Nutritional Support for Critically Ill Animals

By Catherine Sumner, DVM, DACVECC
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MSPCA-Angell West
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Throughout all of the patients presenting to the emergency service with various types of critical illness, one of the common clinical signs described is inappetance, ranging from decreased food intake (hyporexia) for days or weeks, or in some patients a progression to anorexia (complete food refusal). It is well documented that addressing nutritional needs of the animal is critical to effective management and recovery of these patients. Patients with critical disease enter a negative energy balance where they mobilize protein thus depleting their lean body mass. This can result in decreased wound healing and negative effects on immune function, as well as a negative prognosis. Patients with a negative energy balance may have more complications and an extended hospital stay. Additionally, lack of enteral nutrition can predispose a patient to gastrointestinal bacterial translocation, which can lead to sepsis. Brunetto et al. (JVECC 2010) investigated the relationship between nutritional support and discharge from the hospital in dogs and cats, and they found that there appeared to be a positive association between providing nutrition and hospital discharge. Other veterinary studies have shown a more rapid clinical improvement and shorter hospitalization in patients receiving early nutritional support.

When developing a nutritional treatment plan for a patient, a multimodal approach is necessary. It is important to address any pain and discomfort the animal may be experiencing, as this could be a cause for decreased food intake. However, use of opiate medications for pain can worsen nausea and cause constipation. Additionally, opiate medication administration can result in a sedate patient that will be even less likely to take in nutrition voluntarily. Thus, it is important to balance pain control needs and medication administration, as well as consider local analgesic options (such as local blocks, soaker catheters) to decrease overall systemic need.

Many of these patients are treated with injectable anti-nausea medications such as maropitant, dolasetron, and metoclopramide (more effective as a pro-motility agent); sometimes patients are placed on more than one of these medications concurrently. Critically ill patients are often receiving antibiotics, opiate medications, and other medications that can worsen nausea, ileus, and other gastrointestinal signs. It can be of use to administer these medications at the same time as anti-nausea medications to decrease the potential for adverse side effects. Historically, critically ill patients have also been treated aggressively with acid suppressant drugs, such as histamine 2 receptor blockers (i.e. famotidine) and proton pump inhibitors (i.e. pantoprazole). However, recently there has been a movement towards more judicious use of acid suppressant drugs, as there is data to support that they are less effective than initially thought. PPIs are of the most use, but are most effective in patients with gastrointestinal ulcerative disease.

Another consideration is the use of appetite stimulants. Historically, patients have received mirtazapine and cyproheptadine as appetite stimulants. Recently, a selective ghrelin receptor agonist medication, capromorelin, has been released to the market, which acts as a powerful appetite stimulant. Typically, ghrelin is produced by cells in the gastrointestinal tract and acts in the brain on hypothalamic cells to increase hunger, increase the secretion of gastric acid, and increase gastrointestinal motility. It also acts in the pituitary gland to increase growth hormone secretion. Capromorelin is currently FDA approved for use in canine patients, appears to have few side effects, has no minimum age or weight requirements, and can be used in the short term or as a chronic medication (with no limit to how long it can be used). Recommended oral dosing is 3 mg/kg administered once a day.

Options for providing nutrition include enteral (via the gastrointestinal tract) and/or parenteral (via an intravenous route). Whenever possible, enteral support is the favored option, as it has physiologic benefits for the gastrointestinal tract, maintaining the intestinal villi and mucosa. Enteral nutrition can be provided via voluntary food ingestion by the patient, syringe feeding, or via an enteral feeding device. While it is important to provide nutrition early in a patient’s hospitalization, it is important to address hypothermia and hypotension, as these can result in decreased gastrointestinal perfusion and motility.

Feeding tube options include a nasoesophageal or nasogastric tube, esophagostomy tube, gastrostomy tube, or jejunostomy tube. In our practice, nasoesophageal, nasogastric and esophagostomy tubes are used most commonly and will be discussed in this review. In many cases, we find that it is important to initiate a discussion about a potential feeding tube with the family early in a patient’s hospitalization, as it is often a step that requires consideration and which generates numerous questions. Nasoesphageal/nasogastric tubes are easy to place, requiring only sedation, rather than full general anesthesia. However, due to their small diameter, a liquid diet is necessary, and they can only be used for short term care. Also, some animals find them to be uncomfortable and irritating, and occasionally, a patient may sneeze the tube out or vomit up the tube. If the tube is displaced during emesis, it is important to remove the tube quickly, as the patient may chew the tube and ingest part of it (if it is not detached).

If the patient will require longer term nutritional support and the owner is amenable, an esophagostomy tube would be recommended. Esophagostomy tube placement is a procedure that can easily be performed in general practice; as it does not take a significant amount of time and does not require specialized surgical skills. These tubes are placed under general anesthesia, so it is important to ensure that the patient is stable for general anesthesia. Commercially available wet food diets can be used with these tubes. Many practitioners use a mouth gag when placing these tubes, but this is not advised as it can lead to compression of the maxillary artery. Complications are rare with these tubes, but can include infection at the insertion site and esophageal irritation.

There are some situations in which enteral nutrition may not be the appropriate choice, including intractable vomiting, gastrointestinal conditions of severe malabsorption or maldigestion or ileus, and an inability to protect the patient’s airway (along with a concern for vomiting). In situations where the patient’s airway is unprotected, another option would be an enteral feeding tube lower in the gastrointestinal tract (i.e. jejunostomy tube). Otherwise, parenteral nutrition can be considered, but a discussion of this modality is beyond the scope of this article.

Addressing nutritional needs is a crucial part of managing patients with critical illness. It is important to obtain a thorough diet history at the time of patient presentation and develop a plan to provide nutrition early in the patient’s hospitalization.

Further reading:

• Journal of Veterinary Emergency and Critical Care, Volume 16, Issue s1, 2006. This entire issue is dedicated to the topic of critical care nutrition.