Central and peripheral parenteral nutrition

Scott J. Campbell
BVSc (Hons), MACVSc, Dipl. ACVN
 

Margo J. Karriker
PharmD
 

Andrea J. Fascetti
VMD, PhD, Dipl. ACVIM, Dipl. ACVN
 

Introduction

The provision of appropriate enteral nutrition or parenteral nutrition (PN) to critically ill hospitalized animals is an important part of their supportive care. Studies show the benefit of timely provision of nutritional support to critically ill humans and animals, in order to prevent deterioration in immune function, and to improve wound healing and tissue synthesis (1, 2). Animals presented to veterinarians may already have been suffering from malnutrition for extended periods. This energy deficit could be further exacerbated by the increased metabolic demands of their disease conditions. PN is generally reserved as a bridging modality for those animals with conditions that preclude adequate enteral feeding (1, 3, 4, 5, 7). Many studies have shown equivalent or improved outcomes when using both parenteral and enteral modalities together or aggressive enteral support as an alternative to PN alone in critical care patients with conditions such as pancreatitis, hemorrhagic gastroenteritis or small bowel resection (4, 8, 9). It should be noted however that some animals will not tolerate enteral feeding and PN may be the only option available to provide nutritional support. Studies in healthy fasting dogs have shown that PN administered centrally or peripherally can improve nitrogen balance (10, 11). The use of PN involves four equally important steps:

• First is the assessment of an animal to ensure that it is a candidate for PN administration
• Second is the formulation or selection of a PN solution formula that is suitable for that individual animal
• Third is the physical compounding of the PN admixture • Last is the administration of the PN solution with appropriate monitoring and frequent reassessment

The selection of animals to receive PN is covered by Kathy Michels’ article on page 17 in this publication and will not be further examined here.

Formulation or selection of parenteral nutrition solutions

The formulation of a PN solution requires consideration of the caloric needs of the animal, the ingredients available for inclusion and the nutrient profile indicated for the medical conditions and metabolic state of the animal. Caloric needs at this hospital are calculated using the exponential formula for daily resting energy requirement (RER) in kilocalories per day; 70 (BW in kg). While some previous PN worksheets and published papers have suggested feeding at higher caloric intakes (using illness energy requirements, disease factors, etc.), we have found that feeding at RER (inclusive of calories from protein) in the short term is sufficient to attenuate significant weight loss in a majority of animals and is able to reduce many of the other adverse effects of malnutrition. The rate of solution administration can be increased above that required to provide calculated RER to address further weight loss if required, but hyperglycemia, hypertriglyceridemia and other adverse effects may occur more frequently (12). Table 1 lists ingredients commonly used in PN solutions. Generally PN solutions will contain an amino acid source, a fat source, a carbohydrate source, electrolytes (depending on the ion status of the animal) and B vitamins. Fat-soluble vitamins and other minerals are not generally added to the PN admixture, unless the animal has been without complete and balanced nutrition for an extended period. Lists of drugs compatible with PN admixtures are available in the medical literature (13). [...]