The provision of adequate and timely nutritional support for patients during recovery from illness, trauma or surgery is vital. The majority of patients will recover from fairly mild illness or elective surgical procedures without any issues, but patients presenting with more severe disease or trauma, or those undergoing more complex surgical procedures, are likely to have prolonged recoveries, and therefore nutrition will need to be addressed early during the hospitalisation period.

The appropriate absorption of essential nutrients and energy, along with fluids, is of primary importance during the first 14 days following trauma or the onset of severe illness, in order to ensure the effective functioning of the gastrointestinal and immune systems. Wherever possible the enteral route should be selected, vs. parenteral nutrition, as intraluminal nutrition will stimulate the gastrointestinal tract and help reduce the incidence of bacterial translocation.

The majority of critically ill patients will not have sufficient voluntary food intake to meet even minimal nutritional needs. When dealing with trauma patients, this situation is even more acute. All too often is it perceived that this lack of adequate food intake, whilst not desirable, will have no serious implications on the patient’s clinical outcome. For many patients, this will be the case; however, the more serious the illness, and the more metabolically stressed the patient is, the more likely that the patient’s nutritional status will deteriorate to an extent where it may suffer nutritionally related complications such as immunosuppression or poor wound healing. Whilst the more critical patients can be more challenging in terms of providing assisted feeding, the initial nutritional assessment will greatly help in the process of choosing the route of feeding a suitable diet, and the development of a plan for monitoring the patient during feeding so that problems or complications can be prevented or at least recognised early and quickly addressed. Individual patient’s nutritional assessment serves several purposes. It allows a determination of the patient’s nutritional status. This evaluation is based on the patient’s medical history and physical examination. Once an assessment of the patient’s nutritional status and food intake has been made, these factors along with the severity of the patient’s current illness and whether there are any pre-existing or current medical conditions can be taken into consideration when deciding upon whether some type of assisted feeding will be required for the patient, and how proactive the approach should be to initiating assisted feeding.

Calculating Calorie Requirements

The resting energy expenditure (RER) is the number of calories necessary for a non-stressed animal in the post-prandial state in a calm, thermoneutral environment. In other words, it is the amount of energy necessary for basic functions not including obtaining and digesting foodstuffs. Caloric goals are based on the resting energy requirements (RER), which are calculated by one of two formulas:

• Linear formula:
• RER in kcal/day=(30 x body weight in kg)+70
• Exponential formula:
• RER in kcal/day=70x(body weight in kg)^0.75

The patient should be fed approximately 25% to 30% of its caloric requirement on the first day of feeding, with subsequent gradual increases of 25% to 30% of its caloric requirement per day. We previously added an illness energy requirement (IER) to the RER. The IER is the energy requirement associated with illness, injury, infection and inflammation. The IER is an arbitrary number multiplied by the RER to combat the proposed increase in caloric requirements associated with various forms of illness. However, studies have found no increase in RER in numerous hospitalised patients, so this value is generally the value selected when calculating the patient’s nutritional requirements. At minimum daily weighing and reassessment of body condition scoring should be performed, and the patients RER should be increased or decreased dependent on these parameters.

For any patient that has undergone a period of prolonged starvation a longer period of food introduction should be considered, for example:

• Day 1—1/6 RER with electrolyte monitored q 4–8 h
• Day 2—2/6 RER with electrolyte monitoring q 4–8 h
• Day 3—3/6 RER with electrolyte monitoring q 4–8 h

Common side effects of starting feeding patients that have undergone prolonged periods of malnutrition may include nausea, vomiting, diarrhoea, changes in the electrolyte balance and if refeeding syndrome develops acute haemolytic anaemia in cats. It is important to note that if refeeding syndrome does develop we should not stop feeding these patients as we need to move them from a catabolic state to an anabolic state, however we may alter the amounts fed or the constitution of food administered. It is essential that we monitor any patient with an extended period of anorexia for refeeding syndrome. This can be signified by changes in patient demeanour, changes in patient’s electrolyte and acid-base balance and can be extremely dangerous if undetected.

Refeeding syndrome is characterised by changes in the patient’s electrolyte balance following reintroduction of nutritional support following a prolonged period of malnutrition/anorexia. Hypophosphataemia is the most significant disturbance of refeeding syndrome. “Refeeding syndrome” is a description of multiple metabolic disturbances that occur during and complicate the reinstatement of oral, enteral, or parenteral nutrition in malnourished or starved patients. In contrast to the human literature, which states that hypophosphataemia is frequently associated with reinstatement of alimentation in at-risk patients, only a handful of reports document the same occurrence in veterinary patients.

Creating the Nutritional Plan

One of the first stages in creating a nutritional plan is to ensure fluid deficits, e.g., hypovolaemia or dehydration, have been addressed, ensuring the patient is haemodynamically stable, along with correction of electrolyte or acid-base imbalances. Once these issues have been corrected then the nutritional plan can be instituted, which aims to achieve target levels of nutrient delivery within 48–72 hours. It is also essential that the nutritional plan is reassessed, which includes assessment of the patient toleration of feeding, regular assessment of bodyweight and body condition scoring, along with monitoring patients for complications associated with nutritional support, e.g., electrolyte disturbances, hyperglycaemia, vomiting, regurgitation, aspiration and infections related to the presence of a feeding tube.

In patients that do not have any contraindications to enteral feeding, e.g., vomiting, then the placement of a feeding tube should be considered early in the hospitalisation period, particularly if injuries are present which indicate the requirement of prolonged nutrition, e.g., jaw fractures.

An additional consideration, often overlooked, with trauma patients is the requirement for daily sedation or anaesthesia for procedures such as dressing changes, or wound debridement. It is not uncommon for these patients to be fasted for periods of 8–12 hours prior to having these procedures performed, and if this is not factored into a nutritional plan, these patients are at risk of malnourishment.

Choice of Feeding Tube

The best feeding tubes for prolonged use are made of polyurethane or silicone. For short-term feeding (<10 days), polyvinylchloride can be used. Silicone is softer and more flexible than other tubing materials and has a greater tendency to stretch and collapse. Polyurethane is stronger than silicone, which allows for thinner tube walls and a greater internal diameter, despite the same overall French size. Both silicone and polyurethane tubes do not disintegrate or become brittle in situ. The French (Fr) unit measures the outer lumen diameter of a tube; each unit is equal to 0.33 mm.

Naso-Oesophageal and Nasogastric Tubes

Naso-oesophageal tubes can be inserted using minimal equipment and standard techniques. Nasogastric tubes are inserted in a similar fashion as naso-oesophageal tubes, but they should be long enough to reach 7–10 cm past the last rib. Both types of tubes are useful for providing short-term nutritional support (usually <7 days). They can be used in animals with a functional oesophagus, stomach and intestines. Naso-oesophageal tubes are contraindicated in animals that are vomiting, comatose, lack a gag reflex or have respiratory diseases. Complications include epistaxis, intolerance of the insertion procedure and inadvertent removal by the animal. Because of the small internal diameter of these tubes, only liquid enteral diets can be used. Feeding may be delivered via a syringe pump as a continuous rate infusion or as bolus feedings. If a syringe pump is used, the delivery equipment must be completely changed every 24 hours to help prevent bacterial growth within the system. Clogging of these tubes is a common problem, due to the narrow bore, but the incidence can be decreased by using a syringe pump or flushing the tube well before and after bolus feedings. A column of water should always remain within the feeding tube in between feeds. If the tube becomes clogged, replacement may be necessary, or carbonated drinks may be used to remove the blockage. Diluting the liquid diet with water may also help prevent clogging, but this decreases the caloric concentration of the diet and increases the volume necessary to meet caloric needs. Maintenance of the tube should be carried out by cleaning the external nares gently using a warm, damp cotton wool ball. If tubes do become blocked, then carbonated drinks may be used to unclog the blockage. The tube can be removed at any point following placement. When removing the tubes, they are simply pulled out after the skin adhesive or sutures are removed.

Oesophagostomy Tubes

Oesophagostomy tubes are ideal for patients with head or jaw injuries, and are particularly useful in cats. The placement of oesophagostomy tubes requires general anaesthesia, with the animal intubated and in lateral recumbency. Complications include tube displacement from vomiting, removal or damage to the tube by the animal, and skin infection around the exit site. Depending on the insertion technique used and the size of the animal, an 8–20 Fr catheter may be used. The large bore of these catheters allows the feeding of a thicker recovery diet. These catheters are also easy for owners to use and maintain, as long as vomiting is not a problem. The tube may simply be pulled out after the sutures are removed. The exit hole is allowed to heal by second intention. A light bandage may be applied over the exit site for the first 12 hours.

Oesophagostomy Tube Removal

After every bolus feeding the tube will require a flush of water to rinse it of food debris. The tube exit site will require topical cleaning using sterile saline or chlorhexidine solution, the use of topical antimicrobials rather than antibiotic cream at the stoma site should be encouraged. A light bandage is applied and the entire dressing is changed every 6–12 hours. When the tube is no longer needed, it is simply removed by cutting the skin sutures and the tube is pulled out. The wound can be stapled or left to granulate. The exit site will granulate within a few days.

Gastrostomy Tubes

Gastrostomy tubes can be inserted blindly using specialised equipment, placed with the aid of a gastroscope (i.e., percutaneous endoscopic gastrostomy [PEG] tube), or be surgically inserted. These tubes can be placed in any animal that can withstand general anaesthesia. A minimum of 12 hours, preferably 24 hours, is needed for a temporary stoma to form before feeding can begin, and the feeding tube should be left in place a minimum of 7–10 days to allow a permanent stoma to form before removal. These tubes can be left in long term (1–6 months), often without replacement. Complications associated with PEG tubes include those that arise acutely during tube placement (e.g., splenic laceration, gastric haemorrhage, pneumoperitoneum) and those that are delayed (e.g., vomiting, aspiration pneumonia, tube removal, tube migration, peritonitis and infection around the stoma). Most animals are able to eat normally with gastrostomy tubes in place, and the tubes can easily be used as a source of additional nutritional supplementation until the animal is eating normally. For animals that are difficult to medicate or require long-term medications, many medicines can be given through the feeding tube at the clinician’s discretion. The major disadvantages of gastrostomy tubes are the need for general anaesthesia during insertion and the risk of peritonitis from inadvertent removal before a permanent stoma develops. For animals requiring feeding tubes over a long duration, the initial gastrotomy tube can be replaced with a low-profile silicone tube. The low-profile silicone tube can be placed through the external stoma site without an endoscope.

Jejunostomy Tubes

Jejunostomy tube feeding is indicated when the upper gastrointestinal tract must be rested or when decreased pancreatic stimulation is desirable. Jejunal tubes can be placed either surgically or threaded through a gastrostomy tube (transpyloric placement). Standard gastrojejunal tubes designed for humans are unreliable in dogs because of the frequent reflux of the jejunal portion of the tube back into the stomach so for this reason ‘weighted’ tubes should be selected. Common complications of jejunostomy tubes include osmotic diarrhoea and vomiting. It is recommended that the jejunal tube be left in place for 7–10 days to allow adhesions to form around the tube site, preventing leakage into the abdomen. Completely changing the delivery equipment every 24 hours helps to prevent bacterial growth within the system. Clogging is a common problem. Use of a syringe or intravenous pump and flushing the tube well every 4 hours may help to decrease the incidence of clogging. When removing the tube, it may simply be pulled out after the sutures are removed. The exit hole is allowed to heal by second intention. A light dressing should be applied for the first 12 hours following removal.

Procedure

Unplug the tube, then flush the tube with 5–10 ml sterile water, 10–20 ml warm water after each feed. Avoid cold water as this can induce vomiting and diarrhoea and the animal also has to expend energy to warm it. The tube should be flushed regularly even when not in use.

Feeding Via a Tube

It is important to start feeding any patient with a feeding tube in place gradually. The patient’s full RER should be introduced over 2–3 days. This allows the patient’s gastrointestinal tract and metabolism time to adjust to tube feeding. It is generally advised to start with one-third to half the calculated amount of food diluted with water and gradually increase the volume fed each day. A good protocol to use is 10 ml/kg every 2–3 hours on day 1, increasing gradually to 50 ml/kg 3–4 times per day. A minimum of three feeds should be given per day. Food must be iso-osmolar and given slowly (over 10–15 minutes) and warmed to approximately body temperature. During the early stages of introducing nutritional support, electrolyte monitoring should be carried out every 4–8 hours in order to detect the occurrence of refeeding syndrome.

How Long to Feed?

Patients should be tube fed until they voluntarily eating more than 85% of their calculated daily requirements. Tube feeding should be withdrawn gradually, just as it was introduced gradually, to allow the necessary gastrointestinal and metabolic adjustments. It is important to continue feeding a specialist diet at increased requirements for a period after the patient goes home. The following periods are currently used by the author:

• 2 weeks following uncomplicated major surgery
• 2–4 weeks after trauma
• 4–12 weeks after major trauma including head trauma
• Months in cases of chronic disease and neoplasia

Summary

Nutritional support in critical patients is all too often not considered a priority, but careful consideration needs to be given to the individual patient’s nutritional status on presentation, the injuries the patient has sustained, any alterations in metabolic condition, requirement for periods of fasting to allow procedures to be performed during the hospitalisation period, and the provision of continued nutrition once the patient has been discharged from the hospital. Careful consideration of all these factors along with planning and execution of a nutritional plan can play a major role in the successful recovery of these patients.