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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 patient is receiving both oral feedings or tube feedings (enteral nutrition or EN) and IV feedings simultaneously.

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 osmolality of PPN solutions is usually limited to about 900 mOsm/L. Peripherally inserted central catheters (PICC lines) are often utilized for PN administration. PICC lines provide central venous access through which hypertonic PN formula may be administered.

Parenteral nutrition is preferred over EN only when EN cannot be used safely. Parenteral nutrition 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 sometimes controversial. In a previously well-nourished patient in the intensive care unit (ICU), PN may be delayed and therefore no feedings delivered for 7 to 10 days. In the ICU patient who was malnourished prior to hospitalization, PN should be started earlier in a course of illness precluding EN.1,2 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 33-1 for a list of more common situations in which PN is indicated. Central PN 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 33-1 Indications for Parenteral Nutrition

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