metabolic demands, such as in pregnant, lactating and growing animals (foals), or in animals with pre‐existing metabolic diseases or severe illnesses (sepsis, trauma) resulting in catabolism. Obese, over‐conditioned animals, donkeys, ponies and lactating mares are at a particular risk of hyperlipidemia, and nutritional support should be instituted early to prevent this condition.
Complications associated with parenteral nutrition include catheter‐associated complications, metabolic aberrations such as hyperglycemia, hyperlipidemia, electrolyte abnormalities, protein intolerance and overfeeding [59, 60]. An additional aspect to consider is the detrimental effect on the gastrointestinal tract when oral feeding is withheld. Enterocytes need nutrients.
Catheter‐Associated Complications
See Chapter 3: Complications of Intravascular Injections and Catheterization.
Definition
Thrombophlebitis
Risk factors
Self‐made solutions carry a higher risk of bacterial contamination
Use of small veins for parenteral nutrition
Single lumen catheter used for all medication, fluid therapy and parenteral nutrition
Pathogenesis
Parenteral nutrition solutions are hyperosmolar and can therefore lead to an increased risk of thrombophlebitis, particularly when peripheral small veins are used. The nutrients in parenteral solution provide a breeding environment for bacteria, leading to an increased risk of catheter‐associated sepsis/toxemia.
Prevention
Self‐made solutions should be prepared aseptically under a lamellar flow hood under aseptic conditions. A sterile bag should be used and injection ports should be wiped with alcohol to reduce bacterial contamination. Dextrose and amino acids should be added first followed by lipids to avoid lipids coming out of emulsion. Once compounded the solutions should be refrigerated and used within 24 hours. Commercial solutions have a longer shelf‐life (~2 years) and can be kept in stock. They are also less likely to become contaminated but are more costly than self‐made solutions. Factors such as pH, sunlight and addition of other solution can affect the stability of the lipid emulsion. This can lead to lipid droplets coalescing; the large lipid droplets cannot be cleared and could lead to lipid embolization of small vessels.
Initially, recommendations were to use large central veins; however, due to the size of the jugular vein and its accessibility, this vein is commonly used and few complications have been reported in horses. The lumen of the catheter should be designated for parenteral nutrition only. If only one catheter can be placed, a double lumen catheter can be used to allow for concurrent administration of medication and fluid therapy. Bags and tubing should be changed every 24 hours to avoid contamination of bacteria. The bag and tubing should not be detached from the horse during the day. If the horse has to be walked, the tubing and bag should go with the horse.
Diagnosis and clinical signs
Clinical signs of thrombophlebitis are fever, heat and swelling around the catheter insertion or distal to the catheter insertion, distended jugular vein and reduced emptying or prolonged filling of the jugular vein. Inflammatory parameters in the blood such as leukocytes, serum amyloid A and fibrinogen are often elevated.
Treatment
Parenteral nutrition through the affected vein has to be discontinued and the catheter removed. The reader is referred to Chapter 3: Complications of Intravascular Injection and Catheterization, for treatment and expected outcome of thrombophlebitis.
Metabolic Aberrations
Definition
Inadequate or excessive energy provision
Abnormalities is glucose homeostasis
Hypoproteinemia
Electrolyte abnormalities
Complications associated with parenteral nutrition‐containing lipids include hyperlipidemia and hypertriglyceridemia [59, 61]
Risk factors
Animals with existing hyperlipidemia are at risk for worsening of the condition if lipid solutions are used
Animals with severe disease
Pathogenesis
Critically ill patients may have metabolic abnormalities and endocrine dysfunction resulting in glucose intolerance and hyperglycemia. Hyperglycemia is a common complication of parenteral nutrition, occurring in up to 65% of patients, depending on underlying disease [59, 62]. Animals with severe disease might not be able to hydrolyze lipids to the same extent as healthy animals due to a decrease in the activity of lipoprotein lipase and therefore are at risk of developing hyperlipemia.
Prevention
Energy requirements should be calculated according to size, age, condition and metabolic stress. Overfeeding is fraught with complications and costly. Maintenance requirements for an adult healthy horse standing in a stall are approx. 33–40 kcal/kg/24 h. It is unknown how disease states such as trauma, surgery or burn affect the caloric need. Providing between 25–65% of energy requirements has been shown to be optimal in humans. Restricted intake is associated with decreased inflammatory cytokines, improved metabolic profiles and better survival compared with increased amounts of calories [63]. The reader is referred to an excellent review for calculating and instituting caloric needs for parenteral nutrition [64].
Commercially available PN solutions are available with or without electrolytes. This should be taken into account when formulating a fluid plan and adjusting the rate of additional fluids given. Electrolytes including potassium, sodium, chloride, calcium, magnesium and phosphorus should be monitored every 24 hours to avoid complications. Administration of glucose and insulin can lead to decreased levels of serum potassium levels. This should be taken into account when formulating a fluid plan. The amount of fluid provided with PN should be factored into overall fluid amounts to prevent fluid overload. The reader is referred to an excellent review for further information on composition and preparation of self‐made PN solutions [65].
To avoid hyperglycemia, parenteral nutrition should be administered with a pump to allow for continuous support. All PN solutions contain large amounts of glucose, therefore care should be taken when starting PN therapy. The initial flow rate should be calculated to provide 25–30% of the calculated daily requirement per hour. Blood and urine glucose concentrations should be monitored frequently during the first 24 hours (every 4–6 h). If blood glucose is maintained between 4 and 10 mmol/L, and urine is negative for glucose, the rate of administration can be increased every 6–8 hours by 25%. If blood glucose levels rise and the renal threshold is reached (appearance of glucose in urine)
