enteral or parenteral nutrition after bariatric surgery as a result of complications such as those listed above. Kumpf et al. (5) conducted a survey of American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) members regarding use of enteral nutrition (EN) and parenteral nutrition (PN) after bariatric surgery; 467 clinicians participated in the survey. The most common indications for initiation of enteral or parenteral nutrition were anastomotic leak/fistula, chronic nausea/vomiting, and severe malabsorption or diarrhea.
Learning Objectives:
After reading this
article, the reader
will be able to:
1. List three indications for initiation of nutrition support therapy in the bariatric surgery patient.
2. List three complications associated with enteral nutrition.
3. List three complications associated with parenteral nutrition.
Introduction
T
he number of bariatric surgery cases continues to grow, withapproximately 200,000 procedures done in the United States each year (1). In 2007, Roux-en-Y gastric bypass (RYGB) represented approximately 80% of bariatric procedures; but laparoscopic adjustable gastric banding (LAGB) is gaining in popularity. Other bariatric procedures include biliopancreatic diversion (BPD) and biliopancreatic diversion with duodenal switch (BPD/DS), and staged bariatric surgery procedures that start with a sleeve gastrectomy and then progress to RYGB, BPD, or BPD/DS once the patient loses weight and has improvements in co-morbidities such as diabetes (1). The complication rate continues to improve, but some risk remains. A recent study (2) of over 4,000 patients undergoing either open or laparoscopic RYGB or LAGB demonstrated a 30-day mortality rate of 0.3%, with the following 30-day morbidity: 0.4% with deep-vein thrombosis or venous thromboembolism, 0.4% requiring tracheal reintubation, 1.1% requiring reintervention with endoscopy, 0.2% requiring tracheostomy, 0.3% requiring reintervention with a percutaneous drain, 2.6% requiring reintervention with abdominal surgery, and 0.4% failed to be discharged at the 30-day mark. These complications, particularly
those related to a reintervention, may lead to a patient requiring some type of nutrition support therapy.
Nutrition support therapy is necessary when patients are unable to eat or take adequate nutrition by mouth, or have gastrointestinal (GI) compromise that precludes use of the intestinal tract for feeding over an extended period of time, typically more than seven to ten days or five to seven days if the patient is critically ill (1, 3-4). Patients may require either
Nutrition Support Therapy for the bariatric
surgery patient
By Kris M. Mogensen, MS, RD, LDN, CNSD
Table 1. Indications for Nutrition Support Therapy (3-4)
Enteral nutrition:• Inability to take oral nutrition for >7-10 days (5-7 days in ICU setting; must have functional gastrointestinal tract and ability to safely insert an enteral feeding tube)
• Cerebral vascular accident with significant dysphagia • Dysphagia with aspiration
• Enterocutaneous fistula where the enteral feeding tube can be inserted distal to the fistula
• Head/neck cancer
• Inadequate oral intake to meet metabolic demands (e.g., trauma, burn, or other critically-ill patients)
• Significant malnutrition
Parenteral nutrition:
• Inability to take oral or enteral nutrition for >7-10 days (5-7 days in ICU setting)
• Diffuse peritonitis
• Enterocutaneous fistula where the enteral feeding tube can not be inserted distal to the fistula
• Gastrointestinal ischemia
• Ileus
• Intestinal obstruction • Intractable vomiting • Intractable diarrhea
• Perioperative PN (7-10 days) for moderately-to-severely malnourished patients
• Severe gastrointestinal bleeding
• Severe pancreatitis (if enteral feeding trial fails)
• Severe malabsorption
• Severe malnutrition with inability to obtain enteral access, contraindication to enteral nutrition, or poor tolerance to enteral nutrition
• Short bowel syndrome (severe cases) • Significant exacerbation of Crohn’s disease
Boldedindications are those that may be seen in the bariatric surgery patient Abbreviations: ICU, intensive care unit; PN, parenteral nutrition
Kris M. Mogensen, MS, RD, LDN, CNSD
transfer to the floor is unlikely to require EN or PN. However, a patient who has experienced severe respiratory failure leading to reintubation and transfer back to the ICU after surgery may be facing a longer ICU stay and may need initiation of nutrition support therapy. For a non-GI complication, the team could consider inserting a nasoenteric feeding tube with endoscopic guidance if necessary. RYGB patients may not tolerate enteral feeding into the small pouch because of the small size of the gastric remnant, so jejunal feedings (using endoscopic guidance to insert the
nasoenteric feeding tube into the Roux limb of the jejunum) may be better tolerated. The surgeon may also consider inserting a feeding tube into the bypassed, or excluded, portion of the stomach. In cases where enteral nutrition is impossible, PN should be started. The joint A.S.P.E.N. and Society of Critical Care Medicine (SCCM) guidelines (13) for nutrition support therapy in the ICU setting give an excellent overview and guidance for the decision process for when to start feeding and which mode of nutrition support therapy should be used.
Determining Energy and Nutrient
Requirements
In any situation, the patient’s clinical status drives the determination of energy and protein requirements. For the bariatric surgery patient, this is especially important,
particularly when evaluating energy requirements. For a patient with a
postoperative complication that does not lead to a hypermetabolic and/or hypercatabolic state, it is reasonable to restrict energy delivery to promote safe weight loss while providing adequate protein to assure postoperative wound healing. Patients with postoperative nausea and vomiting, without other complications, would fit into this category. Typical protein recommendations for non-critically ill, post-bariatric surgery patients are between 60-120 g/day (1). The dietitian should use the higher end of the range for patients with higher protein requirements, such as patients with poor wound healing or wound drainage leading to significant protein losses. Close monitoring remains essential to assure that the patient is healing well and otherwise has normalized nutrition parameters after surgery. For critically-ill, obese patients, there may be Nutrition support therapies are not without
risk, particularly for parenteral nutrition, so it is essential to select the most appropriate feeding modality and monitor patients carefully to avoid nutrition-related complications. This review will cover the indications for enteral and parenteral nutrition with emphasis on the adult bariatric surgery patient; determination of energy,
macronutrient, and micronutrient
requirements; and specific information related to enteral and parenteral nutrition including potential complications and monitoring guidelines.
Indications for Nutrition Support
Therapy
When a patient cannot eat by mouth or has a significant limitation in the ability to take oral nutrition for an extended period of time, nutrition support therapy should be considered. EN is often the first choice for nutrition support therapy in cases where a patient cannot eat by mouth, has a functional intestinal tract, and has no contraindications to inserting an enteral feeding tube. Parenteral nutrition (PN) is indicated in instances where patients have GI compromise or who cannot have an enteral feeding tube inserted safely. Indications for EN and PN are summarized in Table 1 (3-4).
There are a number of GI complications that can occur after bariatric surgery, including abdominal pain, nausea and vomiting, diarrhea, hernia, and ulcers (6-7). Surgical complications associated with RYGB, BPD, and BPD/DS include anastomotic leak,
anastomotic strictures, and intestinal obstruction (6-7). Some complications specific to LAGB include band erosion, gastric prolapse, and esophageal dilatation (6,8). Not all of these complications are indications for nutrition support therapy, but may be depending on the severity.
Severe nausea and vomiting after bariatric surgery may be an indication for PN,
particularly if the patient is unable to maintain hydration and take an oral multivitamin-mineral preparation for an extended period of time. Initial therapy for severe nausea and vomiting should include correction of dehydration with intravenous (IV) fluids; patients may also respond to addition of antiemetic medication or prokinetic agents to the IV fluid (7,9). Bariatric surgery patients also
benefit from addition of IV multivitamins to the IV fluid, as well as an additional 100 mg thiamin per day (10). There is a high risk of Wernicke’s encephalopathy in these cases of severe vomiting and the risk is particularly enhanced if the IV fluid provided contains dextrose, which increases the demand for thiamin (11). If the patient is unable to take any solid food, the IV fluid can be changed to PN to meet all of the patient’s nutrient needs. Once the nausea and vomiting subsides, the patient should be able to wean off of PN.
The cause of the severe nausea and vomiting must be explored; these symptoms are often indicative of other serious problems such as anastomotic strictures or intestinal obstruction (6). Close communication with the team to determine the therapeutic plan will be helpful in determining if the patient will require EN or PN. Anastomotic stricture is typically managed successfully with endoscopic dilatation; however, if symptoms persist and the patient is developing signs of protein-energy malnutrition, PN should be considered (1). Intestinal obstruction is often caused by internal hernia and usually requires surgical repair. Some patients recover rapidly from this surgery, but if the patient was found to have a significant complication (e.g., necrotic bowel or prolonged postoperative ileus), diet advancement may need to be slow and PN required to assure adequate provision of energy, protein, vitamins, and minerals to support wound healing (1,3).
Anastomotic leak is an acute postoperative complication that occurs in approximately 5% of cases (1,12). This serious complication is typically found early, but if there is a delay in diagnosis, may lead to intra-abdominal sepsis and a prolonged postoperative course. After repair of the leak, PN may be preferred over EN if the surgeon is unable to insert an enteral feeding tube at the time or if the risk of enteral feeding will outweigh the benefit.
Occasionally, patients require transfer to the intensive care unit (ICU) to manage severe complications such as respiratory failure or sepsis. The dietitian must work closely with the surgeon and intensivist to determine the reason for ICU admission, anticipated length of stay in the ICU, and how this critical illness will affect the patient’s nutrition care plan. A patient requiring a short stay in the ICU for optimization of pulmonary status prior to
some temptation to allow patients to use their own reserves for energy and avoid feeding altogether. However, metabolism is shifted during critical illness, with demand for all three macronutrients, not just fat (14). Obese patients, just as lean patients, will break down lean body mass during critical illness. This does not necessarily mean that patients should be overfed, but that they should be fed
appropriately with the right balance of energy and protein. Indirect calorimetry with a metabolic cart is the gold standard for determining energy requirements for critically-ill, obese patients (13). For institutions without ability to measure resting energy expenditure, the A.S.P.E.N.-SCCM guidelines suggest 11-14 kcals/kg of actual weight for critically-ill, obese patients. Protein delivery should be high, at 2 g/kg ideal body weight (IBW) for Class I and Class II obesity, and 2.5 g/kg IBW for Class III obesity (13). This should be considered a starting point for determining energy and protein requirements, and ongoing
monitoring of response to nutritional therapy with timely adjustment of the nutrition care plan as needed is an important part of managing these patients.
The question often arises about which weight to use for estimating energy and protein requirements—actual weight, adjusted weight for obesity, or IBW. The A.S.P.E.N.-SCCM guidelines recommend using actual weight to determine energy requirements and IBW to determine protein requirements (13). There are a number of other equations available to determine energy requirements for both healthy and critically-ill patients, which have been reviewed elsewhere (15-16). After deciding which equation to use, clinicians should apply the weight used in development and validation of the equation. For protein requirements, IBW is often used for calculation of needs, as in the A.S.P.E.N.-SCCM guidelines (13). Clinical indicators are useful to determine if a patient is being adequately fed. One can monitor wound healing or functional status as indicators of adequate nutritional support when other measures are not reliable or available.
Determining fluid requirements can be difficult since the question of which weight to use arises again. Dehydration can cause severe harm to patients, leading to a readmission, renal failure, and at worst, death. Table 2 lists a number of methods for determining fluid
requirements, but there is no consensus about which method is best to determine fluid requirements for obese patients (1). Typical post-bariatric oral diets recommend that patients drink at least 1500-1900 mL per day, so it seems reasonable to use oral fluid guidelines as a starting point for estimating enteral and parenteral fluid needs (1,6). Estimated fluid requirements should then be adjusted based on the patient’s clinical condition—give more fluid if the patient has increased losses (e.g., for patients with severe diarrhea) and restrict fluid if the patient is at risk for volume overload (e.g., renal failure or congestive heart failure) (17).
Micronutrient needs are often met easily with both EN and PN. Many enteral formulas meet 100% of the Dietary Reference Intakes in relatively low volumes (i.e., 1000-1500 mL of formula, providing about 1000-1500 kcals) (18). Multivitamin and trace element preparations must be added daily to PN solutions; parenteral vitamin requirements are listed in Table 3 and parenteral trace element requirements are listed in Table 4.
Standardized multivitamin preparations (with and without vitamin K) and standard multiple trace element preparations are available to meet these needs (4).
There are some special micronutrient considerations for the bariatric surgery patient. All bariatric surgery patients are at risk for vitamin and mineral deficiencies, but the risk varies depending on the type of surgery. Patients who have undergone procedures that include a malabsorptive component are at higher risk for micronutrient deficiencies compared to those who have undergone purely restrictive procedures, and those who have undergone BPD or BPD/DS are at highest risk (6). Vitamins of concern include vitamin D, thiamin, B12, and folate; for BPD or BPD/DS
patients, there is risk of deficiency of all of the fat-soluble vitamins (1,6,19). Bariatric surgery patients are also at risk for mineral deficiencies, with iron deficiency a particular problem. Up to 49% of bariatric surgery patients are iron deficient (20). Liquid iron preparations are available to administer via an enteral feeding tube and parenteral iron preparations are also available. It is important to note that parenteral iron is not compatible with fat-containing PN admixtures and must be given as a separate infusion, or may be added to fat-free PN admixtures (21). There is a risk of hypersensitivity and/or severe anaphylactic reactions with parenteral iron, thus, these preparations must be given in a controlled environment (21). Other minerals of concern include calcium, magnesium, chromium, copper, selenium, and zinc (1,22). For any of these micronutrients, additional
Table 2. Selected Methods
for Determining Fluid
Requirements (17)
• Age 18-50: 1500 mL for first 20 kg plus 20 mL/kg for each additional kg • Age >50: 1500 mL for the first 20 kg
plus 15 mL/kg for each additional kg • Age 18-65: 35 mL/kg • Age >65: 30 mL/kg • 1 mL/kcal
Table 3. Parenteral
Vitamin Requirements (4)
Vitamin Amount A 1 mg (3300 IU) D 5 mcg (200 IU) E 10 mg (10 IU) K 150 mcg Biotin 60 mcg B12 5 mcg C 200 mg Folic acid 600 mcg Niacin 40 mg Pantothenic acid 15 mg Pyridoxine 6 mg Riboflavin 3.6 mgTable 4. Parenteral Trace
Element Requirements (4)
Trace element Amount
Chromium 10-15 mcg Copper 0.3-0.5 mg Manganese 60-100 mcg, or based on serum levels Selenium 20-60 mcg Zinc 2.5-5 mg
supplementation may be required beyond what the patient would receive in a standard enteral formula or in the parenteral vitamin and multiple trace element preparations. Many of these vitamins and minerals can be given individually via the enteral or parenteral route. In cases of severe deficiencies, IV or intramuscular repletion (depending on the micronutrient being repleted) may be preferred over the enteral route, with transition to enteral supplementation once normal levels are attained (1,23). Routine monitoring is critical to identify and treat deficiencies early.
Enteral Nutrition
As previously stated, enteral nutrition is the preferred method of feeding patients who cannot eat by mouth at all, cannot achieve adequate nutrition intake through oral diet alone, have a functional GI tract, and will require nutrition support for more than 7-10 days (5-7 days for ICU patients) (1,3). This mode of nutrition support therapy is associated with fewer complications and is considered to be more “physiologic”compared to parenteral nutrition (3,24). However, in the bariatric surgery patient, achieving enteral access presents unique complications. For a patient with normal GI tract anatomy, insertion of a nasogastric or nasoenteric feeding tube for short-term EN is typically a simple bedside procedure. This is not so for RYGB patients; for this group, the feeding tube may need to be inserted with direct visualization (e.g., with endoscopy). This method was used successfully by Kushner (25) who repleted a severely malnourished post-RYGB patient with night cycled tube feedings and oral
vitamin/mineral supplementation. Nasogastric feedings may also be used successfully, as demonstrated in a case report by Pigeyre et al. (23) who successfully used nocturnal cycled enteral feeding in a patient who developed portal vein thrombosis, daily vomiting, anorexia, and subsequent micronutrient deficiencies and neurological complications. The patient improved with IV micronutrient supplementation, enteral nutrition, and physical therapy and was able to eventually transition to an oral diet after approximately four weeks. Nasogastric and nasoenteric tubes are most appropriate for short-term (<6-8 weeks) EN (26). For patients requiring long-term EN, a surgically-placed gastrostomy tube could be inserted into the bypassed stomach, as successfully used by Barbour et al. (27) in a
Table 5. Selected Enteral Nutrition Complications and
Management Strategies (24,30)
Complication Abdominal pain/bloating Aspiration Constipation Dehydration Diarrhea Electrolyte disturbancesFeeding tube clog
High gastric residual volume
Hyperglycemia
Infection around tube insertion site
Vitamin or mineral deficiency
Management
Assess for constipation Decrease flow rate of infusion
If bolus feeding, change to continuous infusion Elevate head of bed >30° (preferably >45°)
during infusion
Do not bolus feed patients at high risk for aspiration Consider post-pyloric feeding
Try fiber-containing formula Provide adequate fluid Initiate bowel regimen
Monitor for early signs/symptoms Provide adequate water flushes
Use standard dilution (i.e., 1 kcal/mL) enteral formula Check for infectious causes (e.g. Clostridium difficile) Use sterile technique when preparing formula
for administration
Review medication list—avoid elixirs, known cathartics Try fiber-containing formula
Check osmolarity of formula—switch to isotonic formula if necessary
Add antidiarrheal medications Consider use of probiotics
Monitor daily while initiating feedings; correct imbalances promptly
Monitor long-term enteral patients every 1-3 months Flush frequently with a minimum of 30 mL water
every 4 hours
Flush with at least 30 mL water before and after medication administration
Use liquid forms of medication when possible Do not flush tube with cola or juices—these will
coagulate proteins, worsening the clog
Use a solution of pancreatic enzymes plus sodium bicarbonate or a commercial declogging device to address tube clogs
Elevate head of bed >30° (preferably >45°) during infusion
Assure adequate glucose control Consider pro-kinetic agent
Consider post-pyloric tube insertion Avoid excessive energy delivery Consider fiber-containing formula Consider diabetes-specific formula Provide insulin as needed
Meticulous tube care
Refer to physician—may need antibiotics or antifungals Assure that formula meets 100% of daily
recommended intake
Provide multivitamin/mineral elixir Provide separate vitamin and/or mineral
case series of five RYGB patients requiring pancreatic resection. The decision ultimately lies with the surgeon to determine the best route of enteral access. For in-depth reviews of enteral access devices, three excellent reviews by Vanek (26,28-29) are available.
Once enteral access is achieved, enteral formula selection depends on a number of factors including energy, protein, and fluid requirements as well as any disease-specific requirements. For example, a patient with renal insufficiency would benefit from a volume-restricted enteral formula that is also low in potassium and phosphorus; a patient with diabetes may benefit from a diabetes-specific formula; a patient with severe malabsorption may benefit from a peptide-based or an elemental formula (1,18).
The method of feeding—continuous, intermittent, or bolus—depends on where the tip of the feeding tube is located. For small-bowel feeding, pump-assisted feeding is best to assure controlled infusion into the intestine, maximizing tolerance to feedings. Feedings can infuse continuously over 24 hours, or can be cycled over a shorter period of time for patients who are going home on EN. For patients with normal gastric anatomy, bolus feedings or intermittent feedings are options. For RYGB patients, if the tip of the tube is in the small gastric pouch, bolus feeding may not be tolerated and may induce dumping-syndrome symptoms. In that case, continuous feeding with an enteral pump should minimize the risk of these symptoms. If the patient has a gastrostomy tube inserted in the bypassed stomach, bolus or intermittent feeding may be an option (24). Once the goal is calculated, the next step is to develop an initiation and advancement plan. For continuous feedings, the EN should be started at a relatively low rate (e.g., 20-30 mL/hour) and advanced gradually, usually by 10-40 mL/hour, every 8-12 hours to the goal rate. A similar approach can be taken with bolus and intermittent feedings, starting with a smaller volume (e.g. 60-120 mL) and increasing by 60-120 mL every 8-12 hours to the goal volume. It is important to note that full-strength formula should be used; there is no clinical indication for starting with dilute formula (24).
Enteral Nutrition Monitoring and
Complications
Once a patient starts EN, the clinician must monitor for any complications associated with the feedings. A summary of typical EN
complications with suggested prevention strategies and interventions is listed in Table 5. Patients should be weighed routinely (daily initially, then at least once per week when stable) and have input and output documented while admitted. Electrolytes, blood urea nitrogen, creatinine, and blood glucose should be monitored daily for the first 3-5 days of feeding with abnormalities addressed promptly. If possible, patients should be interviewed and asked about any GI symptoms, including nausea, vomiting, abdominal pain or bloating, constipation, or diarrhea (30). For patients who cannot be
interviewed, (e.g., mechanically-ventilated ICU patients), interviewing the patient’s nurse regarding issues such as abdominal pain/tenderness, increased abdominal girth, diarrhea or constipation as well as a thorough review of the nursing flow sheets are important sources of data to determine tolerance to EN. Gastric residual volume (GRV) is another monitoring tool to determine adequacy of gastric emptying and risk of aspiration of gastric contents into the lungs; GRVs >200-250 mL are typically cause for concern (24). However, GRVs can be difficult to measure accurately through a small-bore 1. Calculate energy, protein, and fluid requirements; round up fluid requirements to
the nearest tenth of a liter (e.g., round up 1.78 liters to 1.8 liters) 2. Determine calories from protein (grams protein x 4 kcal/gram)
3. Determine calories from fat, anywhere between 20-30% of total energy requirements; if using 20% IV fat emulsion, divide calories from fat by 2 kcal/mL, then multiply the volume in mL by 0.2
a. Example: 500 kcals of fat ÷ 2 kcal/mL = 250 mL; 250 mL x 0.2 = 50 g fat 4. Determine grams of dextrose: subtract calories from protein and fat from total
energy requirements and then divide by 3.4 kcal/gram 5. Determine final concentrations of each macronutrient:
a. Convert fluid requirements from liters to deciliters b. Divide grams of amino acids by fluid requirements in dL c. Divide grams of dextrose by fluid requirements in dL d. Divide grams of fat by fluid requirements in dL
6. Add 10 mL MVI-13 (or MVI-12 if the patient should not get vitamin K), additional 100 mg thiamin if indicated, and appropriate trace elements (standard preparation, or each trace element individually)
7. Determine electrolytes using standards in Table 7, or work with the infusion pharmacist and/or clinical team to determine the appropriate amount based on the patient’s clinical status
Example (calculations only):
1. A patient requires 1800 kcals, 110 g protein, and 1.8 liters fluid 2. 110 g protein x 4 kcal/g = 440 kcals
3. 1800 kcals x 0.25 = 450 kcals (The middle of the range, giving 25% kcals from fat) a. 450 kcals ÷ 2 kcal/mL = 225 mL 20% IV fat emulsion
b. 225 mL x 0.2 = 45 g fat
4. 1800 kcals – [440 kcals (from protein) + 450 kcals (from fat)] = 910 kcals left for dextrose
a. 910 kcals ÷ 3.4 kcal = 267.6 g dextrose (round to 268 g) 5. Calculating final calculations:
a. 1.8 L = 18 dL
b. 110g amino acids ÷ 18 dL = 6.1% c. 268 g dextrose ÷ 18 dL = 14.9% d. 45 g fat ÷ 18 dL = 2.5%
Note: The pharmacy may prefer “round” numbers, for example, 6% amino acids instead of 6.1%, 15% dextrose instead of 14.9%; communication with the pharmacy is an important part of this process. For the example in the text, the goal solution will be 1.8 L 6% amino acids 15% dextrose 2.5% IV fat emulsion.
Table 6. A Method for Calculating a PN Goal Prescription,
Non-Fluid Restricted Patient
feeding tube; for RYGB patients being fed into the gastric pouch, it may be difficult to check and interpret GRVs, given the size of the pouch. Residuals should only be checked in patients being fed into the stomach, and not for small-bowel feedings.
Parenteral Nutrition
Parenteral nutrition is comprised of crystalline amino acids, dextrose, intravenous fat emulsion, electrolytes, vitamins, and trace elements; PN admixtures are compounded in a sterile environment under the supervision of an infusion pharmacist (4). This allows for an individualized approach to the PN
prescription. Some institutions use premixed solutions, which are commercially-prepared products that contain standardized amounts of PN components. These products decrease pharmacy compounding time, but do not allow tailoring of the PN prescription to an individual patient’s needs (31). It is important to work closely with the infusion pharmacists to assure that orders are calculated and entered correctly as per the pharmacy’s standards.
There are two types of PN: peripheral PN (PPN) and central PN (CPN). The differences between the two are dependent on the osmolarity of the PN solution; PPN must be less than 900 mOsm/L. For PN solutions with an osmolarity greater than or equal to 900 mOsm/L, central venous access, with the tip of the catheter in the superior vena cava or right atrium, is required for infusion to avoid venous complications (3-4). It is difficult to meet a patient’s energy and protein requirements with the limitations associated with PPN. Amino acids, dextrose, and electrolytes contribute significantly to the osmolarity of the solution, thus, PPN solutions are quite low in these components. Patients receiving PPN require large volumes (often upwards of 3 liters or more) of the solution to come close to meeting maintenance requirements, which many patients cannot tolerate. Overall, CPN is preferred over PPN when feasible since it allows for a more concentrated solution to meet a patient’s nutritional needs in a reasonable volume (3).
The PN prescription is driven by the patient’s energy, protein, fluid, and other nutrient requirements. There are a number of different ways to calculate a PN prescription—one method is demonstrated in Table 6. Dextrose
and IV fat emulsion need to be calculated carefully as overfeeding of either one can lead to complications (discussed in the monitoring and complications section). Dextrose delivery should not exceed 5 mg/kg/minute, and fat should not exceed 2.5 g/kg; typical fat delivery is 20-30% of total energy requirements (4). The question often arises about which weight to use for these calculations; some use adjusted weight for obesity [(actual weight-ideal body weight) x 0.25 + ideal body weight], others use IBW, and some may consider using actual weight. Adjusted weight for obesity may be desirable to use for calculation of dextrose and fat delivery since use of that weight may help avoid underfeeding or overfeeding calories. However, it is important to recognize that the adjusted weight for obesity equation has not been validated (32). An additional challenge with PN that is not seen with EN is the need to determine electrolyte content of the admixture. Table 7 lists typical ranges of electrolytes added to PN solutions and suggestions for where modification may be necessary (4).
Just as EN is initiated at a low rate and slowly advanced to the goal rate, a similar practice is done with PN. Since only one bag of PN is
made daily, changes can only be made once per day. To avoid hyperglycemia associated with rapid infusion of dextrose, limit dextrose to 150-200 grams on the first day of infusion (4). If glucose control is adequate, electrolytes are stable in the normal range, and
triglycerides are less than 400 mg/dL, the PN can be increased over the next 1-2 days to the goal. One way to advance PN is to start with the goal concentrations and increase the volume once daily until the goal rate is achieved. To illustrate this method using the example PN solution in Table 6 (1.8 liters 6% amino acids, 15% dextrose, 2.5% IV fat emulsion), start with 1 liter of the solution on day one; if the patient’s electrolytes and blood glucose are stable, the PN can be advanced to 1.4 liters on day two; if the patient remains stable (normal blood glucose, electrolytes, and triglycerides < 400 mg/dL) increase to the goal of 1.8 liters on day three.
Parenteral Nutrition Monitoring and
Complications
As with EN, the clinician must monitor the patient receiving PN closely for complications. Table 8 summarizes typical PN complications and management strategies. Since PN is infused directly into the bloodstream,
Table 7. Parenteral Electrolyte Requirements (4)
Electrolyte Typical needs When to adjust
Sodium 1-2 mEq/kg Limit for renal or liver failure
Increase to offset losses (e.g., severe diarrhea) Potassium 1-2 mEq/kg Limit or eliminate for hyperkalemia or renal failure
Increase to offset losses (e.g. severe diarrhea) or to account for increased needs (e.g., refeeding syndrome)
Chloride Enough to maintain Adjust to maintain acid/base balance
acid/base balance May need increased amounts with increased losses (e.g., gastric decompression)
Acetate Enough to maintain Adjust to maintain acid/base balance
acid/base balance May need increased amounts with increased losses (e.g., severe diarrhea)
Calcium 10-15 mEq/day Limit or eliminate for hypercalcemia Increase for osteoporosis
Magnesium 8-20 mEq/day Limit or eliminate for renal failure
Increase for increased losses (e.g., severe diarrhea) or to account for increased needs (e.g., refeeding syndrome)
Phosphorus 20-40 mmol/day Limit or eliminate for renal failure Increase to account for increased needs (e.g., refeeding syndrome)
metabolic complications are a particular risk. Electrolytes, blood urea nitrogen, creatinine, and blood glucose should be monitored daily for the first 3-5 days of initiating PN (or longer, if the patient is particularly unstable), and any abnormalities must be addressed promptly (33). Patients at risk for the refeeding syndrome may develop hypokalemia, hypomagnesemia, and/or hypophosphatemia when PN is initiated (34). Severely
malnourished patients may require lab monitoring twice/day with IV repletion of these key electrolytes. Patients with renal insufficiency may experience the opposite of malnourished patients, with hyperkalemia and hyperphosphatemia in particular. It can be easy to “overshoot”the electrolyte amounts added to PN solutions; it is important to remember that it is easy to replete electrolytes outside of the PN solution, but once the PN bag is hung, the electrolytes cannot be taken out. Other components of monitoring include daily weights and input/output records to monitor fluid balance. Major day-to-day weight fluctuations often represent changes in fluid balance, and should be correlated with the input/output record (33).
Hyperglycemia is a particular risk because of the direct infusion of dextrose into the bloodstream. Provision of excessive dextrose (>5 mg/kg/minute) is one major contributor to hyperglycemia (3-4). Patients with diabetes, obese patients with insulin resistance, and critically-ill patients are all at risk for hyperglycemia and should be monitored carefully when initiating and advancing PN. Patients at high risk for hyperglycemia should start with lower amounts of dextrose (i.e., 100-150 grams) on the first day of infusion and should not have dextrose increased if blood glucoses (BGs) are difficult to control. Finger-stick BGs should be checked every 6 hours and the patient should be covered with regular insulin. After the first day, two-thirds of the prior day’s insulin requirement can be added to the PN bag. Only regular insulin is compatible with PN; long-acting insulin should not be used (4). A continuous insulin infusion may be used in the ICU setting. For ambulatory patients, the goal BG is <180 mg/dL (1,35). Goal BG for ICU patients is not as clear; work by Van den Berghe (36) suggested that the goal should be 80-110 mg/dL, however, the results of the NICE SUGAR (37) study show increased mortality with such tight control and lower mortality when the ICU
Table 8. Selected Parenteral Nutrition Complications and
Management Strategies (3-4,32-34,39)
Complication Catheter-related blood stream infection Dehydration Electrolyte disturbancesEssential fatty acid deficiency
Hyperglycemia
Hypoglycemia
Intestinal atrophy
Metabolic bone disease
Parenteral nutrition-associated liver disease Volume overload
Vitamin and/or trace element deficiencies or excess
Management
Use aseptic technique for insertion and catheter care Use aseptic technique when preparing PN for infusion Dedicate one port for PN infusion only
Assess fluid requirements carefully
Account for all fluid losses (diarrhea, fistula output, etc) Monitor daily weight and input/output
Provide supplemental IV fluid separately from PN if necessary
Monitor daily while initiating PN; consider twice/day labs for patients at high risk for the refeeding syndrome Correct abnormalities promptly
Once stable, can decrease frequency of monitoring Provide adequate IV fat emulsion to meet essential
fatty acid needs
Monitor fatty acid profile, including triene:tetraene ratio, every 6 months
Give no more than 150-200 g dextrose on the first day If BG is >180 mg/dL, start every 6 hour FSBG checks and
regular insulin coverage
Do not advance dextrose concentration until BG is in control
Add regular insulin directly to PN based on prior day’s requirements (typically give 2/3 of prior day’s requirements)
For cycled PN, check mid-cycle FSBG
Follow BG trends carefully and decrease insulin if necessary
For ambulatory, non-ICU patients goal BG is <180 mg/dL; too tight of a BG goal may lead to hypoglycemia For cycled PN, decrease infusiion rate by 1/2 before
discontinuing PN
Check FSBG 1 hour after PN is discontinued Transition to EN as soon as possible
For long-term patients, allow small amounts of oral nutrition, if possible
Provide adequate calcium and vitamin D Monitor bone density yearly
Initiate appropriate therapy as indicated Avoid overfeeding
Avoid excessive fat delivery Cycle PN
Assess fluid requirements carefully
Review medical history for conditions requiring fluid restriction
Concentrate PN solution as needed Treat with diuretics as indicated
Provide vitamins and trace elements daily in PN
Monitor vitamin and trace element panel every 6 months Replete individual vitamins and trace elements as
indicated, either via PN, separate infusion, or orally (if that is the only available route)
High levels are most often seen with trace elements; if any levels are high, remove the commercial
preparation and add back individual trace elements Abbreviations: PN, parenteral nutrition; IV, intravenous; BG, blood glucose ;
glucose target was <180 mg/dL. Current guidelines (1,13) continue to recommend tight glucose control for ICU patients. Clinicians need to continue to pay close attention to the literature as it seems that there is still some debate as to what the optimal target is for glucose control. Hyperglycemia receives a great deal of attention because of the risk of a number of complications, particularly increased risk of infectious complications (38). However, one needs to be aware of the risks associated with hypoglycemia, so there needs to be a balance between adequate glucose control and prevention of clinically-significant hypoglycemia (38). Hypertriglyceridemia is a risk for patients receiving IV fat emulsion. Patients may become hypertriglyceridemic because of the inability to clear IV fat emulsion from the bloodstream, or as a result of hyperglycemia. Patients with a history of hyperlipidemia are also at risk, so it is important to know if this is part of a patient’s medical history. Hypertriglyceridemia can induce pancreatitis if the patient’s triglyceride level is >500 mg/dL; IV fat emulsion is typically held when triglyceride levels are >400 mg/dL (3-4). Triglyceride levels are typically monitored weekly once the PN is at goal (33). Excessive fat delivery can also be problematic as it can be immunosuppressive. The IV fat emulsion available in the United States is primarily omega-6 polyunsaturated fatty acids; providing excessive amounts of this type of fat leads to overproduction of arachidonic acid and eventually, excessive production of proinflammatory eicosanoids. In addition, excessive fat will inhibit neutrophils and macrophages, and also interferes with the reticuloendothelial system (39). These are the key reasons why fat delivery should be restricted. However, some IV fat should be provided daily, as long as triglyceride levels are normal, to assure that essential fatty acid requirements are met. Patients should receive 2% to 4% of total energy delivery as linoleic acid and 0.25% to 0.5% of total energy delivery as alpha-linolenic acid to meet essential fatty acid requirements (3-4). Signs of essential fatty acid deficiency have been reported in obese patients receiving fat-free PN for 20 days (4). Liver disease is a complication associated with long-term PN infusion. Routine monitoring of
liver function tests is an important part of monitoring for hepatic complications associated with PN: steatosis, cholestasis, and gallbladder sludge/stones (40). Steatosis, which is fatty infiltrates of the liver, is often seen with overfeeding calories. Bariatric surgery patients may already have steatosis present as a result of their severe obesity, so it will be useful to have baseline liver function tests prior to initiation of PN (41). Once PN is at goal, liver function tests should be monitored on a weekly basis. Careful attention to adequate, but not excessive, energy delivery is an important component of avoiding this complication (40). Cholestasis refers to impaired secretion of bile or complete biliary obstruction; this and gallbladder
sludge/stones can result from inadequate enteral stimulation as well as a number of other factors that are beyond the scope of this article. The readers are directed to a review by Kumpf (40) for an in-depth discussion of PN-associated liver disease
Assessing Response to Nutrition
Support Therapy
In addition to monitoring for complications associated with EN and PN, it is important to monitor clinical response to nutrition support therapy. Basic monitoring should include adequacy of the infusion and assurance that the patient received what was ordered, and energy and protein goals were met. Lab measures such as prealbumin can be helpful, but may be difficult to interpret if the patient has a concurrent inflammatory process (42). Monitoring C-reactive protein along with prealbumin will be useful for interpretation. Nitrogen balance studies may also be useful, as long as the patient has normal renal function and urine can be collected reliably for 24 hours. Weight trends should be monitored; significant day-to-day fluctuations are likely related to fluid shifts, but long-range trends over time (e.g., slow weight loss, weight gain, or weight stability) can help guide adequacy of energy delivery. The patient’s clinical status can be an excellent indicator of response to nutritional therapy—adequate wound healing and/or improvements in functional status can be very useful markers of adequate nutrition support.
Conclusion
Enteral and parenteral nutrition are not often used in the bariatric surgery patient. However,
with the increasing number of cases, there is more potential for dietitians to see patients with significant complications that warrant initiation of nutrition support therapy. These therapies are complex and can lead to significant complications. Careful patient selection, appropriate determination of nutrient needs, and close monitoring for complications are all important contributors to a positive patient outcome.
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Kris M. Mogensen, MS, RD, LDN, CNSD is Clinical Manager, Metabolic Support Service Department of Surgery at Brigham and Women’s Hospital in Boston, MA.
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