Nutritional supplementation is vital to the healing process for most disease processes and after traumatic injury. However,
many of these patients do not receive sufficient nutrition during the healing and recovery process. Over time, this lack
of proteins, minerals, and energy substrates can lead to a state of general illness, malnutrition, and profound disability,
a condition defined as cachexia. A cachexic patient has the potential to develop anemia, reduced cardiac mass and function,
decreased pulmonary function and respiratory drive, and altered intestinal morphology and impaired absorptive ability. By
providing nutrition to a patient unable to consume sufficient food, we can improve immune function, improve tissue synthesis
and repair, improve intermediary drug metabolism, suppress the body's hypermetabolic response, reverse any carbohydrate imbalance,
and reduce protein catabolism.
The first key in assessing whether a patient requires supplemental nutrition is to determine which patients are at risk for
malnutrition. These patients may include patients in the ICU, patients with a recent weight loss >5% of body weight, patients
with partial or complete anorexia of >3 days duration, patients with recent severe trauma or major surgery, patients with
chronic vomiting or diarrhea, patients unable to intake food due to oro-facial trauma or neurologic deficit. For some patients,
proactive nutritional intervention is beneficial. These are those patients we suspect will not eat for 3-5 days, as well
as neonatal and juvenile puppies & kittens and obese cats.
Once those patients who may benefit from supplemental nutrition are identified, the next key to a nutritional program is determining
what type of nutrition will suit them best. When all or part of the gastro-intestinal tract is available and functional, it
is best to attempt to provide at least a portion of the patient's nutritional needs via the enteral route. This route has
advantages since there are more options for nutritional supplementation and the cells lining the gastro-intestinal tract derive
their nutrition via direct absorption from the intestine, rather than through the blood. If the gastro-intestinal tract is
not functioning sufficiently, then the parenteral or intravenous route is preferred. Indications for parenteral nutrition
include protracted vomiting, severe pancreatitis (controversial), and recent intestinal surgery. In some instances, there
is some function to the gastro-intestinal tract but still a reason that not all nutritional requirements can be provided through
enteral routes, so a combination of enteral and parenteral nutrition can be given.
Multiple forms of enteral nutrition are available. There is no need to be fancy since many basic forms of nutrition can be
found at the local grocery store as well as from our pet food representatives. Enteral nutrition can, in its simplest form,
consist of a carbohydrate source supplemented with electrolytes. More complex forms of enteral nutrition include liquid elemental
diets, and critical care diets that can be mixed with water and blenderized.
These liquid enteral diets can be delivered in multiple different ways depending on the clinical condition of the patient.
The easiest options for us for feeding our patients include offering food and coercion feeding. However, there are potential
drawbacks to these methods including stress and insufficient or inconsistent caloric intake. Because of these, many times
we do have to rely on assisted feeding through tubes. Options for feeding devices include naso-gastric or naso-esophageal
feeding tubes, gastrostomy tubes, and enterostomy tubes. Placement of gastrostomy tubes can be performed either surgically,
endoscopically assisted, or with the assistance of a specialized device called an "ELD". In neonates, gavage feeding can
also be performed.
Providing nutrition does not end at determining which patients require nutrition, choosing the diets that we are to feed,
and determining a method of delivering the nutrition. We must also determine how many calories and volumes of components
to feed our patients. Many different calculations for determining caloric requirements are available. Most of these methods
of calculating nutritional requirements are based on a patient's ideal body weight. Some of these methods also incorporate
an "illness factor", although these are falling out of favor. The reason behind this is that studies are now showing that
these "illness factors' tend to lead to over supplementation of nutrients and calories. A commonly accepted formula for
determining caloric requirements in a patient receiving nutrition enterally is:
Resting Energy Requirement (RER)
70 (BW in kg) x 0.75 = kcal/day
30 (BW in kg) + 70 = kcal/day for patients with BW between 2.0 - 45.0 kg