While critically ill patients are often not regarded as in urgent need of nutritional support given their more pressing problems, the severity of their injuries, altered metabolic condition, and necessity of frequent fasting (repeat sedation/general anaesthesia), place these patients at high risk of becoming malnourished during their hospitalization. Identification of these patients and careful planning and execution of a nutrition plan can be key factors in the successful recovery of these patients.

Nutritional status in people is an important determinant of outcome following surgery, with studies showing a clear association between malnutrition and poor clinical outcome. We do not have similar studies in veterinary species and are, therefore, unsure of this association. That being said malnutrition imparts a similar metabolic effect in animals and it is fair to assume that nutritional support is equally as important. We then need to consider how soon and aggressively we should implement a nutritional plan.

Metabolic Changes Related to Illness and Disease

Animals requiring surgical interventions may be afflicted with serious conditions. The metabolic responses to illness or severe injury are complex and place these animals at high risk for malnutrition and its deleterious effects. These effects, which are likely to negatively impact overall survival, include alterations in energy and substrate metabolism, compromised immune function, and impaired wound healing. These effects are of particular interest in surgical patients where proper wound healing is of paramount importance.

While generalizations tend to oversimplify complex systems, the concept of “ebb/flow” offers a basic description of the metabolic response to critical illness or severe injury. According to this model, there is an initial hypometabolic response (“ebb phase”), followed by a period of a more prolonged course of hypermetabolism (“flow phase”). The ebb phase is usually a period of hemodynamic instability associated with decreased energy expenditure, hypothermia, mild protein catabolism, decreased cardiac output, and poor tissue perfusion. Without intervention, this may progress to a state of refractory or irreversible shock characterized by severe lactic acidosis, decreased tissue perfusion, multiple organ failure, and death. Nutritional intervention at this stage carries a greater risk of complications such as electrolyte abnormalities, which may result in further detrimental effects to some critically ill animals. Following successful resuscitation, patients enter the flow phase during which profound metabolic alterations occur. Increases in energy expenditure, glucose production, insulin and glucagon concentrations, cardiac output, and profound protein catabolism are the hallmarks of this response. Provision of nutritional support during this stage of illness can attenuate and sometimes reverse the detrimental effects of malnutrition and this forms the basis for peri-operative nutritional support. There is some controversy of the applicability of these models of metabolic responses with clinical patients and the ideal timing for initiation of nutritional support in animals has not been determined.

Nutritional Planning in the Trauma Patient

Trauma patients tend to present acutely and usually do not have other chronic morbidities. So, despite their injuries they have a normal nutritional status. However, as previously mentioned, traumatic injury will lead a stressed metabolic condition, whereby the inflammatory response will shift the body towards metabolizing protein rather than fat stores. So, what becomes a major decision point is whether a traumatized patient that requires surgery will also require a feeding tube to facilitate nutritional support. Part of this decision will largely depend on the severity and extent of injuries, and whether these injuries will impede the patient from eating adequately postoperatively. For example, a patient with severe facial trauma can be assumed to be at high risk of not eating sufficiently postoperatively. Therefore, placement of an oesophagostomy tube at the time of surgery may be quite useful. However, in a multi-trauma patient that has a prolonged surgery, should one extend the time under anaesthesia for placement of a feeding tube? In patients that are not particularly stable under anaesthesia, delaying the placement of a feeding tube is sensible. Since a cardiovascularly unstable patient will be unlikely be eating in the immediate postoperative period, the placement of a feeding tube could be delayed. How long? Unfortunately, the ideal period for commencing feeding in small animals is unclear but it is likely before the patient becomes catabolic.

Enteral Nutrition

The enteral route of nutritional support is usually the preferable route. Enteral nutrition is safer and less expensive than parenteral nutrition, and helps to maintain intestinal structure and function. Even with the use of feeding tubes, patients can easily be discharged for home-care with good owner compliance. The majority of complications with feeding tubes include tube occlusion and localized irritation at the tube exit site. More serious complications include infection at the exit site or rarely, complete tube dislodgment and peritonitis if the tube was a gastrostomy or jejunostomy tube. Complications can be avoided by using the appropriate tube, proper food selection, and preparation and careful monitoring.

Although the enteral route should be utilised if at all possible, there are contraindications to its use. Contraindications include persistent vomiting, severe malabsorptive conditions, and an inability to guard the airway. If the enteral route is chosen for nutritional support, the next step is selecting the type of feeding tube to be used. Feeding tubes commonly used in dogs and cats include naso-oesophageal, oesophagostomy, gastrostomy, and jejunostomy tubes. Once the desired feeding tube is placed, radiography or fluoroscopy should be used to confirm satisfactory tube placement.

Based on the type of feeding tube chosen and the disease process being treated, an appropriate diet should be selected. This will also depend upon the animal’s clinical parameters and laboratory results. The amount of food is then calculated and a specific feeding plan devised. Generally, feedings are administered every 4–6 hours and feeding tubes should be flushed with 5–10 mL of water after each feeding to minimise clogging of the tube. By the time of discharge, however, the number of feedings should be reduced to 3–4 times/day to facilitate owner compliance. Commercially-available veterinary liquid diets should be used for naso-oesophageal and jejunostomy tube feedings. Jejunostomy tubes are primarily for in-hospital use because they require administration of a liquid diet by continuous rate infusion and this technique also requires more vigilant monitoring. Oesophagostomy and gastrostomy tubes are generally larger (>12 Fr) and allow for more calorically-dense, blenderised diets to be administered. This decreases the volume of food necessary for each feeding. These tubes can be used for long-term enteral feeding. A volume of 5–10 mL/kg per individual feeding is generally well tolerated but this may vary with the individual patient. In patients that are generally healthy but cannot consume food orally, e.g., jaw fracture, larger volumes of food per feeding (15–20 mL/kg) may be tolerated. As enteral diets are mostly composed of water (most canned foods are already >75% water) the amounts of fluids administered parenterally should be adjusted accordingly to avoid volume overload. Prevention of premature removal of tubes can be accomplished by using an Elizabethan collar and by wrapping the tube securely. Care should be taken to avoid wrapping too tightly as this could lead to patient discomfort and even compromise proper ventilation.

Monitoring and Reassessment

Body weights should be monitored daily in patients receiving nutritional support. However, the clinician should take into account fluid shifts in evaluating changes in body weight. The use of the resting energy requirements (RER) as the patient’s caloric target is merely a starting point. The number of calories provided may need to be increased to keep up with the patient’s changing needs, typically by 25% if well tolerated. In patients unable to tolerate the prescribed amounts, the clinician should consider reducing amounts of enteral feedings or supplementing the nutritional plan with parenteral nutrition.

Possible complications of enteral nutrition include mechanical complications such as clogging of the tube or early tube removal. Metabolic complications include electrolyte disturbances, hyperglycaemia, volume overload, and gastrointestinal signs (e.g., vomiting, diarrhoea, cramping, bloating). In critically ill patients receiving enteral nutritional support, the clinician must also be vigilant for the development of aspiration pneumonia. Monitoring parameters for patients receiving enteral nutrition include body weight, serum electrolytes, tube patency, appearance of tube exit site, gastrointestinal signs (e.g., vomiting, regurgitation, diarrhoea), and signs of volume overload or pulmonary aspiration.

Summary

Adequate nutrition is still not being delivered in the majority of hospitalised patients and we need to make sure that we consider and implement nutritional support as required.

Notes kindly reproduced from Prof Dan Chan.

References

References are available on request.