IT has been estimated that up to 50% of hospitalised small animal patients are malnourished.
Malnutrition and wasting contribute to many aspects of critical illness – including impaired immune function, increased susceptibility to infection, delayed wound healing, decreased strength and vigour and increased morbidity and mortality. Therefore ensuring adequate nutrient intake in these patients is crucial.
Indications
The decision as to when nutritional support should be initiated requires early assessment of the patient to identify either those at risk of malnutrition or those who already require nutritional support.
Nutritional support will be needed for a patient with inadequate food intake (real or anticipated) of three days or more.
Cachexia, an unintentional acute weight loss of 10% or chronic weight loss of 20%, hypoalbuminaemia and significant vomiting or diarrhoea are also indications for nutritional support.
Energy requirements
Once the decision to implement nutritional support has been reached, a process to calculate the energy requirements and to select the appropriate nutrient profile is needed.
Specific nutrients, including glutamine, arginine, branched-chain amino acids, L-carnitine, B vitamins, zinc, omega-3 fatty acids and antioxidants, may be beneficial in the nutritional management of critical care patients.
It is recommended to avoid overfeeding the critically ill patient. Generally, one-third to one-quarter of the daily caloric intake is administered on the first day, divided into 4-6 small meals.
If no complications occur, the amount fed is successively increased to reach the total caloric requirements by the third or fourth day.
Close monitoring of the patient’s body weight and body condition can then be used to help to adjust the caloric intake for each individual patient.
High fat diets
Calories can be provided to the critically ill patient by balancing the level of fat, protein and carbohydrate in the diet.
High fat diets (>40% of calories) have been recommended because free fatty acids rather than glucose provide the principal fuel in the catabolic patient. In addition, fat provides more than twice the energy density per unit weight compared to protein or carbohydrate.
In the stressed or traumatised patient, the administration of reduced volumes of highly energy dense foods may be critical. Finally, fat is a major palatability factor, an obvious necessity in patients with a poor appetite.
Carbohydrates
Unless the animal is pregnant or lactating, there is no requirement for carbohydrates other than as an alternative source of energy. However, supplementation with carbohydrates may help to preserve lean body mass by down-regulating gluconeogenesis.
Nitrogen balance
The protein content should be sufficient to maintain a positive nitrogen balance. In dogs, provision of 25-45% of total calories from protein (30-50% in cats) helps combat loss of lean body mass.
However, the amount of protein intake will need to be tailored to each individual patient depending on the severity of the hepatic encephalopathy, uraemia or protein loss. The dietary source of protein should be highly digestible and contain all the essential amino acids.
Fibres
Complex indigestible carbohydrates such as insoluble fibre are often limited in diets formulated for the critically ill patient. This is because insoluble fibre may increase the overall feeding volume and reduce digestibility.
Conversely, the inclusion of fermentable fibres or prebiotics such as beet pulp or fructooligosaccharides may have several beneficial effects in critical illness.
Fermentable fibres may have a positive effect on the mucosal barrier by stimulating the growth of intestinal bacteria such as lactobacilli and bifidobacteria. In addition, they produce the short-chain fatty acids which provide fuel for colonocytes.
Antioxidants
In critical illness, an imbalance between free radical production and antioxidant protection can arise. Therefore it is prudent to supplement the diet of the critically ill patient with antioxidants.
Finally, attention must be given to the physical presentation of the food – its consistency, viscosity and texture – and the patient’s requirements in terms of feeding method and preferences.
A cat which has always been fed wet food is unlikely to eat dry food if presented with this for the first time during a period of convalescence. Royal Canin’s Recovery diet has a unique texture which allows voluntary feeding and lapping, as well as syringe feeding and tube feeding.
In summary, malnutrition is far too common in critically ill companion animal patients. Numerous studies have demonstrated that nutritional support reduces both morbidity and mortality and so should form an important part in the management of critically ill patients.
