Feeding the critically ill
SAN ANTONIO, TX – Recent advances in both human and veterinary medicine have shown that nutritional support can aid in the management of diseases. Historically, nutritional support was not considered necessary until animals had inadequate intake for 10 days. Evidence now suggests a more appropriate goal in most cases is to initiate nutritional support within three days of hospitalization, at the latest, explained Kara M. Burns, MS, MEd, LVT, speaking at the Veterinary Emergency and Critical Care Society Conference.
Candidates for nutritional support include those with a history of inadequate nutritional intake lasting more than five days, serious underlying disease, and large protein losses (e.g. protracted vomiting, diarrhea, protein-losing nephropathies, draining wounds, burns). To minimize risks, the patient’s cardiovascular system must be stable before nutritional support begins. In addition, feeding should be delayed until preexisting fluid and electrolyte abnormalities are corrected to avoid exacerbating gastrointestinal hypoxia secondary to increasing cellular metabolism, and to prevent hypophosphatemia and hypokalemia related to re-feeding syndrome.
How to feed?
The rule of nutritional support is “if the gut works use it”. An indwelling feeding tube is the method of choice if enteral assisted feeding is necessary for more than two days. Nasoesophageal, esophagostomy, gastrostomy, and jejunostomy feeding tubes are the most commonly used. The decision to use one tube over another is based on the anticipated duration of nutritional support (days vs. months), the need to circumvent certain segments of the gastrointestinal tract (e.g. oropharnyx, esophagitis, pancreatitis), clinician experience, and the patient’s ability to withstand anesthesia.
Food boluses must be infused slowly (approximately one minute per bolus) to allow gastric expansion. Daily food dosage should be divided into several meals according to the expected stomach capacity. Capacities for cats and dogs are 5 to 10 ml/kg body weight during initial food reintroduction. Salivating, gulping, retching, and even vomiting may occur when too much food has been infused or when the infusion rate is too fast, at which point the meal size should be reduced by 50% for 24 hours and then increased by 25% gradually. Foods provided via J-tubes must be infused slowly and often in either very small quantities or by a slow gravity drip or enteral pump with an hourly rate equal to resting energy requirement (RER)/24 hours because the jejunum is volume sensitive.
Each meal should be followed with a water flush to clear the feeding tube of food residue. The patient's daily fluid requirement must also be met and additional tap water may be administered through the feeding tube to meet that requirement, along with any liquid oral medications. In general, endport tubes are easier to maintain than sideport tubes because food tends to become trapped in the blind end of sideport tubes. All tubes except orogastric and nasoesophageal tubes require standard every-other-day bandage care
What to feed?
Nutritionists debate the exact formula for determining daily energy requirements in critically ill patients. Ms. Burns said that a good starting point is to calculate the resting energy requirements for the patient’s current weight. If a patient’s ideal weight is used, underweight animals may be at greater risk for complications from overfeeding. Resting energy requirements (RER) can be calculated using the following equation: RER = 70 x (current body weight in kg)0.75. Another equation that may be used is RER = (kg x kg x kg, √, √) x 70.
Ms. Burns stressed that the nutritional status of the patient must be monitored vigilantly as caloric intake may need to be adjusted to prevent weight loss or unintended weight gain. Food selection depends on tube size and location within the GI tract, the availability and cost of products, and the experience of the clinician. Nasal and jejunostomy tubes usually have a small diameter, which requires use of liquid foods. Orogastric, pharyngostomy, esophagostomy, and gastrostomy tubes have large diameters and are suitable for blended pet foods.
Most human liquid foods are adequate for adult dogs but are too low in protein for cats, puppies, and adult dogs with increased protein losses. Human liquid enteral products may not contain adequate concentrations of protein, taurine, arginine, and arachidonic acid for long-term feeding of cats, but are satisfactory for fewer than seven days. It is recommended that veterinary liquid products be used when managing veterinary patients.
There are several liquid foods on the human medical market that are positioned as monomeric or hydrolyzed diets and are suitable when initially feeding dogs and cats. Monomeric foods are indicated in disease conditions such as inflammatory bowel disease, lymphangiectasia, parvoviral enteritis and pancreatitis cases, and any other condition in which a patient's digestive capabilities are questionable.
Polymeric products contain mixtures of more complex nutrients. These foods require normal digestive processes and are appropriate for most veterinary clinical situations, especially when a small tube has been placed and particular nutrient profiles are needed (e.g., low sodium, high protein, soluble fibre).
One of the leading liquid veterinary foods is a polymeric form that meets the current AAFCO nutrient allowances for adult dogs and cats. This liquid food is the best option currently available in North America when small-diameter nasogastric and jejunostomy feeding tubes have been placed, or when continuous drip feedings are necessary.
Module products are concentrated powdered or liquid forms of nutrients and are primarily supplemental. These products may be added to a liquid product to increase the concentration of a specific nutrient. There are protein, fat, and carbohydrate modules (e.g., cascien powder, vegetable oil, or corn syrup).
Blended pet foods refer to commercial products, nutritionally complete and balanced according to AAFCO allowances for dogs and cats. These products can easily be blended with a liquid to make a consistency that flows through a feeding tube. Some products have a blended texture, a high water content, and very small particle size, whereas others are products that must be blended with water and may have to be strained to remove particulate matter.
Ms. Burns recommended that when using the blended pet food method to use a product that has been tested in feeding trials and is proven to be balanced and complete for dogs or cats. These products are more readily available, better tolerated, and less expensive than the human liquid foods. However, she cautioned, blended products are more likely to plug the feeding tube if the tube is not properly flushed after feeding. These products are appropriate for patients in catabolic states that are using fat and protein substrates from body stores.
Meat and egg human baby foods packed in jars have been used by veterinarians to treat sick animals because they are high in protein and fat, which compares favourably with blended pet food products. However, baby foods are more costly, contain only one or two food types (protein, protein/grain), and do not contain a balanced mixture of other essential nutrients. The human and veterinary liquid products have a better nutritional profile and thus should be used rather than human baby food products.
Summary
Ms. Burns reiterated by saying that the consequences of malnutrition in all patients, especially sick or injured patients, are decreased immunocompetence, decreased tissue synthesis and repair, and altered drug metabolism. The veterinary technician must provide constant monitoring, careful calculations, and exceptional nursing care to manage malnutrition and facilitate healing and recovery. CVT
