Parenteral nutrition (PN) is a method of providing nutrients tothe body by an IV route. It is a very complex admixture of indi-vidual chemicals combined in a single container. The components of a PN admixture are proteins, carbohydrates, fats, electrolytes, vitamins, trace minerals, and sterile water. The goals of PN are to improve nutritional status, establish a positive nitrogen balance, maintain muscle mass, promote weight gain, and enhance the healing process.
When a patient’s intake of protein and nutrients is significantly less than that required by the body to meet energy expenditures, a state of negative nitrogen balance results. In response, the body begins to convert the protein found in muscles into carbohydrates to be used to meet energy needs. The result is muscle wasting, weight loss, fatigue, and, if left uncorrected, death.
The average postoperative adult patient requires approximately 1500 calories per day to keep the body from using its own store of protein. Traditional IV fluids do not provide sufficient calories or nitrogen to meet the body’s daily requirements. PN solutions, which supply nutrients such as dextrose, amino acids, elec-trolytes, vitamins, minerals, and fat emulsions, provide enough calories and nitrogen to meet the patient’s daily nutritional needs. In general, PN can provide 30 to 35 kcal/kg of body weight and 1.0 to 1.5 g of protein/kg of body weight (Rombeau & Rolandelli, 2000).
The patient with fever, trauma, burns, major surgery, or hy-permetabolic disease may require up to 10,000 additional calo-ries daily. The volume of fluid necessary to provide these calories would surpass fluid tolerance and lead to pulmonary edema or heart failure. To provide the required calories in small volume, it is necessary to increase the concentration of nutrients and use a route of administration (ie, a large, high-flow vein [subclavian vein]) that will rapidly dilute incoming nutrients to the proper levels of body tolerance.
When highly concentrated glucose is administered, caloric re-quirements are satisfied and the body uses amino acids for pro-tein synthesis rather than for energy. Additional potassium is added to the solution to maintain proper electrolyte balance and to transport glucose and amino acids across cell membranes. To prevent deficiencies and fulfill requirements for tissue synthesis, other elements, such as calcium, phosphorus, magnesium, and sodium chloride, are added (Rombeau & Rolandelli, 2000).
The indications for PN include a 10% deficit in body weight (compared with preillness weight), an inability to take oral food or fluids within 7 days after surgery, and hypercatabolic situations such as major infection with fever. In both the home and hospi-tal setting, PN is indicated in the following situations:
• The patient’s intake is insufficient to maintain an anabolic state (eg, severe burns, malnutrition, short bowel syndrome, AIDS, sepsis, cancer).
• The patient’s ability to ingest food orally or by tube is im-paired (eg, paralytic ileus, Crohn’s disease with obstruction, postradiation enteritis, severe hyperemesis gravidarum in pregnancy).
• The patient is not interested in or is unwilling to ingest ad-equate nutrients (eg, anorexia nervosa, postoperative elderly patients).
• The underlying medical condition precludes being fed orally or by tube (eg, acute pancreatitis, high enterocuta-neous fistula).
• Preoperative and postoperative nutritional needs are pro-longed (eg, extensive bowel surgery).
A total of 2 to 3 L of solution is administered over a 24-hour period using a filter (1.2-micron particulate filter). Before admin-istration, the PN infusion must be inspected for clarity and any pre-cipitate. The label is compared with the physician’s order, noting the expiration date. Fat emulsions (Intralipid) may be infused si-multaneously with PN through a Y-connector close to the infusion site. Fat emulsions should not be filtered. Before administration, the fat emulsion solution is inspected for frothiness, separation, or oily appearance. Usually 500 mL of a 10% emulsion is admin-istered over 4 to 6 hours, one to three times a week. Fat emulsions can provide up to 30% of the total daily calorie intake.
Lipid emulsions can be admixed with other components of PN to create a total nutrient admixture (TNA). TNA is com-monly called a “three-in-one” formulation. All the parenteral nu-trient components are mixed in one container and administered to the patient over a 24-hour period. A special final filter (1.5 micron filter) is used with this solution. Before administration, the solu-tion is observed for oil droplets that have separated from the so-lution, forming a noticeable layer (cracking of lipid emulsion); such a solution should be discarded. Advantages of the TNA over PN are cost savings in preparation and equipment, decreased risk of contamination, decreased risk of catheter contamination, decreased pharmacy preparation time, less nursing time, and increased patient convenience and satisfaction. Ideally, the pharmacist, nutritionist, and physician collaborate to determine the specific formula needed.
PN solutions are initiated slowly and advanced gradually each day to the desired rate, as the patient’s fluid and glucose tolerance per-mits. The patient’s laboratory test results and response to PN therapy are monitored on an ongoing basis by the nutritional support team. Standing orders are initiated for weighing the pa-tient; monitoring intake, output, and blood glucose; and baseline and periodic monitoring of complete blood count, platelet count, and chemistry panel, including serum carbon dioxide, magne-sium, phosphorus, triglycerides, and prealbumin. A 24-hour urine nitrogen determination may be performed for analysis of nitrogen balance. In most hospitals, the physician prescribes PN solutions on a daily standard PN order form. The formulation of the PN solutions is calculated carefully each day to meet the com-plete nutritional needs of the individual patient.
Various vascular access devices are used to administer PN solu-tions in clinical practice. PN may be administered by either pe-ripheral or central IV lines, depending on the patient’s condition and the anticipated length of therapy.
To supplement oral intake when complete bowel rest is not indi-cated and NG or nasoenteric suction is not required, a peripheral parenteral nutrition (PPN) formula may be prescribed. PPN is ad-ministered through a peripheral vein; this is possible because the solution is less hypertonic than PN solution. PPN formulas are not nutritionally complete. Protein and dextrose are limited. Dex-trose concentrations of more than 10% should not be adminis-tered through peripheral veins because they irritate the intima (innermost walls) of small veins, causing chemical phlebitis. Lipids are administered simultaneously to buffer the PPN and to protect the peripheral vein from irritation. The usual length of therapy using PPN is 5 to 7 days (Hamilton, 2000).
Because PN solutions have five or six times the solute con-centration of blood (and exert an osmotic pressure of about 2000 mOsm/L), they are injurious to the intima of peripheral veins. Therefore, to prevent phlebitis and other venous compli-cations, these solutions are administered into the vascular system through a catheter inserted into a high-flow, large blood vessel (the subclavian vein). Concentrated solutions are then very rapidly di-luted to isotonic levels by the blood in this vessel.
Four types of central venous access devices (CVAD) are available—nontunneled (or percutaneous) central catheters, pe-ripherally inserted central catheters, tunneled catheters, and im-planted ports. Whenever one of these catheters is inserted, catheter tip placement should be confirmed by x-ray studies before PN therapy is initiated. The optimal position is the midproximal third of the superior vena cava.
Nontunneled central catheters are used for short-term (less than 30 days) IV therapy in the acute care, long-term care, and home care settings. The physician inserts these catheters. Examples of non-tunneled central catheters are Vas Cath, Percutaneous Subclavian, and Hohn catheters. The subclavian vein is the most common ves-sel used, because the subclavian area provides a stable insertion site to which the catheter can be anchored, allows the patient freedom of movement, and provides easy access to the dressing site. The jugular or femoral vein also may be used. Single-, double-, and triple-lumen central catheters are available for central lines. To en-sure accessibility, a triple-lumen subclavian catheter should be used, because it offers three ports for various uses (Fig. 36-11). The 16-gauge distal lumen can be used to infuse blood or other viscous flu-ids. The 18-gauge middle lumen is reserved for PN infusion. The 18-gauge proximal port can be used for administration of blood or medications. A port not being used for fluid administration can be used for obtaining blood specimens if indicated.
If a single-lumen central catheter is used for administering PN, various restrictions apply. Blood cannot be drawn from the catheter and medications cannot be administered through it, because the medication may be incompatible with the components of the nu-tritional solution (insulin is an exception). If medications must be given, they must be infused through a separate peripheral IV line, not by piggyback into the PN line. Transfusions of blood products also cannot be given through the main line, because red cells may possibly coat the lumen of the catheter, thereby reducing the flow of the nutritional solution.
Peripherally inserted central catheters (PICC) are used forintermediate-term (3 to 12 months) IV therapy in the hospital, long-term care, or home setting. These catheters may be inserted at the bedside or in the outpatient setting by a specially trained nurse. The basilic or cephalic vein is accessed through the ante-cubital space, and the catheter is threaded to a designated loca-tion, depending on the type of solution to be infused (superior vena cava for PN). Taking of blood pressure and blood specimens from the extremity with the PICC is avoided.
Tunneled central catheters are for long-term use and may remain in place for many years. These catheters are cuffed and can have single or double lumens; examples are the Hickman, Goshong, and Permacath. These catheters are inserted surgically. They are threaded under the skin (reducing the risk of ascending infection) to the subclavian vein, and the distal end of the catheter is ad-vanced into the superior vena cava 2 to 3 cm above the junction with the right atrium.
Implanted ports are also used for long-term home IV therapy; ex-amples include the Port-A-Cath, Mediport, Hickman Port, and P.A.S. Port. Instead of exiting from the skin, as do the Hickman and Groshong catheters, the end of the catheter is attached to a small chamber that is placed in a subcutaneous pocket, either on the anterior chest wall or on the forearm. The subcutaneous port requires minimal care and allows the patient complete freedom of activity.
Implanted ports are more expensive than the external catheters, and access requires passing a special needle (Huber-tipped) through the skin into the chamber to initiate IV therapy. Taking of blood pressure and blood specimens from the extremity with the port system is avoided.
The procedure is explained so that the patient understands the importance of not touching the catheter insertion site and is aware of what to expect during the insertion procedure. To insert the catheter, the patient is placed supine, in head-low position (to produce dilation of neck and shoulder vessels, which makes entry easier and prevents air embolus). The area is shaved if necessary, and the skin is prepared with acetone and alcohol to remove sur-face oils. Final skin preparation includes cleaning with tincture of 2% iodine or chlorhexidine. To afford maximal accuracy in the placement of the catheter, the patient is instructed to turn the head away from the site of venipuncture and to remain motion-less while the catheter is inserted and the wound is dressed.
The preferred insertion route is the subclavian vein, which leads into the superior vena cava. The external jugular route can be used, but usually only in emergency situations. Because a non-tunneled central catheter is always a potential source of serious infection, the site should be changed every 4 weeks or as recom-mended by the Centers for Disease Control and Prevention.
Sterile drapes are applied to the upper chest. The patient may be asked to wear a facemask to prevent the spread of micro-organisms. Procaine or lidocaine is injected to anesthetize the skin and underlying tissues. The target area is the inferior border at the midpoint of the clavicle. A large-bore needle on a syringe is inserted and moved parallel to and beneath the clavicle until it enters the vein. The syringe is then detached and a radiopaque catheter is inserted through the needle into the vein.
When the catheter is positioned, the needle is withdrawn and the hub of the catheter is attached to the IV tubing. Until the sy-ringe is detached from the needle and the catheter is inserted, the patient may be asked to perform the Valsalva maneuver. (To do this, the patient is instructed to take a deep breath, hold it, and bear down with mouth closed. Compression of the abdomen may also accomplish the maneuver.) The Valsalva maneuver is per-formed to produce a positive phase in central venous pressure, to lessen the possibility of air being drawn into the circulatory sys-tem (air embolism). The physician sutures the catheter to the skin to avoid inadvertent removal.
The catheter insertion site is swabbed with either tincture of 2% iodine or a chlorhexidine solution. A gauze or transparent dressing is applied using strict sterile technique. An isotonic IV solution, such as dextrose 5% in water (D5W), is administered to keep the vein patent.
The position of the tip of the catheter is checked with fluo-roscopy to confirm its location in the superior vena cava and to rule out a pneumothorax resulting from puncture of the pleura. Once the catheter position is confirmed, the prescribed PN so-lution is started. The initial rate of infusion is usually 50 mL/hour, and the rate is gradually increased to the maintenance rate or predetermined dose (eg, 100 to 125 mL/hour). An infusion pump is always used for administration of PN or PPN.
An injection site cap is attached to the end of each central catheter lumen, creating a closed system. IV infusion tubing is connected to the insertion site cap of the central catheter with a threaded needleless adapter or Luer-lock device. Each lumen is la-beled according to location (proximal, middle, distal). To ensure patency, all lumens are flushed with a diluted heparin flush initially, daily when not in use, after each intermittent infusion, after blood drawing, and whenever an infusion is disconnected. Force is never used to flush the catheter. If resistance is met, aspiration may be effective in cleansing the lumen; if this is not effective, the physician is notified. Low-dose t-PA (alteplase) may be prescribed to dissolve a clot or fibrin sheath. If attempts to clear the lumen are ineffective, the lumen is labeled as “clotted off.”
The PN solution is discontinued gradually to allow the patient to adjust to decreased levels of glucose. After administration of the PN solution is terminated, isotonic glucose is administered for several hours to protect against rebound hypoglycemia. Provid-ing oral carbohydrates will shorten the tapering time. Specific symptoms of rebound hypoglycemia include weakness, faintness, sweating, shakiness, feeling cold, confusion, and increased heart rate. Once all IV therapy is completed, the nurse (with a physi-cian’s order) removes the nontunneled central venous catheter or PICC and applies an occlusive dressing to the exit site. Tunneled catheters and implanted ports are removed by the physician.
In cases of serious illness when death is imminent, some pa-tients or families may request that PN be discontinued. This dif-ficult issue poses many ethical questions, some of which are discussed in Chart 36-3.