Planning & Implementing Nutritional Support in Sick, Injured or Anorectic Cats
Debra L. Zoran, DVM, PhD, DACVIM, SAIM
Nutrition is a vital aspect of the medical management of many, if not all, feline patients with critical illness or severe trauma. However, it is easy to forget that any cat with an illness that results in significant weight loss, inability to eat, or special dietary needs, may require nutritional support. It is the successful implementation of nutritional support that determines whether or not there is a successful outcome. Because of the unique nutritional needs of the cat, the role of nutritional support in the management of illness or trauma becomes even more essential. This paper will review the development and implementation of an appropriate feeding plan, using either enteral nutrition techniques, for cats that are anorectic or unable to eat due to injury or illness. In addition, the selection of the best diet, feeding frequency and amount of food for the problem at hand will be reviewed.
Stressed versus Non-Stressed (Simple) Starvation
There are two important types of starvation that confront our feline patients in practice: 1) simple starvation and 2) stressed starvation. When a healthy animal does not consume adequate calories, this is called simple starvation, and the body's response is to increase the breakdown of fat for energy, to conserve lean muscle mass, and to down regulate energy expenditure. This metabolic process is universal for most species; however, cats are unique in that while they can down-regulate their energy requirements and increase utilization of fat, their need for protein is unchanged and not conserved. Cats have an obligate need for a constant source of protein and amino acids in their daily diet, as the metabolic machinery that controls their utilization of protein for energy is not able to be down-regulated during periods of low protein availability. Thus, in contrast to a dog, a cat that is anorectic (e.g., undergoing simple starvation) for more than a day or two, begins to break down muscle and other proteins, in addition to fat, to maintain their metabolic and energy needs (in addition to their protein needs for immune function, repair, and synthesis of new proteins). The consequences of simple starvation (purposefully or accidentally) in cats, especially obese cats, are well known and potentially devastating: development of hepatic lipidosis. However, this concept is also key to understanding the importance of early nutritional support in apparently healthy cats that are injured or are suddenly unable or unwilling to eat.
Stressed, or hypermetabolic, starvation is a process set into motion in critically injured or ill animals that places them at high risk for malnutrition and its deleterious effects. In contrast to simple starvation, where both glucose and fat are utilized as energy sources, hypermetabolic starvation results in alterations in energy metabolism (e.g., inability to efficiently utilize glucose for energy due to the anti-insulin effects of stress hormones), and increased utilization of protein and fat. The consequences of this hypermetabolic condition in the presence of lack of intake is compromised immune function (resulting in increased susceptibility to sepsis and bacterial translocation), decreased wound healing (due to protein malnutrition), and an overall negative impact on survival. In sick cats, the increased metabolic demand for protein and fat-based energy sources that occurs only compounds the critical need for early nutritional support. The 3-5 day rule is used as a reminder for determining when nutritional support should be considered or implemented. In cats that have been anorexic for 3 days (including the time before the cat enters the hospital), nutritional support planning should be initiated, and if the cat has not started consuming adequate calories by day 5, nutritional support should be instituted. In short, if oral intake is inadequate, it is vitally important to provide nutritional support by either enteral or parenteral means in a very clearly defined period of time.
Enteral Nutrition: Selecting a Route
Oral feeding remains the ideal means of intake, but there are several factors that must be considered in utilizing oral feeding in cats. First, it is essential to know how much food they should consume in a day, and monitor this amount carefully to see if that goal is being reached. Second, appetite is affected by many non-illness factors (e.g., palatability of food, environment the cat is fed in, and food consistency, temperature and texture) that may influence whether or not a cat will eat in the hospital environment. These factors must be taken into account before completely abandoning oral intake in an anorectic cat. Finally, food aversion is a phenomenon occurring in cats following force feeding, or when nausea or vomiting occurs after consuming a food. Food aversion is a major reason why many cats will not eat a therapeutic diet when they return home that has been force fed in the hospital or fed to them before nausea and vomiting was completely controlled. Once food aversion has developed, it may last months or longer. In anorectic cats that have no apparent medical reason for their unwillingness to eat, appetite stimulants should be considered before started more aggressive enteral or parenteral nutrition. The most commonly recommended, and safest, appetite stimulant for cats is the serotonin antagonist, cyproheptadine (1 mg/cat/day). Other appetite stimulants suggested for cats are the benzodiazepines, such as mirtazapine, anabolic steroids, megesterol acetate, and propofol, but of these, only mirtazapine has been shown to be effective, safe, and may be considered for use in cats.
The feeding route selected for a particular cat is based on the premise that it is best to feed via the gastrointestinal (GI) tract if at all possible, and to use as much of the GI tract as is functional. The second rule of thumb is to determine what feeding method is best suited for the patient's situation. There are several key questions to ask when making this determination: Is the feeding tube going to be required long term? Is there an anesthetic risk for placement that makes tube placement an unacceptable risk? What types of diet does the patient require (can the necessary food be fed through the tube selected)? Is the GI tract working, and if so, is it safe to use it? Finally, it is extremely important to include the owner in the decision making process, as they must be willing and able to provide the necessary nutrition if the cat is to be able to go home. Many owners can handle the 3-4 feedings per day which is typically required for esophageal or stomach tubes. However, in animals with jejunostomy tubes, feeding is best implemented using very frequent (e.g., every 2-3 hours), small meals or by continuous infusion of food (using a fluid pump). Thus, choosing the best feeding method requires not only a nutritional assessment of the individuals needs, but also an assessment of ability of the caregivers to provide the nutrition appropriately.
Enteral Nutrition: Setting Up a Plan
There are many feeding methods available for enteral nutritional support, and they include: nasoesophageal (NE), esophageal (E), gastrostomy (G), endoscopically placed gastrostomy (PEG), and jejunostomy (J) tubes. Each of these different enteral nutrition routes has its own advantages and disadvantages. The reader is referred to several recent reviews for the pros and cons of these options. Once the feeding route is selected, the next step is to set up a feeding plan. There are several steps involved in setting up a feeding plan, and the first is to determine how many calories are needed for that animal. The second is to determine the type of food to be fed (based on the type of tube placed, food availability, and the nutritional needs of the patient). Finally, the timing, frequency, and amount of food to be fed at each meal must be determined.
The caloric needs of an individual can be determined by a number of different equations, but in general, for very sick patients that have not be eating well or have been unable to hold food down, the goal should be to reach the animal's resting energy requirement (RER) for calories. In the past, many nutritionists recommended calculating an illness energy requirement (multiplying the RER by a factor of 1.5 or more) to meet the higher energy needs of metabolic stress. However, recent evidence suggests that in illness, the RER more accurately reflects their true nutritional needs, and excess calories may result in greater GI upset, bloating, or diarrhea. The equation for calculation of RER used by most nutrition experts is the exponential equation: RER = 70(BWkg)0.75. However, the easiest equation to use in the clinical situation is the linear equation: RER = 30(BWkg) + 70. This equation works well for calculating RER for cats because it is more accurate (closest to the exponential equation) in small animals. In kittens or cats weighing less than 2 kg, the exponential equation should be used for accuracy.
Once the RER is calculated, the next step is to select the diet that meets the needs of the cat's medical condition (highly digestible or high energy/recovery diet, hypoallergenic or hydrolyzed diet, renal diet, etc.). The reader is referred to several recent reviews covering this subject for an in-depth treatise of appropriate diet selection for enteral nutrition of specific diseases. However, a few key points critical to the proper selection of diets for the type of feeding to be placed must be considered. For tubes of a smaller diameter, especially NE or J tubes (which are usually 5 French or smaller) a liquid diet will be required--as even well blenderized and strained canned foods will plug the tube. The most widely available liquid diet for dogs and cats is a balanced, but high energy (moderate fat, high carbohydrate) diet (Clinicare® Abbott Labs). This is a very good "illness" diet for cats with normal GI function; however, in animals with significant GI disease, or those that are fat intolerant or require a low carbohydrate diet, this food may not be an appropriate choice. There are a wide range of products available for human enteral nutrition that have varying fat, protein, and carbohydrate concentrations, and can be used for short term feeding. However, because human enteral diets do not provide adequate protein (most have 15-18% protein) and are deficient in a number of amino acids (e.g., taurine, arginine, and carnitine) and other nutrients (e.g., arachidonic acid, certain B vitamins, etc) that cats require, they should not be fed for more than 2-3 days without supplementation of these nutrients. Most E or PEG tubes are 10 French or larger, and thus, will accommodate most canned foods that are blenderized into a gruel or slurry. Remember that when water is added to the food for blenderization, the calories are diluted. This effect can be decreased by using Clinicare instead of water to dilute and liquefy the canned food.
Once the amount and type of food is determined, a plan is developed to deliver the nutrients efficiently but to minimize vomiting or other complications. In most cats, small, frequent meals are tolerated more readily than large boluses of food because the feline stomach is not as readily distensible as dogs or other species. Gastric volume in small animals is approximately 60 ml/kg, and a good rule of thumb to reduce of the risk of vomiting due to overfeeding in cats is to avoid feeding a volume of food at any one feeding that exceeds 50% of this capacity. When initiating feeding in cats, the goal on the first day is to provide 4-6 meals over the course of the day using half of the RER as the caloric goal. If that amount of food is tolerated, on the second day the feedings are increased by one-fourth, and so on. Some cats with GI disease will not be able to tolerate the volume of food required to meet RER; however, even a small amount of food will provide nutrients to the GI epithelial cells, and thus preserve intestinal mucosal health and minimize the risk of intestinal bacterial translocation.
Placement of Feeding Tubes for Enteral Nutrition
Once the feeding plan has been developed, it is time to place the tube and begin nutritional support. The reader is referred to several recent reviews for specific information about tube placement. However, a few comments about the different types of tubes, their use in specific situations, and the potential complications associated with their use is presented.
Nasoesophageal (NE) Tubes
Nasoesophageal tubes are an important feeding option for all hospitalized cats requiring short term feeding but are unable or unwilling to eat. These tubes are easily placed in most cats after instillation of local analgesia (proparacaine ophthalmic drops) in the nose, or mild sedation (e.g., buprenorphine) for those animals that are extremely anxious. The main contraindication to using NE tube feeding is severe nasal disease for which passing the tube may be difficult or impossible, animals with a coagulopathy (the tube placement may cause epistaxis), severe/uncontrolled vomiting (the tube will not stay in place), and in any patient that is unable to protect their airway (comatose, laterally recumbent animals that are at risk for aspiration). This type of feeding is best used short term, as most cats will not tolerate the tube in their nose for more than a few days. Because the NE tubes placed are generally 3.5 or 5 French sized tubes, only liquid diets can be fed. Cats with NE tubes can be fed intermittently with small, frequent (4-6) meals administered by syringe, or continuously, by attaching the tube to an infusion pump for slow, continuous feeding. It is important to avoid feeding the cat a large bolus of food, as that may result in vomiting due to overfilling the stomach, or diarrhea, caused by rapid gastric emptying of the liquid diet into the small intestine (a condition similar to "dumping syndrome" in humans).
Esophageal (E) Tubes
E tubes offer several advantages to practitioners over PEG tubes or G tubes placed surgically, because they can be placed without having specialized equipment or expertise. In addition, in our experience, cats seem to tolerate the E tube much more readily (i.e., they do not mind the neck wrap). Furthermore, while E tubes require anesthesia for proper placement, the amount of time required is much shorter than for other procedures. For that reason, and many others, these tubes are a useful method of providing short or long term enteral nutrition, as well as a means of providing fluids or medication, for sick cats. E tubes may remain in place for months, as long as the tube site is kept clean and free of infection, and is wrapped to prevent it from being inadvertently removed by the cat. The only major complication reported in association with E tube placement is infection at the ostomy site. The key to prevention of ostomy site infection is daily cleaning of the site, and if needed, due to oozing, placement of an antibiotic ointment such as silver sulfadiazine. However, the ostomy site will close rapidly once the tube is removed (inadvertently or purposely), so if a tube must be replaced, it should be done as soon as possible after it is removed (within 4-8 hours). The ostomy site will heal rapidly by granulation, and despite the potential for esophageal stricture or fistula formation, this complication has been rarely encountered.
Gastrostomy Tubes: PEG and Blind Percutaneous Gastrostomy Techniques
Gastrostomy (G) tubes are the best feeding method for feeding animals with severe esophageal disease, animals that are vomiting (because E tubes may be vomited up), or in animals for which long term feeding is anticipated. The size of the tubes is large enough (14-18 Fr.) to allow almost any blenderized cat food to be used. The major drawbacks of using G tubes are that their placement is more complicated and requires specialized equipment (e.g., endoscopy), placement requires more anesthesia time, and, if they are not placed surgically and the animal is vomiting, the tube site can leak gastric content into the abdomen. The contraindications to G tube feeding are similar to that for E tubes, in that they should be avoided in comatose animals (e.g., inability to protect their airway), or any animal with a gastric outflow obstruction. If these things are taken into consideration, G tubes are a efficient and very effective means of delivering nutrition to cats over long periods (months to years).
It is important to recognize that there are several options available for tube placement, but the key is to become very familiar with one or two so that the procedure becomes second nature. Once a G tube is placed, it should remain in place for at least 10-14 days before it is removed, so that the gastric stoma will form a seal that prevents leakage but also forms an attachment between the stomach and the body wall. If a G tube is accidentally removed before intended, a tube can be replaced through the same stoma site if the procedure is performed rapidly (e.g., within 24 hours of the tube removal). There are commercial kits available (Bard) that allow replacement of the tube through the stoma.
Jejunostomy (J) Tubes
There are some situations when enteral feeding is best accomplished if the food is delivered directly into the small intestine (e.g., some cases of pancreatitis, gastric outflow disruption, or animals with other duodenal or upper intestinal outflow issues). Until recently, placement of jejunostomy tubes was a surgical procedure performed during an exploratory laparotomy; however, there are several recent descriptions outlining the placement of J tubes via endoscopic procedures. This method may be preferred in cats for which surgical placement of the J tube is considered dangerous or the procedure deemed to stressful to the cat. The method requires placement of a J tube through an existing PEG tube, and is also called a PEG-J. This procedure is relatively straightforward, but not necessarily easy to accomplish. The interested reader is referred to the above references for specific details about placement of the PEG-J tube. An alternative method for J tube placement that is frequently used in humans is the nasojejunostomy (nasoJ) tube. Placement of this type of J tube is described in cats and dogs, but they are more technically challenging to place, and as with NE tubes, they are not as well tolerated as are J tubes placed through the G tube. For that reason, the use of the PEG-J or traditional (surgical) placement of the J tube is recommended.
Complications of Feeding Tubes
Major complications of feeding tube placement in cats are uncommon and can usually be avoided with proper technique and careful client counseling. The most common complications are tube clogging, infection at the tube site, tube is dislodged by animal, and vomiting following feeding. Other complications include leakage around the tube site, abnormal gastric outflow or function, diarrhea due to overfeeding the small intestine, necrosis of gastric wall, stricture of esophagus at the tube site, and splenic or other organ laceration/injury. Most of the time, tube clogging can be avoided by carefully flushing the tube with water following each feeding, and by using appropriate food for the size of the tube. If the tube does become clogged, it can often be unclogged by forcefully expelling water into the tube, by using a guide wire to dislodge the attached food, or by instilling a small amount of carbonated cola into the tube. In most situations, infections at or around the tube site can be prevented by careful tube site care. If the animal is irritated by the tube, a careful assessment of the tube should be undertaken, as the tube may be getting infected or there may be some other problem, as most cats will not disturb the tube unless there is a problem Finally, if the patient vomits after feeding, check to be sure that the amount (volume) of food being given is not excessive (e.g., feed smaller more frequent meals initially), or add a prokinetic (e.g., metoclopramide, cisapride, ranitidine) or antiemetic drug to the regimen (dolasetron, chlorpromazine). In most cases, the complicating factors can be resolved and successful enteral feeding completed if alterations in volume, frequency or the type of food are completed.
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