Online Medical Reference

Principles of Nutrition Support

Donald F. Kirby, MD

Mandy L. Corrigan

Published: August 2013

Introduction and Definitions

While humans often enjoy the ability to "live to eat" rather than "to eat to live" (survive), there are instances where individuals cannot or perhaps will not be able to meet their nutritional needs by volitional oral intake alone. Loosely, nutrition support can refer to oral intake with or without the need for special supplements, enteral nutrition by specialized tube feeding or the use of intravenous methods.

Basic Nutritional Requirements

Nutrition Assessment

The goal of nutrition assessment is to evaluate for the presence and degree of malnutrition as well as identifying patients that are nutritionally at risk. Even the most basic nutrition assessment incorporates data from anthropometric measurements, biochemical studies, clinical examination, and dietary intake. A complete nutrition assessment combines both subjective information from the patient as well as the available objective medical data. A patient interview or a review of the chart to identify conditions that may influence oral intake, absorption, or metabolism is critical and of paramount importance.

Determining the patient's nutritional status is clinically not always straightforward as there is no universal definition for malnutrition. Commonly hospitalized patients are labeled as "malnourished" due to the presence of low albumin or prealbumin values. Unfortunately, many dated studies solely determined nutritional status based on alterations in hepatic markers and did not consider the influence of injury or inflammation on the ability of the liver to synthesize albumin. The current understanding of hepatic proteins takes into account that many non-nutritional factors impact these values thereby not allowing for a true representation of nutritional status in the presence of stress or inflammation.1 Albumin, prealbumin, and transferrin are negative acute phase proteins and decrease during stress or inflammation regardless of the premorbid nutritional status. Low albumin levels are more reflective of surgical morbidity and mortality than nutritional status.

Malnutrition usually refers to protein-energy malnutrition resulting from extended periods of negative balance of energy and protein below metabolic requirements. The American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) is currently involved in defining the influence of inflammation on nutritional status and a new standard method of coding for malnutrition based on the impact of inflammatory response to nutritional status.2

Interpretation of Weight Data

Body mass index (BMI) is frequently used to compare height and weight and is calculated as weight in kilograms divided by height in meters squared [BMI= weight (kg) / height (m2)]. A BMI less than 18.5 meets criteria for malnutrition, a BMI between 18.5 and 24.9 indicates a healthy weight status, a BMI from 25-29.9 is overweight, and a BMI greater than or equal to 30 is classified as obese.3 BMI is simple to calculate and provides a snapshot of the current weight category. BMI alone provides current weight status, but doesn't account for the rate of weight change that is important to identify when screening for malnutrition. Changes in recent weight most accurately assess current nutritional risk.4 Involuntary weight loss of greater than 10% of usual body weight over 6 months or loss of greater than 5% of usual body weight in 1 month is considered strong evidence of malnutrition.

Clinical Examination

A nutrition focused physical examination (NFPE) assists clinicians in gathering information about the patient's nutritional status. A NFPE provides objective information that may not be uncovered when gathering a nutritional history from the patient or medical chart. Typically, the NFPE begins with a general visual inspection of the patient from head to toe. Overt or obscure signs of malnutrition may be identified and require further testing to confirm the presence of the nutritional deficiency.

A NFPE may help the clinician gain a better understanding of weight changes by accounting for the presence of edema or ascites. Frequently, the patient may have fluid accumulations that mask weight loss (i.e., lean body mass losses) or over inflate current weight status.

Diet History

A registered dietitian (RD) utilizes many tools to obtain a diet history including dietary recall methods, food diaries, or intake and output records. The RD also obtains information on changes in weight, appetite, and oral intake along with physical activity levels/functional status, food allergies/intolerances, bowel habits, use/dose of vitamin supplements, religious diet restrictions, and nutrition support regimes (oral nutritional supplements, enteral tube feeding regimes, or parenteral nutrition regimes). If a change in oral intake was noted, the RD would also gather more data on the time frame and identify possible reasons for the change (i.e. chewing/swallowing problems, nausea/vomiting, early satiety, pain associated with oral intake, reflux, depression, inability to prepare or procure food, etc.).

Combining findings from the NFPE, diet history, laboratory studies, and anthropometric measures helps determine the presence of malnutrition. The subjective global assessment (SGA) is a well recognized validated method that easily captures the following elements: history (weight change, dietary intake changes, persistent gastrointestinal symptoms, functional status, and disease impact on nutritional requirements) and physical exam findings (loss of subcutaneous fat, muscle wasting, sacral edema, lower extremity edema, ascites). Numeric values are assigned and then the SGA rating determines the presence of severe malnutrition, moderate malnutrition, or a well-nourished status.

Methods of Assessing Nutrient Requirements

Indirect calorimetry (IC) is the gold standard for determining caloric requirements. Often, IC is not available for use. The presence of obesity further complicates assessing nutritional requirements when IC is not available. When IC is not available for use, predictive equations are commonly used, but these all lack precision and are approximations at best. Table 1 lists many of the equations presently used.

Table 1. Method & Equations for Determining Nutritional Requirements
Name of Method / Equation Equation Definitions
Harris Benedict Men: BMR = 66.47 + 13.75 (Weight) + 5 (height) − 6.76 (age) Weight in kilograms (kg)
Height in centimeters (cm)
Age in years
Basal metabolic rate (BMR)
Women: BMR= 655.1 + 9.56 (weight) + 1.85 (height) − 4.67 (age)
Mifflin St Jeor Men BMR = 9.99 (weight) + 6.25 (height) − 4.92 (age) + 5 Weight in kilograms (kg)
Height in centimeters (cm)
Age in years
Basal metabolic rate (BMR)
Women BMR = 9.99 (weight) + 6.25 (height) − 4.92 (age) − 161
Penn State 2003a: RMR= BMR (0.85) + VE (33) + TMax (175) − 6433 Basal metabolic rate (BMR) from Harris Benedict Equation
VE minute ventilation in L/min
Max temperature in 24 hours in Celsius (TMax)
Calorie/Kilogram Method BMI <25 : 25-35 kcal/kg Acute
BMI 25-29.9 : 20-25 kcal/kg
BMI 30-34.9 : 15-20 kcal/kg
BMI ≥35 : 10-15 kcal/kg

Adapted from Cleveland Clinic Nutrition Support Team Manual 48

Timing of Nutrition Intervention

The nutrition assessment helps to gather necessary data to direct the timing of nutrition support in hospitalized patients based on the route for feeding. In 2009, the Society for Critical Care Medicine (SCCM) and A.S.P.E.N. jointly developed evidence based nutrition guidelines in 2009 for hospitalized intensive care unit patients. One specific guideline addresses when to initiate either enteral nutrition (EN) or parenteral nutrition (PN) based on the nutritional status of the patient (topics of EN and PN will be discussed in depth in upcoming sections). The EN route is the preferred route for delivery of nutrition support, and the timing of the use of EN is not affected by nutritional assessment.5

In patients that were previously healthy prior to critical illness with no evidence of protein calorie malnutrition, the SCCM/A.S.P.E.N. guidelines suggest that PN support therapy not be implemented for the first 7 days of ICU admission. The basis for this recommendation comes from 2 important studies. Heyland and colleagues showed that use of PN in the absence of malnutrition showed a trend towards greater rates of complications compared to the use of standard therapy (i.e., no nutrition support with delivery of standard intravenous fluids).6 Similarly Branschweig and coworkers showed that the use of standard therapy (i.e., no nutrition support and standard intravenous fluids) was associated with reduced infectious morbidity and a trend towards and overall reduction in complications compared to the use of PN when there is no evidence of protein-calorie malnutrition.7

In the presence of protein calorie malnutrition upon admission to the ICU and when EN is not feasible, PN should be utilized as soon as possible (after adequate resuscitation and hemodynamic stability). Heyland showed that when PN was used in patients exhibiting protein calorie malnutrition, there were fewer overall complications compared to use of standard therapy (i.e., no nutrition support with standard intravenous fluids).6

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Enteral Nutrition

In this portion of the chapter, enteral nutrition (EN) refers to the use of specialized methods to deliver nutrition. Table 2 lists common reasons why enteral nutrition is provided. Table 3 lists the available methods for delivery of this type of nutrition support while Figure 1 shows the options for enteral access more visually.

Nasally or orally placed feeding tubes have been used for centuries with the first tube feeding being credited in 1598 by His to Capivacceus.8 In the late 18th century, Hunter was known to have fed patients into the stomach.9 In 1921, nasogastric feeding via Levin tube was introduced.10 Improvements in tube construction technology saw a shift from polyethylene to polyvinyl materials followed by silicone and polyurethane which are still used today.11

Table 2.
Common Reasons for Enteral Nutrition
Functional Gastrointestinal Tract
Anoxic Encephalopathy
Neurological Disorders (e.g., stroke, Amyotrophic Lateral Sclerosis)
Oropharyngeal-Esophageal Disease
Patients with altered oral intake for whatever reason
Table 3.
Available Methods for Enteral Access
Oro/naso-enteric Access
Gastric Access
Jejunal Access

Enteral Access – Oro-/Nasoenteric Tubes

Enteral access is usually decided by estimating if a tube will be required short-term or long-term. Sometimes, it may be difficult to predict how long a patient may require access. Nasoenteric feeding is commonly used, and nasogastric tubes have the additional advantage of being able to quantify gastric residuals; they are also less likely to become clogged. However, standard nasogastric tubes are less comfortable than smaller size tubes intended for small bowel feeding. The smallest size tube that satisfies the specific intended use for a particular patient should guide tube selection, especially when it is believed that the need for the tube or tube feeding is predicted to be less than 30 days.

Many tube options are currently available and may depend on the age and size of the patient and/or possibly anatomical challenges. Smaller feeding tubes that are placed in the stomach usually vary from 8-18 French (Fr). Nasoenteric tube indications, contraindications, and complications are listed in Table 4.

Table 4. Indications, Contraindications and Complications of Oro-Nasoenteric Feeding Tubes
  • Feeding
  • Gastric acid analysis
  • Gastric decompression
  • Possible luminal stenting after Lye-induced esophageal injury
  • Monitor gastric pH
  • Monitor GI bleeding
  • Medication delivery
  • Coagulopathya
  • Combative patienta
  • Facial trauma with fracturesa
  • Nasal obstruction
  • Severe esophageal obstructiona
  • Patient refusal (competent patient)
  • Arrhythmia
  • Clogging
  • Duodenal perforation
  • Empyema
  • Epistaxis
  • Esophageal perforation
  • Gastric rupture
  • GI Bleeding
  • Knotted tubes
  • Myocardial infarction
  • Nasal mucosal ulceration
  • Nasal trauma
  • Otitis media
  • Pneumothorax
  • Pulmonary aspiration
  • Pulmonary intubation
  • Pyriform sinus perforation
  • Reflux esophagitis/ulceration/stricture
  • Tube feeding into Pulmonary tree
  • Tube dislodgement
  • Tube obstruction

a Relative Contraindication
b Does not include all reported problems related to tube feeding

After Kirby DF, DeLegge MH. Enteral Nutrition: The Challenge of Access. In: Practical Handbook of Nutrition in Clinical Practice. Eds., Kirby DF, Dudrick SJ. pp90. 1994. CRC Press, Inc. Boca Raton, FL. Used with permission.

Tubes that are placed nasally are usually meant for short-term use. Due to the gag reflex, orally placed tubes are often only feasible in sedated or comatose patients, most of whom are receiving mechanical ventilation. Problems may occur with the placement of oro- or nasoenteric tubes where they may be passed into the lung, often with serious consequences such as pneumothorax or rarely tube feeding being delivered to the lungs. More often, there can be tube clogging, tube feeding-related aspiration or dislodgment. Clogging can be minimized by flushing water on a regular basis and avoiding putting substances into the tubes that are known to have a higher risk of clogging such as crushed pills, fiber supplements and exchange resins like sodium polystyrene.

Dislodgment of nasal tubes can be minimized by the use of bridles. Prior to their introduction, some physicians would suture these tubes to a nares. This gave way to innovative ways to fashion tubes placed through the nasal passages with the need for oral transfers and possible fingers being bitten. Presently, a simplified bridle technique is available that is easy to use and highly successful in decreasing tube dislodgment.12-14

Enteral Access – Oro-Nasoenteric Tubes – Methods of Placement

Table 5 lists the common methods of oro- or nasoenteric tube placement. "Blind" placement simply refers to passage of a tube through a nares or mouth with the intention of passing the tube to the stomach or beyond. "Facilitated" passage generally refers to a method of attempting to pass a tube that has been passed into the stomach and then beyond into the small intestine. Methods may utilize bedside techniques involving air instillation and stethoscopes to track the progress of the tube with the goal of passing the tube into the duodenum and possibly beyond the ligament of Treitz into the jejunum with the intention of reducing tube feeding-related pulmonary aspiration.15,16

Table 5.
Common Methods of Placement of Oro-/Nasal Feeding tubes
"Blind" Placement
Facilitated Placement
  • Air insufflation/ Corkscrew methods
  • Medications
    • Metoclopramide (off label use)
    • Erythromycin (off label use)
  • Electromagnetic method - Cortrak® Enteral Access System (Corpak MedSystems. Buffalo Grove, IL)
  • Magnets - Gabriel™ Feeding Tube (Synchro Medical Innovations. Macon, GA)

Additional facilitated techniques may use medications such as metoclopramide or erythromycin (both off-label uses) to improve gastric emptying to help the feeding tube pass into the small bowel. These medications may be combined with other techniques including fluoroscopic passage of tubes to try and increase the success rate of duodenal placement.17-21

Other available methods for faciltated tube passage into the small bowel include the following: Cortrak® Enteral Access System (Corpak MedSystems. Buffalo Grove, IL) and a magnet-assisted system Gabriel™ Feeding Tube (Synchro Medical Innovations. Macon, GA). The Cortrak® Enteral Access System uses a computer-assisted electromagnetic guided feeding tube that is highly correlated with tube passage into the small intestine. Placement beyond the ligament of Trietz may still occur only in a small portion of placements.22,23

The Gabriel™ feeding tube uses a small magnet in its distal tip. After the tube has been placed through a nares or the mouth into the esophagus, an external magnet is used to pull the tube's tip beyond the pyloric sphincter and further into the small intestine. Although there has been an 89% success rate in getting the tube beyond the pyloric sphincter, there are limitations of use unique to this tube that include absolute contraindications with an either an implanted pacemaker or a Greenfield inferior vena cava filter.24 Also, the tube must be removed if the patient has a magnetic resonance image (MRI) examination.

Oro- or nasoenteric tubes can also be facilitated by fluoroscopy.25 This technique can be very successful and can be performed at the bedside with a C-arm portable fluoroscopy unit or if patients are transported to the Radiology Department, but can be associated with morbidity and mortality. The latter is usually associated with initiation of arrhythmias that can be fatal.25 Use of this placement is more common after other less invasive methods have been unsuccessful. Thurley and colleagues showed successful tube placement in the distal duodenum or jejunum 92% of patients, and placement in either the distal stomach or proximal duodenum in 3%, and a failure rate of 5%.26

Endoscopic techniques can facilitate feeding tube placement and include oral and nasal endoscopic methods with varying degrees of success in obtaining postpyloric tube placement. These techniques can be especially useful when bedside fluoroscopy or transportation of a critically ill patient from an intensive care setting to a fluoroscopy unit may be unavailable or difficult to accomplish. Multiple variations of the "drag and pull" technique have been used such as use of a distal suture tie on a feeding tube, endoscopic placement of a guidewire and passage of a tube over the wire, or transnasal endoscopic techniques. Patrick and coworkers reported on 54 consecutive critically ill patients who were referred for endoscopic feeding tube placement.27 They used a combination nasogastric-nasojejunal tube that was advanced under direct endoscopic vision through the pylorus and into an appropriate small bowel position. Initial placement was successful in 94% of tubes, which was radiologically defined as tube placement in the distal duodenum or jejunum. The average procedure time was 12 minutes.

Mahadeva et al reported on the utility of transnasal endoscopic placement of nasoenteric feeding tubes in noncritically ill patients.28 Postpyloric placement was noted in 86% of their series with 16% in the second part of the duodenum, 47% in the distal duodenum, and 37% in the jejunum. Thus, 30% of tubes in this series placed by this method were in a suboptimal position. They also reported limitations of this method in patients who had altered duodenal anatomy.

Nasoenteric feeding tubes have been placed in the operating room during intraabdominal procedures for many years. However, the actual incidence and success of this technique is impossible to know. An anesthsiologist would pass a tube through a nares and into the stomach. The surgeon would then "milk" the tube into a postpyloric position. It is likely that in the era of laparoscopically performed surgery that this technique is much less commonly used and only possible in those cases that are done as open procedures and will not be considered further.

Enteral Access – Gastro/Jejunal Endoscopic Options

When long-term (>30 days) enteral access is required, then other methods can be used and often depend on a Medical Center's local expertise for whether the procedure is accomplished endoscopically, radiologically or surgically. It is often less costly to obtain gastro/jejunal access by endoscopic or radiologic techniques. In 1980, the first published account of an endoscopic technique to place a gastrostomy without surgery appeared.29 The technique has been refined over the years and is commonly performed by gastroenterologists and endoscopically trained surgeons. Table 6 lists the indications and contraindications as well as the special challenges to nonsurgical tube enterostomy placement. Tube enterostomy refers to any tube placed through the skin into the stomach or other portion of the GI tract. Tube size can vary depending on the size of the patient, placement technique or intended use. Pediatric sizes usually vary from 14-18 Fr or may be from 18-24 Fr in adults. The most commonly endoscopically placed percutaneous endoscopic gastrostomy (PEG) tube is a 20 Fr. Larger tubes may be placed and are often used either for decompression or venting when there is distal intestinal obstruction or severe gastrointestinal dysmotility or to facilitate the placement of a jejunal extension (percutaneous endoscopic gastrojejunostomy [PEG/J] or jejunal extension of a PEG [JET-PEG]) for the purpose of feeding into the small intestine. Several techniques for jejunal extensions exist, but the over-the-wire method is relatively easy and reliably places a feeding tube into the distal duodenum or jejunum.30 Tubes can also be endoscopically placed into the small bowel either with normal anatomy or after previous gastric resection.31,32 However, the technique is technically more difficult and not as often successful as a gastric placement.

Table 6. Indications, Contraindications and Special Challenges for Endoscopic or Radiologic Tube Enterostomy Placement
Indications / Uses
Medication delivery
Contraindicationsa or Special Challengesb
Inability to transilluminatea
Intestinal obstructiona
Marked hepatomegalyb
Morbid obesityb
Peritoneal dialysis
Peritoneal metastasesb
Portal hypertensionb
Previous gastrectomyb

a Relative Contraindication
b Special Challenge

After Kirby DF, DeLegge MH. Enteral Nutrition: The Challenge of Access. In: Practical Handbook of Nutrition in Clinical Practice. Eds., Kirby DF, Dudrick SJ. pp93. 1994. CRC Press, Inc. Boca Raton, FL. Used with permission.

Enteral Access – Radiologic Options

Percutaneous radiologic gastrostomy (PRG) techniques were reported shortly after the seminal paper by Gauderer and coworkers on PEGs.29-33 Radiologic tubes have sometimes been criticized for using smaller sized tubes, and subsequent techniques have used variations of placing one or more T-fasteners to tether the stomach up to the anterior abdominal wall to allow more control in performing the procedure.34 In addition, radiology techniques can place a tube initially through the gastric wall and place a tube into the small bowel.35 Table 7 lists the potential complications of the percutaneous techniques.

Table 7. Potential Complications of Percutaneous Enterostomy Techniques
Aspiration Bleeding Bowel obstruction
Buried bumper syndrome Candida cellulitis Clogged tube
Colocutaneous fistula Dehydration Extrusion/migrationa
Gastric outlet obstruction Hematoma Hypopharyngeal/esophageal tube impaction
  • Prolonged
  • From migrated PEG
Incisional pain Inability to transilluminate
Intraperitoneal placement Intraperitoneal displacement Mallory-Weiss tear of esopohagus
Misplaced T-fastener MRSA skin infectionb Multiple punctures of stomach
Necrotizing fasciitis Peritonitis Placement/technical failure
Pneumoperitoneum Pneumonia Small bowel perforation
Stomal leakage Suture/wire breakage Subcutaneous emphysema
Tube deterioration Tube displacement Volvulus
Wound infection    

a May also be part of the buried bumper syndrome
b Methicillin-resistant Staphylococcus aureus

After Kirby DF, DeLegge MH. Enteral Nutrition: The Challenge of Access. In: Practical Handbook of Nutrition in Clinical Practice. Eds., Kirby DF, Dudrick SJ. pp98. 1994. CRC Press, Inc. Boca Raton, FL. Used with permission.

Enteral Access – Surgical Options

Sedillot is credited with the first surgical gastrostomy in 1846.36 Several variations have been made, but the Stamm gastrostomy is often performed as the standard technique.36,37 Laparoscopic versions were reported in the early 1990's and are commonly performed today.38

In 1878, Surmay performed the first surgical jejunostomy.39 Many modifications have been created over the years, and many techniques are still in common practice. Laparoscopic techniques were reported shortly after successful gastrostomy placments.40

Again, multiple enteral access techniques are available, and clinicians need to review the need for a short term or a long term tube feeding option. In addition, each technique has its risks and benefits, and local expertise will be important in helping to decide what is most appropriate for an individual patient.

Enteral Access – Choosing a tube feeding

Multiple products are available for enteral tube feeding. The products are generally grouped into several categories that include the following: 1) standard, 2) semi-elemental/elemental, and 3) disease specific formulations. Standard enteral tube feeding products are composed of intact protein and are usually isotonic. Standard enteral tube feeding products may have fiber (either soluble, insoluble, a blend of both types of fiber, or no fiber), and range in caloric density (1 calorie/mL, 1.2 calories/mL, 1.5 calories/mL, or 2 calories/mL).41 Standard enteral formulas are typically well tolerated in patients with an intact gastrointestinal tract and are the first line formula choice when initiating enteral feeds. Standard enteral feeding may also be used for patients with short bowel syndrome to promote intestinal adaptation.

Semi-elemental formulas have hydrolyzed protein sources (such as dipeptides or tripeptides) to facilitate "easier" absorption. Elemental formulas are composed of free amino acids. Both semi-elemental and elemental formulas have medium chain triglyceride oil (non essential fat source) in higher proportions compared to standard formulations to aid in absorption. These types of formulas may be utilized for patients with pancreatitis or pancreatic dysfunction, or after a trial of a standard enteral formula has been unsuccessful (short bowel syndrome, massive bowel resection/abdominal surgery, etc).

Disease specific formulations are available, but are often not supported by evidenced based research and can be costly.41 Specialized formulas exist for the following disease populations: diabetes, renal, pulmonary, hepatic, immune-modulating, and respiratory failure. There is a good body of evidence available for the use of immune modulating enteral formulas and formulas for use with patients suffering from acute respiratory distress syndrome.6,41 Most often patients with diabetes, renal failure, and hepatic failure are candidates for intact standard enteral tube feeding products. Renal specific enteral tube feeding products lack adequate protein for patients receiving hemodialysis. Diabetic specific enteral feeding formulations are higher in fat to offset carbohydrate delivery with the intent to improve glycemic control. The increase in the composition of fat often leads to difficulty with further delaying gastric emptying in patients with diabetic gastroparesis. Utilizing an enteral access device that extends below the pylorus may circumvent problems with the high fat content delaying emptying from the stomach. There is no evidence to support the routine use of specialized diabetic formulations at this time. The usefulness of hepatic failure enteral products is extremely limited since protein restriction is no longer recommended as patients with hepatic failure are chronically malnourished and hepatic encephalopathy is treated with medications such as lactulose.41

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Parenteral Nutrition

When it is not possible to use the gastrointestinal tract for feeding, then intravenous nutrition can be administered. Many areas had to be medically conquered before the provision of intravenous nutrition could be attempted. Drs. Dudrick, Vars and Rhoads are credited with the first successful use of intravenous nutrition support showing normal growth and development in beagle puppies.42 This was quickly followed by successfully treating an infant and then adults.44-46.

Intravenous nutrition techniques are divided into peripheral vein and central vein nutrition. Peripheral vein nutrition uses the smaller veins of the body and is limited by what can be safely infused. The osmolality of the solution should be less than 900mOsm/L because use of higher concentrations can cause pain at the infusion site, infiltration of the intravenous site, and possible thrombosis of the vein. Concentrations of dextrose are limited to no more than a D10 (Dextrose 10%) concentration. So higher volumes of solutions must be provided, but may be a problem with patients who have cardiopulmonary or renal disease. Often more lipid is infused with peripheral vein nutrition because the lipid helps to limit the osmolality, but provides significant calories, and the lipid also helps to coat the vein and decrease the incidence of phlebitis.

Figure 2 illustrates the possible areas for temporary (in hospital) venous access, and Figure 3 highlights more appropriate options for long term (home) venous access. After the decision of venous access has been made, then writing of a solution can be done. It is not the intention of this chapter to teach all of the basics of writing a PN formula. There are several resources that can assist with this.47-49. However, some basic concepts are important as an overview. Table 8 lists the common components of a bag of PN which are as follows: dextrose (glucose), proteins (as amino acids), fats (available as fat emulsions which differ in composition in the United States and other parts of the world), electrolytes, vitamins, trace elements and compatible medication additives. Once prepared, these nutrient components are delivered with the assistance of an in-line filter (filters impurities and bacteria) and an infusion pump. The delivery rate is determined by the patient size (infant, child, or adult) and medical condition (cardiopulmonary or renal issues). Other factors in the PN delivery rate may be the concentration of dextrose and/or potential toxicity of certain electrolytes, such as potassium, where rapid infusion rates may cause important metabolic imbalances.

Table 9 lists the possible complications of PN that simply stated include getting access, problems related to keeping access, and the metabolic complications associated with the infusion of concentrated nutrient solutions. Issues related to placing catheters will not be considered further here except to state that some patients become very challenging with regards to obtaining access. Patients who experience multiple thromboses can have limited access which often taxes the creativity and expertise of interventional radiologists or others who place these life-saving routes of access. In fact, such difficulty with venous access is one of the indications for intestinal transplantation in appropriate long-term patients who require parenteral nutrition.49 In addition, a few guiding principles are useful when selecting and obtaining access as follows: 1) select a catheter type with the fewest number of lumens necessary (more is not necessarily better and increases the risk of more complications), 2) use of maximal barrier protection and aseptic technique prior to and during insertion of the central venous access device (CVAD) (no matter where the catheter is placed – bedside, interventional radiology suite, or operating room), and 3) promptly remove a CVAD upon discontinuation of IV therapy.50

Table 8. Common Components of a Bag of Parenteral Nutrition
Varying concentrations From D5-70
A, D, C, E, and K
B1, B2, B6, B12
Folic Acid
Variations currently limited in the U.S.
Trace Elements
Common compatible additives
H2-receptor antagonists (e.g., famotidine)
Morphine sulfate
Iron (small amounts only)

Not used in every formulation of parenteral nutrition - when used in central vein nutrition it is often called "All-in-One" TPN or "3-in-1" TPN.

Table 9. Possible Complications of Parenteral Nutrition
Technical problems with line insertion
Air embolism
Arterial puncture
Cardiac perforation & tamponade
Brachial plexus injury
Catheter fragment embolism
Post-insertion catheter problems
Catheter related
Metabolic complications
General electrolyte disorders - hypo/hyper - Sodium, Potassium...
Glucose abnormalities
Phosphorus abnormalities
Calcium abnormalities
Magnesium abnormalities
Vitamin & Trace element abnormalities

After PN has begun, it is vital to try to minimize potential complications. Catheter issues for peripheral vein nutrition often dominate this option. Many patients have poor peripheral vein access after being hospitalized for a prolonged time or just poor peripheral venous access in general. The solutions may be irritating to the peripheral vein and can cause significant phlebitis. This type of therapy is meant to be for short periods of time while the patient is either expected to get better or change to central vein nutrition support.

The use of a peripherally inserted central catheter (PICC) was to be a less invasive method of attaining central access that was intended to be "short term". However, over time the concept of "short term" has become blurred and instead of an in-hospital option for central access, it is often used to send patients home or to facilities to receive treatments such as long-term antibiotic therapy or PN. There are many patients that receive PN for "shorter periods" of time where a PICC may be preferred to a tunnel catheter. To decrease potential complications, if the proposed length of time for use of a PICC is greater than 6 weeks, then serious consideration should be given to placing a tunneled catheter. Also because the catheter, which is usually placed in an upper extremity, is subject to more motion due to movement of the extremity, the catheter may become dislodged from the optimal distal superior vena cava position and be prone to more complications, especially thrombosis.

Issues related to caring for a PICC include requiring a homecare RN or another trained caregiver to care for the line since the patient does not have use of both hands to complete procedures or dressing changes (i.e. lack of independence). In contrast to tunneled catheters, PICCs have increased risk of infection, thrombosis, and tip dislodgement.

When central access is required for use of parenteral nutrition, methods to decrease the incidence of both infections and thrombosis are important. As inpatients, attention to the catheter site is important. Some institutions have adopted use of the Biopatch® (Ethicon, New Jersey). The Biopatch® is a commercially available chlorhexidine impregnated sponge that is applied over the exit site of the catheter and changed weekly (it provides a continuous release of chlorhexidine). Studies have shown a reduction in catheter colonization and catheter sepsis when the Biopatch® is used.51 These well-designed studies showed positive results with short-term catheters, but there is no supportive data for its use in long-term tunneled/long-term catheters. Typically, the entry of bacteria in short-term access devices is skin contamination whereas hub contamination is the site in long-term catheters. The exit site of the catheter cannot be visually monitored when the Biopatch® is used. This is a strong drawback as the CDC recommends monitoring catheter sites on a regular basis. Exit sites are easily viewed through transparent dressings daily when not obstructed by the Biopatch®. If tenderness or fevers develop, the dressing should be removed for examination of the site.

Adherence to infection control techniques is paramount. With regard to use of the line for other reasons, such as medication delivery, blood transfusions, blood draws, or other therapies, the infection rates rise with number of "entrances" of the catheter. One lumen should be dedicated for PN while hospitalized, and it is important to select the fewest number of lumens possible especially for home going. Patients, caregivers, and nurses should be educated on catheter care, hand washing policy, and aseptic technique for infection prevention.

While many factors can contribute to the risk of thrombosis, including hydration status, hypercoagulable states and even the catheter presence (as a foreign body), position of the tip of the catheter is also important. Cadman et al showed that the optimal position of the catheter tip for hyperosmolar parenteral nutrition solutions was in the distal superior vena cava (SVC).52 Catheters that were in the proximal SVC had approximately a 10-fold increase in the rate of thrombosis.

Various infection prevention measures such as site care, education, and sterile placement practices exist, but ethanol lock (ETL) may offer an additional benefit to patients. Although it is not an approved FDA therapy, ETL is intended to prevent catheter-related bloodstream infection (CRBSI). Ethanol is instilled into the lumen of the catheter while cyclic PN is not infusing. The ETL dwells within the lumen of the catheter for the longest number of hours the patient is not infusing PN until the next time the infusion occurs. Adult patients instill 3 mL of 70% ethanol after disconnecting from PN solutions and then allow it to dwell until the next PN infusion (usually 12 hours), and flush the ETL through the catheter with normal saline before starting PN.

ETL is an ideal locking solution since ethanol has the following benefits 1) inexpensive, 2) no concerns for development of resistance, and 3) bactericidal and fungicidal properties to prevent infection.53 ETL is only used in silicone catheters, but there is some data from laboratory studies showing that ETL does not degrade polyurethane catheters. Currently there are no large commercial ETL products available so pharmacies must compound the ETL into a pre-filled syringe. Stability data within the syringe has been documented elsewhere.54

The ideal time for ETL to be started is directly after a new catheter is placed. Biofilm begins to form on the internal surface of the catheter so utilizing ETL soon after placement seems prudent. There is some debate if starting ETL is effective in older catheters where biofilm has had a chance to form.

Data for use of ETL has come from many patient populations including pediatrics, dialysis patients, and home PN patients. Small studies have demonstrated statistically significant decreases in CRBSI, hospital readmissions for CRBSI, and catheter changes.55-59 The pediatric literature cites case study reports of occlusions or thrombosis with use of 70% ETL,60 but this has not been studied in the adult HPN population to date.

Other locking solutions available outside of the United States include Taurolidine and have had shown good results in prevention of CRBSI. Taurolidine is an antiseptic agent derived from aminosulphonic acid taurinamide.61 Similar to ETL, Taurolidine has bactericidal and fungicidal properties, but the mechanism of action is unique. Taurolidine prevents bacteria from adhering to biological surfaces by methylotaurinamide reacting with bacterial cell walls. Many patient populations have been studied including chemotherapy, hemodialysis, and home PN patients.62-64

Many questions remain unclear with the use of ETL or Taurolidine lock such as the ideal dwell time and concentration, long-term stability of the catheter materials exposed to these locking solutions, and the potential for development of "super bugs." Research is warranted, but the current data available shows promising results that should be expanded to multicenter, prospective trials.

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The provision of nutrition within the hospital and later in the home can be a challenging area of care delivery for our patients. It is imperative that this care be carefully considered and that adequate resources be available. Most importantly, the coordination of care from multiple caregivers such as physicians, nurses, dietitians, pharmacists, social workers, et al. is vital to the success of this venture. Physicians must understand that they are not alone either in the hospital, outpatient clinic or at home when caring for these issues and that they should utilize these resources for the benefit of their patients.

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