Current Strategies in Surgical Nutrition

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Nutritional Assessment and Indications for Nutritional Support

Lloyd

c.

Smith, MD,* and James L. Mullen, MDt

Malnutrition has long been recognized as a potential source of increased morbidity and mortality in surgical patients. The reported incidence of malnutrition has ranged from 10% to 50% in different series of hospitalized patients. 2 . 3 This variability is attributable in part to difficulty in defining and assessing the malnourished state and in part to the different patient populations studied. Malnutrition can be defined as a nutritional deficit associated with an increased risk of adverse clinical events such as morbidity or death and with a decreased risk of such events when corrected. The goal of nutritional assessment is to identify those patients who are at increased risk so that th~y can receive appropriate nutritional therapy. Since the development of total parenteral nutrition in 1968, the number of available assessment measures has been continually increasing. If a large number of tests are used, almost all patients manifest some abnormalities. 21 The difficulty is in deciding which subset of patients will benefit significantly from nutritional support and which will not. The ideal test would therefore identify prospectively all those individuals who have a nutrition-related complication and would not falsely identify as at-risk anyone who would have no such adverse event. In clinical practice, no such perfect test exists. The best tests have cut-off values designed to have a high sensitivity in order to avoid missing any malnourished patients. To identify all malnourished patients, it is better to sacrifice some specificity and thus to overtreat a few patients rather than to miss a malnourished patient who would benefit from nutritional intervention. The complications related to overtreating are minimal and easily corrected. This article reviews the clinically available methods of assessment of *Lecturer, Department of Surgery, University of Toronto, and Surgeon, St. Joseph Health Center, Toronto, Canada t Associate Professor of Surgery, University of Pennsylvania School of Medicine, and Director, Nutrition Support Service, and Surgeon, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania

Surgical Clinics of North America-Vol. 71, No.3, June 1991

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nutritional status and then offers a practical description of nutritional assessment and indications for nutrition support. CLINICAL ASSESSMENT OF NUTRITIONAL STATUS Body Size and Composition Weight loss is probably the most common variable considered in nutritional assessment, and there is a definite correlation between significant weight loss and morbidity. As far back as 1936, Studley reported a mortality of 33% in patients undergoing gastrectomy for peptic ulcer disease and having a 20% preoperative weight loss. 24 The mortality in patients with less than a 20% weight loss was 5%. Most studies suggest that a weight loss of 10% is associated with increased morbidity. It is important to note that chronic weight loss is much better tolerated by the surgical patient than acute weight loss. In assessing the importance of weight loss, current body weight is compared with the usual and ideal body weights. Usual weight is the patient's recollected weight when he or she was last well; such figures usually are quite reliable. The ideal body weight is obtained from standard reference tables of age, height, and sex, such as the Metropolitan Life Insurance tables. 19 The limitation of overall weight loss as a nutritional assessment index is that the specific compartments of the body contributing to the lost mass are not identified. For example, in unstressed starvation, significant depletion of fat stores occurs with relative preservation of lean body mass. 15 In trauma patients, however, the weight lost may represent primarily loss of lean body mass. Acute loss of weight often reflects only changes in fluid balance. Weight loss measurements alone are not sufficiently discriminating to be reliable for nutritional assessment. One also needs to consider the composition, the rate, and the cause of the weight loss. Therefore, weight loss is usually combined with other measures of nutritional assessment to interpret its significance. Anthropometry Anthropometric data are used in two ways in nutritional assessment. The first is to compare the measured values with standardized controls; the second is to compare serial measurements over time in the same patient. The problem with the first method is that its interpretation is dependent on the normal range. Thus, an inherent error occurs when the patient started out well above the normal range but at the time of measurement is within this range. The patient therefore may have been in a negative nutritional state for some time but at the time of assessment is mistakenly classified as normal. 15 The pitfall with comparing serial data is the variance of the individual measurements. The validity of anthropometry is greatly enhanced when the measurements are obtained by skilled, conscientious personnel. Of the two methods, serial measurements over long periods of time (> 1 month) have the mostalue.

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Anthropometric measurements are used to estimate subcutaneous fat and skeletal muscle stores in a somewhat objective manner. Overall, their usefulness is little better than the clinical judgment of an experienced surgeon. Total Body Fat. Subcutaneous fat constitutes approximately 50% of body fat stores and can accurately reflect the total body fat content. The use of calipers to assess skinfold thickness as a measure of subcutaneous fat is an easy and inexpensive test. The most common measurement is the triceps skinfold thickness, which is compared with percentile standards or serial measurements. Its actual value as a part of nutritional assessment is questionable. In some studies, depletion of fat stores, as detected by triceps skinfold thickness, correlates with a poor outcome. 15 However, this is not a consistent finding; Baker and colleagues 1 found clinical judgment to be a better predictor of outcome. Skeletal Muscle Stores. Skeletal muscle represents 60% of the total body protein pool and is the major source of amino acids during times' of stress and starvation, Anthropometric measurement of muscle mass is accomplished by using midarm circumference and skinfold thickness to calculate midarm muscle circumference and midarm muscle area. The derivation of these measures necessitates assumptions about the relative sizes of the various other tissues in the arm. Jeejeebhoy14 reported finding no correlation between midarm muscle circumference and total body nitrogen. It'has been suggested that patients should not be classified as having abnormal skeletal muscle compartments as estimated by anthropometrics unless they are below the tenth percentile for a single midarm muscle area measurement and below the fifth percentile for arm circumference. 15 Creatinine-Height Index. The amount of urinary creatinine excreted is an indicator of muscle mass and total body nitrogen. 14 The creatinine-height index is a ratio of 24-hour urine creatinine excretion in a subject compared with that in height-matched controls of the same sex, expressed as a percentage. Therefore, an index of 100% indicates a normal muscle mass, provided there is normal excretion of creatinine. Skeletal muscle depletion is defined by an index of less than 80% of normal. A decline in the index correlates with subjective global assessment; however, it has limited predictive power for adverse clinical outcome. 16 For adequate assessment of the index, patients must be on a meat-free diet, have normal renal function, and be steady state normocatabolic. Potential errors associated with this technique include the significant individual variation among patients, extrarenal losses, and variable renal clearance. Plasma Proteins The circulating levels of plasma proteins depend on the rate of synthesis, the volume of distribution, and the rate of catabolism. The rate of synthesis depends on the adequacy of substrate precursors and liver synthetic ability. The volume of distribution deals with the relative sizes of the intravascular and extravascular spaces and oncotic pressures. The catabolic rate deals with plasma protein half-life and losses of protein from

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renal and other sources. Because, many of the plasma proteins are negative acute-phase reactants, it is clear that their levels reflect more than just nutritional factors. However, decreased protein intake produces a rapid decrease in plasma protein synthesis, which is magnified by a decrease in plasma protein levels in the fasting state, thus providing a good nutritional marker. The most commonly measured plasma proteins in nutritional assessment are albumin, transferrin, and prealbumin. The changes in the levels of these proteins should be evaluated together, as they reflect different processes in the body. Albumin. Albumin is the major protein synthesized by the liver and has a half-life of 18 days. Approximately 40% of the protein mass is in circulation. Its prime functions are to maintain plasma oncotic pressure and to transport other substances. Serum albumin concentration is the best single nutritional test for predicting outcome. However, the long half-life limits its value for detecting acute changes in nutritional status. Reinhardt and associates 22 demonstrated a linear correlation between the degree of hypoalbuminemia and the 30day mortality in hospitalized patients. An albumin level between 2.8 and 3.5 g/dL is thought to represent mild protein depletion, 2.2 to 2.7 g/dL moderate depletion, and less than 2.2 g/dL severe depletion. 12 Transferrin. Serum transferrin is a beta-globulin that transports iron in the plasma and may help prevent bacterial infection by binding iron. It has a serum half-life of 8 days. The serum levels are affected by nutritional factors and iron metabolism. 12 The shorter half-life of transferrin gives it a theoretical advantage over albumin as a nutritional marker; however, clinical studies have not demonstrated any Significant difference in their value. 5, 7, 8 Prealbumin. Prealbumin functions in thyroxine transport and as a carrier for retinol-binding protein. 25 The serum half-life is 2 to 3 days. Measurable changes occur in pre albumin levels within 7 days of a change in nutrient intake. 23 These changes occur more quickly than changes in serum albumin levels; however, studies have not shown prealbumin to be a better predictor of poor outcome than albumin or transferrin. 4 Immunologic Function Immune competence is reduced in malnutrition. 26 It appears that cellmediated immunity is affected earlier and to a greater extent than humoral immunity. Early clinical trials suggested that impaired delayed cutaneous hypersensitivity was present in malnourished patients and associated with a poor clinical outcome,26 whereas nutritional support was associated with an increase in reactivity and an improved outcome. However, subsequent authors have criticized these reports because of poor study design. The alterations in reactivity were often found to be secondary to underlying disease or sepsis and not related to malnutrition. The following factors have been shown to alter delayed cutaneous hypersensitivity in the absence of malnutrition: (1) infections (viral and bacterial); (2) trauma, uremia, cirrhosis, hepatitis, and hemorrhage; (3) sterOids, immunosuppressants, cimetidine, and warfarin; and (4) general anesthesia and surgery.15 Considering the high likelihood of coexistence of one or more of these factors with malnu-

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trition, delayed cutaneous hypersensitivity is not recommended for routine nutritional assessment. Protein Balance The most common clinical method for assessing protein turnover is determination of nitrogen balance. Less common methods include tracer studies and 3-methylhistidine excretion. Nitrogen balance is a measure of the daily intake of nitrogen minus the excretion. The intake represents nutritional nitrogen, and the excretion consists of measured urinary nitrogen plus a factor for unmeasured gastrointestinal and cutaneous losses, usually 2 to 4 g. A positive nitrogen balance indicates an anabolic state with an overall gain in body protein for the day, whereas a negative nitrogen balance indicates a catabolic state with a net loss of protein. In monitoring nitrogen balances, there is a tendency to overestimate intake and underestimate losses, usually unmeasured cutaneous and gastrointestinal losses, especially in certain disease states such as gastrointestinal fistulae, where unmeasured losses may be much higher than expected. 12 In renal insufficiency, an increase in total body urea nitrogen must be considered as part of the excreted nitrogen. The formula for the nitrogen balance is: N intake - (urinary N + change BUN + 4) change in BUN (g) = (0.6 X weight) (SUNf - SUNi) where i and f are the initial and final values in the measurement period, SUN is serum urea nitrogen (giL), and weight is body weight in kilograms. Urinary nitrogen excretion is a useful indicator of protein catabolism. During times of extreme stress, such as in trauma patients, it may rise to 30 to 50 glday, which is equivalent to 1 to 1.5 kg of lean body mass daily. Energy Balance Energy balance can be viewed as the difference between energy intake and expenditure. Energy expenditure can be measured using indirect calorimetry or calculated using predictive formulae such as the HarrisBenedict equation. 16 The problem with the formulae is that they were derived using healthy volunteers and have limited applicability in sick patients. Estimating energy expenditure with the Harris-Benedict equation is based on controls matched for age, height, weight, and sex. Indirect calorimetry is a technique for measuring the resting energy expenditure (REE) based on O 2 consumption and CO 2 production. The REE is measured with the patient supine and resting for 30 minutes and 2 hours after eating. In most cases, the daily total energy expenditure will be 130% of the REE. Multiparameter Indices In an attempt to improve the sensitivity and specificity of tests for nutritional assessment, a number of multiparameter indices have been

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developed. It has been hoped that these would help physicians predict poor outcome more accurately. The development of a multiparameter index involves comparing outcome results with a large number of nutritional tests, then selecting those that combine to form the best predictive model. For example, the Prognostic Nutritional Index (PNI), developed at the University of Pennsylvania, is based on four measures selected by discriminant analysis and a computerbased stepwise regression and then incorporated into a linear predictive model: PNI (% risk) = 158 - 16.6(albumin g) - 0.78(triceps skinfold mm) - 0.2(transferrin mg/dL) - 5.8(skin test reactivity 0-2) The index has been validated prospectively in several surgical populations. 6 A number of other investigators have developed multiparameter indices using a combination of objective and subjective criteria. 1. 23. 24 These tests improve specificity without sacrificing sensitivity when compared with the single-parameter tests. 6. 20. 21 Almost all rely primarily on serum protein for their power. PRACTICAL NUTRITIONAL ASSESSMENT AND INDICATIONS FOR NUTRITIONAL SUPPORT In order to decide whether nutrition support is indicated, one must consider the underlying disease process, the current nutrient intake, and the current nutritional status. Disease Process

It is essential to consider the underlying disease process, the prognosis, and the potential effects of not providing nutritional support. One also needs to consider the treatment plan and the effects it might have on oral intake. For example, impending chemotherapy would be expected to produce a decrease in oral intake in many instances. Current Nutrient Intake A patient may be severely depleted after a course of chemotherapy. However, if the patient is consuming an adequate diet, nutritional support is not indicated. In order to assess current nutrient intake, one must have an accurate assessment of nutrient requirements. This is best achieved using indirect calorimetry and nitrogen balance studies. Nonprotein calorie intake is expressed absolutely and as a percentage of the REE. Protein intake is measured and expressed in grams per kilograms of the lower of ideal or current body weight. The current intake can then be compared with the optimal (goal) intake. Nutritional Status Our practice is to use current body weight, midarm muscle circumference, triceps skinfold, serum proteins, and a history and physical examination.

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Body Weight. The current body weight is compared with the patient's usual body weight and ideal body weight. A loss of 10% of the usual weight or a current weight less than 90% of ideal is considered to be a risk factor for nutrition-related complications. Skeletal Muscle Stores. Visual observation and midarm muscle circumference are used to assess skeletal muscle stores. A midarm muscle circumference below the tenth percentile is considered to be abnormal and clinically significant. Fat Stores. Fat stores are assessed by visual inspection and by measuring triceps skinfold thickness. A skinfold thickness below the tenth percentile or a visible loss of subcutaneous tissue on physical examination is thought to be indicative of fat store depletion. Serum Proteins. The serum proteins we measure are albumin, transferrin, and prealbumin. A serum albumin concentration less than 3.5 gldL, a transferrin less than 200 mgldL, or a prealbumin less than 15 mgldL indicates serum protein depletion and substantial risk. Assessment of Nutritional Goals and Forced Feeding Based on the current nutritional status, the current nutrient intake, and the predicted clinical course, nutritional goals are established. Protein and energy should be considered separately. The goals for protein are either maintenance or gain. The goals for energy reflect fat balance and may be gain, maintenance, or loss. After the nutritional goals are set, a decision is made as to whether the patient requires forced feeding. Important factors are the ultimate prognosis, planned therapies, risk of complications, and the estimated time until the patient is consuming adequate food intake voluntarily. Serial Nutritional Assessment With any therapeutic intervention, it is important to assess the effectiveness of the treatment. In nutrition support, this becomes most important with long-term therapy, and it is difficult to assess nutritional effectiveness when the intervention is for less than 2 to 3 weeks. Nitrogen balance is the most responsive indicator and with proper nutrition can become positive within 2 or 3 days. Anthropometric measurements will not be of much value if done more frequently than monthly. Serum proteins levels will change according to their individual halflives. Thus, improvements in prealbumin may occur after 3 days of repletion and those in transferrin within 7 days, whereas significant improvement in albumin usually takes 2 to 3 weeks. Change in the body protein pool is slow and may take 2 to 3 weeks to become measureable. It appears that changes in muscle function occur long before changes in muscle mass. Functional tests may prove to be a better method for assessing the response to nutritional depletion and repletion. 21 SUMMARY The goal of nutritional assessment is to identify prospectively all those patients who would develop a nutrition-related complication. In practical terms, there is no single test capable of achieving this goal.

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At present, the best method of nutritional assessment is an organized step-by-step multifactorial approach. This involves assessment of the primary illness, the patient history, and the prognosis. A nutritional status examination is done, and the current intake is compared with the nutritional goals. A decision is then made whether to force feed. If forced feeding is initiated, the effectiveness of the therapy must be monitored frequently until the patient recovers and is able to be sustained by volitional oral intake.

REFERENCES 1. Baker JP, Detsky AS, Wesson DE, et al: Nutritional assessment: A comparison of clinical judgment and objective measurements. N Engl J Med 306:969-972, 1982 2. Bistrian BR, Blackburn GL, Hallowell E, et al: Protein status of general surgical patients. JAM A 230:858-860, 1974 3. Bistrian BR, Blackburn GL, Vitale J, et al: Prevalence of malnutrition in general medical patients. JAMA 235:1567-1570, 1976 4. Boraas M, Peterson 0, Knox L, et al: Serum proteins and outcome in surgical patients. JPEN 6:585, 1982 5. Braga M, Baccari P, Scaccabarozzi S, et al: Prognostic role of preoperative nutritional and immunological assessment in the surgical patient. JPEN 12:138-142, 1988 6. Buzby GP, Mullen JL, Matthews DC, et al: Prognostic nutritional index in gastrointestinal surgery. Am J Surg 51:594-600, 1980 7. Dempsey DT, Mullen JL: Prognostic value of nutritional indices. JPEN 11(suppl):l09s114s, 1987 8. Detsky AS, McLaughlin JR, Baker JP, et al: What is subjective global assessment of nutritional status. JPEN 11:8-13, 1987 9. Fraser 1M, Russell D, Whittaker JS, et al: Skeletal and diaphragmatic muscle function in malnourished patients with chronic obstructive lung disease [abstract]. Am Rev Respir Dis 129:A269, 1984 10. Garrow JS: Is there a body protein reserve? Proc Nutr Soc 41:373-379, 1982 11. Grant J, Custer PB, Thurlow J: Current techniques of nutritional assessment. Surg Clin North Am 61:437-463, 1981 12. Greenblatt DJ, Rausil BJ, Harmanta JS, et al: Variability of 24-hour urine creatinine excretion by normal subjects. J Clin PharmacoI16:321-328, 1976 13. Howard RJ, Simmons RL: Acquired immunologic deficiency after trauma and surgical procedures. Surg Gynecol Obstet 139:771-782, 1974 14. Jeejeebhoy KN: Bulk or bounce: The object of nutritional support. JPEN 12:539-549, 1988 15. Jeejeebhoy KN, Meguid MM: Assessment of nutritional status in the oncologic patient. Surg Clin North Am 66:1077-1090, 1986 16. Jeguier E: Measurement of energy expenditure in clinical nutritional assessment. JPEN 11(suppl):86s-89s, 1987 17. Kopple JD: Uses and limitations of the balance technique. JPEN 11(suppl):79s-85s, 1987 18. Meguid MM, Debonis D, Meguid V, et al: Complications of abdominal operations for malignant disease. Am J Surg 156:341-345, 1988 19. Metropolitan Life Foundation: Statistical Bulletin 64:2-9, 1983 20. Mullen JL, Buzby GP, Waldman TG, et al: Prediction of operative morbidity and mortality by preoperative nutritional assessment. Surg Forum 30:80-82, 1979 21. Mullen JL, Gertner MH, Buzby GP, et al: Implications of malnutrition in surgical patients. Arch Surg 114:121-125, 1979 22. Reinhardt GF, Myscofski RD, Wilkens D, et al: Incidence and mortality of hypoalbuminemic patients in hospitalized veterans. JPEN 4:357-359, 1980 23. Seltzer MH, Slocum BA, Cataldi-Belcher EL: Instant nutritional assessment: Absolute weight loss and surgical mortality. JPEN 6:218-221, 1982 24. Studley HO: Percentage of weight loss: A basic indicator of surgical risk in patients with chronic peptic ulcer. JAMA 106:458-460, 1936

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25. Tuten MB, Wogt S, Dasse F, et al: Utilization of prealbumin as a nutritional parameter. JPEN 9:709-711, 1985 26. Twomey P, Ziegler D, Rombeau JL: Utility of skin testing in nutritional assessment: A critical review. JPEN 6:50-57, 1982

Address reprint requests to James L. Mullen, MD Nutrition Support Service Hospital of the University of Pennsylvania 4 Silverstein Pavilion 3400 Spruce Street Philadelphia, PA 19104

Nutritional assessment and indications for nutritional support.

The goal of nutritional assessment is to identify prospectively all those patients who would develop a nutrition-related complication. In practical te...
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