"The need to feed" is becoming a well-known term in veterinary practice these days as we recognize that hospitalized patients do far better with proper nutritional support. This is particularly true for patients undergoing surgery in which tissue repair and resistance to infection are paramount.
Tissue synthesis and wound healing depend on local and whole body nutrition. Amino acids and carbohydrates are needed for collagen and ground substance synthesis while fibroblasts require energy to synthesize RNA, DNA and ATP necessary for proteins. The liver and bone marrow require energy and protein for glucose, complement, platelet, leukocyte and monocyte production. Studies show that post operative patients that are fed demonstrate a much higher rate of protein synthesis versus protein degradation while those that are not fed demonstrate higher protein degradation.
The immune system is particularly susceptible to the effects of poor nutrition and post surgical patients depend on a healthy immune system to ward off infection. In people, decreased protein-calorie intake is the most common cause of secondary immunodeficiency and animals are likely similar.
There are other factors that make adequate nutrition following surgery even more critical and these are in response to the injury itself. Following trauma, metabolic and physiologic changes occur in response to the release of catecholamines, adrenocorticoids, glucagon, and a number of other hormones associated with the "fight or flight" response. The result of this hormonal hurricane is:
Suppression of insulin secretion
Increased cardiac output
This metabolic alteration must be met with a nutritional plan that matches the needs of the body.
The resting energy requirement of a non-fasted patient in a cage in a thermoneutral environment can be calculated using the formula RER = 70 + + (30 x Body weight). For a 20 Kg dog this would be 670 kcal. For patients recovering from surgery or other trauma the RER should be multiplied by 1.25 or in the case of our 20 Kg dog this would mean feeding about 840 kcal per day.
Once the number of calories is determined we must ensure the correct balance of nutrients is present to maximize healing and prevent problems associated with the patient's stress response. We have seen that protein requirements are increased due to the rate of tissue and immune component synthesis that must take place. This protein must be of high quality so that it is biologically available to the patient.
Since surgical patients often will not eat as much as normal, the food must be calorie dense. Fat can provide 2.5 times the energy of protein or carbohydrate and unless there are contraindications such as pancreatic disease, fat should be utilized as an energy source. Vitamins, particularly B vitamins, are critical to liver function and can be supplemented in IV fluids as well as delivered in the diet. Most pet foods will deliver enough vitamins and minerals providing the patient is receiving adequate quantities of food.
How to Feed
Many non-injured patients do not eat well in the hospital so those recovering from surgery may be even more challenging due to factors such as anesthetic effects and pain. Proper attention to analgesia and comfort will make your patients more likely to regain their appetite. Depending on the type of surgery, in most cases you will want to start feeding your patients as soon as the noticeable effects of anesthesia have worn off. It is best to select a food with high palatability and it may be necessary to warm the food above room temperature to increase its attractiveness. Hand feeding may be required in some cases combined with some tender loving care (TLC). This seems to be particularly important with cats who we all know can be extremely finicky when it comes to food.
If the patient does not respond within 24 hours of surgery it is time to consider some assisted feeding techniques which can range from simple to quite complicated. Some pharmacological agents will increase appetite in cats and can be tried before physical intervention. These include cyproheptadine (2-4 mg per cat) and diazepam (dosage varies).
Forced feeding involves using a syringe to place a semi-solid food into the pharyngeal area to stimulate the swallowing reflex. This can be met with resistance and care must be taken to avoid injury to the patient or the nurse. In dogs, it is best to place the syringe between the cheek and the molars with the head held in a normal position. For cats the syringe is placed between the four canine teeth. Some animals will refuse to swallow a bolus of food and you must be careful not to be too aggressive or aspiration may result.
The next level of intervention is the use of an orogastric tube and should only be used on cooperative patients that require such feeding for 2-3 days. A lubricated soft rubber tube is pre-measured to the ninth rib and introduced gently with the head held in the normal position. Once the patient swallows, pass the tube to the pre-measured mark and instill some sterile water to ensure proper placement before feeding. There are some mouth gags designed to prevent the patient from chewing on the tube.
For patients that require assisted feeding for a prolonged period it is best to place a fixed feeding tube as this will reduce the stress on the patient and ensure proper delivery.
Nasoesophageal tubes can be left in place for prolonged periods of time (usually 1-2 weeks) and are generally well tolerated if properly inserted. As noted by the term, these tubes are best placed in the distal esophagus rather than the stomach to prevent reflux. A number of different tube types can be used and vary in size from 5-Fr for cats to 8-Fr for most dogs. These tubes can be placed without anesthesia or sedation (in most cases) and are thus preferable for patients considered anesthetic risks. After some drops of local anesthesia, the tube is directed ventromedially to avoid the ethmoturbinate bones and advanced to the pre-measured mark once the swallowing reflex is initiated. Sterile water should be used to ensure proper placement and the tube can be fixed to the skin with a couple of sutures or tissue glue followed by a protective buster collar.
For patients with oral trauma or for those that need a longer term of tube placement (weeks to months), pharyngostomy or esophagostomy tubes can be used. These procedures require anesthetic and complications include infection, hemorrhage and aspiration. Owners can maintain these tubes at home and due to their larger size (8-16 Fr) they can tolerate a wider range of food types than nasogastric tubes.
Gastrostomy tubes have become more popular for enteral feeding now that different placement techniques have been developed. The most common method employs an endoscope but there are blind methods that can be used and special kits that make this much easier. Food is placed directly into the stomach and as in the other tube techniques, the patient is able to eat on its own if it desires.
What to Feed
As mentioned previously, a patient recovering from surgery requires protein and calories at a higher level than its normal resting energy requirement. This can be supplied in many forms but the easiest way is to use one of the many veterinary critical care diets available. Hills Prescription Diet a/d is a syringable diet high in fat, low in carbohydrate (to combat insulin resistance) and high in omega fatty acids, amino acids and glutamine. The diet is very palatable and well received by many patients. There are several other veterinary diets available and home made diets can also be formulated.
It is important to remember that some patients, especially cats, may develop food aversions. When forced to eat a food when in pain or unwell, the patient may refuse to eat the same food once forced feeding is discontinued. Always offer other alternatives so that the patient can resume eating on its own as soon as possible. It is important to remember that a successful surgical outcome depends heavily on post operative care and nutrition is one of the key components.