Parenteral nutrition (PN) involves delivery of nutrients by the intravenous (IV) route. The term total parenteral nutrition (TPN) implies that all of the patient's nutritional needs are being met by this route even though the term is often used when the patient is receiving both oral feedings or tube feedings (enteral nutrition or EN) and IV feedings simultaneously.
PN 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. The osmolarity of dextrose/amino acid containing PPN can be estimated by adding 100 mOsm/L for each 1% final concentration of amino acid and 50 mOsm/L for each 1% final concentration of dextrose. Peripherally inserted central catheters (PICC lines) are often utilized for PN administration and provide central venous access through which hypertonic PN formula may be administered.
PN is preferred over EN only when EN cannot be used safely. PN is indicated in situations when EN is not possible or feasible. When to start PN in these situations is patient- and situation-specific, and is controversial. North American guidelines discourage use of PN in a well-nourished patient and in those not at high nutritional risk during the first 7 days of an intensive care unit (ICU) admission in which EN cannot be established. For ICU patients who were malnourished prior to admission or whose illness puts them at high nutritional risk, the guidelines recommend initiation of PN as soon as possible if EN is not feasible. Typically, if resumption of EN is anticipated within 5 to 7 days, PN should not be initiated as it is unlikely to improve outcomes, is expensive, and is associated with potentially significant adverse events. See Table 38-1 for a list of more common situations in which PN is indicated. CPN may be used long-term; patients with short bowel syndrome may receive home PN for decades. On the other hand, PPN is usually a short-term therapy lasting no more than 7 to 10 days.
TABLE 38-1Indications for Parenteral Nutrition in Adults ||Download (.pdf) TABLE 38-1 Indications for Parenteral Nutrition in Adults
Physical or mechanical (eg, tumor compressing intestinal lumen)
Functional (eg, ileus, colonic pseudo-obstruction)
Major small bowel resection (eg, short-bowel syndrome)
Intestinal fistulas if EN cannot be provided above or below the fistula
Pancreatitis—if patients have failed EN beyond the ligament of Treitz ...