PN is rather complex. To be practiced successfully and safely, it should be administered by a trained TPN team using a strict protocol. An effective TPN team consists of a physician, nutritionist, pharmacist, and nurse.

Each of the following complications should be expected and handled expediently by the TPN team:

Patients receiving TPN often have an increased risk of infection. The predisposing factors include malnutrition, immune incompetence, steroid treatment or chemotherapy, concomitant infections, broad-spectrum antibiotic therapy, and presence of a foreign body (the catheter) in the vascular system. TPN-related infection may result from contamination of the catheter by skin flora, contamination of the TPN solution or tubing, or bacteremia originating from another source in the body. Most pathogens responsible for infected catheters originate from superficial sites such as tracheostomies or abdominal wounds. The most common organisms associated with catheter infections are: Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella pneumoniae, and Candida albicans.

A specific procedure using aseptic technique must be followed in the care of the catheter and dressing. The catheter should be used exclusively for TPN and not for any other purpose (e.g., blood drawing; central venous pressure measurement; administration of drugs, antibiotics, or blood products).

Nutritional support regimens are usually based on estimates of energy expenditure. These estimates were thought to be increased substantially in patients with severe trauma or sepsis because of a presumed hypermetabolic state. However, using actual energy expenditure measurements, a large increase in the metabolic rate has not been seen in stressed patients. Excessive caloric intake can produce complications such as hepatomegaly and liver dysfunction due to fatty infiltration of the liver, respiratory insufficiency due to excessive carbon dioxide production during increased lipogenesis, and hyperglycemia with osmotic diuresis due to glucose intolerance.

The healthy individual needs 0.8 g of protein per kilogram of ideal body weight. Needs may increase up to 2.5 g/kg because of stress. To replace protein lost because of stress or to promote anabolism, 1.2 to 1.5 g/kg is frequently used.

Another common way of estimating protein needs is to use the nonprotein calorie-to-nitrogen ratio. The ratios of 100 to 150 kcal:1 g of nitrogen in stressful conditions to promote anabolism and 250 to 300 kcal:1 g of nitrogen for normal body maintenance are often used. The nonprotein calorie-to-nitrogen ratio is based on the premise that sufficient calories must be ingested before protein will be used for tissue maintenance and repair, that is, 100 to 150 kcal is needed to lay down 1 g of nitrogen.

Ideal calorie-nitrogen ratio = 150:1

Protein (gm)/150 = 6.25 × energy requirement in kilocalories

1 g of nitrogen = 6.25 g of protein

AAs are administered as a substrate for anabolism rather than as an energy substrate except in patients with burns or severe sepsis who cannot utilize lipid or glucose effectively and require AA as a substrate for both energy and anabolism.

AA solutions containing a higher concentration of the branched-chain AAs (BCAA), leucine, isoleucine, and valine, may be metabolized more effectively in patients with hypercatabolic states, such as sepsis and trauma. In some studies, it was noted that septic or injured patients treated with BCAA rather than a conventional AA solution had more rapid improvements in nitrogen balance, total lymphocyte count, and delayed hypersensitivity. Because BCAA solutions require a hypermetabolic state to exert their beneficial effects, they should not be used routinely.

Balanced intake of seven groups of nutrients is needed daily. These are CHOs, lipids, proteins, electrolytes, trace elements, and water. These are ordered by the physician daily.

Glucose solutions and lipid emulsions are calorie sources (energy substrate) used in PN except in patients with burns or severe sepsis who are unable to utilize lipid or glucose effectively. In these patients AAs, preferably BCAAs, are used as both an energy source and a substrate for anabolism. If glucose is used as the exclusive energy substrate in TPN solutions, carbon dioxide production increases markedly with increased glucose loading (>40 kcal/kg per day) because there is increased lipogenesis (net fat synthesis) relative to glucose oxidation. In addition to increased carbon dioxide production, resulting in an increase of the respiratory quotient above 1, there is also an increase in oxygen consumption because fat synthesis requires energy. Therefore, large amounts of glucose may constitute a metabolic stress and cause carbon dioxide retention where respiratory function is impaired. Using lipids plus glucose, instead of isocaloric amounts of glucose alone, decreases the respiratory workload in patients with compromised pulmonary function. Fat is
the favored energy source in sepsis, in which glucose utilization is depressed with increased insulin resistance. It is recommended that in the septic hypermetabolic patient, glucose intake be restricted to one half or less of the REE.

Commonly used dextrose solutions are 5% (170 kcal/L), 10% (340 kcal/L), 50% (1,700 kcal/L), and 70% (2,380 kcal/L).

Commonly used AA solutions are 3.5%, 8.5%, 10%, and 11.4%.

Lipid 10% (500 mL [1.1 kcal/mL]) or 20% (500 mL [2.0 kcal/mL]).

is determined by the extent of the patient’s ability to utilize lipid as an energy source. The TPN solution in a septic or injured patient should provide an energy-nitrogen ratio of 80 to 200 kcal/g of energy to 13 to 32 kcal/g of protein. An energy-protein ratio of 24 kcal/g of energy to 150 kcal/g of nitrogen may be ideal in hospitalized patients.