The 3-5-7 Rule is a guideline for nutritional support used at Texas A&M. What this means is if the patient has not voluntarily consumed his or her minimum energy requirement estimated as the resting energy requirement (RER, 70(Wt(kg))0.75 for 3 days, a plan needs to be made to provide those minimum calories. If the patient has not consumed RER for 5 days a plan needs to be implemented to begin to provide calories and nutrients. And, the longer a patient goes past 7 days without consuming RER the worse their nutritional status is becoming and the less chance there is of nutritional support having a beneficial effect on outcome.
Nutritional support of critical care patients involves assessment of the animal's condition to determine what kind of nutritional support is needed. There are two broad categories that most critical care patients can be placed into. The first category is the animal that is chronically malnourished and has suffered significant weight loss over a period of time. The second category is the animal that has suffered a traumatic event or illness that has caused it to stop eating or it is unable to eat due to injury or illness. Both groups require careful consideration of energy needs and how those needs should be met.
Starvation
Many metabolic changes occur in an animal that has suffered from starvation. These changes are variable between animals depending on how long food has been withheld and the animal's physical status prior to starvation (underweight, optimal or overweight). When planning a program to begin feeding an animal that has suffered from starvation, the veterinarian must take this information into account to plan a ratio of carbohydrates, protein and fat that will not cause metabolic problems as the animals system adjusts to receiving nutrients from food as opposed to using its own body stores for energy.
Trauma and disease
Animals that have suffered trauma, or are suffering from disease, often stop eating due to metabolic changes that occur due hormonal responses brought on by the stress of the injury or disease. These patients experience many similar metabolic changes to those of animals in starvation, however the feeding of these patients needs to include consideration of the type of trauma or disease and what nutrients the animal will be in greatest need of during recovery. For example patients suffering from severe head trauma, multiple trauma, burns and sepsis have a high need for protein to prevent excessive muscle wasting. Other disease states (infection, cancer) have different nutrient requirements that the veterinary nutritionist takes into account when developing a feeding plan. Often times these patients cannot or will not eat on their own. In these cases enteral (assisted feeding to the gastrointestinal tract) or parenteral (delivery of nutrients via an intravenous catheter) feeding is necessary.
Reference:
Michael S. Hand, Craig D. Thatcher, Rebecca L. Remillard and Philip Roudebush. Metabolic Changes Through Days of Food Deprivation. Small Animal Clinical Nutrition 4th Edition. p359-361, 2000.
