Nutrition Support in the Surgery Patient 3

3

Nutrition Support in the Surgery Patient

Stephen F. Lowry

Objectives

1. To understand the decision-making process for initiating, maintaining, and terminating Special- ized Nutritional Support (SNS) in surgical patients.

2. To understand the decision-making process for calculating nutritional requirements, gaining access for SNS, and monitoring for complications during SNS.

Cases

Case 1

A 67-year-old man with obstructing esophageal cancer presents for consideration of surgical therapy. He has lost 25 pounds (15% of normal body weight) over the past 4 months, is unable to swallow anything except liquids, and has near-complete loss of appetite. He has no other past history of significance and takes medications only for hyperten- sion. His appearance is gaunt with obvious loss of body fat and muscle wasting. There is mild peripheral edema. The remainder of the physi- cal exam is unremarkable. Workup suggests that he is a candidate for esophageal resection. His albumin is 2.7 g/L and his hemoglobin is 9 g/L with microcytic indices. All other determinations are normal.

Case 2

A previously healthy 27-year-old woman is the restrained driver in a head-on collision. She is diagnosed with intraabdominal injuries and undergoes emergency laparotomy. At operation, a crush injury to the pancreas and duodenum is repaired as is a mesenteric tear and grade II liver laceration. Appropriate external drainage of the injury sites is undertaken. She has lost approximately 1000 mL of blood and has

42

received 4000 mL of crystalloid solutions intraoperatively. She will be transferred to the intensive care unit (ICU) for initial postoperative care. No other major injuries are noted.

Implications of Nutritional Support for Clinical Outcomes

Many of the illnesses and injuries subject to surgical intervention and care promote alterations of metabolism that place patients at some risk of malnutrition-specific morbidities. It widely is assumed that mal- nutrition, especially within the context of hypermetabolism, increases the risk of infection, leads to wound-healing failure, prolongs rehabil- itation, and diminishes responses to adjunctive therapies. Active intervention, in the form of specialized nutrition support (SNS) tech- nologies, provides the potential to attenuate these consequences and, at least partially, to restore adequate nutritional status.

Consideration of SNS in surgical patients requires an under- standing of the therapeutic risks and benefits as well as the timing of intervention, and an analysis of the effectiveness of therapy. Algo- rithm 3.1 provides a logical approach to these issues. These consider- ations are undertaken repeatedly during the course of surgical care and may be modulated by changes in patient status and prognosis. It is axiomatic that it is always preferable to provide nutrients via the intestinal tract, but the capacity to effectively and efficiently do so may be altered by changes in clinical condition.

Assessing Nutritional Status

When considering SNS intervention, there are several issues that must be addressed at the outset. The most pressing issue is whether the patient already has manifestations of “malnutrition.” There is a strong inverse correlation between body protein status and the incidence of postoperative complications in patients undergoing major elective (gastrointestinal) surgery. Unfortunately, the consensus regarding the most appropriate manner used to assess protein status is lacking, and the clinician often faces the dilemma of a continuum of nutritional situations ranging from seemingly normal to that of severe cachexia and wasting. Readily obtainable parameters, such as weight loss (especially in relation to normal or ideal body weight), circulating protein levels (such as albumin), surrogate markers of immune func- tion (such as lymphocyte count), as well as physical examination for evidence of muscle wasting (loss of temporal or other skeletal muscle mass), should be sought in all patients was done in Case 1. How such parameters translate into nutritional risk is a matter of some conjecture.

There is clearly no “gold standard” for determining nutritional

status because the influence of disease and injury independently may

44 S.F. Lowry

influence most biochemical or anthropometric parameters. Malnutri- tion appears to be a continuum that is influenced by altered intake and the degree of antecedent/concurrent metabolic stress. At a minimum, accurate documentation of weight loss over prior weeks and months is an indicator of the potential degree of malnutrition. Decisions regard- ing the immediacy or need for SNS can be undertaken with an evidence-based approach when considered in conjunction with the magnitude and duration of future metabolic stresses imposed by injury or major surgery. In summary, there are several general categories that define the current indications for SNS. They include (1) patients who are overtly malnourished and require restoration of protein and energy stores in preparation for or in conjunction with other therapies;

Yes No

No

No

No Yes

Yes

Yes Will patient

become so?

Now Later

I.V. Enteral (or)

(or)

Outpatient No

Oral Diet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Is this patient malnourished?

Will the patient benefit from nutrition support?

When should nutrition support be given?

How shall nutrition support be given?

How much is needed?

1. Consider basic requirements a. energy

b. protein

c. fluids/micronutrients

2. Does the patient have organ failure?

3. Does basic formula need modification?

Monitoring progress and complications?

1. Metabolic monitoring 2. Problems related to access Should nutrition support be terminated?

Algorithm 3.1. Algorithm for decision analysis for nutritional support.

(2) patients who are unable or unwilling to eat and who will become malnourished without SNS intervention; (3) patients in whom use of the digestive tract is inadequate or unsafe; and (4) patients in whom the magnitude and duration of hypermetabolism likely will lead to malnutrition without SNS.

Defining the Benefits and Timing of Nutritional Support

Although the effect of SNS in patients with modest malnutrition is unclear, there are significant class I data describing the impact of SNS in nontrauma/noncritically ill well-nourished and severely malnour- ished surgical patients. As noted in Table 3.1, SNS, either enteral or parenteral, generally demonstrated little or no impact on postoperative patient outcome and, in some series, was associated with increased complications. By contrast, patients with severe malnutrition (weight loss >10–12%) (Case 1) did benefit from preoperative or perioperative SNS. At present, it is unclear in these patients whether the benefit of SNS was derived from the pre- and/or postoperative phase of SNS.

The above results raise the issue of whether patients with elective surgery should undergo a period of preoperative SNS. At present, resource constraints likely will preclude any efforts unless the patient already is receiving SNS for the underlying illness. It is prudent, however, to be attentive to preoperative nutrient intake and urge sup- plemental oral feedings, where possible.

In the absence of antecedent malnutrition, indications instituting postoperative or injury SNS involves a more complex decision process (Case 2). The clinician is required to consider the complexity of the surgical/injury process, the magnitude and duration of hypermetab- olism, and the prospects for early return to oral feeding. Absent a favorable response to each of the above parameters, the im- mediate or early (within 5 days) institution of SNS at least must be considered.

In some patients, such as those with extensive burns or severe, complex injuries (Case 2) or patients expected to require additional surgery or cytotoxic therapies, the decision for early initiation of SNS is straightforward. Despite a general lack of class I evidence to support this decision, few would argue with such a decision. Indeed, SNS should be considered during the operative planning or intraoperatively so that an access route can be provided (such as a jejunostomy tube or central venous catheter).

The majority of patients do not require postoperative SNS. But the nutritional status should be reassessed throughout the hospital stay.

Should clinical conditions change and/or complications develop, it

may be prudent to initiate SNS at a subsequent point. As a general rule,

SNS should be considered in any patient who does not return to

nearly adequate or normal oral intake status within 5 to 7 days of

admission. As a general rule, SNS is not of benefit unless provided for

7 days or more.

Table 3.1. Perioperative and early feeding studies with substantial number of well- nourished or moderately malnourished patients.

Class of

Author Year evidence Conclusions

Veterans 1991 I Of 395 malnourished patients requiring laparotomy or Affairs Total noncardiac thoracotomy randomized to 7–15 days Parenteral preoperative nutrition (n= 192) or no perioperative Nutrition nutrition support (n= 203) and monitored for 90 days Cooperative following surgery, the rates of major complications

Study were similar in patients with mild or moderate degrees

Group^a of malnutrition with more infectious complications in the TPN group (p= .01) but more noninfectious complications in the control group (p= .02); 90-day mortality rates were also similar. Only in severely malnourished patients did TPN significantly reduce noninfectious complications (5% vs. 43%, p= .03) with no increase in infectious complications.

Fan^b 1994 I A randomized prospective study of 124 patients undergoing resection of hepatocellular carcinoma randomized to perioperative intravenous nutrition with 35% branched-chain amino acids, dextrose, and lipid (50% medium-chain triglycerides) for 14 days in addition to oral diet or control group (oral diet alone).

Postoperative morbidity rate reduced in perioperative fed group (34% vs. 55%) because of fewer septic complications (17% vs. 37%) and less deterioration of liver function as measured by indocyanine green.

There were no significant differences in deaths although most of the benefit occurred in cirrhotic patients undergoing major hepatectomy.

Brennan^c 1994 I A prospective, randomized trial of 117 moderately malnourished patients randomized to postoperative parenteral nutrition (n= 60, albumin = 3.1, 5.8%

preoperative body weight loss) or standard i.v. fluids (n= 57, albumin = 3.3, 6.8% preoperative body weight loss). Complications were significantly greater in TPN- fed patients with a significant increase in intraabdominal abscess and major complications.

Heslin^d 1997 I Of 195 well-nourished patients undergoing esophageal, gastric, pancreatic, or gastric resection randomized to jejunal feedings (n= 97; albumin 4.08 ± 0.04g/dL) or i.v.

feedings (n= 98; albumin = 4.1 ± 0.06g/dL), no significant differences found in the number of major, minor, or infectious wound complications between groups and no difference in hospital mortality or length of stay. There was one small-bowel necrosis in the enterally fed group.

Doglietto^e 1996 I Their 678 patients with normal or mild malnutrition undergoing major elective abdominal surgery randomized to protein-sparing therapy or no specialized nutrition had similar operative mortality rates and postoperative complication rate.

Watters^f 1997 I Patients undergoing esophagectomy or

pancreatoduodenectomy were randomized to

postoperative early jejunal feedings (n= 13; albumin = 4.08± 5g/dL) or no enteral feeding (n = 15; 4.1 ± 4g/dL) during the first 6 postoperative days. Postoperative vital capacity and fractional expired volume were lower in the fed group and postoperative mobility was lower in the fed group in this well-nourished group of patients at low risk of nutrition-related complications.

This study was confounded by increased epidural anesthesia in the enterally fed group.

Defining the Route of Nutritional Support

Specialized nutritional support may be provided intravenously, enterally, or by some combination of both. Although parenteral and enteral nutrition likely promote similar metabolic efficacy, current class I data strongly suggest that enteral feeding is associated with a lower overall rate of complications. No data exist currently to suggest that mortality is influenced adversely by the choice of feeding route.

The clinician always should consider feeding options during the decision-making process. While it is clearly preferable to establish an enteral feeding conduit, some conditions may preclude full use of this route for a variable period of time. Some patients tolerate limited Table 3.1. Continued

Class of

Author Year evidence Conclusions

Daly^g 1992 I Studied 85 patients randomized to standard (n= 44;

albumin= 3.0 ± 1.2g/dL) vs. supplemented (n = 41;

albumin= 3.3g/dL) enteral diets with 77 eligible patients. Infectious and wound complications (p= .02) and length of stay (p= .01) significantly shorter for supplemented group. Diets were not isonitrogenous.

Daly^h 1995 I Studied 60 patients with upper gastrointestinal lesions requiring resection randomized to standard enteral diet (n= 30) or diet supplemented with arginine, omega-3 fatty acids, and nucleotides (n= 30). Patients were moderately malnourished with albumins less than 3.4.

Length of stay and infectious/wound complications significantly reduced (p< .05 for both) in

supplemented group. Patients also randomized to jejunal feedings during radiation chemotherapy tolerated chemotherapy significantly better.

TPN, total parenteral nutrition.

a The Veteran Affairs Total Parenteral Nutrition Cooperative Study Group. Perioperative total parenteral nutrition in surgical patients. N Engl Med 1991;325:525–532.

b Fan ST, Lo CM, Lai EC, et al. Perioperative nutritional support in patients undergoing hepatectomy for hepato- cellular carcinoma. N Engl J Med 1994;331:1547–1552.

c Brennan MF, Pisters PWT, Posner M, et al. A prospective, randomized trial of total parenteral nutrition after major pancreatic resection for malignancy. Ann Surg 1994;220:436–444.

d Heslin MJ, Latkany L, Leung D, et al. A prospective, randomized trial of early enteral feeding after resection of upper gastrointestinal malignancy. Ann Surg 1997;226:567–577.

e Doglietto GB, Gallitelli L, Pacelli F, et al. Protein-sparing therapy after major abdominal surgery: lack of clinical effects. Ann Surg 1996;223:357–362.

f Watters JM, Kirkpatrick SM, Norris SB, et al. Immediate postoperative enteral feeding results in impaired respi- ratory mechanics and decreased mobility. Ann Surg 1997;226:368–377.

g Daly JM, Lieberman MD, Goldfine J, et al. Enteral nutrition with supplemental arginine, RNA, and omega-3 fatty acids in patients after operation: immunologic, metabolic, and clinical outcome. Surgery (St. Louis) 1992;112:56–67.

h Daly JM, Weintraub FN, Shou J, et al. Enteral nutrition during multimodality therapy in upper gastrointestinal cancer patients. Ann Surg 1995;221:327–338.

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery:

Basic Science and Clinical Evidence. New York: Springer-Verlag, 2001, with permission.

48 S.F. Lowry

enteral feedings despite cautionary clinical conditions (e.g., peritoni- tis). Given the objective to provide adequate SNS, extended (days) efforts to establish full SNS via the intestinal tract are unwarranted in the face of severe malnutrition and/or hypermetabolism. Providing at least some intravenous SNS should be considered if a significant caloric and protein deficit will be incurred.

Establishing Access for Nutritional Support

Whether done pre-, intra-, or postoperatively, care must be taken to establish a secure and safe portal for delivery of SNS. The portal should be dedicated solely to the purposes of SNS, as there is evi- dence to suggest that violating the condition increases complications.

Once established and maintained by the above criteria, these portals need not be changed routinely unless there is clinical or laboratory evi- dence of dysfunction or infection.

Access for Parenteral Nutrition

The preferred method for obtaining access for intravenous SNS is with a subclavian vein catheter. This usually provides a secure site that can be maintained in a sterile fashion. In some circumstances, a multiple- lumen catheter is inserted to provide for other monitoring options, but one lumen must be dedicated to SNS administration. Barring a sub- clavian insertion site, other options include jugular vein as well as peripheral catheter insertion sites. Such sites are more prone to complications of infection, dislodgment, and venous thrombosis and should be replaced with a more secure or permanent catheter at the earliest opportunity. Protocols for changing dressings and intravenous tubings for SNS central vein catheters should be maintained.

Access for Enteral Nutrition

Although some patients tolerate direct intragastric tube feedings, this practice is discouraged in patients who are prone to aspiration (criti- cally ill, unconscious, etc.). Most patients with severe injury or after laparotomy have gastroparesis, and hence cannot tolerate gastric feed- ings. It is judicious to assume that any patient requiring prolonged enteral SNS will require feedings distal to the stomach. Numerous options for such feeding conduits are available. Some can be placed at the bedside using flexible small-bore tubes, while others require intra- operative, radiographically guided, or endoscopically assisted place- ment. Consideration of these options should begin as soon as practical after admission. (See Chapter 7, “Nutrition,” by Kenneth A. Kudsk and Danny O. Jacobs, cited above for further details and illustrations.)

Although it is unknown what proportion of nutrients need to be

provided enterally to achieve optimal results, a combination of both

enteral and intravenous feeding may promote early, adequate nutri-

tion. This is accomplished more readily if the parenteral SNS is given

via a central vein catheter, although small-bore peripheral access may

be used for a limited time. Such catheters are prone to vein thrombo-

sis if the dextrose concentration exceeds 10%, and thus this route is more limiting in duration and patient comfort.

Defining the Nutritional Prescription

The initial approach to defining nutritional requirements in surgical patients assumes no difference either between the routes of feeding or among patients on the basis of antecedent nutritional status. While there are differences between commonly prescribed intravenous SNS formulas and available enteral formulas, for purposes of defining indi- vidual patient requirements, initial considerations revolve around esti- mates of energy and protein needs. For these initial calculations, it is important to have a measure or a reasonable estimate of preinjury body weight. For subsequent refinements in the prescription, knowl- edge of current fluid and electrolyte status and of organ function is necessary. (For more details, see Chapter 4.)

Basic Requirements

Although there are several proposed methods for estimating energy needs, the most widely used are the Harris-Benedict equations, which define basal energy expenditure (BEE) (Table 3.2). These equations account for gender, age, height, and weight and provide a rough esti- mate of the basal (nonstressed) energy expenditure. This calculation therefore can be used once these simple parameters are ascertained. In the absence of these parameters, one may utilize the estimates provided in Table 3.3. While there are other, and perhaps more precise, methods of energy needs assessment, all involve obtaining more detailed biochemical or calorimetric data. As a first approximation, the Harris- Benedict formulas usually are sufficient.

Once this calculation has been performed, one next needs to estimate the degree of hypermetabolism arising from the underlying condition.

For instance, an elective operation with minimal blood loss and com- plexity increases the energy expenditure by 10% to 20% above the BEE.

Hence, the prescription for energy needs should encompass this stress factor and be targeted at 1.10 to 1.20 times the Harris-Benedict calcu-

Table 3.2. Calculating resting metabolic expenditure.

Resting metabolic expenditure (RME) in kilocalories per day, can be estimated by using the Harris-Benedict equations:

For men

66.47+ 13.75 (W) + 5 (H) - 6.76 (A) For women

65.51+ 9.56 (W) + 2.86 (H) - 4.68 (A)

W, weight in kilograms; H, height in centimeters; A, age in years.

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer- Verlag, 2001, with permission.

50 S.F. Lowry

lation. As shown in Table 3.3, other surgical conditions increase this stress factor proportionally.

Sources of Nonprotein Calories for SNS

Glucose. The limit of glucose oxidation is approximately 5 to 7 mg/kg/min. Consequently, there is an upper limit of the amount of parenteral or enteral glucose that should be administered. Therefore, patients should not receive more than 500 to 600 g of glucose/day in an effort to keep their respiratory quotient near 1.0. Providing a majority of nonprotein calories as glucose, however, promotes reten- tion of nitrogen. Excess levels of glucose promote fat deposition and may be associated with impairment of respiratory function and hyperglycemia.

Lipids. Alternative sources of nonprotein calories include various forms of lipid. While enteral formulas contain various medium- and long-chain lipid moieties, those available for parenteral administration are primarily omega-6-polyunsaturated long-chain fatty acids derived from vegetable oils. While such formulations are tolerated well by most patients, attention to lipid clearance and lipid sensitive diseases requires vigilance. The maximum recommended dose of lipid admin- istration is 2.0 to 2.5 g/kg/day, and rates of administration in excess of this seldom are indicated. At a minimum, lipids must be provided at

>5% of total calories to prevent essential fatty acid deficiency.

Protein

While the normal intake of protein in healthy, well-nourished adults is approximately 0.8 g/kg/day, these requirements are increased in stressed patients. In the absence of measured nitrogen (protein) losses, it is recommended that such patients receive 1.5 to 2.0 g/kg/day of protein (note: divide by 6.25 to obtain nitrogen equivalent).

Some patients with anticipated excessive losses (e.g., burns or open wounds) may require higher levels of nitrogen intake for maximum benefit. Other patients with severely contracted lean body mass may require less than 1.5 g/kg/day, as do patients with renal impairment and the inability to clear a normal or increased nitrogen load.

Although there is much discussion about the appropriate composi- tion of protein or parenteral amino acid formulas, little data currently exist to suggest that these more expensive mixtures significantly Table 3.3. Energy and protein needs for surgical patients.

Condition Kcal/kg/day Protein/kg/day NPC : N

Normal to moderate (low stress) 1.0 150 : 1

malnutrition 25–30

Moderate stress 25–30 1.5 120 : 1

Hypermetabolic, stressed 30–35 1.5–2.0 90–120 : 1

Burns 35–40 2.0–2.5 90–120 : 1

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer- Verlag, 2001, with permission.

improve outcome. To date, “designer formulas” for enhancing immune function have been documented to benefit only trauma patients. (See Chapter 7, “Nutrition,” by Kenneth A. Kudsk and Danny O. Jacobs, cited above, for more discussion.)

Fluid and Micronutrients

Once the determination of energy and protein needs has been estab- lished, attention turns to defining the concentration of electrolytes, trace minerals, and other micronutrients that must be administered.

Documenting fluid status (as discussed in Chapter 4) also requires careful physical examination and a review of intake/output records and changes in body weight to assess this condition.

It is essential to evaluate recent laboratory determinations for the presence of preexisting micronutrient imbalances. Efforts to correct any severe abnormalities should begin before instituting SNS. Barring the existence of such electrolyte or acid–base disorders, a standard range of micronutrient administration may be initiated at the onset of SNS (Table 3.4). These recommendations for micronutrient administration have been established from common clinical practice, but each patient must be evaluated individually at the outset of SNS therapy and at regular intervals throughout the course of treatment. Dramatic and life-threatening changes in electrolyte concentration as well as other serious metabolic abnormalities may evolve rapidly in patients with serious illness. (For more details, see Monitoring Progress and Complications, below.)

Modifications for Organ Dysfunction

Patients with organ failures require adjustments to both protein and micronutrient prescriptions. Patients with heart failure may require limitations of both fluid (reduced volume) and electrolyte (sodium) administration. Similarly, patients with renal insufficiency require attention to both volume and several electrolyte levels. Such patients

Table 3.4. Electrolyte concentrations in parenteral nutrition (PN).

Recommended Recommended Usual

central peripheral range of

Electrolyte PN doses PN doses doses

Potassium (mEq/L) 30 30 0–120 (CVL)

0–80 (PV)

Sodium (mEq/L) 30 30 0–150

Phosphate (mmol/L) 15 5 0–20

Magnesium (mEq/L) 5 5 0–16

Calcium (mEq/L) 4.7 4.7 0–10

(as gluconate)

Chloride (mEq/L) 50 50 0–150

Acetate (mEq/L) 40 40 0–100

CVL, central venous line; PV, peripheral vein.

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer- Verlag, 2001, with permission.

should continue to receive adequate calories, with adjustments in the glucose load depending on the level of tolerance. Patients with liver disease may need reductions in the protein content as well as fluid and electrolyte levels of SNS formulas. Specialized amino acid formulas for hepatic failure may be used judiciously in selected patients.

Basic Formulations for Nutritional Support

Although there are numerous options for providing both enteral and parenteral formulations, the basic requirements are outlined below and in the referenced tables. The reader is referred to more detailed descrip- tions of these prescriptions elsewhere. (See Chapter 7 “Nutrition,” by Kenneth A. Kudsk and Danny O. Jacobs, cited above.) The standard provisions outlined herein may be modified by the clinical considera- tions outlined above. In addition, the provider must be aware of the varying content of electrolytes in these formulations as well as of other micronutrients and vitamins (such as vitamin K). The latter, for instance, may not be appropriate for patients requiring anticoagulation therapy. The clinicians should familiarize themselves with the content and concentrations of any SNS formulation before it is ini- tiated. An extensive listing of currently available enteral and parenteral nutrition formulations is provided in Tables 3.5, 3.6, 3.7, and 3.8. An outline for standard orders for nutritional support is shown in Table 3.9. This is intended as a template for the initial prescription and should be modified according to clinical conditions.

Enteral Formulas

There are several basic categories of enteral formulas:

Standard, isotonic formulas contain an appropriate balance of carbo- hydrate, protein, and fat and usually are tolerated well because of low osmolarity (approximately 300 mOsm/L) and caloric density (1.0 kcal/mL). These are considered low-residue diets in that they do not contain fiber and are used in stable patients with significant hypermetabolism.

Standard, fiber-containing formulas are similar to the isotonic prod- ucts and usually contain both a higher protein content as well as soluble and insoluble fiber. These often are fed to critically ill patients via jejunostomy tubes and appear to reduce the incidence of diarrhea.

High-density formulas provide a caloric density of 1.5 to 2.0 kcal/ml and may be appropriate for patients requiring volume restriction.

Osmolarity is higher than standard formulas and the propensity for diarrhea is increased. These formulas are tolerated better by intra- gastric feeding.

Elemental/peptide-based formulas contain predigested proteins that may promote absorption in patients with malabsorption. Their higher osmolarity and lower fat content require a slower infusion rate initially.

Special formulas for organ dysfunction have been designed specifi-

cally for patients with established or evolving organ failure. Formu-

Table 3.5.Some enteral feeding formulas. Liters to provide Total100% RDA calorie/vitamins and Product, supplierkcal/mLnitrogenmineralsmOSmProteinCarbohydrateFatNaKFeatures Precision LR, Sandoz1.12391.7530262481.6302.3p, F Travasorb STD, Baxter1184256030190144030P, U, MCT Reabilan, O’Brien1175335032131393032L, U, MCT Travasorb, Baxter11541.945035136353031L, F, MCT Ensure, Ross11531.945037145373740L, F Resource Crystals, Sandoz11541.945037145373740F Resource Power, Sandoz11781.945037145373740P, F Enrich, Ross11481.448040162373740L, F, High residue Compleat, Reg, Sandoz11311.540543128435736L, U Ensure HN, Ross11251.347044141354040L, F Precision HN, Sandoz11252.8525442161.34323P, F Reabilian HN, O’Brien1.31252.949058158524343L, U, MCT Meritene, Doyle11041.255058110323841L, F Sustacal, Mead Johnson179162561140234153L, F Meritene Powder, Doyle11041.269066113324468P, F Sustacal Powder, M.J.1.3800.889977180345487Mixed w/whole milk Isotonic: Precision isotonic, Sandoz11831.630029144302025P, F Isocal, Mead Johnson11671.930034133442334L, U, MCT Entrition, Biosearch1154230035136353131L, U Osmolite, Ross11531.930037145392426L, U, MCT Compleat Modified, Sandoz11311.53004.3141372936L, U Peptamen, Clintec Nutrition1131226040127392216L, U, MCT Osmolite HN, Ross11251.331044141374040L, U, MCT Isotein HN, Sandoz1.2861.830068156342727P, F, MCT For impaired gastrointestinal tract and other special situations: Tolerex, Eaton12841.8550212261.52030P, U Vivonex T.E.N., Eaton11492630382062.82020P, U, BCAA Surgical liquid, Diet Ross0.71171.25453813603621P, F Criticare HN, Mead Johnson11482650382223.42834L, U Continued

54 S.F. Lowry

Table 3.5.Continued Liters to provide Total100% RDA calorie/vitamins and Product, supplierkcal/mLnitrogenmineralsmOSmProteinCarbohydrateFatNaKFeatures Vital HN, Ross11251.546042185112034P, F, MCT Trauma-aid HBC, McGaw113236405616672330P, F, MCT, BCAA Stresstein, Sandoz1.297291070173272929P, U, MCT, BCAA Travasorb MCT, Baxter1.51001.345074185492326L, F, MCT Impact, Novartis1911.537556130284836L, U, MCT, fish oil Perative, Ross1.31221.242567177374544L, U, MCT, arginine Alitraq, Ross11201.548053165164431F, F, glutamine Subdue, Mead Johnson11201.233050127344841L, F, MCT Immun-aid, McGaw177246080120222527P, MCT, BCAA, arginine For specific pathologic entities: Aminiaid, McGaw1.93621095233842514<5For renal failure Travasorb renal, BaxterPackets ofFor renal failure 112g, 467cal, 470mOsm/L Hepatic aid IL, McGaw1.11744604415834<5<6For liver failure Travasorb hepatic, BaxterPackets ofFor liver failure 96g, 378cal, 480mOsm/L Pulmocare, Ross1.5150149063106925749To decrease CO2 production High calorie density: Ensure Plus, Ross1.51461.660055200535054L, F Sustacal HC, Mead Johnson1.51341.265061190573738L, F Ensure Plus HN, Ross1.51250.965062200505147L, F Magnacal, Sherwood2154159070250804432L, F Isocal HCN, Mead Johnson21451.569075224913536L, F, MCT Twocal HN, Ross21260.970084217904659L, F, MCT P, powder; L, liquid; F, flavored; U, Unflavored; BCAA, Branched-chain amino acids; MCT, medium-chain triglycerides. Protein, carbohydrate, and fat are expressed as gram per liter (g/L) standard dilution, Na and K are expressed as milliequivalents per liter (mEq) standard dilution. Source:Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer-Verlag, 2001, with permission.

Novamine Travasol TrophAmine

15% 10% 6%

Protein equivalent (g/100 mL) 15 10 6

Total nitrogen (g/100 mL) 2.3 1.6 0.93

Osmolarity (mOsm/L) 1300 998 525

pH 5.6 6 5.5

Essential amino acids (mg/100 mL)

Isoleucine 749 600 490

Leucine 1040 730 840

Lysine 1180 580 490

Methionine 749 400 200

Phenylalanine 1040 560 290

Threonine 349 420 260

Tryptophan 250 180 120

Valine 960 580 470

Nonessential amino acids (mg/100 mL)

Cysteine <14

Arginine 1470 1150 730

Alanine 2170 2070 320

Proline 894 680 410

Glycine 1040 1030 220

Serine 592 500 230

Tyrosine 15

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer- Verlag, 2001, with permission.

Table 3.7. Fatty acid content of intravenous lipid preparations.

Intralipid Liposyn II Liposyn III

Manufacturer Clintec Nutrition Abbott Abbott

concentration (%) 10 10 10

20 20 20

Oil (%)

Safflower 5

10

Soybean 10 5 10

20 10 20

Fatty acid content (%)

Linoleic 50 65.8 54.5

50 65.8 54.5

Oleic 26 17.7 22.4

26 17.7 22.4

Palmitic 10 8.8 10.5

10 8.8 10.5

Linoleic 9 4.2 8.3

9 4.2 8.3

Stearic 3.5 3.4 4.2

3.5 3.4 4.2

Osmolarity (mOsm/L) 260 276 284

260 258 292

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer- Verlag, 2001, with permission.

55

56 S.F. Lowry

Table 3.8. Central parenteral nutrition.

Central Peripheral

Daily calories 2000–3000 1000–1500

Protein Variable 56–87 g

Volume of fluid required 1000–3000 mL 2000–3500 mL

Duration of therapy ≥7 days 5–7 days

Route of administration Dedicated central Peripheral vein or venous catheter multiuse central

catheter Substrate profile 55–60% carbohydrate 30% carbohydrate

15–20% protein 20% protein

25% fat 50% fat

Osmolarity ~2000mOsm/l ~600–900mOsm/l

Source: Reprinted from Kudsk KA, Jacobs DO. Nutrition. In: Norton JA, Bollinger RR, Chang AE, et al, eds. Surgery: Basic Science and Clinical Evidence. New York: Springer- Verlag, 2001, with permission.

Table 3.9. Standard orders for nutritional support.

1. Confirm correct feeding tube or intravenous device placement.

2. Prescribe the formula composition.

3. Prescribe the rate of advancement and target rate of the nutrient.

4. Add vitamin K.

5. Intake and output should be recorded each shift.

6. Order laboratory tests to monitor complications and efficacy of nutritional therapy.

Initial: Chemistry profile, serum magnesium, complete blood count (CBC), PT/PTT

Start-up: SMA-6 daily for 3 days, Mg, PO4

Maintenance:

SMA-20 every Monday and Thursday Magnesium, CBC every Monday

7. Monitor blood glucose every 6 hours during start-up; continue every 12 hours for CPN (or more often as clinically indicated).

Add vitamin K.

8. Enteral-specific orders

a. Gastric feedings: elevate head of bed 45 degrees.

b. Gastric feedings: Check gastric residuals every 4 hours. Hold feedings for 4 hours if the residual is greater than the hourly rate, and notify physician if two consecutive measurements are excessive.

c. Irrigate feeding tubes with 20 mL of tap water after each intermittent feeding or t.i.d., when tube is disconnected, or before and after medications are administered via tube.

d. For obstructed tubes not cleared with simple pressure, instill 10 mL of a solution of 1 tablet Viokase, one tablet NaHCO3, and 30 mL of warm tap water; repeat once.

e. For jejunal feedings, do not interrupt for diagnostic tests or NPO status.

PT, prothrombin time; PTT, partial thromboplastin time; SMA-6, Sequential Mutliple Analysis—six different serum tests.

Source: Reprinted from Borzotta AP. Physiologic aspects of surgical disease. In: Polk HC Jr., Gardner B, Stone HH, eds. Basic Surgery, 5th ed. St. Louis: Quality Medical Publish- ing, Inc., 1995.

las for renal and hepatic failure as well as newly promoted “immune enhancing” products are available. These formulas may prove useful in managing the complications associated with specific conditions, although evidence that they prolong life is limited.

Complications of Enteral Feeding: The most common complications of

enteral feeding include diarrhea, aspiration, vomiting, distention, metabolic abnormalities, and tube dislodgment. Aspiration is reduced by avoiding intragastric feeding in patients with reflux or in those who must be recumbent. Gastric residual volumes should be checked regu- larly, and prokinetic agents may benefit some patients. Diarrhea may represent a more complex diagnostic dilemma, and patients should be evaluated for Clostridium difficile infection and other medications as an etiology. Fiber containing feedings may reduce this problem.

Attention always must be given to the new onset of pain or distention in patients with intestinal feeding tubes. Small-bowel intussuscep- tion, necrosis, perforation, and pneumatosis intestinalis have been reported in such patients. Other causes of abdominal pathology, in- cluding (a)calculous cholecystitis, are not infrequent in patients who require SNS.

Parenteral Formulas

The basic content and prescription of parenteral nutrition formulations are shown in Table 3.8. Central parenteral formulas are often standard- ized by hospital pharmacies and usually include a hypertonic (>10%) dextrose source combined with amino acids. Intravenous fat emulsions may be mixed with this solution or provided as a separate infusion.

Electrolytes and trace minerals are added to these solutions before infu- sion, and virtually all such solutions are given via volume controlled pumps. Additional additives, such as insulin, may be included in the solutions or provided by other means, as needed.

Peripheral parenteral contains lower concentrations of dextrose (<10%)

in combination with amino acids. Additives similar to those used in central vein feedings may be used. Peripheral vein nutrition is a less optimal form of feeding in that adequate caloric support cannot be achieved except in unusual circumstances. Consequently, it is seldom used except where there are no other options or during the transition phase to full enteral feeding status.

Complications of Parenteral Feeding: Tolerance to parenteral feedings

should be evaluated throughout the course. In that acute parenteral

nutrition is most common in patients who are critically ill, considera-

tion always must be given to fluid status as well as glucose intolerance

and electrolyte abnormalities. An acute shift toward anabolism may

unmask preexisting body electrolyte deficiencies (see Monitoring

Progress and Complications, below.) Control of blood glucose is impor-

tant as well as an awareness that acute discontinuation of feedings may

result in hypoglycemia. Abnormalities of acid–base balance also occur

more frequently in such patients, and alterations in electrolyte compo-

sition (such as acetate salts) of solutions may be indicated. As always,

patients with indwelling catheters must be monitored carefully for

infection. An abrupt change in glucose tolerance may indicate infection related to the catheter or another source.

Monitoring Progress and Complications

Defining a plan for monitoring the results of SNS is an integral part of the prescription and, like all therapies, an awareness that changes in formulations and that life-threatening complications can arise is essential. In general, all patients should be metabolically and hemo- dynamically stable before the initiation of SNS. This may require a modest delay before such therapy begins, but it allows a determination of any associated morbidities that might influence the progress of treatment or, in some cases, the preclusion of SNS from terminally ill patients. Emergencies related to SNS begin after efforts to initiate therapy have begun.

Problems Related to Access

These problems can be life-threatening and include misadventures related to placement of enteral or parenteral feeding portals. Acute pneumothorax, inadvertent arterial puncture, air embolism, and per- foration of the vena cava or heart can accompany attempts at central venous access. These must be dealt with expeditiously and definitively.

Insertion of catheters by experienced personnel serves to minimize these complications.

More frequently, however, it is the initial misplacement of the catheter or latent events such as insertion-site infection or vessel thrombosis that provide troubling morbidities to patients. Current practice dictates that the proper placement of any feeding catheter must be confirmed before SNS is begun. These complications are monitored by a rigorous adherence to sterility guidelines and protocols and by regular physical examination of the patient. A constant awareness of the potential for these events promotes early intervention and treatment.

Problems related to placement of enteral feeding portals arise with similar, if not greater, frequency. Although it is increasingly popular to return to intragastric feeding, proper tube placement and function also must be assured. The ability to frequently monitor gastric residual volumes is helpful. Problems of aspiration, especially in patients prone to reflux, may preclude this route of enteral nutrient provision. Under such circumstances, the placement of small-bore feeding catheters either transgastrically or transcutaneously requires experienced per- sonnel. Careful attention to maintenance of tube patency is important.

Ideally, only nutrient solutions should be provided by these tubes. As noted above, enteral feeding tubes may cause abdominal distention or symptoms that must be investigated.

Metabolic Monitoring

It is essential that all patients have adequate biochemical screening

before and after the initiation of SNS. While it is unclear how frequent

these parameters should be determined, as a general rule, critically ill patients should have determinations performed at least two to three times per week or during the initiation of SNS, while more stable patients may be evaluated one to two times per week. Careful, daily physical examination is an essential component of the monitoring regimen. Problems related to access portals as well as organ dys- function and fluid imbalance may be detected initially, or solely, on this basis.

Problems of Deficiency

The initial prescription, as outlined above, includes provisions for routine electrolytes as well as for those that may be dramatically altered during SNS (magnesium, phosphate). Routine monitoring for trace minerals (zinc, copper, etc.) is not done unless there is suspicion of a deficiency. A determination of red blood cell indices may help to define iron deficiency (not routinely provided in intravenous nutrition). Eval- uation of basic bleeding parameters is undertaken to detect the pres- ence of vitamin K deficiency, which also may develop in parenterally fed patients. Liver biochemical tests may detect changes in hepatic function. Although these parameters may increase during SNS by 1.5 to 2.0 times above normal even in the absence of significant pathology, further increases may indicate the need for additional evaluation.

As noted above, relatively rare deficiencies may become manifest during the course of SNS. Thiamine deficiency may occur in patients receiving large carbohydrate loads. Megaloblastic anemia also may occur secondary to folate deficiency. Trace mineral deficiencies may be a latent problem, especially in patients with preexisting malnutrition and prolonged inflammatory conditions. Attention should be given to patients with previous compromise of intestinal absorption.

Problems of Excess

Significant changes in overall clinical status as well as specific organs may provoke a state of excess provision. The most overt of these is glucose intolerance, which may occur for many reasons. Stress diabetes is a common event in severely injured patients. At least daily evalua- tion of glucose tolerance, by blood or urine sampling, is indicated in all patients. More frequent determinations are warranted during initi- ation of SNS in critically ill patients. An abrupt increase in glucose levels in an otherwise stable patient must suggest infection until proven otherwise.

Glucose excess also may precipitate or aggravate pulmonary prob- lems in some patients. If the rate of endogenous glucose oxidation is exceeded, carbon dioxide retention may result in respiratory distress or weaning problems in ventilated patients. Glucose excess also may cause liver dysfunction in some patients.

Other evidence of nutrient excess occurs during conditions of evolv-

ing organ dysfunction. While a modest rise in blood urea nitrogen fre-

quently may accompany SNS, any increase above twice normal or

in association with increases in creatinine warrants consideration of

protein or amino acid intolerance. A reduction in volume and nitrogen load as well as evaluation of electrolyte tolerance may be indicated.

Protein intolerance also may occur in patients with underlying liver dysfunction. Under such circumstances, a reduction in nitrogen load or alteration in amino acid formulation may be indicated.

Terminating Nutritional Support

The decision to terminate SNS rests upon several factors, including the ability of the patient to tolerate oral feedings, the achievement of initial therapeutic goals, and the expectation of additional therapies that will improve quality of life and prolong outcome. Once SNS has been initiated, the decision to terminate therapy must rely on sound clinical judgment, but the clinician should be able to address each of the above issues in the affirmative. The vast majority will be able to be weaned from SNS before hospital discharge. It is preferable to assure that the patient is capable of taking oral intake before complete termi- nation of SNS. This may be done by reducing the amount of SNS by one half while assessing swallowing and digestion of oral diet. There is no evidence to suggest that this level of SNS suppresses appetite.

Some patients may require liquid diets as a transition to solid food, but this does not necessitate an interruption of the tapering schedule. Once the oral diet is tolerated, SNS may be discontinued. In patients who have been receiving supplemental insulin, peripheral low-dose dex- trose infusions minimize the chances of hypoglycemia.

A limited number of patients may require continuation of SNS after discharge from the hospital. This decision requires input from several sources, including family and home healthcare agencies as well as social work and nursing professionals. Efforts to identify at the earli- est possible time patients in need of outpatient SNS are warranted. This provides time to arrange for this more complex therapy.

For some patients none of the weaning indications are reasonable expectations. In such cases, the judgment as to continuation of SNS requires a mutual decision among patient and family, the provider, and other interested parties.

Summary

Specialized nutritional support (SNS) is a necessary adjunctive therapy in some portion of hospitalized surgical patients. An understanding of the indications, techniques, and complications of SNS is necessary to practice modern surgical care. While most surgical patients do not require SNS, the continued monitoring of patients and appropriate ini- tiation of SNS may reduce the incidence of complication and promote the early restoration of functional status.

Examples of the judicious use of SNS can be derived from the pre-

sented cases. In Case 1, where the patient has established cachexia, the

initiation of SNS before operation might serve to diminish postopera-

tive complications. In Case 2, SNS should be instituted at an early

juncture, particularly if the patient does not steadily recover from her injuries.

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