Clinical nutrition of the hospitalised animal

Nutrition is a key factor in the support of and recovery from functional disturbance. The power of appropriate nutrition and the impact of inappropriate nutrition is often underestimated. Poor or delayed nutrition can trigger a number of complications such as:

Slowed tissue healing due to insufficient intracellular nutrients
Compromise of normal function of body systems
Muscle wasting and weakness
Lowered energy levels resulting in reduced mobility, circulation and so recovery
Immunosuppression, increasing the risk of secondary bacterial infection and reliance on antimicrobial medication. This can have an added concern regarding antibiotic resistance and the potential development of a carrier status
Atrophy of intestinal mucosa
Intestinal bacterial relocation to the portal blood stream resulting in septicaemia

there are a number of additional points of universal relevance to be considered when providing for a patient's nutritional requirements

A structured approach to nutritional management should apply to all inpatients on admission. This will ensure that ant need for nutritional support will be recognised at the earliest opportunity and so enable prevention rather than treatment of nutritional deficiencies

Each patient requires a written feeding protocol which will ensure that it's identified nutritional requirements are communicated effectively across the practice team

All food given should be measured and its nature and quality recorded. Any food not eaten should then be re-measured and recorded in the patient notes

The patient should be weighed at regular intervals so that fluctuations may be monitored. where a patient's weight changes, allowances should be made for changes in hydration status and for changes in elimination before attributing the change to increases or decreases in body mass

Food and water should only be withheld for the essential minimum period required when preparing for sedation, anaesthesia or diagnostic procedures. This is generally 1 hour

Anorexia

An animal may become anorexic for a number of reasons. The patient may be unstable to eat due to interference with GI tract function or may be unwilling to eat due to nausea, stress due to their environment or food preferences

Withholding of food mat be appropriate in some cases and may be prescribed by the veterinary surgeon as part of a treatment protocol. In all other cases, steps should be taken to encourage the patient to feed voluntarily before resorting to artificial feeding such as:

Ensuring food is accessible to the recumbent or debilitated animal
Hand feeding: many patients do not eat due to fear or stress triggered by their surroundings. In many such cases time, attention and TLC are all a patient needs to encourage them to eat
Offering very smelly foods especially to cats whose principle food selection technique is smell
Warming food to body temperature
Seeking advice from owners regarding the patient's normal food preferences of daily diet
Some cats may be encouraged to eat if small amounts of food are smeared onto their paws stimulating them to groom themselves
Highly concentrated and digestible diets ensure maximum nutritional benefit from minimal intake
The general well-being of a patient that has not eaten for whatever reason may be improved by regularly wiping the mouth with damp cotton wool to remove excess saliva and any remaining vomit, moisten the mucous membranes and freshen the mouth
Medications such as anti-emetics, acid inhibitors or buffers and dietary supplements may aid reestablishment of normal digestive processes
Avoiding placing pressure on the abdomen when handling

Malnutrition refers to a state in which an animal has an improper nutritional balance. It may refer to over-nutrition, resulting in weight gain, dietary imbalance or vitamin/mineral toxicity, but most commonly refers to under-nutrition

Under-nutrition may occur for a number of reasons. It may be due to inadequate food intake due to owner neglect or ignorance, deliberate withholding of food for clinical or weight control reasons, an inability to eat due to illness or injury or anorexia. It may also be due to the inability to absorb ingested nutrients or the excessive loss of nutrients due to digestive, metabolic or other body system disturbances. the net result in either case is a lack of sufficient nutrition to maintain homeostasis

An animal may be malnourished or likely to become malnourished where one or more of the following apply:

There has been an acute loss of more than 5% body weight (excluding that attributable to fluid loss
Body condition score is below optimal
Muscle wasting or weakness is accompanied by hypoalbuminaemia (low serum albumin)
Oral intake has been or is predicted to be likely reduced for three days or more

The mammalian body's digestive and metabolic systems have adapted to compensate for periods of poor or low nutrition. During the first few days, the body will react to insufficient intake of nutrition by slowing metabolic rates and releasing glycogen stored in the liver. This will enable it to maintain circulating glucose levels without affecting lean body tissue. However, after a few days glycogen levels will be depleted. the body will then need to rely on fat reserves to provide energy to the cells. Most cells in the body can adapt to using fatty acids as their source of energy. However, such tissues as the brain, kidneys and erythrocytes are glucose dependent. The body therefore also needs to metabolise some protein into glucose to fulfil their needs, leading to reductions in body mass

Nutritional requirement calculations for the malnourished patient require inclusion of an element to allow for restoration of body mass and nutritional deficiencies. In the case of body mass, this is ordinarily achieved by calculating feeding requirements to the patient's ideal as opposed to its actual weight. Supplementation may also be required

Where an animal has been deprived of nutrition for whatever reason for more than 3 days, food must be reintroduced gradually to prevent re-feeding syndrome.
Re-feeding syndrome occurs for a number of reasons:

There is a sudden increase in the movement of glucose from the bloodstream into the tissues, taking potassium and phosphorus with it causing hypophosphatemia and hypokalemia. This can cause muscle weakness, neurological dysfunction or potentially fatal cardiac compromise
Tissues that had adjusted to utilising fatty acids as their principle source of energy have to revert to utilising glucose. This can cause fluid and electrolyte imbalances
A sudden increase in circulating insulin levels reduces sodium excretion through the kidneys. This can lead to water retention and extracellular fluid overload
Thiamine deficiency may occur due to increased utilisation as a result of high levels of carbohydrate metabolism. This can cause ataxia and coma
Re-feeding syndrome can be prevented by ensuring that where nutritional status has undergone severe compromise, whether acute or chronic the reintroduction should follow:
Reintroduce food in stages over 72 hours; 33% RER on day 1, 66% on day 2 and 100% on day 3
Provide high protein, high fat, low carbohydrate food. Gradually reintroduce normal carbohydrate levels from day 4
Support with parenteral thiamine supplementation
Repopulate enteral bacterial populations with probiotics

The post surgical patient

The metabolism of diseased animals is accelerated to provide the building blocks for healing and immune system function, many of which are highly glucose dependant. Such hypermetabolism will increase the animal's nutritional requirement and if this increase isn't met, any shortfall will be compensated for by utilisation of glycogen reserves, fat and lean tissue leading to muscle wasting and weakness. The degree of hypermetabolism will depend on the part of the body undergoing assault, with illness or injury to the brain, septicaemia and severe burns causing the greatest increases. However, even routine minor surgery is detected by the body as an injury and so will trigger an estimated 10% increase in metabolic rate. It is therefore essential that appropriately increased nutrition is provided for all post-surgical patients

Enteric Surgery: Following oesophageal or gastric surgery all food and water may be withheld for an initial period to allow wound healing to take place. This is supported by IVFT and parenteral or enteral nutrition administered caudal to the surgical site. Oral fluids are initially offered and if this is tolerated, food is slowly reintroduced. Food reintroduction should be over a period of 72 hours where the animal has not had any kind of nutrition for more than 3 days.
Where the animal has undergone intestinal surgery feeding should be reinstated immediately following recovery from anaesthesia to prevent gut stasis. This is usually well tolerated and as initial pre pyloric digestion has rendered the diet acceptable to the intestine

Illness or non-surgical injury: Animals with systemic illness or with injuries that do not require surgical intervention trigger the same increases in metabolic rate described for the surgical patient. Their increased nutritional requirements are therefore equally important.

Neoplasia: Tumours significantly increase glucose requirement and the first sign of illness may be weight loss as lean body mass is metabolised for glucose

Megaoesophagus: Even after surgery, this condition will require feeding from a raised platform to utilise gravity to aid passage of food to the distal oesophagus. Some texts suggest liquid or semi-solid food is given although others recommend a more textured diet. Coupage post feeding may also aid smooth movement of the food along the alimentary canal

Acute digestive upset: This is generally managed through 24-72 hour bowel rest supported with enteral or parenteral electrolyte management. A highly digestible bland diet is then gradually reintroduced and replaced by the patient's normal diet over 48 hours

GDV: Generally linked to excessive ingestion of air during or close to eating. It is therefore best prevented in susceptible dogs by taking the following steps:

Feeding smaller, more frequent meals to minimise associated air ingestion
Feeding a highly digestible meal to enable rapid stomach emptying
Feed away from other dogs to slow feeding habits
Prevent exercise 1 hour before and after feeding
Prevent excessive water consumption around feed times

Chronic Diarrhoea: Ordinarily caused by one of the following:

Interference with normal nutritional digestion or absorption. The resulting increased nutrient composition in the distal part of the intestinal tract has an osmotic effect drawing fluid back into the intestine changing the consistency of normal stools
Nutritional overload causing increased concentrations of nutrients in the distal parts of the intestines. This will have the same effect as compromised digestion or absorption
Enteric bacterial products may increase fluid secretion into the abdomen to 'flush them out'
Mucosal damage increasing intestinal permeability and allowing increased levels of fluid back into the intestine, often accompanied by proteins
Altered intestinal motility. This is usually initially slowed causing stagnation and bacterial proliferation. This leads to increased faecal volume which then stimulates hypermotility
Poor overall digestion causing increased faecal volume causing hypermotility
Diarrhoea is treated according to its underlying cause. Food may be withheld although this is not recommended for more than 24 hours as it may trigger atrophy of intestinal villa

Assisted Feeing

Where an animal is unable to eat normally has a dysfunction in a proximal selection of the digestive system assisted feeding may be indicated. It may be enteral or parenteral

Enteral Feeding

Syringe Feeding: Where tolerated feeding via an oral syringe may be the simplest method. Care must be taken to allow the patient to adopt a natural position and patience is required to ensure food is only ingested at a natural speed. Food is best syringed into the buccal pouch to avoid risk of aspiration pneumonia although this also enables the patient to spit out the food if they are reluctant. Smaller, more frequent meals are advised due to the stress associated with this method of feeding

Tube Feeding: Food may be delivered by a tube inserted into the oesophagus or stomach where a more cranial part of the digestive system is injured or obstructed. Tubes may follow a variety of routes (see notecards)

There are 3 principle gastrostomy tube insertion techniques;

A foley catheter may be surgically placed and sutured to the stomach wall via a laparotomy
A guide wire may be passed through the stomach wall and along the oesophagus to the mouth. A PEG tube is then attached to the wire, which is then drawn back into the stomach through the stomach wall
A wire is passed through the abdominal wall into the stomach. A series of dilators gradually increase the gastrostomy diameter until it is large enough for the PEG tube to be passed over the guide wire. Progress is monitored via an endoscope. The tube is held in place by a silicone button externally and an endogastric balloon

For all tube feeding, the following steps should be observed:

The tube opening should be plugged when not in use
Feeding may commence 6 hours post-surgical placement
Maintenance requirements should be introduced gradually over 2-3 days
Diets chosen should be highly concentrated to enable practical administration of the required quantities without stimulating vomiting. Most recovering animals require a high fat, high protein, low carbohydrate food
Diet consistency must pass easily along the tube. Liquidised food rarely breaks down sufficiently to achieve this. Therefore specialised convalescent feeds that are reconstituted from a powder or paste
Required quantities should be broken down into 4 meals given at natural feeding times
Avoid feeding at night, most companion animals would not normally eat during the night and digestion processes will interfere with normal rest patterns
Warm food to room temperature
Administer the meal over a 10 minute period to mimic normal food intake
Monitor the animal's reaction to the food - remember the stomach will not have had the normal messages that food is on its way and so feeding may initially trigger nausea or distress
The tube should be flushed before water before and after feeding to maintain patency and prevent food deposits that may attract bacterial invasion
The point of insertion of surgically implanted tubes should be cleaned and redressed daily and monitored for signs of infection

Total Parenteral Nutrition

Involve provision of all nutritional requirements intravenously. This method is only used as a last resort and is indicated when:

It is not possible to administer food orally due to injury or surgery
The patient's digestive system is not functioning
Total parenteral nutrition is delivered via an infusion pump linked to a central venous catheter placed in a central vein such as as the jugular. Rates of infusion vary but tend to be set to reflect normal variations in feeding patterns to minimise disruption of normal metabolic processes. TPN is uncommon in veterinary practice due to both cost and potential complications which inlcude
Bacterial infection linked with catheter insertion
increased rate of general infections due to hyperglycaemia
Liver failure due to hepatic lipidosis arising from metabolic variations where nutrition is introduced directly into the bloodstream