Care of the surgical patient does not end when the procedure is finished. Postoperative care of surgical patients often determines the ultimate outcome; with critical patients, it may determine whether they survive. Postoperative care involves monitoring vital signs, normalizing homeostasis, controlling pain, and recognizing complications early. Early recognition of potentially catastrophic conditions facilitates treatment and ultimately recovery.

An important component of postoperative care is nutritional support of debilitated or anorexic patients. Malnutrition is defined as the progressive loss of lean body mass and adipose tissue because of inadequate intake of or increased demand for protein and calories. Possible consequences of protein-calorie malnutrition (PCM) are organ and muscle atrophy, impaired immunocompetence, ineffective wound healing, anemia, hypoproteinemia, diminished resistance to infection, and death. For these reasons, patients with PCM require nutrient supple-mentation during treatment of underlying disorders.

A variety of conditions can cause PCM, including starvation, anorexia, malabsorption syndromes, severe trauma, surgical stress, sepsis, large surface area burns, and various types of malignancies. Surgery, postoperative complications, and surgically induced anorexia also increase metabolic demand for protein and calories. PCM shows no age, sex, or breed predisposition; it is common in severely ill animals, with an incidence ranging from 25% to 65%.

Diagnosis of PCM is possible if three or more of the criteria listed in Box-1 are present. Physical examination may reveal poor hair coat, pressure sores or wounds that will not heal, tissue wasting, skeletal muscle atrophy, emaciation, or all of these. Additional physical findings vary depending on the cause of malnutrition. Thoracic and abdominal radiographs of malnourished patients generally are nonspecific. Imaging techniques occasionally reveal an underlying cause for the patient's hyporexia, anorexia, or emaciation, such as an intestinal obstruction, or an abdominal or thoracic mass. Biochemical changes with PCM may include hypoproteinemia, anemia, hypoglycemia, hyperglycemia, hyperlipidemia, or a combination of these. Other changes may be related to the specific underlying disease.

Box 1. Diagnosis of protein-calorie malnutrition*

 Weight loss of more than 10% normal body weight.

 Anorexia or hyporexia (i.e., suboptimal intake of nutrients) for more than 5 days or an expected decrease in nutrient intake of more than 5 days.

 Increased nutrient loss (i.e., through vomiting, diarrhea, severe wounds, or burns).

 Increased nutrient needs (i.e., due to trauma, surgery, infection, burns, or fever).

 History of chronic illness.

 Serum albumin concentration less than or equal to 2.5 g/dl.

*These are findings that suggest PCM. The more of these findings that are present, the more likely it is that PCM is present. However, not all of these will be found in a patient with PCM, and not every patient with one of these findings will have PCM.

Nutritional supplementation should not be limited to malnourished patients. Acutely ill patients with severe systemic disease (e.g., peritonitis) are unlikely to eat in the postoperative period. In these critical patients, inadequate food intake causes metabolic shifts towards catabolism of lean muscle tissue and other consequences leading towards an acute malnourished state, as described above. Similarly patients that are mechanically unable to eat (e.g., maxillary/mandibular fractures, oropharyngeal tumors) should also be evaluated for methods to provide adequate nutrition.

Hyperalimentation is the administration of adequate nutrients to malnourished patients or those at risk of malnutrition. Enteral hyperalimentation provides nutrients to a functional gastrointestinal tract by means of a nasoesophageal, pharyngostomy, esophagostomy, gastrostomy, or enterostomy tube. Parenteral hyperalimentation provides nutrients intravenously; total parenteral nutrition (TPN) provides all the animal's protein and caloric requirements and must be provided through a central vein, while partial parenteral nutrition (PPN) provides only part of an animal's nutritional needs and can be provided through either a central or peripheral vein.

Specific treatment depends on the patient's calculated energy needs, dietary formula chosen, and route of administration (i.e., enteral, parenteral, or partial parenteral). Basal energy requirement (BER) (also called resting energy requirement [RER]) is based on body weight. Traditionally, maintenance energy requirement (MER) is then determined by multiplying the BER by an arbitrary factor) to accommodate for the presumptive increase in metabolism associated with the severity of the clinical problem (i.e., cage rest, postsurgical stress, trauma, cancer, sepsis, or major burn). Recently, a more conservative approach of starting with BER is advocated to avoid overfeeding and subsequent complications. Such complications include hyperglycemia, gastrointestinal upset, hepatic dysfunction, and increased carbon dioxide production.

Diets For Enteral Use

The ideal enteral dietary formula should be well tolerated, easily digested and absorbed, contain essential nutrients, be readily available and inexpensive, have a long shelf life, and be easy to use. The most cost-effective, well-balanced diets for enteral administration are those blenderized from prescription pet food or homemade diets. Caloric density and protein content vary with the diet chosen. Examples of blenderized diets and their compositions are given in Table 1. Blenderized diets can be administered through tubes with a diameter of size 8 French (Fr) or larger; a commercially available liquid diet is recommended when feeding through smaller diameter tubes (e.g., 5 Fr).

Liquid diets should be isotonic (i.e., approximately 300 mOsm/L), have a caloric density of approximately 1 kcal/ml, include fiber at 1 to 1.5 g/100 kcal, and provide approximately 16% of total calories as protein (i.e., protein content of at least 4 g/100 kcal) and approximately 30% as fat. Liquid diets for enteral use are generally categorized as monomeric (elemental) or polymeric. Monomeric diets use small molecular weight compounds for nutrients such as crystalline amino acids as the protein source, glucose and oligosaccharides as the carbohydrate source, and medium- or long-chain triglycerides as the essential fatty acid source. These diets generally have twice the normal osmolality and can be used in patients with malabsorptive or inflammatory gastrointestinal disorders (e.g., short bowel syndrome, severe inflammatory bowel disease) but are expensive. A commonly used commercially available monomeric elemental diet is Vivonex® RTF.

Polymeric enteral diets contain complex large-molecular-weight proteins, carbohydrates, and fats. These diets approach isotonic osmolality, require normal gastrointestinal digestive processes, supply about 1 kcal/ml, and are more economical than monomeric diets. These diets include blenderized diets, commercially available partially hydrolyzed diets, and commercially available liquid diets. Commercial polymeric diets are available in a variety of osmolalities, caloric densities, and compositions. These diet formulas are indicated for malnourished patients with intact digestive and absorptive function or those suspected of having food allergies. These diets also should be used for patients that must be fed through small-diameter tubes, such as nasoesophageal, gastroduodenostomy, or enterostomy tubes. Polymeric liquid enteral diets have been shown to be effective for nutritional support in critically ill and injured animals.

Table 1. Blenderized diets for dogs and cats

From Hand M. Small Animal Clinical Nutrition. 5th ed. Mark Morris Associates; 2010.
* Predicted as fed energy density of blended mixture.

Diets for Total Parenteral Nutrition

Diets available for TPN should be customized to meet an animal's protein, carbohydrate, and fat requirements. A common composition is 8.5% amino acids with electrolytes (protein source), 10% to 20% lipids (fat source), and 50% dextrose (carbohydrate source). B-complex vitamins are added at 1 to 2 ml/L.

Diets for Partial Parenteral Nutrition

Diets for PPN are made with the same ingredients used for TPN except that 5% dextrose in water (D5W) is used instead of 50% dextrose (D50W). The use of D5W instead of D50W means fluid composition will be determined by patient size. Smaller patients generally have 25% of their calories come from D5W with 50% of calories obtained from 20% lipid emulsion to allow for smaller volumes of fluid to be administered each day; larger patients may be the reverse. Partial parenteral nutrition (PPN) tends to be much less expensive than TPN with overall fewer complications.

Oral feeding is preferable to parenteral nutrition if adequate nutrients can be consumed to meet protein and caloric requirements. Several techniques have been used successfully to encourage an animal to eat. If the owners can manage the patient at home, the likelihood of eating is higher in a familiar environment. Petting and vocal reassurance are also helpful, albeit time-consuming. Highly palatable foods or food coverings, such as gravy, may stimulate the appetite while warming foods increases aroma and palatability. Supplementing potassium (i.e., 0.5 to 1 mEq/kg per os), vitamin B complex (in maintenance fluids), and/or zinc may also increase appetite. Multiple pharmacologic appetite stimulants are available; recommended dosages are listed in Box 2. These drugs are rarely adequate for stimulating a severely anorexic animal to eat sufficiently, but they may stimulate partly anorexic patients to resume eating.

Box 2. Drugs used as appetite stimulants

 Cyproheptadine (Periactin)*

 Cats: 2 mg/cat PO q12hr

 Mirtazapine (Remeron)**

 Dogs: 1.875–3.75 mg PO q48–72hr

 Cats: 3.75–7.5 mg PO q24hr or 0.6 mg/kg/day

 Diazepam (Valium)

 Cats***: 0.2 mg/kg IV q24hr

 Oxazepam (Serax)

 Cats: 2.5 mg/cat PO q12–24hr

 Vitamin B₁₂ (Cobalamin)

 Dogs: 100 to 200 µg, IV, IM, or SC q24hr

 Cats: For inappetence: 50–100 µg/day PO, SC, IV, or IM For cobalamin deficiency:

 < 5 kg give 250 µg/cat IV, IM, or SC, once weekly

 ≥ 5 kg give 500 µg/cat IV, IM, or SC, once weekly

* Administer 1 hour before feeding.
** This drug may have dangerous interactions with other drugs, especially those that can cause a "serotonin storm" such as cytochrome P-450 inhibitors (ketoconazole, cimetidine, macrolides), furazolidone, monoamine oxidase inhibitors, amitriptyline, and warfarin.
*** Incidence of idiosyncratic hepatic necrosis with oral diazepam in the cat is very low.