CHAPTER 15 NUTRITION
Practice of Geriatrics
CHAPTER 15 NUTRITION
Adil Abbasi, M.D.
Principles of Clinical Nutrition
Age-Related Pathophysiologic Changes and their Influence on Nutritional Status of Older People
Nutritional Requirements of Older People
Tube Feeding for Enteral Nutrition
Nutritional problems frequently complicate the course of medical illness. Nutritional problems in hospitalized and institutionalized patients have been linked to increased morbidity, mortality, and medical care expenditures. Prevention, early diagnosis, and treatment of such problems are therefore prudent to increase the chances of favorable clinical outcomes. This chapter reviews the principles of clinical nutrition, pertinent age-related pathophysiologic changes, nutritional assessment, nutritional requirements, and nutritional problems of older people.
PRINCIPLES OF CLINICAL NUTRITION
Food provides essential and nonessential nutrients for the metabolic needs as well as the growth and maintenance of our body systems. An essential nutrient is defined as one that cannot be produced in the body from ingested food and therefore must be supplied by the diet. Identification of essential nutrients became feasible when investigators in the field of nutrition and metabolism developed purified diets. An animal or a human being under study was fed a mixture consisting of known purified nutrients. Failure of growth or other indications of illness were identified when they accompanied a diet deficient in one or more essential nutrients. Useful indicators that reflect the withdrawal of an essential nutrient in healthy older adults are nitrogen balance and body weight.
The essential nutrients that have been identified in this fashion can be divided into macronutrients and micronutrients based on the daily amount of the essential nutrient required in humans. For macronutrients this amount is more than 100 mg/day, and for micronutrients it is less than 100 mg/day. Nutrients can also be divided into organic products (proteins, essential fatty acids, vitamins) and inorganic factors (water, minerals, trace elements).
For each essential nutrient there are three dosage thresholds: minimal daily requirement (MDR), recommended daily allowance (RDA), and maximum daily tolerance. The MDR is determined in a group of healthy subjects of specified age, sex, and physiologic status and represents the mean value, in the subjects tested, of the lowest amount of the nutrient that will prevent clinical or chemical manifestations of a deficiency illness. The RDA, the amount estimated to prevent deficiency in at least 97% of the population, takes into account the interindividual variation in MDR and is usually 30% to 100% higher than the MDR. The maximum daily tolerance reflects the fact that every dietary component, essential or nonessential, will cause illness if sufficient excess is taken for a sufficient time period. RDAs that specifically address the needs of the geriatric age group, 65 years and older, do not exist. According to current recommendations, the RDAs are the same for all subgroups 51 years and older.
AGE-RELATED PATHOPHYSIOLOGIC CHANGES AND THEIR INFLUENCE ON NUTRITIONAL STATUS OF OLDER PEOPLE
Normal aging is associated with profound developmental changes in cells, tissues, and organs as well as changes in physiologic processes. It is important to remember that older people are the most hetergeneous group of our population, and therefore wide interindividual variations in age-related physiologic changes are seen. Some of the pathophysiologic changes that influence the nutritional status of older people are discussed in the following sections.
Changes in Height, Weight, and Body Composition
For a variety of reasons, including decline in bone mineral density, older people tend to lose height with age. The mean height loss over the life span for women and men is 4.9 cm and 2.9 cm, respectively. Body weight also changes with age. It increases in both men and women until the late sixties and tends to decline thereafter. Total body fat as a proportion of total body composition increases with age and doubles between the ages of 25 and 75. This increase in total body fat is associated with a corresponding decline in lean body mass. Age-associated changes in height, weight, and body composition are important in nutritional planning and assessment of older people. Some age-associated changes in body composition and the significant interindividual variations in these changes make it difficult to interpret some of the anthropometric measurements commonly used in older people. A balanced diet and an exercise program may retard the proportional decrease in lean body mass and increase in total body fat associated with aging.
Oral health is often related to dietary habits and nutritional status. Some of the oral health problems that affect the elderly include dental caries, periodontal disease, and changes in salivary gland function resulting in xerostomia, mucositis, and tooth loss. According to some reports, up to 40% of the older population is edentulous. Some recent surveys have shown that the prevalence of edentulous adults is decreasing. This decline in prevalance of edentulous adults is most likely due to the better dental care available to the population in general. Lack of teeth leads to difficulty in chewing food, which makes it difficult to eat a regular diet and thereby increases the likelihood of undernutrition. Prosthetic replacement of teeth reduces taste sensation and does not fully restore the ability to masticate. Older people do not chew as efficiently as younger people and tend to swallow larger pieces of food. Owing to subtle neuromotor changes in the swallowing mechanism, the oral phase of swallowing takes 50% to 100% longer. Some recently published studies have shown an association between loss of teeth, oral problems, and undernutrition in older people. Some other oral health problems common in the elderly that may increase the risk of undernutrition include mouth dryness (xerostomia), dental caries, temporomandibular joint dysfunction, periodontal disease, and ill-fitting dentures.
The gastric mucosa changes with age, leading to an increase in nonparietal cells. This may result in a decline in gastric acid output, which may influence the absorption of certain essential nutrients, including vitamin B12, folic acid, and iron. The intestine’s ability to absorb food particles generally does not change significantly, but declines in the metabolism and absorption of carbohydrates (especially lactose), calcium, and iron may occur.
Taste and Smell Sensation
Several changes take place with age in the senses of taste and smell. Taste sensitivity may decline with age, but the evidence is inconclusive and varies significantly among individuals. Age-associated declines in the number of lingual papillae and salivary flow may be associated with diminished taste sensation. The sense of smell declines rapidly after the fifth decade, and by the eighth decade smell detection is almost 50% poorer than it was at its peak, but there is wide individual variation. Age-associated changes in taste and smell sensation make the discrimination and enjoyment of food difficult and therefore may contribute to undernutrition.
NUTRITIONAL REQUIREMENTS OF OLDER PEOPLE
For optimum management of nutritional problems, a knowledge of the nutritional requirements of older people and the impact of disease on these requirements is essential. Caloric balance indicates energy intake that maintains steady body weight. Caloric insufficiency or caloric undernutrition is reflected by weight loss, and excess caloric intake may cause weight gain. Conditions that can modify nutritional requirements include infection, surgery, trauma, medications, alcohol abuse, and malabsorption.
Caloric requirements decline by approximately 22% from age 30 to age 80. One third of this decline is believed to be due to a decrease in metabolic rate secondary to a decline in lean body mass with age. The remaining two thirds of this decline are due to a decline in energy expenditure secondary to a decrease in physical activity. Furthermore, some investigators have reported that caloric intake also declines in older people. According to one report, 17% of subjects 60 years and older consumed less than 1000 calories/day. The decline in caloric requirements and caloric intake in older people puts them at high risk for undernutrition of various essential nutrients.
A useful approximation of the actual caloric needs of patients in the clinical setting can be obtained from the following chart:
No stress, minimal activity
Mild stress (e.g., upper respiratory tract infection, grade I to II pressure ulcer)
Moderate stress (e.g., grade III pressure ulcer, urinary tract infection, pneumonia)
Severe stress (e.g., sepsis, grade IV pressure ulcer)
The current recommendations for protein intake in older people is 0.8 g/kg body weight. A balanced diet of a healthy older adult should contain 12% to 14% of the total caloric intake from various protein sources. During periods of stress, such as during infection or trauma, the protein intake should be increased to 1.0 to 1.5 g/kg body weight.
Vitamin and Mineral Requirements
Recommended dietary allowances (RDAs) for various vitamins and minerals are shown in Table 15-1. In a recent review by Russell and Suter, the authors concluded that, based on the current body of knowledge, the 1989 RDAs are too low for the elderly population for riboflavin, vitamin B6, vitamin D, and vitamin B12.1 The authors also concluded that present RDAs for older people appear to be appropriate for thiamine, vitamin C, and folic acid but are probably too high for vitamin A. In general, healthy older people eating a balanced diet do not need a multivitamin and mineral supplement. However, such supplements may be valuable in a subgroup of older people who are at higher risk for developing deficiencies of calories, proteins, and micronutrients. Older people who are at high risk for developing nutritional deficiencies include eating-dependent nursing home residents and house-bound elderly. Some studies have shown that underweight, hypoalbuminemia, anemia, and an incidence of pressure sores are higher in eating-dependent nursing home residents.
TABLE 15-1 RECOMMENDED DIETARY ALLOWANCES FOR THE ELDERLYa
A number of studies have shown that up to three fourths of older people have intakes of vitamin D that are less than two thirds of the RDA. Older people are at higher risk for vitamin D deficiency because of insufficient dietary vitamin D intake, impaired renal synthesis of 1,25-dihydroxyvitamin D, and inadequate sunlight exposure. High-risk groups of older people for low vitamin D level include nursing home residents living in the northern climates, residents taking chronic anticonvulsant therapy, and house-bound patients. Similarly, a large proportion of older Americans fail to meet the currently recommended guidelines for optimal calcium intake. A National Institutes of Health (NIH) consensus statement for calcium and vitamin D intake suggests that the current RDAs for calcium and vitamin D are suboptimal and therefore should be revised.2 Table 15-2 summarizes the optimum daily calcium requirements as recommended by the NIH consensus statement. Since vitamin D metabolites enhance calcium absorption and vitamin D deficiency has been shown to be associated with an increased risk of fractures, the NIH consensus statement recommends a higher daily intake of vitamin D than the current RDA. It recommends a vitamin D intake of 200 to 400 IU or 5 to 10 mg cholecalciferol/day.
TABLE 15-2 OPTIMUM DAILY CALCIUM REQUIREMENTS
Fluid or Water Intake
Older people are at increased risk for dehydration due to age-associated declines in thirst sensation, inadequate fluid intake, and excessive fluid loss. Subgroups of older people at highest risk for dehydration include nursing home residents, patients with dementia, patients with chronic debilitating illness, and patients taking multiple medications. Recommended fluid intake (water) is 30 mL/kg body weight/day.
Nutritional assessment involves gathering data such as dietary history, clinical observations during physical examination, anthropometric and biochemical measurements, and possible drugnutrient interactions. The assessment starts with a dietary history followed by physical examination and biochemical measurements.
Dietary History and Physical Examination
The dietary history begins with a history of recent unintentional weight gain or weight loss, recent surgery, or trauma; a history of any chronic illness such as diabetes, hypertension, renal failure, hepatic failure, heart failure, malignancy, or peptic ulcer disease; a history of any recent illness such as recurrent nausea, vomiting or diarrhea, drug or alcohol abuse; use of multiple medications; and a detailed social history. The patient’s recent dietary intake is estimated as accurately as possible from either a diet history or, if possible, an actual calorie count based on meals eaten, preferably spanning a period of the previous 5 to 7 days and including a weekend.
A careful physical examination including a search for signs of nutritional deficiencies is important in performing a nutritional assessment. Evidence of body fat and muscle wasting is characteristic of marasmic malnutrition. Loss of skin turgor, loss of hair color and softness, pitting edema, and enlargement of the liver and parotid glands are more characteristic of a kwashiorkor type of malnutrition. Some of the characteristics of kwashiorkor and marasmic malnutrition as listed in the American Medical Association’s International Classification of Diseases (ICD-9-CM) are outlined in Table 15-3. Signs and symptoms of various nutrient deficiencies are outlined in Table 15-4. Findings characteristic of trace element deficiencies should also be recognized. Examples include the association of zinc deficiency with diarrhea, dermatitis, hair loss, poor wound healing, and alteration in the senses of taste and smell; chromium deficiency with weight loss, glucose intolerance, and diabetic neuropathy; copper deficiency with anemia and leukopenia; and iron and iodine deficiency with anemia and goiters, respectively.
TABLE 15-3 ICD-9-CM CODES FOR CLASSIFICATION OF MALNUTRITION
TABLE 15-4 SYMPTOMS AND SIGNS OF NUTRIENT DEFICIENCY IN ELDERLY PERSONS
Anthropometric measurements include measurements of height, weight, body mass index, and skin and muscle folds.
Weight loss is considered the strongest predictor of morbidity and mortality in hospitalized and institutionalized patients. Expressing body weight as a percentage of the ideal weight is one method of assessing optimum body weight. Metropolitan Insurance Company height and weight tables are the most commonly used reference source for estimating ideal body weight. The most current Metropolitan table was derived from the 1983 Build Study on Americans and was based on subjects aged 25 to 59 years old who carried life insurance. However, these tables do not include subjects over 65 years of age. Master and colleagues reported data on the weights and heights of white Americans aged 65 to 94 years.3 According to this report, body weight continues to increase into the late sixties and then gradually declines in the later decades of life. This is the best available information on height and weight for people 65 years and older (Table 15-5 and Table 15-6).
TABLE 15-5 AVERAGE WEIGHT IN POUNDS FOR MEN AGED 65 TO 94 YEARS
TABLE 15-6 AVERAGE WEIGHT IN POUNDS FOR WOMEN AGED 65 TO 94 YEARS
Use of the patient’s own best weight for a reference standard is preferable for nutritional assessment because it allows a more accurate determination of recent or chronic weight loss than a weight as a percentage of the ideal. This weight is also called the percentage of usual body weight (UBW). The best source of this information is the patient’s previous medical record. The percentage of UBW can be determined by the following formula:
Hamwi’s method is quick and is probably the most commonly used method of estimating ideal body weight, but it tends to underestimate ideal body weight, especially for people older than 60 years of age. Hamwi’s formula for estimating ideal body weight is as follows:
BODY MASS INDEX
Body mass index (BMI) is a ratio of body weight (kg) to the square of body height (m2). BMIs of 23 or less and 30 or more have been shown to be associated with increased mortality in the 60-year and older age group. In other words, the association of BMI and mortality is a U-shaped curve in people 60 years and older. Furthermore, the BMI associated with minimal mortality increases with advancing age. Therefore, a BMI that may be considered excessive in a 20-year-old person may be normal for a person who is 60 years old. The formula for calculating BMI is as follows:
SKIN FOLD AND MUSCLE MASS MEASUREMENTS
The mid-arm circumference can be used to estimate the body’s skeletal muscle mass, whereas the triceps skin fold and subscapular skin fold thickness can be used to estimate the subcutaneous fat reserves. These measurements are less reliable in people 60 years and older due to age-related declines in lean body mass and increases in body fat. Chumlea and colleagues reported anthropometric measurements in 119 white men and 150 white women aged 60 to 104 years living in Ohio.4 These are the best available standards for skin fold and muscle mass measurements in older people to date.
ALTERNATE METHODS FOR MEASURING HEIGHT AND WEIGHT IN PATIENTS WITH DISABILITIES AND DEFORMITIES
In patients who have lost a body part, estimation of desirable body weight is more difficult. Total arm length measurement, arm span measurement, and knee height measurements are alternative methods of measuring height in nonambulatory patients and patients with disabilities and deformities. The following list of percentages of total body weight contributed by individual body parts, described by Grant and Dehoog,5 can be used to estimate desirable weight in these patients.
Lower leg with foot
Trunk without limbs
Biochemical Indicators of Nutritional Status
Several biochemical indicators can be used to assess nutritional status. Kwashiorkor-type malnutrition is associated with depletion of the visceral protein mass. Affected patients may not have any evidence of weight loss and may even be overweight. It is therefore sometimes difficult clinically to diagnose this type of malnutrition on the basis of the physical findings alone. Because visceral protein mass cannot be measured directly, the serum concentration of proteins synthesized by the liver is used as an indirect method of determining visceral protein mass. Serum transport proteins that have been found useful for this purpose include albumin, transferrin, thyroxine-binding prealbumin, and insulin-like growth factor-1 (IGF-1).
Several investigators have shown that hypoalbuminemia (serum albumin levels of less than 3.5 g/dL) is associated with increased morbidity and mortality in hospitalized and institutionalized patients. It is easily measured and quite accurately reflects the visceral protein status in the absence of acute changes in hydration or stress. The total albumin pool varies from 3 to 4 g/kg for women and 4 to 5 g/kg for men. The half-life of albumin has been estimated to be 18 to 21 days. Protein undernutrition has been shown to be associated with a decrease in albumin synthesis by the liver. Because of its large body pool and long half-life, the serum concentration of albumin changes slowly with malnutrition, thereby limiting its clinical usefulness in hospitalized or institutionalized patients with acute malnutrition. Furthermore, several investigators have reported that because albumin is a negative acute-phase reactant, its concentration in the serum may decline during an acute illness. It is therefore not considered a reliable marker of nutritional status. However, this does not diminish the association of hypoalbuminemia with increased morbidity and mortality in hospital and institutional settings.
Prealbumin plays a major role in the transport of thyroxine and serves as a carrier molecule for retinol-binding protein. It has a short half-life of 2 to 3 days, and its serum concentration changes rapidly with changes in protein nutrition status. It has also been shown that the prealbumin concentration increases with improvements in nutritional status. Therefore, it can be used not only as a marker of malnutrition but also as a method of monitoring response to therapy in patients with malnutrition. Prealbumin levels of between 10 and 15 mg/dL, 5 and 10 mg/dL, and less than 5 mg/dL are labeled mild, moderate, and severe visceral protein depletion, respectively.
Transferrin is a beta globulin that transports iron in the plasma. Its serum concentration appears to be less significantly altered by the state of hydration than that of albumin owing to its smaller body pool mass. Several conditions other than malnutrition can alter its serum concentration. The serum concentration of transferrin falls markedly with liver disease and in conditions that lead to protein loss. Its serum half-life ranges from 8 to 10 days. Because of the shorter half-life and the smaller body pool, the serum concentration of transferrin is considered a better marker of protein malnutrition than the serum albumin level. Serum concentrations of transferrin of 150 to 200 mg/100 mL, 100 to 149 mg/100 mL, and less than 100 mg/100 mL are considered reflective of mild, moderate, and severe visceral protein depletion, respectively.
INSULIN-LIKE GROWTH FACTOR-1
Insulin-like growth factor-1 (IGF-1) is a peptide synthesized primarily in the liver (although smaller concentrations are secreted by a number of other tissues in the body) that mediates the growth-promoting effects of growth hormone. It has been shown that the serum concentrations of IGF-1 decline with malnutrition, falling as rapidly as less than 5 days after starvation, and they recover just as quickly with refeeding. Studies have shown that a rapid decline in IGF-1 level is associated with both protein and calorie undernutrition. It has also been shown that the IGF-1 level declines with aging. Therefore, its usefulness as a marker of nutritional status in older people remains to be defined.
Subjective Global Assessment
The traditional methods of nutritional assessment rely heavily on objective anthropometric and laboratory test results. Some investigators have proposed basing the nutritional assessment on the findings of the history and physical examination, a method called subjective global assessment (SGA). SGA can be used to identify hospitalized patients at risk for malnutrition. The five guidelines obtained from the history and physical examination for SGA include (1) weight loss, (2) dietary intake, (3) gastrointestinal symptoms that may influence nutritional status, (4) functional capacity, and (5) physical signs. SGA is a subjective screening tool and has various categories that can be interpreted as follows:
Class A indicates less than a 5% weight loss or more than a 5% weight loss but recent evidence of weight gain and improved appetite (well-nourished).
Class B indicates a 5% to 10% weight loss without recent weight gain, poor dietary intake, and mild (1 +) loss of subcutaneous fat (moderately malnourished).
Class C indicates weight loss of more than 10% with severe loss of subcutaneous fat and muscle wasting, often with edema (severely malnourished).
The effectiveness and usefulness of SGA in a clinical setting have yet to be established.
Nutrition Screening Initiative
The nutrition screening initiative was developed by the American Academy of Family Physicians, the American Dietetic Association, and the National Council on the Aging Inc. to screen older Americans who are at increased nutritional risk.6 Older people may have an increased nutritional risk due to a variety of factors, including a decline in caloric intake after age 60 and increased prevalence of functional disability, undesirable psychological or social environment, one or more medical problems, and use of multiple medications. Since a compromised nutritional status has been shown to be associated with increased morbidity and mortality, early recognition and treatment of increased nutritional risk in older people is recommended.
The nutrition screening initiative is a tiered approach to screening. The first level of screening is a checklist completed by the older people or caregiver; this is followed by a two-level approach accomplished in a professional setting. The nutrition screening initiative is designed to facilitate early recognition and treatment of nutritional deficiencies in older Americans.
Drug-induced nutritional deficiencies result from drug-induced malabsorption, renal loss of a nutrient, or inhibition of biosynthesis of a nutrient. These deficiencies are more common in patients with poor oral intake, compromised nutritional status, or prolonged or chronic illness. Older adults are at increased risk for drug-induced deficiencies because they consume proportionately larger numbers of prescription medications and because malnutrition is common, particularly in institutionalized older people, in whom, coincidentally, polypharmacy is also more common.
Several drugs (e.g., digoxin) can cause anorexia, thereby leading to lower caloric intake. A variety of drugs (e.g., antihistamines, antipsychotics, tricyclic antidepressants) can cause dryness of mouth because of their anticholinergic side effects and therefore can impair oral intake. Diuretics can cause deficiencies of various electrolytes, including sodium, potassium, and magnesium, as well as dehydration. Concurrent use of a laxative and a diuretic can cause the electrolyte deficiency and dehydration to become worse. Several drugs can adversely influence calcium and vitamin D metabolism, including phenytoin, phenobarbital, and isoniazid. In addition, drugs such as anticonvulsants, corticosteroids, heparin, thyroxine, and loop diuretics can negatively influence bone mineral density. A careful review of all medications taken should be part of the nutritional assessment of an older person.
Surveys of community-dwelling healthy elderly people have shown that up to one third of subjects have a caloric intake below the RDA and that mineral and vitamin intake is below the RDA in up to 50% of subjects. In these surveys, the blood levels of various vitamins and minerals were subnormal in up to 30% of subjects. Despite low intake and subnormal nutritional indicators, body weight, adipose mass, and muscle mass were rarely depleted, and protein intake was generally adequate. The interpretation of these findings is that the diminishing energy expenditures of the elderly lead to a lower energy requirement and therefore to a reduced food intake. But unless the nutrient density of the diet is simultaneously increased, subclinical mineral and vitamin deficiencies are likely to occur.
Several surveys have shown that the nutritional status of institutionalized elderly is less favorable than that of those living independently in the community.7 In institutionalized elderly low caloric and protein intake is common, and up to 50% of residents are underweight or hypoalbuminemic or show evidence of significant depletion of muscle mass and adipose mass. Blood levels of both water-soluble and fat-soluble vitamins are frequently low.
Protein-calorie undernutrition is associated with increased morbidity, mortality, and medical expenditures in both hospitalized and institutionalized elderly. Several reports have shown that weight loss, body weight below 90% of ideal, cholesterol level of less than 160 mg/dL, and albumin concentration of less than 4 g/dL are associated with increased morbidity and mortality. Therefore, knowledge of the potentially reversible causes of protein-calorie undernutrition as well as its early recognition and optimum treatment are important.
Patients with a significant weight loss—i.e., more than 5% in 1 month, more than 7.5% in 3 months, or more than 10% in 6 months—or with a body weight of less than 90% of ideal or a serum albumin level of less than 3.5 g/dL are at increased risk for developing protein-calorie undernutrition. Several reports have shown that subjects who require feeding assistance are at increased risk for undernutrition of various vitamins and minerals as well as calories and proteins. Poverty, isolation, and depression are some of the other common risk factors for protein-calorie undernutrition in old people. Table 15-7 can be used to identify subjects at increased risk for undernutrition.
TABLE 15-7 RISK FACTORS FOR NUTRITIONAL PROBLEMS IN THE ELDERLY
In the institutionalized setting, where protein-calorie undernutrition is most common, an interdisciplinary team approach is the ideal way of managing this problem. The physician should help in recognizing the problem early and treating it optimally. The dietitian and nurses play vital roles in estimating caloric intake, satisfying caloric needs, and monitoring the response to therapy by taking frequent body weights. Periodic blood tests for some of the readily available biochemical markers can help in monitoring progress as well.
The role of various pharmacologic agents in the management of protein-calorie undernutrition in older people has not yet been proved. No pharmacologic agents have been approved by the Food and Drug Administration (FDA) for use in the treatment of protein-calorie undernutrition in older people. Some studies have shown that use of anabolic hormones such as growth hormone has a beneficial effect, but larger trials are needed to prove the efficacy of hormonal intervention in the management of protein-calorie undernutrition. Megestrol acetate, which has been shown to be helpful in some patients with acquired immunodeficiency syndrome (AIDS) and malignancy, has not been shown to be effective in older people with protein-calorie undernutrition.
Vitamin B12 and Folic Acid Deficiency
It is well known that the prevalence of low serum vitamin B12 is higher in older people.8 Since the majority of older people with low serum B12 levels do not develop megaloblastic anemia, the significance of low serum vitamin B12 levels is questionable. Many studies have shown that a low serum B12 level is not very specific in diagnosing a tissue deficiency of vitamin B12. It has been reported that up to 50% of subjects with low serum B12 levels do not have tissue deficiency of vitamin B12. A number of studies have shown that elevation of serum and urinary methylmalonic acid and total serum homocysteine levels are more specific and sensitive markers of tissue vitamin B12 deficiency. Using these markers and serum vitamin B12 level, it has been shown that the prevalence of vitamin B12 deficiency in older people varies from 5% to 15%.
The exact cause and mechanism of vitamin B12 deficiency in older people cannot be clearly explained at this time. Pernicious anemia, a disease of late middle age, is uncommon in older people. The majority of older people with vitamin B12 deficiency do not show positive results on the Schilling test or have anti-intrinsic factor antibodies. It is believed that vitamin B12 deficiency in older people is, at least in part, due to a defect in extraction and absorption of proteinbound vitamin B12 in food. Other risk factors for vitamin B12 deficiency in older people include a high prevalence of atrophic gastritis (40%) and frequent use of antacids and H2 blockers. It is well known that vitamin B12 deficiency can cause memory impairment and dementia and gait and balance disorders, all of which occur in the absence of specific hematologic or neurologic signs. It is therefore recommended that a serum vitamin B12 level be determined in older people (65 years and older), and if it is found to be less than 350 pg/mL, a serum or urinary methylmalonic acid with or without a serum homocysteine level should be obtained. If the methylmalonic acid and homocysteine levels are elevated, vitamin B12 deficiency is confirmed.
In patients with severe vitamin B12 deficiency and associated clinical symptoms a daily dose of 1000 µg of vitamin B12 should be given intramuscularly for 7 days. This is followed by weekly injections for 6 weeks and monthly injections thereafter. In patients with milder forms of this deficiency, 100 to 1000 µg of vitamin B12 per month can be administered intramuscularly. The role of high-dose oral vitamin B12 supplements (1000 µg or 1 mg/day) in patients with mild vitamin B12 deficiency needs more clinical investigation.
Low serum folic acid levels8 have been found in 10% to 20% of older people. This problem is believed to be due to poor oral intake as well as poor absorption due to gastric atrophy. Folic acid is an essential cofactor in amino acid and nucleic acid metabolism. Folic acid depletion therefore must be recognized and treated. The vitamin B12 level should be determined before folic acid supplements are initiated because repletion doses of folic acid in the presence of vitamin B12 deficiency can precipitate neurologic damage due to vitamin B12 deficiency.
Obesity can be defined as a body weight greater than 130% of ideal, or a body mass index greater than 28 kg/m2. According to some surveys, up to 26% of white men and 37% of white women over the age of 65 are overweight. With advancing age, the waist-to-hip ratio increases (upper body obesity as opposed to lower body obesity). This increase has been associated with an increased risk for diabetes, hypertension, and coronary artery disease. Furthermore, in older people obesity is associated with a decline in functional status and an increased incidence of pressure sores and sleep apnea syndrome.
A combination of diet, exercise, and behavior modification should be the mainstay of therapy for obesity. Weight loss can be achieved through decreased caloric intake and increased energy expenditure, or both. A balanced, low-calorie diet should be designed with the goal of achieving 1 to 2 pounds of weight loss per week. An exercise program designed to increase energy expenditure will not only help the patient lose weight, it will help to maintain that weight once a desirable weight has been achieved.
It has been shown that up to 10% of healthy older people consume 10 times the RDA of certain vitamins. Excess consumption of vitamins A, C, D, E, K, B6, and niacin can result in toxicity syndromes (Table 15-8). Several reports have shown that vitamin E is a protective antioxidant and membrane stabilizer. An association between higher vitamin E concentration or vitamin E intake and lower prevalences of cataracts, cancer, and reduced high-density lipoproteins has been reported. However, the data are considered inconclusive, and the current recommendations for vitamin E intake therefore remain unchanged.
TABLE 15-8 HYPERVITAMINOSIS
TUBE FEEDING FOR ENTERAL NUTRITION
Advances in medical technology during the past two decades have made tube feeding a more acceptable and readily available procedure for enteral nutrition.9 Tube feeding for enternal nutrition may be used for a short time or as a permanent method of nutritional support. Tube feeding is indicated in patients with a functional gastrointestinal tract who
Cannot swallow because of a disease process, for example, head and neck malignancy, untreated esophageal cancer, or major trauma.
Have had protein-calorie undernutrition and continued suboptimal nutritional intake for more than 1 to 2 weeks despite all efforts to improve oral intake.
Recently, it has been shown that without intraluminal nutrients, intestinal integrity may deteriorate, allowing translocation of bacteria in the gastrointestinal tract to invade local intestinal defense barriers, which may result in systemic invasion of the body by the gastrointestinal bacteria. Therefore, it is recommended that prolonged starvation (more than 7 days for most healthy and well-nourished people) should be avoided and the gastrointestinal tract should be used as soon as is safely possible, not only for growth and maintenance of the body but also to protect the local defense barriers of the gastrointestinal tract.
Methods of Tube Feeding
Nasogastric, nasoduodenal, and nasojejunal tubes are referred to as nasoenteric tubes. Nasoenteric tubes are used when a patient needs enteral nutritional support for less than 30 days. Nasoduodenal and nasojejunal tubes may be indicated in patients who are at high risk for aspiration. Tubes placed past the ligament of Treitz have been shown to be associated with a decreased risk of aspiration. Nasogastric tubes can be placed at the bedside with the head of the bed elevated to 45 degrees or more. Nasoduodenal and nasojejunal tubes generally are smaller in size than nasogastric tubes, and therefore clogging of the tubes with nutrients and medications is more common. Metoclopramide, cisapride, or erythromycin given prior to placement of a nasoduodenal or nasojejunal tube may be beneficial in helping to position these tubes beyond the ligament of Treitz. In general, it is easier to insert an unweighted tube. Usually, depending on the expertise of the clinician, nasoduodenal and nasojejunal tubes can be placed at the bedside. In selected patients, nasoduodenal and nasojejunal tubes can be placed under endoscopic or fluoroscopic guidance.
Gastrostomy tube placement is indicated in patients who require tube feeding for more than 30 days. In general, gastrostomy tubes are inserted through a percutaneous gastrostomy under endoscopic or fluoroscopic guidance. Gastrostomy tubes have been shown to be safe, effective, and more acceptable for long-term nutritional support than nasogastric tubes.
Jejunostomy tubes are indicated in patients who need tube feeding for more than 30 days and are at high risk of gastric retention or aspiration due to gastroparesis, reflux esophagitis, or gastrectomy; occasionally they are indicated in patients with gastric or pancreatic cancer. Jejunostomy tubes have been shown to be associated with a decreased risk of aspiration. Data about the efficacy of feeding through a jejunostomy tube as a long-term feeding option are lacking. It has been assumed, without adequate support in the literature, that elemental diets should be fed through a jejunostomy tube.
Techniques of Tube Feeding
Tube feeding may be delivered by bolus, gravity, or pump-controlled techniques. Bolus feeding is the administration of formula using a 50-mL syringe. Depending on the patient’s caloric needs, 400 to 500 mL may be delivered over a period of 10 to 15 minutes every 4 to 6 hours. It is a convenient method that can easily be taught to family members or the patient himself for use at home. Bolus feedings, however, are more likely to generate higher residuals. The tube must be flushed with at least 30 to 50 mL of plain water at the end of each feeding.
Gravity feedings can be delivered through intermittent or continuous drip. The rate of delivery is not precise and may result in high residuals. Intermittent gravity feedings are generally the preferred modality. New closed enteral feeding systems allow the delivery of a specified measured amount of formula. An alternative method is to pour the cans of tube feeding formula into the delivery system. At the end of intermittent feeding, the system should be flushed with plain water.
Tube feeding using a pump-controlled technique is the preferred route for intrajejunal feedings. Feedings can be delivered by either intermittent or continuous technique. Since the delivery is accurately controlled, high residual volumes and the risk of aspiration are less likely than with bolus and gravity feeding techniques.
Continuous intragastric feedings are associated with fewer episodes of diarrhea and aspiration than intermittent feedings. Continuous feedings in infants with diarrhea are associated with fewer fecal losses, more positive nitrogen balance, and weight gain compared with intermittent feedings. Also, continuous feedings have been associated with less energy expenditure, primarily due to diet-induced thermogenesis and more effective prophylaxis against stress ulcers.
Some earlier reports recommended withholding tube feeding for at least 2 hours if the residual volume is high. A recently published report does not agree with the earlier recommendations. The authors of this recent study conclude that tube feeding should not be delayed following a single high residual volume (more than 200 mL obtained from a nasogastric tube and more than 100 mL from a gastrostomy tube) because often the next measured residual value is within an acceptable range.10 The higher the infusion rate, the higher the expected residual volume. Positioning of the patient (in the supine versus the right lateral decubitus position) seems to have no impact on residual volume. Tubes smaller than 10 French have been shown to be unreliable for determining residual volume.
Most institutions have a specific enteral feeding protocol following placement of a new tube.
Complications of Tube Feeding
Fluid and electrolyte problems are common in patients receiving tube feedings. Hyponatremia, hyperglycemia, hypokalemia, hypophosphatemia, and hypomagnesemia are among the most common metabolic complications. Most institutions have standard guidelines for monitoring body weight, fluid intake and output, and serum glucose and electrolytes for patients on tube feedings.
Diarrhea is the most commonly reported complication of tube feeding. The incidence varies from study to study, depending on the definition of diarrhea, from 2.3% to as high as 68%. Some reports have suggested that the severity of illness is the most important factor predicting diarrhea. Besides medications, several pathophysiologic factors, including infection and changes in absorption, blood supply, influence of cytokines, and motility, may predispose tube-fed patients with multiple medical problems to diarrhea.
Medications are a common cause of diarrhea in tube-fed patients. Elixirs of acetaminophen, cimetidine, and theophylline (among others) contain large amounts of sorbitol, which may cause diarrhea. Antacids, laxatives, and drugs containing magnesium may also cause diarrhea. Antibiotics may cause diarrhea owing to the overgrowth of Clostridium difficile or other bacteria and Candida.
The composition of the formula is a less likely cause of diarrhea. In one study, normal volunteers tolerated full-strength isotonic polymeric small bowel tube feedings at rates as high as 340 mL/hour without incurring significant diarrhea.11 The use of fiber-containing formulas to control diarrhea related to tube feeding is controversial. Several studies have shown that no significant difference occurs in the incidence of diarrhea in patients receiving enteral formula with fiber compared with those receiving enteral formula without fiber.9
Data on low serum albumin levels (less than 2.6 g/dL) in relation to diarrhea are controversial. Hypoalbuminemia (serum albumin less than 3.5 g/dL) is a well-established marker of morbidity and mortality and may identify patients with advanced disease and critical illness who are more prone to diarrhea induced by tube feeding.
Aspiration is a serious complication associated with tube feeding. Patients with an altered gag reflex, a swallowing disorder, or an altered level of consciousness are at higher risk for aspiration. Either aspiration of oropharyngeal secretions or gastric aspiration of the tube-feeding formula may occur. The risk of gastric aspiration can be minimized by elevating the head of the bed 30 to 45 degrees during tube feeding and for up to 1 hour afterward. Intermittent and continuous feeding rather than bolus feeding have been associated with a reduced risk of aspiration. Tubes placed in the small intestine beyond the ligament of Treitz (e.g., jejunostomy tubes) may lower the risk of gastric aspiration and should be considered in patients with recurrent gastric aspiration (tube feeding aspiration), not oropharyngeal aspiration.
Administering Medications Through Feeding Tubes
Feeding tubes are commonly used to administer medications. Certain guidelines must be followed to avoid complications that may result from administration of medications in this manner. Clogging of the tube may result when medications are administered through a tube smaller than 10 French. Flushing the tube with 20 to 30 mL of plain water following administration of medication may minimize the risk of clogging.
Drug absorption and drug metabolism may be altered during tube feedings. Slow-release medications and enteric-coated medications should not be crushed because crushing these medications may increase the rate of absorption and expose them to degradation in the stomach. Absorption of phenytoin may be reduced in some patients when it is given with continuous tube feedings. This change in rate of absorption of phenytoin may or may not influence its bioavailability. Therefore, blood levels of phenytoin should be monitored and the dose adjusted if necessary in patients who require continuous tube feedings and phenytoin. Similarly, the dose of phenytoin may have to be adjusted when a patient is switched from continuous to intermittent tube feedings or oral feedings.
The vitamin K in tube feeding formulas may interfere with the effect of warfarin. Prothrombin time should be monitored when tube feedings are initiated, discontinued, or interrupted.
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Stabler SP: Screening the older population for cobalamin (vitamin B12) deficiency. J Am Geriatr Soc 1995;43:1290–1297.
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McClave SA, Snider HL, Lowen CC, McLaughlin AJ, et al: Use of residual volume as a marker for enteral feeding intolerance: Prospective blinded comparison with physical examination and radiographic findings. JPEN 1992;16:99–105.
Kandil HE, Opper FH, Switzer BR, Heiser WD: Marked resistance of tube-feeding induced diarrhea: The role of magnesium. Am J Clin Nutr 1993;57:73–80.