Preoperative Total Parenteral Nutrition

Total parenteral nutrition (TPN) should be administered to patients who are severely malnourished with nonfunctioning gastrointestinal tracts. Dextrose and lipid formulas are used to provide nonprotein calories, usually in a 70:30 ratio. The caloric values of TPN substrates can be found in Table 2. The amount of dextrose administered should be 4–6 mg/kg/min. However, in patients with chronic obstructive pulmonary disease or diabetes, it is recommended to keep the dextrose administration at 4 mg/kg/min or less. Blood sugars must be monitored and kept tightly controlled between 85 and 120 mg/dl.

Table 2 Caloric Value of Parenteral and Enteral Nutrients

Intravenous fat can be utilized to supplement nonprotein calories; however, there is data to suggest that preoperative lipid therapy should be limited to less than 30% of the total calories. Lipids are administered as a 20% emulsion and depending upon caloric needs anywhere from 100 to 250 ml may be prescribed daily.

Protein is administered as a free amino acid solution at 1.5 g/kg of body weight daily to promote protein anabolism, and should not be calculated as a source of calories. Adequate nonprotein calories must be administered to support protein synthesis in a 150/1 calorie to nitrogen ratio, along with multivitamins and trace elements as part of the nutritional regimen.

While providing preoperative parenteral nutrition for patients with gastrointestinal dysfunction, it is important to consider fluid requirements. A more dilute solution may be needed in patients with large fluid losses, while more concentrated solutions will be necessary in patients who have volume restrictions due to heart failure, renal failure, or hepatic insufficiency.

With protein-calorie malnutrition there is loss of the intracellular ions potassium, magnesium, and phosphorus, and a gain in sodium and water. During refeeding, sodium balance may become markedly positive and cause water retention. Potassium, phosphorus, and magnesium levels may drop precipitously upon initiation of nutritional support. It is important to monitor electrolytes and fluid balance to avoid the risk of refeeding syndrome. In addition, potassium and magnesium deficiencies must be corrected if anabolism is to occur (Table 3).

Trace minerals are inorganic compounds, and vitamins are complex organic compounds that regulate metabolic processes (Table 4). The majority act as coenzymes or as essential elemental constituents of enzyme complexes regulating the use of carbohydrates, proteins, and fats. Iron, zinc, copper, chromium, selenium, iodine, and cobalt are known to be necessary for health in man. However, in malnourished and seriously ill patients, requirements for zinc and selenium should be assessed and replenished as necessary.⁴

Table 4 Vitamins and Minerals

If the patient’s fluid and electrolyte status stabilizes on parenteral support with blood glucose levels in good control, the patient may be discharged home on cyclic overnight feedings while awaiting surgery. The parenteral cycle is gradually decreased from 24 to 18 hours and then to 14–16 hours daily. A permanent access port will be needed for home care.

Preoperative Enteral Nutrition

Enteral nutritional support is the delivery of nutrients into the gastrointestinal tract and may require a temporary or permanent feeding tube. Enteral feeding is the preferred route of nutritional support and should be used whenever possible. Surgical patients benefit from enteral nutrition due to the maintenance of the gut-associated lymphoid tissue, enhancement of mucosal blood flow, and maintenance of the mucosal barrier.

The initial gastrointestinal barrier function is provided by mucous containing lactoferrin and lysozyme, both of which are effective, nonspecific inhibitors of microbial growth. Normal, undisturbed bacterial flora exert a similar effect. Epithelial tight junctions form the next line of nonspecific defense, with junctional integrity being energy dependent, and at least partially reliant on the presence of intraluminal energy substrates. Specific intestinal immunity is governed by the gut-associated lymphoid tissue (GALT). The inductive sites in the Peyer’s patches provide an interface between antigen-presenting cells and circulating lymphocytes. Animal studies have demonstrated improved immunity in enterally fed groups.⁵

Patients may have inadequate appetite or gastrointestinal function to maintain optimal nutrition on oral intake alone. Enteral feeding has been used successfully to meet the nutritional needs of patients with a wide range of surgical diseases including cancer, inflammatory bowel disease, and pancreatic disorders. However, its use is contraindicated in cases of bowel obstruction, persistent intolerance, hemodynamic instability, major gastrointestinal bleeding, and inability to access the gastrointestinal tract safely.

Once it has been decided to administer enteral nutrition, the optimal type of enteral access must be selected. Factors that determine the choice of enteral access include which components of the gastrointestinal tract are available, how long a course of enteral therapy is planned, whether the patient is at risk for aspiration, and finally, the nutritional status of the patient. When available, the gastric route is usually preferred. Postpyloric feeding into the duodenum or jejunum may be indicated when there is early satiety, gastric pathology or a risk of aspiration. Nasogastric and nasoenteral tubes are recommended for short-term feeding because of their ease of placement, low cost and low complication rate. Percutaneous endoscopic gastrostomy has become one of the most common methods for placing gastrostomy tubes. Interventional radiology can also place feeding tubes percutaneously into the stomach as well as in the jejunum. If these less-invasive techniques are not successful, feeding tubes may be placed by open or laparoscopic techniques; however, this approach is less desirable in the preoperative patient with severe malnutrition.

The appropriate selection of enteral formulation requires knowledge of the physiologic mechanisms of the digestion and absorption of each macronutrient. Sources of carbohydrate found in enteral formulas range from simple sugars to starches. The larger molecular weight of starches exert less osmotic pressure in the intestinal lumen, are less sweet and require more time for digestion prior to absorption. Different enteral formulas contain variable amounts of carbohydrates that can range anywhere from 28% to 70% of total calories. Patients with diabetes or carbon dioxide retention due to chronic obstructive pulmonary disease should be given formulas with fewer carbohydrate calories. (See “Preoperative Total Parenteral Nutrition” section.)

Many enteral formulas now contain fiber, which may be soluble or insoluble. Insoluble fiber improves colonic function and bowel transit time, but there is no nutritional benefit or requirement. In contrast, soluble fiber binds to cholesterol and bile salts, and thus lowers serum cholesterol levels. Colonic bacteria digest soluble fiber and produce short-chain fatty acids that are utilized by the colonocyte as a fuel source.

Enteral formulas contain fats derived from corn, soy, and safflower oil. Fat serves as a concentrated energy source and enhances the flavor of enteral formulas without increasing osmolality. The absorption of fat-soluble vitamins requires the intake of a minimum of 15–25 g of fat per day. Linoleic or linolenic acid must be provided to prevent essential fatty acid deficiency. Because omega-6 fatty acids have been shown to have immunosuppressive effects due to the production of inflammatory end-products, omega-3 fatty acids have been added to some enteral products. Medium-chain triglycerides may be a useful caloric source for patients with fat malabsorption, as they do not require pancreatic lipase for hydrolysis, are absorbed without micelle formation, and do not require carnitine for transport into the mitochondria.

Enteral protein may be in the form of intact protein such as casein, partially hydrolyzed oligopeptides, or crystalline L-amino acids. Intact and protein hydrolysates require further digestion by pancreatic and brush-border pancreases into short peptides and amino acids. These nutrients are then freely absorbed by the enterocyte, primarily in the proximal intestine. Patients with malabsorption may benefit from enteral protein in the form of short peptides and free amino acids. Preoperatively, patients should be given 1.5 g/kg/day to support protein synthesis.

Currently, there are over a hundred enteral products on the market. Most formulas have a caloric density of 1-2 kcal/ml, are lactose-free, and provide the recommended daily allowances of vitamins and minerals in less than 2 liters of formula per day. The majority of patients tolerate standard enteral formulas; however, elemental formulas may be necessary in patients with malabsorption. Recently, excellent results with improved immune function and surgical outcomes have been obtained with the preoperative administration of immunoenhancing formulas.⁶ Other disease specific formulations have been created for patients with liver disease, renal failure, pulmonary insufficiency, and diabetes. Formulas for patients with liver disease and encephalopathy contain a higher percentage of protein in the form of branched-chain amino acids with almost no aromatic amino acids. Renal failure formulas have very low levels of potassium and phosphorus. However, hepatic and renal formulas have a very low protein content, which must be considered. Patients with advanced pulmonary disease need to receive most of their calories as fat in order to decrease carbon dioxide production. Diabetic formulas also contain additional calories as fat, but also contain soluble fiber to decrease blood sugar levels. It is important to note that all of these specialty formulas are very expensive, and should only be used when a standard formulation with an appropriate nutrient profile has failed.

It is important to monitor patients on enteral feeding for improvement in nutritional status, gastrointestinal tolerance, and fluid and electrolyte balance. When gastric feedings are administered, it is important to monitor gastric residual volumes. Increased residual volumes lead to vomiting, aspiration, pneumonia, prolonged hospital stays, and mortality. Another complication that can occur in the malnourished patient is diarrhea, which may precipitate fluid and electrolyte abnormalities. Diarrhea may be due to medications, formula composition, or infections. If infectious causes are eliminated and there are no offending medications, the formula should be changed to one that is more elemental to increase absorption. If necessary, medications can be tried in incremental dosages to slow down intestinal transit time.

Because most formulas only contain 65% water, it may be necessary to administer hypotonic enteral fluid boluses to achieve satisfactory fluid and electrolyte balance. Electrolyte levels should be monitored to avoid hyperosmolar states and to replete serum levels of potassium, phosphorus, and magnesium during refeeding. Patients may develop fluid retention and electrolyte imbalances that can result in life-threatening cardiac dysrythmias. Blood sugars must be carefully monitored, and hyperglycemia should be treated to avoid the increased risk of infections and the development of hyperosmolar states.

Preoperative enteral feedings have been demonstrated to decrease postoperative complication rates by 10%–15% of controls, but there is debate over the length of therapy needed to achieve this. The literature supports a course of enteral feedings for 5–20 days prior to surgery. Recently, it has been shown that there may be an advantage to utilizing immune-enhancing formulas, either alone as preoperative supplements, or in combination with postoperative support.⁶

Postoperative Nutrition

When developing a plan for postoperative nutrition, it is important to anticipate the length of time that the patient may require ventilatory support or have an intestinal ileus. The condition of the patient with attention to premorbid nutrition, and the state of hypermetabolism and catabolism must be assessed to maximize the opportunity for intraoperative enteral access (Figure 4). However, this type of detailed assessment may not be possible in patients scheduled for emergency surgery or those with traumatic injury. In order to simplify these decisions, we developed a model for use in patients who have suffered from traumatic injury (Figure 5). This simple algorithm using the indication for emergency surgery and Injury Severity Score has an accuracy of 88% in selecting trauma patients that are candidates for early nutritional support. In our series, we found that 80% of all trauma patients admitted to the intensive care unit met criteria for nutritional support following traumatic injury.⁷

Figure 4 Algorithm for postoperative nutritional support. GI, Gastrointestinal; ICU, intensive care unit.

Figure 5 Trauma care nutritional support algorithm. ICU, Intensive care unit; ISS, Injury Severity Score.

(Data from Byers P, Block E, Albornoz J, et al: The need for aggressive nutritional intervention in the injured patient: the development of a predictive model. J Trauma 39:1103, 1995.)

Although protein requirements in stable adults are only 0.6 g/kg/day, the increased catabolism that occurs during critical illness raises the basal needs for balance. Improved nitrogen equilibrium occurs with increased protein synthesis in the majority of postoperative patients when 25–30 kcal/kg of total calories is provided along with 1.5–2.0 g/kg of protein daily. Carbohydrates should be administered with a maximum of 4–6 mg of dextrose per kilogram per minute with serum blood sugars maintained between 85 and 120 mg/dl. Fat should be used to meet less than 30% of total calories.⁸ If indirect calorimetry is available, it should be utilized to measure caloric needs to avoid overfeeding. Supplements of enteral glutamine should be given in doses of 0.5 g/kg/day, as well as multivitamins and trace minerals, including zinc and selenium.

In addition to monitoring blood sugar, electrolytes, and fluid balance, patients receiving postoperative nutrition should be monitored for efficacy of therapy. Serum protein markers with short half-lives are most effective in measuring improvement in the visceral protein compartment (Table 5). Failure to achieve improvement in these values should prompt assessment of the nutrition administered over the past several days along with a search for untreated infection or inflammation. Nitrogen balance studies may be performed where the amount of protein administered is evaluated against the amount of nitrogen lost in the urine, stool, and wound drainage (Table 6). Critically ill patients should be kept in neutral nitrogen balance while anabolic patients should be kept in a slightly positive balance. After visceral protein markers have normalized, it may become important to evaluate the somatic muscle compartment. If renal function is stable, this can be done by performing a 24-hour urine creatinine measurement and calculating the creatinine height index (Table 7). Improvement in this value will require aggressive physical therapy in addition to nutritional support.

Table 5 Visceral Protein Markers

Table 6 Nitrogen Balance

a Total urinary N can either be measured directly or estimated by measuring urine urea N and dividing by 0.8

Table 7 Estimation of Creatinine Height Index

Data from Heymsfield SB, Arteaga C, McManus C, Smith J, Moffitt S: Measurement of muscle mass in humans: validity of the 24-hour urinary creatinine method. Am J Clin Nutr 37:478–494, 1983.

Postoperative Parenteral Nutrition

Because most well-nourished patients tolerate inadequate nutrition postoperatively for 7–10 days, there is no justification for the use of routine postoperative parenteral nutrition (see Figure 4). Well-nourished patients with severe stress or preoperatively depleted patients should receive postoperative nutrition when a 7–10-day period of inadequate intake is anticipated. Additional candidates for postoperative parenteral feedings are patients who have been treated with preoperative parenteral nutrition, but are unable to receive postoperative enteral feedings and patients who develop complications that preclude utilization of the gastrointestinal tract. Parenteral nutrition may be life-saving in patients with high-output proximal enterocutaneous fistulae, massive intestinal resection, and end-jejunostomy syndrome.

Central venous access with a designated port for parenteral nutrition must be established. For patients that do not require fluid restriction, dextrose concentrations may be kept between 12%–18% with 5%–6% amino acid solutions. Lipids should be limited to 20% of total calories.⁸

There are new modalities that may increase the efficacy of postoperative parenteral nutrition. The addition of growth hormone has been shown to improve wound healing in burn patients, but has been harmful in critically ill surgical patients, and cannot be routinely recommended. Intravenous glutamine has also shown promise. In the future, antioxidants may be indicated as part of a nutritional regimen.⁹ Although scientific studies demonstrating potential benefit are available, more clinical trials proving efficacy are needed.

Postoperative Enteral Nutrition

There is a substantial amount of data supporting the enteral route of postoperative nutrition following elective and emergency surgery as well as in patients who have sustained trauma and thermal injury. Delivery of nutrients by the enteral route attenuates the metabolic response to stress, yields better control of blood sugar, reduces clinical infections, and has been found to be associated with increased intestinal anastomotic strength.

In patients who undergo laparotomy, enteral access can be best achieved intraoperatively. Postoperative enteral support should begin 12–72 hours following surgery or injury. Hemodynamic stability should always be attained first to avoid intestinal necrosis from ischemia. Continuous tube feedings usually start at 10–20 ml/hr and may be increased by the same amount every 8–24 hours depending on the clinical scenario. Abdominal distension should prompt the immediate decrease in the tube feeding rate by half, and should prompt cessation of feedings if it persists. Gastric feedings should only be advanced if the residual volumes are 200 ml or less. Bolus feedings into the stomach of 200–300 ml every 2–6 hours may also be given and may help to maintain adequate amounts of feeding despite daily care and diagnostic tests. Enteral feedings should be continued until it has been documented that the patient has an adequate dietary intake.

When feeding directly into the jejunum, fully or partially elemental formulas should be utilized. Standard formulas are better tolerated in the stomach and duodenum. Immune-enhancing formulas are now available and have been developed by enriching enteral formulas with specific micronutrients. Newer formulas have added omega-3 fatty acids which decrease inflammation and the resultant tendency toward multisystem organ dysfunction. These formulas also contain glutamine, arginine, and nucleotides. Wound-healing formulas contain higher levels of zinc, Vitamin C, and Vitamin A. Although studies have demonstrated improved outcomes in length of stay and infectious morbidity, there has been no effect on mortality.¹⁰

Central Venous Access

Central venous access catheters should be performed by an experienced operator with full aseptic precautions including gown, gloves, mask, and cap after antibacterial handwashing. These antimicrobial catheters may be placed temporarily at the bedside or permanently in an operative suite. In addition, the catheters may be placed by accessing a central vein directly, or by utilizing a peripheral route. The routine use of venous Doppler devices has been demonstrated to decrease complications from venipuncture.

Peripherally inserted central venous catheters (PICC) can be placed by trained clinical specialists. These catheters may be made of silicone or polyurethane and are available in single a double lumen in gauges 16–23. A flexible stylette or guidewire is provided in the kit to help with insertion using a Seldinger technique with a peel-away sheath or by using a catheter-over-the-needle technique. Veins at or below the antecubital space are used for venipuncture. A supine position with the arm at a 90-degree angle from the body is recommended. Catheter advancement should stop if any resistance is encountered. A radiograph of the chest following the procedure is required to document catheter tip position in the central venous system.

Femoral vein cannulation is relatively safe and may not be associated with increased risk of infection. However, it is not a preferred site for long-term venous access due to the morbidity of thrombotic complications. Thoracic venous access can be obtained, and if tolerated, should be performed with the patient in Trendelenburg’s position. The internal jugular vein is a preferred site of venous access, with three different approaches available: anterior to the sternocleidomastoid muscle, centrally between the bellies of the sternocleidomastoid, and posterior to the sternocleidomastoid. The external jugular vein may also be used; however, successful cannulation is only achieved 50% of the time. Due to stability of location, the subclavian route, although the most treacherous, is the preferred site for long-term venous access with tunneled catheters, such as the Hickman and Groshong.

Gastrointestinal Access

In patients with adequate gastric emptying, nasogastric feedings with small-bore, flexible, weighted tubes are adequate. These tubes are 5–8 French in diameter, made of polyurethane, and have a stylette for insertion. The tube should be lubricated and the patient should have a topical anesthetic placed in the nostril. The tube is placed through the nostril, advanced through the pharynx and esophagus for approximately 50 cm. Next, 50–100 ml of air are injected, and the tube is advanced along the greater curvature toward the pylorus. An abdominal radiograph should always be obtained prior to initiating feeds through a small-bore tube.

This technique can be modified for postpyloric placement. Intravenous metoclopramide is given prior to the procedure. As the tube is advanced along the greater curvature of the stomach, a point of resistance at the pylorus is met. Gentle pressure is maintained until the pylorus opens and the tube is advanced. Again, an abdominal radiograph is obtained.

If long-term gastrointestinal access is needed, a more invasive approach will be needed. The endoscopic placement of percutaneous gastrostomy tubes is standard and can be performed at bedside in the intensive care unit. This procedure can also be performed safely in patients with a history of previous abdominal surgery, if additional care is taken. First, it is important to know of any gastrointestinal anatomic changes that have resulted from the previous surgery. It is important to obtain abdominal films and review prior scans to be certain that the stomach is approachable through a safe window. During endoscopy, a bright light should be seen in an area accessible for tube placement. A finder needle should be used to ensure that as air is aspirated into the syringe, the needle is visualized in the lumen of the stomach. Gastrostomy tubes may be placed with a push or a pull technique and should have a bolster holding them in place. Combination tubes are made so that an inner jejunostomy portion of the gastrostomy tube can be placed transpylorically. These tubes can also be placed in the radiology suite by the interventional radiology team. It is important to remember that tubes placed by fluoroscopy alone puncture the stomach, but do not fasten it to the abdominal wall. When using the radiology approach, using a postpyloric tube and feeding distally are recommended to guard against gastric distension, until a tract has formed in approximately 3–5 days following puncture.

Patients should have enteral access placed during the primary operative abdominal procedure when it is anticipated that nutritional support will be needed postoperatively. The type of access selected depends on the procedure performed and the gastrointestinal function anticipated. A gastrostomy is easily placed in the left upper quadrant when there is sufficient gastric remnant to do so. Stamm sutures should be placed to bring the stomach up to the abdominal wall. An inner jejunostomy tube can be placed if post-pyloric feedings are desired along with gastric drainage. A jejunostomy tube can also be placed, but may be associated with torsion and potential volvulus. To avoid this risk, it is better whenever possible to access the jejunum via the stomach with long gastrojejunostomy catheters.

Metabolic Complications

Some complications arise due to administration on exogenous substrates. Malnourished patients may develop electrolyte derangements and congestive heart failure when fed too aggressively. This can be avoided by limiting fluids and sodium, and carefully monitoring phosphorus, potassium, and magnesium, while hypocaloric feedings are initially administered. In addition, feeding with excessive carbohydrates can cause the development of hyperglycemia with an increase in infections, electrolyte derangements, and polyuria with dehydration. Patients with compromised respiratory function may develop hypercarbia and respiratory failure.

Complications of Enteral Nutrition

It is important to be aware of complications that can arise with enteral access. There is a 45% incidence of dislodgment of nasoenteral tubes in intensive care units. Dislodgment of percutaneous enteral access catheters into the peritoneum is more serious and may be associated with peritonitis. Radiographic confirmation of tube placement or replacement with contrast studies should be obtained to help avoid this complication. Another problem that may occur with gastrointestinal access is catheter occlusion. Care of these catheters must include frequent flushes with water. Long-standing enteral tubes may leak and cause skin breakdown. The placement of a smaller catheter will usually allow the stoma to contract and thus prevent leaking when the original catheter is replaced.

Adynamic ileus may occur in postoperative patients due to decreased splanchnic perfusion, injury, manipulation, sympathetic tone, inflammatory response, or high-dose opiates. Gastrointestinal tract dysmotility can also result in aspiration and pneumonia. Aspiration can be minimized by keeping the head of the bed elevated whenever clinically feasible.

Nonocclusive intestinal necrosis can occur when splanchnic perfusion is severely compromised. The most common signs are tachycardia, fever, leukocytosis, and distension. Tolerance of tube feeding may be optimized by minimizing opioid use, utilizing epidural anesthetics to blunt sympathetic outflow, and by using promotility agents. However, abdominal distension must be addressed with decreasing the rate or stopping the feedings. When intestinal necrosis occurs, early intervention and definitive surgical therapy have a survival rate of 56%.

Frequent interruption of tube feedings has been shown to impair adequate delivery of nutritional support and result in malnutrition. In one series, only 52% of the feeding goal was administered in a 24-hour period. Feedings are stopped due to procedures, diagnostic tests, and nursing care protocols. New feeding pumps allow nurses to record the exact amount of feedings administered each shift, so that this problem can be recognized and treated.

Complications of Parenteral Nutrition

It is important to be aware of complications that may occur while obtaining central access for total parenteral nutrition. An air embolus may occur and present with hemodynamic collapse. The patient should be immediately placed in Trendelenburg’s position with the right side up. If possible, an attempt may be made to aspirate air. This complication can be avoided by hydrating the patient and creating venous hypertension with Trendelenburg’s position. Adjacent anatomic structures may be injured; subclavian and internal jugular line placements may result in the development of hemothoraces or pneumothoraces due to vascular or lung injuries. Access on the left side may be associated with thoracic duct injury with clear lymph drainage from the insertion site or chylothorax formation. After catheter removal, the pleural space must be evacuated until lymphatic drainage ceases. Misplacement of the catheter into the pleural space or mediastinum is another complication that may occur. Malposition of a catheter tip into the atrium may cause dysrhythmias, injury, or infected thrombosis, and has been associated with atrial perforation and pericardial tamponade.

Line sepsis is the most common complication of indwelling central catheters and necessitates catheter removal. Primary catheter infections are usually characterized by the development of fever and positive blood cultures. In the presence of bacteremia, lines should be removed, but may be changed over a guide wire with a semiquantitative culture of the intracutaneous portion if there is doubt about the diagnosis. A semiquantitative tip culture is diagnostic when there are 15 or more colony-forming units reported. Typically, removal of the catheter results in resolution of symptoms; however, intravenous antibiotic therapy may be required for 2 weeks with bacteremia due to Streptococcal line sepsis or other organisms.

Another common complication of indwelling central venous catheters is venous thrombosis, which may occur with resultant thrombophlebitis and extremity edema. This can usually be treated by catheter removal and extremity elevation. Patients with subclavian vein thrombosis have a risk up to 30% for the development of pulmonary embolism and should receive anticoagulation. Catheter thrombosis is another complication and may be treated successfully with the instillation of thrombolytic agents.