Date: January 7, 2013; Updated December 16, 2014
Key words: critical, energy, gastrointestinal, malnutrition, anorexia, underfeed, overfeed
Early enteral nutrition: Not just for exotics anymore
Although conventional medicine ignored the nutritional needs of critically ill patients for many years, exotic animal veterinarians have never had that luxury. Small animal size and rapid metabolic rate have meant that many of our patients require rapid and intensive nutritional support to survive (Fig 1).
Malnutrition in the critically ill patient is associated with adverse outcomes such as morbidity, infection, and prolonged length of hospital stay (Rubinsky 2012, Burns 2012). Current evidence suggests that, in the presence of a functional gastrointestinal tract, the early provision of nutrients to patients admitted for critical medical and surgical conditions results in enhanced recovery and fewer complications. Early oral feeding is associated with improved tissue repair, preservation of immunocompetence, and conservation of gastrointestinal (GI) tract health (de Aguilar 2012, Rubinsky 2012). Clinical benefits related to GI flora, GI permeability, and intestinal protein loss have also been documented (Mohr 2003).
A positive outcome with early enteral nutrition has even been documented in conditions that previously were thought to require “bowel rest,” such as acute and severe pancreatitis, hemorrhagic gastroenteritis (HGE), parvovirus enteritis, and even gastrointestinal anastomosis (de Aguilar 2012, McClave 2006, Qin 2002, Mohr 2003). Therefore it is reasonable to pursue enteral feeding in select cases believed to suffer from significant gastrointestinal dysfunction.
Candidates for early intervention
Obvious candidates for early intervention include patients with a history of partial or complete anorexia or chronic disease (Larsen 2012). Many critical patients require medical stabilization (stabilization of the cardiovascular system, fluid therapy, correction of electrolyte imbalances, supplemental heat) before nutritional support is initiated.
Not all patients are suitable candidates for enteral feeding in general, or early feedings in particular (Michel 2012). Oral feedings are contraindicated in patients with:
- Uncontrolled vomiting or regurgitation
- Reduced level of consciousness
- Reduced gag reflex
- Poor anesthetic risk (for tube placement) or impaired hemostasis
Risks associated with early enteral nutrition
Even when favorable effects have not been documented, early enteral nutrition is generally well-tolerated, producing few complications. Probably the most common adverse effect with early oral feedings is regurgitation or vomiting. In one study, young dogs with HGE tolerated early feeding after a short adaptation period, in which vomiting was a severe adverse sign (Will 2005).
How early is early?
Early intervention is preferable to delayed nutritional support (Burns 2012, Chan 2012), however how early should intervention begin?
In dogs, a period of anorexia as brief as 3 days has been shown to produce metabolic changes consistent with starvation. In cats, loss of immune function has been demonstrated by Day 4 of total anorexia.
When clinical status allows, nutritional support should be provided as soon as malnutrition is recognized or anticipated to occur.
- At the very least, nutritional support should be initiated in dogs and cats when anorexia lasts for 3 to 5 days (or less). If the need for nutritional support is anticipated, plans should be made to provide nutritional support if the patient is not expected to eat within 2 to 3 days (Larsen 2012).
- In human patients, enteral nutrition is typically initiated within 24 to 48 hours of intensive care unit admission (Rubinsky 2012, de Aguilar 2012).
- In many exotic animal patients, early oral feedings are initiated within hours as opposed to days, whenever possible.
Is SOME enteral nutrition better than NONE at all?
There is probably some benefit to underfeeding a patient, with respect to energy and/or protein, but only to a certain degree. When 15% to 25% of total energy requirement in rats was delivered by enteral nutrition, intestinal integrity was maintained and bacterial translocation was prevented (Sax 1996, Omera 2000). These findings are similar to parenteral nutrition, however the presence of food within the gastrointestinal tract provides the additional benefit of serving as a direct source of nutrients to enterocytes, colonocytes, and gastrointestinal immune cells. When patients receive lower levels energy and/or protein (< 15%), this is associated with poor patient outcomes (Schulman 2013).
Overfeeding carbohydrates, lipids, and/or protein can result in metabolic complications such as hyperglycemia, hypertriglyceridemia, hepatic dysfunction, and/or azotemia (Schulman 2013).
Careful monitoring is key
Each patient requires a unique nutritional treatment plan. Although the precise caloric target remains controversial, the general consensus advocates the avoidance of prolonged hypocaloric or hypercaloric feeding (de Aguilar 2012). Instead the goal is to meet at least 75% to 80% of calculated energy requirements by 72 hours post-presentation. Careful clinical monitoring guides the adjustments that are inevitably necessary to avoid harm.
Is there an exotic animal exception to the early oral feeding ‘rule of thumb’?
Small patient size and rapid metabolic rate mean that many exotic animals require rapid and intensive nutritional support to survive. As in all species, nutritional support will be beneficial only in those patients with cardiovascular stability that have been warmed and rehydrated. However it is particularly important not to rush feeding of the hospitalized reptile as it is far easier to feed too soon before the patient can reasonably absorb and assimilate nutrients.
The concept of early enteral feeding is becoming widely accepted and practiced in both veterinary and human medicine. Provision of early enteral nutrition is therapeutic, changing the patient’s hospital course in a favorable manner while reducing the risk of morbidity.
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Written by Christal Pollock, DVM, Dipl. ABVP-Avian; Lafeber Company veterinary consultant.