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Veterinarian Technician January 2012 (Vol 33, No 1)

Nutrition Know-How: Nutritional Support: Why, When, and How

by Charlotte Higgins, CVT

    Assessing whether a patient requires nutritional supplementation and determining how to provide it are two of the most important tasks of veterinarians in critical care situations. Although veterinary technicians generally do not assess nutritional needs, determine the type of supplementation, or place feeding tubes, knowing how these tasks are accomplished and understanding the role of the technician are very important for monitoring and caring for affected patients.

    Why to Consider Nutritional Support

    Sometimes, nutritional support must be delayed until a patient is hemodynamically stable. Other times, nutritional support is not a priority of a treatment plan. Even a patient that is well nourished at admission can rapidly become nutritionally depleted during hospitalization. Patients that are already malnourished at admission and that require prolonged hospitalization are at risk for increased morbidity and mortality due to poor nutritional status. Therefore, veterinary staff must be proactive to ensure that nutritional support of hospitalized patients is not overlooked.

    Although there is no gold standard for diagnosing malnutrition, a study at MJ Ryan Veterinary Hospital at University of Pennsylvania found that critically ill dogs that had hypoalbuminemia at admission were twice as likely to die as dogs that had a normal albumin concentration at admission.1

    Nutritional status should be thoroughly assessed before aggressive nutritional support is initiated. Is your patient well nourished, undernourished, or at risk for becoming undernourished? A nutritional assessment can help identify patients that could develop a nutrient deficiency without nutritional intervention. A nutritional assessment should include a complete history (including a diet history), a complete physical examination, a body condition score, and laboratory testing (i.e., a complete blood count, a chemistry profile, and urinalysis).

    It is important to try to predict the duration of hospitalization for patients that are undernourished at presentation. Even patients that present for treatment in good body condition can quickly become depleted during lengthy hospitalization. A study performed at MJ Ryan Veterinary Hospital at University of Pennsylvania documented urine nitrogen losses reflecting a loss of lean body tissue of up to 800 g/d in critically ill dogs.2

    When to Initiate Nutritional Support

    If a patient has not eaten for 4 days or longer, nutritional support should be considered if it is not contraindicated because of vomiting, regurgitation, or megaesophagus or because nothing can be given by mouth while the patient awaits sedation for diagnostic procedures or surgery. Before initiating aggressive nutritional support, try warming the food and using coax-feeding techniques (e.g., hand feeding; petting and/or talking to the patient in a soothing manner during feeding time). Some hospitalized patients may eat only when alone and undisturbed. Because cats are more likely than dogs to develop fixed food preferences, cats are more likely to eat a familiar food. Patients that usually eat dry food often ignore canned food, and patients that usually eat canned food often ignore dry food. Therefore, it is always important to obtain a complete diet history from the client so that the patient’s food preferences are known before feeding is initiated.

    Syringe feeding may be attempted because it is acceptable to some patients. If the patient shows signs of nausea (e.g., turning away from the food, lip smacking, hypersalivating, regurgitating, vomiting, trying to bury the food) or food aversion, coax feeding should be stopped and administration of antiemetic drugs should be considered.

    When used appropriately, appetite stimulants can be useful; when used improperly, they can be very harmful. The misuse of appetite stimulants can create a learned food aversion if the patient is forced to eat before being ready. The patient should be thoroughly evaluated before the decision is made to use an appetite stimulant. An appetite stimulant may be considered if the patient is otherwise healthy and blood work results confirm that the patient has fully recovered. Diazepam, a benzodiazepine tranquilizer, is often used as a short-term appetite stimulant, especially in cats. Adverse effects of the drug include sedation and, sometimes, agitation and hyperactivity; rare cases of liver failure have been reported in cats after repeated use. Cyproheptadine can have antihistamine and antiserotonin effects in cats. The drug is administered orally and may not be effective for up to 24 hours. Adverse effects reported by owners include hyperactivity, agitation, and aggression. Mirtazapine, a tetracyclic antidepressant, appears to be well tolerated in dogs and cats. Reported adverse effects include sedation, vocalization, hypotension, and tachycardia. Patients with renal disease or hepatic disease should be closely monitored. Antidepressants may affect the blood glucose concentration, so patients with diabetes mellitus should also be closely monitored. 

    How do you know if a patient is eating enough? A good starting point is to calculate the patient’s resting energy requirement (RER). Several formulas are available for calculating this, so use the one with which you are most comfortable. Next, writing adequate feeding orders is essential for determining whether a patient is eating enough. Feeding orders should include the name of the food, the amount of food to be offered, and the number of times per day that the food should be offered. The quantity of food consumed should be recorded as a percentage (e.g., “consumed 50% of food offered”). If a patient cannot consume its RER (at a minimum) for 4 or more days, more aggressive nutritional support must be considered to ensure adequate nutritional intake.

    Which Type of Nutritional Support Is Best?

    A broad range of options is available for nutritional support. First, it must be decided whether the patient will be fed enterally (orally) or parenterally (intravenously). Every method of nutritional support has advantages and disadvantages, so it is important to identify which method will be the most beneficial for each patient.

    Enteral nutrition is physiologically the most beneficial method and should be used whenever possible: as nutritionists often say, “If the gut works, use it.” Some research has suggested that the enteral route may be important for maintaining the immune system, decreasing bacterial translocation from the gut to the portal circulation, and blunting the hypermetabolic response in critically ill patients.

    Parenteral nutrition is the optimum choice if the patient has the following:

    • Inadequate digestive or absorptive capacity

    • Intestinal obstruction or ileus

    • A high risk for aspiration due to intractable vomiting, an inability to protect the airway when vomiting or regurgitating, an obtunded mentation, or heavy sedation

    • A need to completely rest the bowel because of digestive disease, gastrointestinal (GI) tract lesions, or bowel resection

    • Pancreatitis

    It is important to remember that parenteral feeding carries a greater risk for sepsis and metabolic disorders. Therefore, parenteral nutrition should be used only if (1) enteral feeding is contraindicated and (2) 24-hour care can be provided.

    How to Deliver Nutritional Support

    If enteral feeding is chosen for a patient, the next step is to choose the method of administration. Consider the best choice for the patient, the available materials and equipment, and the anticipated duration of nutritional support. Various feeding tube options are available for veterinary patients.

    Nasoesophageal Tube

    A nasoesophageal tube may be a good short-term option. Tube sizes range from 5 to 12 French and from 38 to 140 cm in length. The lumens of tubes do not correspond to the French gauge and vary depending on the manufacturer and the material of the tube.

    Nasoesophageal tubes are relatively easy to place and usually do not require sedation of the patient. These tubes are a good option for patients that are too compromised to undergo an anesthetic procedure or that have head trauma.

    Patients with intractable vomiting, regurgitation, or physical or functional abnormalities of the upper GI tract should not be considered for nasoesophageal tube placement. A feeding tube can easily become displaced during vomiting, putting the patient at high risk for aspiration pneumonia.

    The tube size and length must be appropriate for the patient. A 5-French tube works well for most cats and small dogs, and an 8- to 10-French tube works well for most medium-size to large dogs. The appropriate length can be determined by measuring the patient from the nasal planum to the caudal margin of the last rib. With an indelible marker, mark the rostral end of the tube at the point of insertion so that you know when the tube has been fully inserted. To help with placement, instill a few drops of topical anesthetic (e.g., 2% lidocaine), into the nostril. Care must be taken with cats because they are especially sensitive to the effects of lidocaine. To administer the anesthetic, tilt the patient’s head back, insert a few drops into the nostril through which the tube will be placed, and let the patient sit for a few minutes to allow the anesthetic to take effect. Lubricate the end of the tube with water-soluble ointment or lidocaine ointment or jelly to facilitate insertion of the tube.

    While holding the patient’s head in a forward-facing position, pass the tube in a caudoventral, medial direction into the ventrolateral aspect of the nares. Caution should be used in patients with coagulopathies because an occult bleed could easily occur during placement of the tube. In dogs, when the tube reaches the medial septum at the floor of the nasal cavity, the external nares can be pushed dorsally (“pig nose”) to open the ventral meatus, facilitating passage of the tube into the oropharynx. In cats, the tube can be inserted in a ventromedial direction and passed directly into the oropharynx. Secure the tube with sutures to a tape or butterfly tab where the tube enters the nares, and then suture the tube to the patient. Alternatively, a Chinese finger trap friction suture may be used to secure the tube.3 A lateral radiograph or endoscopy is the only way to ensure that the tube has been properly placed in the caudal esophagus.

    Most patients must wear an Elizabethan collar to prevent them from removing the tube. Before each feeding, placement of the tube should be checked by placing a syringe on the end of the tube, aspirating for negative pressure, infusing water through the tube (3 to 5 mL is usually sufficient, depending on the length of the tube), and watching for coughing or gagging, which would indicate displacement of the tube.

    A disadvantage of nasoesophageal tubes is that they can only accommodate liquids. Anything other than liquid (e.g., pills) can easily obstruct these tubes. Even administering crushed medications through nasoesophageal tubes is not advised.

    Esophagostomy Tube

    Esophagostomy tubes are surgically placed and offer more versatility than small-French nasoesophageal tubes because the former allows feeding of gruels in addition to liquids. Additionally, esophagostomy tubes seem to be more comfortable and are, therefore, better tolerated by patients, usually making Elizabethan collars unnecessary.

    Placement of a midcervical esophagostomy tube is a surgical procedure requiring general anesthesia. First, the tube is measured and marked with an indelible marker in the same manner as for a nasoesophageal tube. The cervical region from ventral to dorsal midline is clipped and aseptically scrubbed.

    Several different techniques are used for placing esophagostomy tubes. In one method, an appropriately sized curved forceps is inserted into the proximal cervical esophagus. The tip of the forceps is turned laterally and pressed outwardly so that it is visible and palpable through the tented skin in the neck region. A small incision is then made through the skin. The feeding tube is grabbed by the forceps, drawn into the pharynx through the incision, and redirected down the esophagus. The tube is capped and sutured in place, and a light bandage is placed around the patient’s neck. Placement can be confirmed with an endoscope or a lateral radiograph. Complications include displacement of the tube due to vomiting or infection at the tube site. Every other day, the tube should be cleaned and rewrapped and the patient checked for signs of infection.

    Gastrostomy Tube

    A gastrostomy tube may be placed surgically or endoscopically (i.e., percutaneous endoscopic gastrostomy [PEG]). Placement of a gastrostomy tube is a good choice for patients in which placing a tube proximal to the stomach is contraindicated because of megaesophagus, penetrating bite wounds to the neck region, esophageal dysmotility, esophagitis, or vascular ring anomalies. If a patient requires nutritional intervention and abdominal surgery, this surgery is a perfect time to place a feeding tube. If a gastrostomy tube is placed surgically, the patient should not be fed through the tube for the first 24 hours to allow a stoma to form between the stomach and the body wall. This is a good opportunity to check gastric residuals to ensure that the patient has gut motility before feedings begin (BOX 1) . In the meantime, the tube may be flushed with water every 6 hours to maintain patency.

    A PEG tube can also be placed with the aid of an endoscope while the patient is under general anesthesia. A complete description of the procedure is beyond the scope of this article. PEG kits with tubes ranging from 16 to 28 French are available for small animal patients.

    Enterostomy (Jejunostomy) Tube

    For some patients, bypassing the stomach may be necessary, such as in cases of pancreatitis. Enterostomy tubes are most often placed surgically but may also be placed through a gastric tube and then directed through the pylorus using endoscopy or fluoroscopy. Feedings must be carefully controlled. Bolus feeding is risky because it can cause pain and cramping if a large volume of food is delivered into the jejunum.

    What to Feed

    The type of food to feed can be determined by the following:

    • The patient’s disease process (e.g., protein or fat tolerance)

    • The type of assisted feeding chosen for the patient

    • The types of diets available

    If a nasoesophageal tube has been placed, a liquid diet is required. Complete and balanced liquid formulations are available for dogs and cats. If you cannot obtain these products, a human product can be used if it is supplemented to be complete and balanced for the appropriate species. An example of the need for appropriate supplementation is that a cat can quickly develop hyperammonemia if fed a human formulation that has not been adequately supplemented with arginine. In addition, human products are very low in protein compared with similar veterinary products.

    An esophageal tube allows more options when choosing diets. The larger the gauge of the tube is, the better. Blended diets work well, especially if the patient will be transitioned to the nonblended form of the diet when the feeding tube is removed. Some manufacturers make foods especially for tube feeding, and some of these foods do not require blending or the addition of water.

    How Much to Feed

    The energy requirements of critically ill dogs and cats can be determined; however, many clinicians continue to use illness (“stress”) factors to determine energy requirements, and much of the literature regarding this method has been found to be inaccurate.4 The patient’s RER is usually sufficient to maintain current body weight, except under certain conditions. The best way to ensure that a patient is receiving adequate nutrition is to weigh the patient daily and adjust the feeding plan as needed.

    Complications

    Problems associated with tube feedings can be categorized as mechanical, GI, or metabolic.

    Mechanical Complications

    Mechanical complications are related to the placement and maintenance of the feeding tube. The position of the tube should be checked immediately after placement using radiography or endoscopy. A good safety measure is to check the placement of nasoesophageal and esophagostomy tubes by aspirating for negative pressure and flushing water through the tubes before each feeding. The amount of flush used should be sufficient to clear the tube (e.g., 3 mL is sufficient to clear a 5-French, 15-inch nasoesophageal tube). When these tubes are used, residuals cannot be checked because there is no reservoir in which food can collect. Regurgitation may result from improper placement of a tube.

    Improper administration of medications may also cause mechanical complications. Care must be taken when administering crushed medications through small-gauge tubes, which can easily become clogged. In addition, viscous medications may build up and clog the lumen of tubes; diluting medications with water and flushing tubes well after administration can minimize this risk. The lumen of a tube may be several sizes smaller than the French gauge of the tube. If a liquid form of a medication is available, it is the safest choice.

    Gastrointestinal Complications

    GI problems can result from feeding (1) too quickly, (2) a cold formula, or (3) an excessive amount. Maximum gastric capacities of dogs and cats can be as high as 45 to 90 mL/kg; however, assuming a maximum capacity of 20 mL/kg for dogs and cats can ensure that the gut does not become overdistended. When a feeding tube is used, the patient cannot regulate food intake. The 20-mL/kg guideline not only minimizes the chance of GI upset but also encourages the patient to begin eating on its own.  I have often found that the longer a patient remains anorectic, the more difficult it is to encourage the patient to eat on its own. These cases are often complicated by the presence of a learned food aversion brought on by force-feeding.  After assisted feeding begins, the presence of food in the stomach often makes the patient feel better. Sometimes, this is all the patient needs to “jump start” its appetite and encourage it to eat on its own. Most patients will eat on their own with a feeding tube in place.

    Alkaline or hyperosmolar medications that are not diluted with water before administration may cause GI upset and vomiting, followed by inappetence.  TABLE 1 lists the osmolality of commonly used oral medications.

    Metabolic Complications

    Metabolic complications from diets containing highly digestible carbohydrates include rapid absorption of glucose, resulting in hyperglycemia. Other metabolic complications include azotemia, hyperammonemia, lipemia, and hypophosphatemia, as in refeeding syndrome.

    Refeeding syndrome is a metabolic disturbance that occurs when patients that have been starved or severely malnourished are reintroduced to food. This syndrome occurs more rapidly in patients receiving parenteral nutrition than in patients receiving enteral nutrition. At presentation of a patient, serum electrolyte levels may be normal. However, when nutrition is reintroduced, there are significant electrolyte shifts from the extracellular compartment to the intracellular compartment. The rapid repletion of nutrients most commonly results in hypokalemia, hypophosphatemia, and hypomagnesemia. Clinical signs include generalized muscle weakness, tetany, myocardial dysfunction, dysrhythmias, seizures, and hemolytic anemia. Death may result from cardiac and respiratory failure. Electrolyte levels should be monitored at least once a day. Patients should not receive feedings in excess of their RER, and food should be introduced very slowly by dividing the RER into multiple meals throughout the day. Start by feeding 25% of the patient’s RER and slowly work up to 100% by day 4. Patients that have been starved or critically ill for ­>4 days are at high risk for refeeding syndrome.

    Conclusion

    Nutritional support can be an important part of a patient’s treatment plan. However, because nutritional support can have disadvantages (e.g., higher risk of infection, increased cost, prolonged hospitalization), it should be reserved for cases in which patient outcome would otherwise be negatively affected.

    Suggested Reading

    Saker KE, Remillard RL. Critical care nutrition and enteral-assisted feeding. In: Thatcher CD, Hand MS, Remillard RL, et al, eds. Small Animal Clinical Nutrition. Topeka, KS: Mark Morris Institute; 2010:439-476.

    1. Michel KE. The prognostic value of clinical assessment in canine patients. J Vet Emerg Crit Care 1993;3:96-104.

    2. Michel KE, King LG, Ostro E. Measurement of urinary urea nitrogen as an estimate of total urinary nitrogen loss in dogs. J Am Vet Med Assoc 1997;210:356-359.

    3. Abood SK, Buffington CA. Improved nasogastric intubation technique for administration of nutritional support in dogs. J Am Vet Med Assoc 1991;199(5):577-579.

    4. Hurley KJ, Michel KE. Nutritional support of the critical patient.In: King L, Boag A, eds. BSAVA Manual of Canine and Feline Emergency and Critical Care. London, UK: British Small Animal Veterinary Association; 2007:327-338.

    References »

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