exclusively fed parenterally?
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Although patients with pancreatitis have traditionally been given “gut rest” and total parenteral nutrition (TPN), some studies demonstrate improved outcome with enteral feeding past the ligament of Treitz. The type of formula and level of the GI tract into which nutrients are infused determine the degree to which pancreatic exocrine stimulation is stimulated. TPN is not superior to enteral nutrition in patients with pancreatitis who require nutritional support.
6. Are IV lipids contraindicated in patients with pancreatitis?
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In instances of pancreatitis caused by congenital hyperlipidemia, lipids should be withheld. This cause is rare in clinical practice.
7. When should concentrated amino acid and dextrose solutions be used?
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Standard amino acids are generally in an 8.5% (8.5 g/100 mL) or 10% concentration. Concentrated solutions are 15% amino acid. Dextrose is maximally concentrated at 70% solution, although D50% is more commonly used in standard TPN solutions. Maximally concentrated TPN may be desirable in patients with CHF, hepatic failure, or acute renal failure with hemodialysis. Because of increased expense, concentrated amino acids should be used judiciously.
8. Should iron be included in parenteral nutrition?
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Iron deficiency is rarely an acute intensive care unit (ICU) issue. Blood transfusion delivers 250 mg of elemental iron per unit. In longer-term TPN, iron supplementation may become necessary. Ideally, this should be by the enteral route because of the high anaphylactic potential of IV and intramuscular iron.
9. What complications are associated with parenteral nutrition?
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Fluid and electrolyte imbalance, altered glucose metabolism, increased liver function tests (LFTs), hepatic steatosis, systemic candidiasis, site infections, and gut atrophy are associated with TPN. Hemothorax or pneumothorax may occur during central line placement. Although rare, air emboli or extravascular placement of central lines have been reported. The reported incidence of catheter-related sepsis (CRS) is variable.
10. What factors play a role in CRS?
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Preventative measures can be divided into three categories:
1. Catheter insertion
2. Catheter maintenance
3. Catheter removal
During insertion, the skin should be prepared with chlorhexadine rather than alcohol or povidone iodine, and maximal sterile barriers should be used. Although it is commonly thought that multiple lumen catheters have a higher rate of CRS compared with single lumen catheters, randomized studies using rigorous central venous catheter protocols demonstrate comparable rates of CRS. Catheter care should entail scheduled dressing and tubing change every 48-72 hours; antibiotic ointment is of questionable merit (but is commonly used), and gauze is superior to transparent occlusive dressing. Finally, removing the catheter at set intervals effectively reduces CRS, but the benefits must be weighed against the risks of mechanical complications associated with a new catheter placement at a different site. Guidewire changes at set intervals are of debatable value but may be an effective method for early diagnosis of local catheter colonization or infection. Antimicrobial and antiseptic-bonded catheters are now available, and studies indicate that their use reduces the incidence of CRS. These devices cost substantially more than standard catheters and should therefore be limited to usage in high-risk patients.
11. Why do parenterally fed patients often develop hyperglycemia?
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Parenterally fed patients may develop hyperglycemia because of increased stress and the inflammatory response, limited mobility, concurrent steroid therapy, and excessive kilocalorie intake. Glucose infusion rates should not exceed 5 mg/kg/min.
12. How should hyperglycemia be managed?
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Information on the home glucose control regimen should be taken from the medication history. Regular insulin may be required in the initial TPN in patients with baseline hyperglycemia, insulin resistance, or insulinopoenia. Supplemental insulin needs should be evaluated daily before reordering TPN. Maintaining the blood glucose < 110 mg/dL has been shown to significantly improve patient outcome. Tight control may merit the usage of continuous IV regular insulin (i.e., insulin drip). NPH insulin is geared toward patients consuming meals at regular intervals and, thus, is not appropriate with continuous IV feedings.
KEY POINTS: HYPERGLYCEMIA SECONDARY TO PARENTERAL NUTRITION
1. Cause: increased stress and inflammatory response, limited mobility, concurrent steroid therapy, overfeeding.
2. Glucose infusion should not exceed 5 mg/kg/min.
3. Supplemental insulin may be required in the parenteral formula.
4. Maintaining blood glucose < 110 mg/dl improves patient outcome.
13. Why are IV fat emulsions used, and when are they contraindicated?
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Theoretically, fat emulsions are used to prevent essential fatty acid deficiency. In reality, this condition is rare, takes several weeks to develop, and requires only 3-4% of kilocalories as linoleic acid (or 10% of kilocalories as a standard fat emulsion). Fat emulsions are also used to provide additional kilocalories after glucose infusion has reached 5 kcal/kg/min. Practically speaking, lipids are packaged and billed in 100-cc, 250-cc, and 500-cc units; therefore, they are generally included in TPN formulations in these standard volumes. Fat emulsions should be avoided with hyperlipidemia-induced pancreatitis (a small percentage of most pancreatitis) and when serum triglycerides are significantly elevated (e.g., < 500 mg/dL). When delivered in total-nutrient admixtures (three-in-one solutions), lipid emulsions are stable for 24 hours. When infused as a sole nutrient, hang times should not exceed 12 hours because of the potential for bacterial growth.
14. What is refeeding syndrome?
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Refeeding syndrome occurs when a patient is moderately to severely malnourished and has limited substrate reserves. Patients typically present with chronic alcoholism or anorexia nervosa, after bariatric surgery, or as a result of chronic starvation. When presented with a large nutrient load, the patient rapidly develops clinically significant decreases in serum potassium, phosphorus, calcium, and magnesium levels because of compartment shifts of these elements. Hyperglycemia is commonly caused by blunted basal insulin secretion.
15. How is refeeding syndrome best managed?
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Ample quantities of potassium, phosphorus, calcium, and magnesium should be provided with the initial parenteral mixtures within the solubility limits of the solution. The initial kilocaloric provision should be reduced by 25% of goal by reducing dextrose kilocalories. Blood glucose is monitored three to four times daily, and serum K, PO4, Ca, and Mg should be evaluated daily for 5 days after initiating feeding while the kilocalories are advanced to goal levels.
16. How should parenteral nutrition be monitored?
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Parenteral nutrition should be monitored daily with a chemistry profile (Na, K, Cl, CO2, glucose), Mg, phosphorus, and Ca during the first several days of initial therapy in the critical care setting. Accucheck blood glucose determinations are needed every 6 hours. As the fluid and electrolyte balance achieves stability, frequency may be reduced to 1-2 times weekly. The adequacy of the regimen may be assessed by evidence of proper wound healing, maintenance of hydrational status, preservation of body cell mass, and a timely repletion of constitutive protein levels. Overfeeding may be evidenced by insulin resistance, hypertriglyceridemia, increased LFTs, and hypercapnia.
17. What infusion schedules are used for TPN?
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TPN is most often delivered by continuous infusion. In more ambulatory patients and those on home therapy, a cyclic or nighttime infusion schedule may be adopted as long as adequate hydration can be maintained. This dictates a 12- to 18-hour infusion period.
18. How should TPN be discontinued? Show answer
When TPN is no longer needed, the infusion rate should be reduced by half for 2 hours, halved again for 2 hours, and then discontinued. This “ramp down” prevents reactive hypoglycemia.
19. What is the cost of parenteral nutrition?
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Parenteral solution costs may vary widely depending on the constituents. The cost of TPN solution components, preparation, access devices, and laboratory monitoring costs approximately 10 times that of a standard enteral feeding. Many third-party payers do not provide more reimbursement for parenteral therapy than enteral in the hospital setting.
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Abernathy’s Surgical Secrets, Updated Edition (Book w / Student Consult)
Author / s: Harken Alden H., Abernathy Charles, Moore Ernest Eugene
Year: 2004
Pages: 473
Publishers: Elsevier Mosby; 5th Bk & Acc edition
ISBN: 0323034160
