Nutritional Assessment

3. Nutritional Assessment

Nutritional assessment identifies malnourished patients that require immediate nutritional support and also identifies patients at risk for developing malnutrition in which nutritional support will help to prevent malnutrition. Moreover, nutritional assessment aims not simply to diagnose whether a patient is malnourished but whether the malnutrition will have an impact on clinical outcome. Currently used indications for nutritional support include a history of illness or weight loss, current poor body condition or acute loss of 5% body weight, or a history of anorexia or inappetence over 3 days (real or anticipated).

Nutritional assessment first determines the patient’s nutritional status. This is a subjective evaluation based on the medical history and physical examination. Next the patient’s caloric intake should be assessed. The patient’s nutritional status and food intake are considered in conjunction with the severity of the patient’s current illness, factors such as cardiovascular instability, electrolyte abnormalities, hyperglycemia, and hypertriglyceridemia and concurrent conditions such as renal or hepatic disease that will impact the nutritional plan.

Considering all this information will allow the clinician to determine what method of feeding is necessary, how aggressive they should be in initiating assisted feeding, and which route of feeding will be the safest, most effective and best tolerated by the patient (Michel, 2006). An important fact to remember is that many critically ill cats present to the veterinarian after several days if not weeks of inadequate nutritional support. Therefore, provision of nutrition to critically ill patients should occur as soon as it is safe to provide nutrition. This will vary from patient to patient, but the tendency has been to wait too long (Chan, 2006; Chan & Freeman 2006).

Determining Nutritional Status

In humans, a technique referred to as Subjective global assessment (SGA) was developed approximately 20 years ago as a standardized tool to assess the nutritional assessment of patients (Detsky et al., 1987). Although no standardized scoring system currently exists in veterinary medicine, the principles of SGA can be applied to ensure the appropriate history, physical examination, laboratory data and diagnostic techniques are applied for the assessment of critically ill patients (Michel, 2006; Elliott, 2008).

Successful treatment of feline hepatic lipidosis is based on early intervention and adequate nutritional support. (© Isabelle Goy-Thollot).

History

The dietary history should record if the patient is or is not consuming food. It is important to record the total duration of inappetance, which is the number of days the cat was inappetant in both in the home prior to hospitalization, and the hospitalized environment. It is also important to differentiate between how much food the pet is offered, versus how much of the food the cat consumed at home and in the hospital. This could be particularly difficult if the cat is both an indoor/outdoor cat, or is in a multi-cat free-feeding environment. The frequency and amount of vomiting and/or diarrhea should also be noted.

Physical Examination

The physical examination focuses on changes in body composition, specifically wasting of fat stores and muscle mass, the presence of edema or ascites, the presence of mucosal or cutaneous lesions, and the appearance of the patient’s hair. Indications for nutritional support include the presence of injuries which 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; hepatic or renal failure; protein-losing nephropathy or enteropathy).

Body Weight

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 mask losses in muscles or fat mass. Conversely, massive tumor growth or organomegaly can mask loss in fat or lean tissues. In addition, body weight can be falsely altered by dehydration or fluid accumulation. There can also be wide variation between scales, so it is important to use the same scale for an animal to avoid inter-scale variation. Finally, body weights are relatively small in cats and variations could be subtle and the scale must be precise (Chan, 2006; Elliott, 2008).

Finally, a single body weight measurement by itself has little meaning. It is important to know if and how it changes.

Body Condition Score

Several excellent body condition scoring systems have been developed for cats. The most common is a 5-point system (Figure 3) where a body condition score of 3 is ideal, 5 is obese, and 1 is cachetic (see Chapter 1). The body condition scoring systems are designed to evaluate fat stores on the body. In critically ill cats, there is often a disproportional loss of lean body tissue, while the fat stores appear to be adequate. Therefore, careful examination of the muscle stores by palpation of the skeletal muscle mass over bony prominences, such as the scapula or vertebral column is also necessary. Indeed, Freeman et al. (2006) have recommended the use of a cachexia scoring system to evaluate lean body mass, where a score of 0 is normal and 4 represents severe cachexia.

Figure 3. Body condition scoring in cats.

Laboratory Indicators of Malnutrition

There are no biochemical analyses that will reliably identify malnourished cats or enable monitoring them during supportive alimentation. Currently used laboratory indicators of malnutrition include hypoalbuminemia, decreased blood urea nitrogen, hypocholesterolemia, anemia and lymphopenia. However alterations of these common indicators are often indistinguishable from those that can occur with concurrent disease. Albumin loss, for example, rather than undernutrition, may decrease plasma albumin levels (Atkinson & Worthley, 2003). Fascetti et al. (1997) reported that anorectic cats have significantly higher serum creatine kinase concentrations compared to healthy cats. Furthermore, the creatine kinase concentration significantly decreased within 48 hours of implementation of nutritional support. The availability and ease of quantification of creatine kinase (CK) activity make it a promising method of nutritional assessment and monitoring in cats .

Other markers of nutritional status including prealbumin, transferrin, total iron binding capacity, fibronectin, IGF1, retinal binding protein, ceruloplastin, α-1-antitrypsin, α-1-acid glycoprotein and C-reactive protein have not been evaluated in feline patients (Elliott, 2008).

Integrating the Data

All steps in nutritional management should be documented completely and clearly in the medical record. The importance of clear documentation is exemplified by the study of 276 dogs in which a negative energy balance occurred in 73% of the hospitalization days. The negative energy balance was attributed to poorly written orders in 22% of cases (Remillard et al., 2001). Accurate documentation facilitates communication between the various members of the veterinary care team and strengthens the importance of nutrition in the overall care of the patient.

Assessment of Voluntary Food Intake

In order to assess whether that patient’s food intake is adequate, it is necessary to determine the caloric goal, to select an appropriate food and to write precise feeding orders for the patient. Precise documentation allows an accurate accounting of how much food is offered to the patient and an easier evaluation of intake based on how much of the food is consumed (Michel, 2006).

Determining the Route of Feeding

Nutritional support of critically ill patients can be administered via enteral or parenteral routes. Considerable debate and controversy has existed for several decades as to which method may be superior. The answer, or at least the current consensus, is that both methods are valuable and have important roles in managing critically ill patients. The goal of nutritional support should remain to utilize all tools that are available to prevent malnutrition in critically ill patients, while maximizing the benefits and minimizing the risks of the modality that is chosen.

The choice of the best route for assisted feeding is based principally upon evaluation of the patient and to a lesser extent upon logistical factors such as the availability of special diets and nutrient solution or access to 24 hour nursing care (Michel, 2006) (Table 4). Whenever possible, the enteral route should be the first choice (Chan, 2006). Enteral nutrition is preferable as it is the most physiological, easy and safe method to institute; it is also the least expansive (Yam & Cave 1998). While the enteral route is commonly held as the method of choice, in practice gastrointestinal dysmotility or diarrhea may cause suboptimal results with failure to deliver the desired daily requirements (Atkinson & Worthley, 2003). However, even if patients can only tolerate small amounts of enteral nutrition, this route of feeding should be pursued and supplemented with PN as necessary to meet nutritional needs. Critically ill cats that are completely intolerant to enteral feeding, should receive parenteral nutrition (Figure 4).

Figure 4. Integrating nutritional support: decision tree (Adapted from Delaney et al., 2006).

The assessment of gastro-intestinal (GI) tract function should include evaluation of the patient for nausea and vomiting and indications of GI dysfunction such as ileus or malabsorption. It is important to consider if the patient is receiving any medications that might cause nausea or GI ileus and whether the patient has had any recent gastrointestinal surgery or injury that will require bypass.

The patient is further assessed for indications of other organ systems that may impact the patient’s ability to tolerate specific nutrients. Renal or hepatic failure may affect protein tolerance. Infiltrative mucosal disease may affect the patient’s ability to assimilate dietary fat.With the exception of nasoesophageal tubes, placement of enteral feeding tubes requires general sedation or anesthesia. Therefore veterinarians should anticipate the need to place an enteral feeding tube when the patient is undergoing diagnostic procedures or surgery. If an enteral feeding tube is to be surgically placed, the patient should be assessed for a coagulopathy. Patients should also be evaluated for underlying conditions or the use of medications that might impair wound healing. Even the placement of a nasoesophageal tube will require physical restraint and some patients with respiratory compromise may not be able to tolerate this simple procedure.

If PN is considered, it is necessary to determine whether venous access can be obtained and whether that access will be central or peripheral. In addition, the patient’s fluid tolerance must be assessed (Michel, 2004; Michel, 2006). The optimal delivery of PN is via a central venous catheter which requires close monitoring of the patient for metabolic complications. Therefore the patient receiving PN should be cared for in a facility that has 24 hour nursing care and the ability to perform serum chemistry tests.

Patients must be stabilized before undergoing anesthesia, regardless of the urgency to implement nutritional support (Chan & Freeman, 2006a). (© ENVL-SIAMU).

The type of nursing care that the patient will receive should influence the choice of tube and feeding route. For example, if a cat is expected to go home with a feeding tube then it must be a type through which bolus feeding is possible unless the owner is capable of caging and monitoring their pet at home for continuous feeding.

The type of diet will influence the choice of tube type and site. If the only available food is blenderized then the choice is limited to using large bore tubes placed in the esophagus or stomach (Michel, 2004; Michel, 2006).