Adequate nutrition is essential for the critically ill patient. Nutrients are necessary to provide substrates for normal cellular
functions, protein synthesis, and daily metabolic processes. The critical patient is often in a hypercatabolic state, so early
nutrition is essential to prevent glycogen depletion, immune dysfunction, and loss of body mass, and to provide substrates
for wound healing.
Common indications for nutritional supplementation in veterinary patients include hepatic disease, chronic renal disease,
trauma, chemotherapy, radiation therapy, esophageal disease (megaesophagus, strictures, ulcers), and face or mouth pathology
(trauma, neoplasia, etc.).
Enteral vs. Parenteral Nutrition
Whenever possible, enteral nutrition is preferred over parenteral nutrition, as it is a more physiologic, safer, and less
expensive route. Enteral nutrition has also been shown to decrease bacterial translocation by maintaining gut mucosal integrity.
Early enteral nutrition has been shown to blunt the release of stress hormones, thus reducing the elevation in metabolic rate.
Enteral nutrition should be considered any time that the gut is functional. Parenteral nutrition should be substituted when
the gut is not accessible or is not functioning adequately. Examples include GI obstruction, severe peritonitis, intractable
vomiting, acute pancreatitis, short bowel syndrome, and ileus.
Enteral feeding provides the necessary calories, protein, and nutrients to the patient as well as glutamine, an essential
amino acid for enterocyte growth. Enteral nutrition enhances enteric IgA production for gut immune function, decreases bacterial
translocation, and decreases stress ulcer production.
Enteral Feeding Routes and Tubes
If a patient is willing and able to eat, oral feeding is the best option. If the patient is unwilling to eat, but can tolerate
oral feedings, syringe feeding is an option. However, this can be very stressful to a patient, it is very difficult to get
adequate calories into the patient via this route, and it poses a risk for aspiration.
In a patient that is unwilling or unable to eat, an indwelling feeding tube is the preferred delivery route for nutrition.
The type of feeding tube will depend on the underlying disease, length of estimated time tube feeding will be necessary, whether
or not anesthesia is an option, whether or not abdominal surgery is being performed, and cost and experience of the clinician.
Types of feeding tubes include nasoesophageal, nasogastric, esophagostomy, gastrostomy, and jejunostomy tubes.
In the postoperative patient, esophageal or gastric feeding tubes may be less useful due to vomiting and higher risks of aspiration
in the depressed patient. Gastric motility and absorptive capacity may not return for 1-2 days post surgery, precluding the
use of this route in the early postoperative period. The small intestines will have motility and absorptive capacity within
hours of surgery, so jejunal feedings may be the best route postoperatively and whenever there is ongoing vomiting.
Nasoesophageal or nasogastric tubes are indicated for short term feeding of a liquid diet (<1 week). These tubes may also
be useful for suctioning air or liquid from the esophagus or stomach. These tubes also may be indicated if anesthesia is not
an option due to cost or condition of the animal or decompression of the stomach or esophagus is needed. Nasogastric is preferable
over nasoesophageal whenever the esophagus is not functioning.
Contraindications of nasogastric or nasoesophageal tubes include severe thrombocytopenia or platelet dysfunction, head trauma,
or protracted vomiting. Advantages of these tubes are that they do not require heavy sedation, do not require expensive equipment,
and they are easily removed when no longer needed. Disadvantages are that they can only can be used for short-term feeding,
they are not easy to use at home for most owners, they have a small diameter so only liquid diets can be used, they pose a
risk of gastric reflux, erosive esophagitis, and aspiration, they can be irritating to the patient, and they are easily displaced
by vomiting or patient interference.
Placement of nasogastric or nasoesphageal tubes is relatively easy to learn. First, numb the nostril with lidocaine (2%) or
proparacaine. Choose a 3-12 Fr sialastic or red rubber feeding tube, depending on the size of the nares (Often a 5 Fr works
in cats, and an 8 Fr for medium and larger dogs). For nasoesophageal, pre-measure to the level of the xiphoid and mark the
tube with pen or tape. For nasogastric, pre-measure to the level of the last rib. Lubricate the tube with lidocaine gel.
In a dog, push upwards on the nasal planum and insert the tube at the ventral nasal meatus and pass in a ventromedial direction.
Hold the head in a neutral or flexed position to allow passage into the esophagus. Gently insert the tube to the pre-placed
mark and suction the tube to check placement. If continuous air is suctioned, the tube may be in the trachea or may have looped
back up into the mouth. Open the mouth and look for the tube in the back of the throat or check to see if is has gone down
the trachea. If negative pressure is reached immediately, the tube may still be in the esophagus, or it may have kinked. If
the tube is in the stomach, it is most common to suction bile-colored liquid and varying amounts of air. A radiograph should
always be taken to check tube placement. You can also inject a small amount of air or water to check placement. If this induces
a cough, remove the tube and start over.