18 Jan 2016
Lisa Weeth
Job Title
Figure 1. A cat with a nasoesophageal tube eating kibble.
In healthy animals, appetite and food consumption are normal adaptive responses to periods of decreased energy intake.
Food refusal can occur in critically ill animals, despite inadequate energy intake, and is a maladaptive response to underlying medical conditions.
The resulting hyporexia (decreased food intake) or anorexia (absent food intake) can be caused by a physical inability to consume food, physiologic abnormalities or metabolic irregularities, or a combination of all three.
Protein-calorie malnutrition results in decreased immune competence, decreased tissue synthesis, increased protein degradation (especially that of the lymphatic system), altered drug metabolism and increased morbidity and mortality in human patients1-3. It should not be neglected.
Studies on the effects of protein-calorie malnutrition in veterinary patients are more limited. Starvation has been shown to decrease in lymphocyte proliferation in cats4, while early enteral feeding results in a positive outcome in dogs with parvovirus enteritis5 and an increased overall energy intake is positively associated with hospital discharge in both dogs and cats6.
Despite the proven benefits of nutritional support in hospitalised patients, the nutritional needs of critical care cases often play a secondary role to their immediate medical and surgical needs.
A survey evaluating nutritional support and feeding orders in four large referral veterinary hospitals in the United States found, of the 276 dogs included in the study, 73% of the days spent in hospital were in negative energy balance7. “Poor feeding orders” was one of the most common reasons given for this occurrence.
Collecting diet history information from owners, either at the time of presentation or within 24 hours of hospitalisation, will help direct an appropriate diagnostic and feeding plan for any hospitalised animal.
The duration of acceptable starvation may be different for an animal that normally eats a complete and balanced commercial pet food compared to one that has been eating a home-prepared diet with suboptimal intake of essential fatty acids, vitamins and minerals.
Additionally, many cats develop fixed food preferences, which can pose a feeding challenge in a hospital setting when changes to food characteristics, such as aroma, texture and mouth feel, may result in food refusal even in the absence of a significant disease state or environmental stressors.
Offering known palatable foods and minimising environmental stressors may help improve voluntary intake without the need for assisted intervention (such as appetite stimulants or feeding tubes).
Indications for nutritional support include:
Appropriate patient selection weighs the benefit of nutritional support against the risk of potential aspiration or worsening metabolic state. Any patient vomiting, regurgitating or unable to protect their airway is not a candidate for enteral nutrition; seek parenteral nutrition.
Energy requirements for hospitalised animals are largely based on meeting calculated resting energy requirements (RER)11-13 for their bodyweight.
The previous use of “illness factors” (calculated RER multiplied by 1.2 to 1.5) added to the daily feeding recommendation of all hospitalised animals is no longer endorsed by veterinary nutritionists.
In animals with voluntary food intake, food offered in excess of need may result in food wastage and additional cost to the clinic or pet owner. With assisted enteral feeding, intolerance to larger food volumes can lead to regurgitation, abdominal cramping, vomiting, diarrhoea and potential aspiration of vomitus or regurgitated material7,9.
The two indirect formulas to calculate RER for dogs and cats are allometric (70 × BWkg0.75) and linear ([30 × BWkg] + 70). The linear formula overestimates RER for animals less than 2kg or greater than 35kg, so the allometric formula is preferred for all animals.
Some disease states, such as protein-losing diseases, persistent diarrhoea or diabetes mellitus, may result in hypermetabolism. The amount of energy delivered for animals with these conditions will need to be increased to accommodate insensible losses.
What to feed will vary largely with the medical condition.
Animals with specific dietary needs, such as food-responsive gastrointestinal disease, pancreatitis, renal disease or hepatic disease, should be fed a diet that will not exacerbate clinical or biochemical signs of illness if possible.
While it is important to ensure the hospitalised animal eats sufficient protein, calories and essential nutrients for recovery, care should be taken when selecting diets for critical care cases as feeding the wrong diet may worsen their clinical outcome and result in subsequent dietary aversion and food refusal.
Examples of problematic feeding attempts include feeding a high-protein diet to an animal with hepatic encephalopathy; feeding a high-fat diet to an animal with a history of hyperlipidaemia, pancreatitis or protein-losing enteropathy; and feeding a known antigen to an animal with a documented gastrointestinal sensitivity to that item.
Give consideration to:
It is also important to consider the effect of drug therapy and therapeutic interventions on gastrointestinal motility and, if indicated, the addition of promotility agents or alteration of medication regime can be made.
Nutritional support of hospitalised animals is important for wound healing, proper immune functions and to prevent loss of lean body mass.
Like any medical treatment, nutritional plans should be dynamic. Start with a goal to reach calculated RER and adjusting the calories delivered each day based on bodyweight changes, physical exam findings and known or expected ongoing losses.
Diet selection should take into account the physiologic state of the animal and the disease states being managed.
