Nutritional Assessment

Chapter 202 Nutritional Assessment



Denise A. Elliott, BVSc (Hons), PhD, DACVIM, DACVN



KEY POINTS



• Nutritional assessment is an important, but often overlooked, aspect of the management of critically ill patients.

• Dietary history, physical examination, and laboratory evaluation are used to determine when, what type, and how much nutritional support to implement for each and every patient.

• All steps in nutritional management should be documented clearly in the medical record.

• All patients should be reassessed daily and changes in nutritional management implemented accordingly.


INTRODUCTION


It has been estimated that up to 50% of hospitalized small animal patients are malnourished.1 Malnutrition and wasting contribute to many aspects of critical illness, including impaired immune function, increased susceptibility to infection, delayed wound healing, decreased strength and vigor, and increased morbidity and mortality. Indeed, malnutrition has been implicated as a significant factor that influences outcome in critically ill humans. Therefore prevention of malnutrition by ensuring adequate nutrient intake is crucial in the management of critically ill patients.


It has been well established that nutritional support in critically ill patients will decrease morbidity and mortality, improve tolerance to invasive procedures, shorten hospitalization periods, decrease incidence of infections, enable earlier ambulation, hasten wound healing, and reduce complications. When to initiate nutritional support requires early assessment of the patient to identify those either at risk of malnutrition or those who already require nutritional support.


In humans, a technique referred to as subjective global assessment (SGA) is used to assess the nutritional status of patients.2 The SGA uses information from the history and physical examination to screen for malnutrition. The SGA classification technique uses historical data on weight change, dietary intake, gastrointestinal signs influencing oral intake and absorption, or any effects of undernutrition that may impact functional capacity. A physical examination is performed to detect clinical characteristics of undernutrition, such as muscle wasting, loss of subcutaneous tissue, edema, or ascites. These results are used collectively to categorize the patient as well nourished (classification A), mild or moderately (or suspected of being) malnourished (classification B), or severely malnourished (classification C).


The SGA is a well-validated tool for screening for malnutrition in a variety of conditions including transplantation, hepatic disease, cancer, and geriatric care. Although subjective, its simplicity allows it to be used by all of the medical staff. The SGA is the only screening tool recommended by the American Society for Parenteral and Enteral Nutrition.3 Although no such standardized scoring system exists in veterinary medicine, the principles of SGA can be applied to ensure that appropriate history, physical examination, laboratory data, and diagnostic techniques are applied for the assessment of veterinary patients with or at risk of malnutrition.



HISTORY


The dietary history should record if the patient is or is not consuming food. If not, then the duration of inappetence or anorexia should be recorded. It is important to record the total duration of inappetence, that is, the number of days the pet was inappetent both in the home before hospitalization and in the hospital. If the patient is consuming food, the name, the manufacturer, the type (dry, wet, semi-moist), the amount fed each day (cans or standard 237-ml cups), the frequency of food intake, and the method of feeding (ad libitum versus meal feeding) should be recorded.


It is also important to differentiate between how much food the pet is offered versus how much of the food is consumed. For example, the client or hospital staff may “feed” the pet 2 cups of food twice a day. This information is meaningless without knowing if the pet actually eats the full 2 cups twice a day. It is vital to know both how much food typically is offered, and how much food is actually consumed. The person responsible for feeding should be identified because this may not be the person presenting the pet for examination; knowing this may help to verify or refute the accuracy of the dietary information provided. The number and type of snacks or human foods that are offered each day and potential access to other pets food (indoor or outdoor) should be determined. Allergies, sensitivities, and intolerances to food should be ascertained. The history should also be explored to fully understand when the current diet was implemented and any changes in the diet or dietary intake that have occurred recently.


The incidence of vomiting or diarrhea should be noted. Injuries that prevent adequate oral intake (facial injuries, prolonged or unmanaged pain, injuries requiring surgical correction) and conditions of excessive protein loss (peritoneal drainage, open discharging skin wounds, protein-losing enteropathy) should be recorded. Nutritional assessment should also identify factors that can impact the nutritional plan such as cardiovascular instability; gastrointestinal, pancreatic, hepatic, or renal failure; fluid, electrolyte, or acid-base abnormalities; hyperglycemia; or hypertriglyceridemia.



BODY WEIGHT


The body weight should be included in the examination of every patient. Body weight provides a rough measure of total body energy stores, and changes in weight typically parallel energy and protein balance. In the healthy animal, body weight varies little from day to day. However, additional challenges may arise in the critically ill patient. Edema and ascites cause a relative increase in extracellular fluid and may mask losses in chemical or cellular components. Conversely, massive tumor growth or organomegaly can mask loss of fat or lean tissues. There can also be wide variation among scales, so it is important to use the same one for an individual animal to prevent interscale variation.


A single body weight measurement by itself has little meaning. For example, knowing that a patient weighs 30 kg does not tell you if it is underweight, normal weight, or overweight. Therefore it is also important to know if the patients’ body weight has changed recently and how rapidly it has changed, that is, over several days, weeks, or months. Rapid changes in body weight are likely to be associated with significant loss of lean body mass. Therefore body weight should not be used in isolation and can be altered falsely by dehydration or fluid accumulation.


Body weight can be subdivided into two or more physiologically distinct components. The traditional two-compartment model divides body weight into the fat mass (FM) and the fat-free mass (FFM).4 This model forms the basis of most of our knowledge of body composition and is dependent on assumptions regarding the character of the FM and the FFM. The composition of the FFM is assumed to be relatively constant, with a density of 1.1 g/cc at 37°C, a water content of 72% to 74%, and a potassium content of 50 to 70 mmol/kg.5 In addition, the major constituents of the FFM are presumed to be present in fixed ratios. In comparison, the FM is relatively homogenous in composition, anhydrous, and potassium free, with a density of 0.9 g/cc at 37°C.


Assessment of body composition in the form of FM and FFM provides valuable information about the physical and metabolic status of the individual. The FM can be considered to represent a calorie or energy storage depot. Conversely, the FFM represents the actual health of the animal. It is a heterogenous entity consisting predominantly of intracellular fluid (ICF) and extracellular fluid (ECF), minerals, glycogen, and protein. The FFM contains the body cell mass (BCM), the metabolically active part of the body responsible for determining most of the resting energy expenditure. BCM encompasses those lean tissues most likely to be affected by nutrition or disease over relatively short periods. Furthermore, the FFM generally is accepted as an index of protein nutrition, so changes in FFM are assumed to represent alterations in protein balance.

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Nutritional Assessment

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