Total parenteral nutrition (TPN)

Overview ㅡ Parenteral nutrition (PN) involves delivery of nutrients by the intravenous (IV) route. Parenteral nutrition may be delivered by either the central (CPN) or peripheral (PPN) route. When delivered centrally, the feeding catheter is typically placed into the subclavian vein with the tip of the catheter near the opening of the right atrium. For PPN, the catheter is placed into a peripheral vein; because hypertonic solutions of PN can cause phlebitis when administered peripherally, the osmolarity of PPN solutions in adults is generally limited to about 900 mOsm/L. 

TPN INDICATIONS

Parenteral nutrition is preferred over enteral nutrition (EN) ONLY when enteral nutrition cannot be used safely. Parenteral nutrition is indicated in situations when EN is not possible or feasible.

Table (1). Indications for TPN
WHEN TO RECOMMEND PARENTERAL NUTRITION IN ADULTS
Bowel obstruction Physical or mechanical (eg, tumor compressing intestinal lumen) Functional (eg, ileus, colonic pseudo-obstruction) Major small bowel resection (eg, short-bowel syndrome) Adult patients with < 100 cm of small bowel distal to the ligament of Treitz without a colon Adult patients with < 50 cm of small bowel if the colon is intact Diffuse peritonitis Intestinal fistulas if EN cannot be provided above or below the fistula Pancreatitis—if patients have failed EN beyond the ligament of Treitz or cannot receive EN (eg, because of intestinal obstruction) Severe intractable vomiting Severe intractable diarrhea Preoperative nutrition support in patients with moderate to severe malnutrition who cannot tolerate EN and in whom surgery can be delayed safely for at least 7 days In critically ill patients without malnutrition who cannot receive oral or EN in the first 7 days of ICU admission, PN should only be initiated after the first 7 days of admission and if oral or EN is still not feasible

COMPONENTS AND DESIGNING A REGIMEN

Parenteral nutrition solutions contain macrosubstrates and microsubstrates. Macrosubstrates consist of a carbohydrate source, lipid emulsion, and amino acid solution. Microsubstrates include electrolytes, vitamins, and trace elements.

Fluids. Fluid requirements of parenteral nutrition patients can vary widely. Some fluid-restricted patients may receive as little as 1000 or 1250 mL of parenteral nutrition per day. Typical parenteral nutrition volumes for patients without fluid restrictions are 1500 to 3000 mL/day. In the hospital, parenteral nutrition is most commonly infused continuously over 24 hours. In the home setting, parenteral nutrition may be cycled over a shorter period of time (e.g., 12-16 hours), often at night, to allow the patient more freedom in mobility.

Carbohydrates. The carbohydrate source is dextrose. IV dextrose provides 3.4 kcal/g. Stock solutions of 10%, 25%, 50%, and 70% dextrose are commonly used in compounding.

Lipids. IV lipid emulsions (Intralipid 10%, Smoflipid 20%) contain fat, glycerin, and phospholipid. When calculating calories from IV lipid emulsions, the following caloric densities are used: 10% emulsion will give 1.1 kcal/mL, 20% emulsion will give 2 kcal/mL, while 30% emulsion will give 3 kcal/mL.

Amino acids. Standard amino acid solutions (Aminosyn, Aminoven) contain essential and nonessential amino acids and are supplied in concentrations ranging from 3.5%, 8%, 10% to 15%. Specialized amino acid formulations designed for pediatrics (Aminoven Infant) are widely utilized. Specialized amino acid formulations designed for adults with renal failure (Nephrostril) and hepatic failure (Aminostril N hepa 8%). Hepatic formulations contain higher amounts of branched-chain amino acids and lower amounts of aromatic amino acids compared to standard formulas. Renal formulas contain mainly essential amino acids. Amino acid solutions provide 4 kcal/g.

TPN RECOMMENDATIONS

Energy (CALORIES). Guidelines call for provision of energy via parenteral nutrition for nonobese adults between 20 and 35 kcal/kg/day. Calories should be divided between dextrose and lipid (as well as protein) such that dextrose does not exceed 7 g/kg/day and lipid does not exceed 2.5 g/kg/day. Lipid kilocalories typically make up about 15% to 30% of non-protein kilocalories.

• You should discourage IV soybean lipid (e.g., Intralipid) administration during the first 7 days of an ICU admission. Smoflipid, which contains soybean oil, medium chain triglycerides, olive oil, and fish oil give potentially less pro-inflammatory lipid options for use in the early days of an ICU admission.

• Note that propofol, a medication used in the ICU for sedation, is compounded in a 10% soybean lipid emulsion; these lipid kilocalories (1.1 kcal/mL) should be taken into account when calculating total kilocalories in a patient's regimen. Clevidipine, an IV antihypertensive agent, is also supplied in a soybean lipid emulsion. Likewise, many medications are compounded in dextrose 5% which may provide significant calories.

     Amino acids are generally supplied in PN solutions at amounts up to about 2 g/kg/day. Guidelines for ICU patients with body mass index (BMI) < 30 kg/m2 call for 1.2 to 2 g/kg actual body weight per day or perhaps higher in burn and trauma patients. Patients receiving hemodialysis or continuous renal replacement therapy may require up to 2.5 g protein per kg body weight per day.

KEY POINTS of TPN

• Parenteral nutrition (PN) is a potentially lifesaving modality of feeding for the patient with severe gastrointestinal compromise precluding adequate oral or enteral feeding.
• Enteral nutrition (EN) is preferred over PN if EN can be administered safely, mainly due to a lesser chance of infectious complications with EN and possibly less stimulation of pro-inflammatory conditions. EN is also generally less expensive than PN.
• PN may be delivered through either a central or peripheral venous access. Peripheral delivery is limited by the osmolarity of solution that can be administered by this route.
• In patients for whom PN is appropriate, timing of PN is controversial. In general, patients who are previously malnourished should be started on PN sooner than those who are not previously malnourished.
• Caloric contribution of the major macrosubstrates used in PN is as follows: dextrose 3.4 kcal/gm, lipid emulsion 20% 2 kcal/mL, amino acid 4 kcal/gm.
• Calories are generally provided via PN at 20 to 35 kcal/kg/day. For the obese patient, recommendations call for less than 14 kcal/kg actual body weight or 22 to 25 kcal/kg/day ideal body weight, depending on BMI.
• Dextrose is generally limited to < 7 g/kg/day (usually 5 mg/kg/min). Lipid is generally limited to < 2.5 g/kg/day.
• Amino acids are generally administered at 1.2 to 2 g/kg/day based on actual body weight. Higher amounts (2-2.5 g/kg ideal body weight per day) are appropriate for obese patients. Patients receiving renal replacement therapy also require higher amounts of amino acid.
• Standard amino acid formulations are appropriate for most patients; specialized amino acid formulations (e.g., hepatic, renal) are more expensive and rarely indicated.

REFERENCES

• Ayers P, Adams S, Boullata J, Gervasio J, Holcombe B, Kraft MD, Marshall N, Neal A, Sacks G, Seres DS, Worthington P; American Society for Parenteral and Enteral Nutrition. A.S.P.E.N. parenteral nutrition safety consensus recommendations. JPEN J Parenter Enteral Nutr. 2014 Mar-Apr;38(3):296-333. Available at: https://pubmed.ncbi.nlm.nih.gov/24280129

  Boullata JI, Gilbert K, Sacks G, Labossiere RJ, Crill C, Goday P, Kumpf VJ, Mattox TW, Plogsted S, Holcombe B; American Society for Parenteral and Enteral Nutrition. A.S.P.E.N. clinical guidelines: parenteral nutrition ordering, order review, compounding, labeling, and dispensing. JPEN J Parenter Enteral Nutr. 2014 Mar-Apr;38(3):334-77. Available at: https://pubmed.ncbi.nlm.nih.gov/24531708

  Critical Care Nutrition. Systematic reviews. Available at: https://www.criticalcarenutrition.com/systematic-reviews

  Choban P, Dickerson R, Malone A, Worthington P, Compher C; American Society for Parenteral and Enteral Nutrition. A.S.P.E.N. Clinical guidelines: nutrition support of hospitalized adult patients with obesity. JPEN J Parenter Enteral Nutr. 2013 Nov;37(6):714-44. Available at: https://pubmed.ncbi.nlm.nih.gov/23976769

  McClave SA, Taylor BE, Martindale RG, Warren MM, Johnson DR, Braunschweig C, McCarthy MS, Davanos E, Rice TW, Cresci GA, Gervasio JM, Sacks GS, Roberts PR, Compher C; Society of Critical Care Medicine; American Society for Parenteral and Enteral Nutrition. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient: Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.). JPEN J Parenter Enteral Nutr. 2016 Feb;40(2):159-211. Available at: https://pubmed.ncbi.nlm.nih.gov/26773077