Nutrition in Clinical Practice

Alterations in sodium and water balance are commonplace and often occur concurrently. Dysnatremias (hyponatremia and hypernatremia) merely reflect a relative excess or deficit of plasma water in relation to plasma sodium. There is no predictable relationship between plasma sodium concentration, extracellular fluid volume, and total body sodium content. Evaluation and management of dysnatremias rely on an understanding of key terminology, normal body fluid composition and distribution, and regulation of water and sodium balance, combined with a directed history and physical and appropriate laboratory tests. Enteral and parenteral nutrition regimens can be modified to help restore normal plasma sodium concentrations. Response to treatment requires close monitoring to avoid potential complications associated with rapid correction of hyponatremia and hypernatremia.

The ability to diagnose and treat acid-base disorders is an important component in the practice of the nutrition support clinician. A complete understanding of the basic principles of metabolic and respiratory disorders allows the practitioner to formulate educated decisions regarding fluids, parenteral nutrition salts, and the management of electrolytes. This review will discuss the diagnosis and treatment of common metabolic and respiratory disorders encountered in nutrition support practice.

The most severe consequence of iron depletion is iron deficiency anemia (IDA), and it is still considered the most common nutrition deficiency worldwide. Although the etiology of IDA is multifaceted, it generally results when the iron demands by the body are not met by iron absorption, regardless of the reason. Individuals with IDA have inadequate intake, impaired absorption or transport, physiologic losses associated with chronological or reproductive age, or chronic blood loss secondary to disease. In adults, IDA can result in a wide variety of adverse outcomes including diminished work or exercise capacity, impaired thermoregulation, immune dysfunction, GI disturbances, and neurocognitive impairment. In addition, IDA concomitant with chronic kidney disease or congestive heart failure can worsen the outcome of both conditions. In this review, the prevalence of IDA related to confounding medical conditions will be described along with its diverse etiologies. Distinguishing IDA from anemia of chronic disease using hematologic measures is reviewed as well. In addition, current diagnostic strategies that are inclusive of clinical presentation, biochemical tests, and differential diagnosis will be outlined, followed by a discussion of treatment modalities and future research recommendations.

Magnesium plays a role in a number of chronic, disease-related conditions. This article reviews current pertinent literature on magnesium, focusing on hypertension and cardiovascular diseases and implications for relationships with diabetes and metabolic syndrome. A major role for magnesium is in the regulation of blood pressure. While data are not entirely consistent, it does appear that an inverse relationship between magnesium intake and blood pressure is strongest for magnesium obtained from food rather than that obtained via supplements. Hypertension associated with preeclampsia appears to be alleviated when magnesium is administered; in addition, women with adequate intakes of magnesium are less likely to be affected by preeclampsia than those with an inadequate intake. A role for magnesium in other cardiovascular diseases has been noted in that increased magnesium intake may improve serum lipid profiles. Dietary magnesium is also recommended to aid in the prevention of stroke and is important for skeletal growth and development. Magnesium may also play a role in the development of diabetes mellitus, obesity, and metabolic syndrome. There are data from some studies, such as the DASH and PREMIER studies, that suggest that lifestyle changes (including adequate magnesium intake) can benefit blood pressure control, promote weight loss, and improve chronic disease risk.

Selenium functions as a part of proteins known as selenoproteins. Through these selenoproteins, selenium functions as a defensive mechanism for oxidative stress, for the regulation of thyroid hormone activity, and for the redox status of vitamin C and other molecules. In several of its roles, selenium functions as a dietary antioxidant and thus has been studied for its possible role in chronic diseases. This article reviews recent studies regarding selenium status or supplementation in hypertension, cardiovascular disease, cancer, and diabetes mellitus. A few studies regarding aging and mortality are also included. What can be ascertained from this current review is that the maintenance of adequate selenium nutriture and, at minimum, the prevention of a deficiency in selenium would be advisable for all individuals. In addition, the indiscriminant use of selenium supplements should be approached with caution until further randomized, controlled trials monitor the effects of such supplementation, especially on a long-term basis.

Many institutions reduce or eliminate copper (Cu) and manganese (Mn) in parenteral nutrition (PN) solutions when cholestasis develops. Little data exist to support this practice. Fifty-four subjects with known serum Cu, whole-blood Mn, and serum-conjugated bilirubin levels were evaluated in this prospective, observational study. Subjects ranged in weight from 760 g to 65.2 kg. Subjects weighing <25 kg received a daily parenteral dose of 20μ g/kg Cu and 5 μg/kg Mn. Subjects weighing ≥25 kg received a dose of 500 μg/d Cu and 150 μg/d Mn. Cholestasis was defined as a conjugated bilirubin level ≥2 mg/dL. Of the 54 subjects, 20 had cholestasis. Fifteen patients had elevated Cu levels, and 21 had high Mn levels. Seven of the subjects had both high Cu and high Mn levels. The regression model comparing cholestasis as a predictor of high, low, or normal Cu level was not significant (P = .9588). Cholestasis was not a significant predictor of high, low, or normal Mn levels (P = .6533). No correlation between Cu and Mn levels was found. The authors found no significant relationship between conjugated serum bilirubin levels ≥2.0 mg/dL, serum Cu, and whole-blood Mn levels. They found insufficient evidence to support the practice of dosing Mn from a Cu level or vice versa. They recommend obtaining Cu and Mn levels on all pediatric patients who develop cholestasis prior to adjusting parenteral doses and at regular intervals for all long-term PN patients.

Commentary is provided on the pivotal paper by Weinsier and Krumdieck from 1981 describing 2 patients who developed profound and fatal refeeding syndrome following initiation of aggressive total parenteral nutrition. This classic description was among the first to describe the overwhelming cardiovascular and pulmonary manifestations that can accompany parenteral refeeding with carbohydrate in chronically malnourished patients. The syndrome has also been described with oral and enteral nutrition. One of the hallmarks of the syndrome is hypophosphatemia. Since 1981, dosing schemes for addressing hypophosphatemia have been refined. Other manifestations of the syndrome include other electrolyte abnormalities such as hypokalemia and hypomagnesemia, hyperglycemia, fluid and sodium retention, and neurologic and hematologic complications. Case reports of refeeding syndrome continue to be published, particularly in the anorexia nervosa population. Stressed, critically ill patients may be at risk of refeeding following short periods of fasting; hypophosphatemia is commonly encountered in this situation. It behooves the current nutrition support practitioner to keep in mind the types of patients at risk of refeeding syndrome and to approach refeeding of such patients with caution and careful monitoring.

Percutaneous endoscopic gastrostomy (PEG) or PEG tube with transgastric jejunostomy tube (PEG-J) feeding has not been shown to decrease aspiration pneumonia. The aim of this study was to determine if direct percutaneous endoscopic jejunostomy (DPEJ) tube placement results in a decreased incidence of aspiration pneumonia in high-risk patients. The design was a retrospective review of all patients receiving DPEJ tube for aspiration pneumonia from 1999 to 2005. Demographics, incidence of aspiration pneumonia, and outcomes were collected and compared before and after the DPEJ placement. Eleven patients (4 women, 7 men) were identified; their mean age was 44.9 years (range, 18-94 years). The etiologies for recurrent aspiration pneumonia were neurologic disease (9), esophageal surgery (1), and severe debilitation (1). The mean follow-up was 20.9 months (range, 6-48 months). The patients' mean weight increased from 43.8 kg (range, 19-55 kg) to 48.3 kg (range, 30-65 kg) after placement (P < .001). The total number of documented aspiration pneumonia episodes for all patients decreased from 29 (mean, 3.64; range, 1-6) before DPEJ placement to 3 (mean, 0.27; range, 0-2) after DPEJ placement (P < .001). The mean number of aspiration pneumonia events per month prior to the DPEJ placement was 3.39 and postplacement was 0.42 (P < .001). DPEJ placement appears to decrease recurrent aspiration pneumonia in patients with history of aspiration pneumonia.

Transnasal endoscopic placement of nasoenteric tubes (NETs) has been demonstrated to be useful in the critical care setting, with limited data on its role in non–critically ill patients. The authors collected data on consecutive patients from a non–critical care setting undergoing transnasal endoscopic NET placement. All NETs were endoscopically placed using a standard over-the-guidewire technique, and positions were confirmed with fluoroscopy. Patients were monitored until the removal of NETs or death. Twenty-two patients (median age = 62.5 years, 36.4% female) were referred for postpyloric feeding, with main indications of persistent gastrocutaneous fistula (n = 6), gastroparesis or gastric outlet obstruction (n = 5), duodenal stenosis (n = 6), acute pancreatitis (n = 4), and gastroesophageal reflux after surgery (n = 1). Postpyloric placement of NET was achieved in 19 of 22 (86.3%) patients, with 36.8% tube positions in the jejunum, 47.4% in the distal duodenum, and 15.8% in the second part of the duodenum. NET placement was least successful in cases with duodenal stenosis. NETs remained in situ for a median of 24 days (range, 2-94), with tube dislodgement (n = 3) and clogging (n = 5) as the main complications. NET feeding resulted in complete healing of gastrocutaneous fistulae in 5 of 6 patients and provision of total enteral nutrition in 3 of 4 cases of acute pancreatitis and 9 of 11 cases of gastroparesis or proximal duodenal obstruction. Transnasal endoscopy has a role in the placement of NET in non–critically ill patients requiring postpyloric feeding. However, there are some limitations, particularly in cases with altered duodenal anatomy.

It is clear that cancer patients develop complex nutrition issues. Nutrition support may or may not be indicated in these patients depending on individual patient characteristics. This review article, the first in a series of articles to examine the A.S.P.E.N. Guidelines for the Use of Parenteral and Enteral Nutrition in Adult and Pediatric Patients Cancer Guidelines, evaluates the evidence related to the use of nutrition screening and nutrition assessment in cancer patients. This first article will provide background concerning nutrition issues in cancer patients as well as discuss the role of nutrition screening and nutrition assessment in the care of cancer patients. The goal of this review is to enrich the discussion contained in the Clinical Guidelines, cite the primary literature more completely, and suggest updates to the guideline statements in light of subsequent published studies. Future articles will explore the guidelines related to nutrition support in oncology patients receiving anticancer therapies.