INTRODUCTION

PN is provided by the IV route. The intraosseous route can also be used for very small patients such as neonatal dogs and cats. Parenteral delivery is used when nutritional support is indicated for a patient but the enteral route is not feasible. Most commonly this happens because per os feeding is contraindicated, as with a patient experiencing nausea and vomiting or a patient unable to guard its airway and thereby at risk of aspirating stomach contents. PN is also indicated in patients in need of nutritional support who are experiencing gastrointestinal malassimilation and are unable to absorb adequate nutrients by the enteral route.

Although enteral nutrition has many advantages over the parenteral route (see Chapter 13, Enteral Nutrition), in patients for whom enteral nutrition is contraindicated or insufficient, PN can be life sustaining. This technique of assisted feeding has been used successfully in many species, including humans, dogs, cats, horses, cattle, birds, and various exotic species.^1-4

TECHNICAL REQUIREMENTS

Parenteral nutritional support may not be feasible in every veterinary practice, but the associated technology and equipment is becoming increasingly accessible and affordable for many small animal hospitals. Three basic requirements must be met in order to provide parenteral nutritional support to a patient. First, it must be possible to obtain and maintain appropriate vascular access aseptically. Second, 24-hour nursing care must be available, along with the ability to do at least basic point-of-care serum chemistry evaluation. And third, there must be the means and the expertise to formulate the PN prescription and compound the nutrient admixture.

NUTRITIONAL ASSESSMENT

The task of evaluating a patient for nutritional support has been covered in detail in Chapter 13, Enteral Nutrition. Additional considerations for candidates for PN include assessing vascular access, fluid tolerance, and preexisting conditions that may affect the patient’s nutrient tolerance or predispose it to metabolic complications.

Ideally PN should be delivered via a dedicated central line; however, central venous access may be unobtainable or contraindicated. For example, central catheter placement via a jugular vein is contraindicated in patients with head trauma or other conditions predisposing to increased intracranial pressure, those at risk of thromboembolic disease (e.g., protein-losing nephropathy or enteropathy, disseminated intravascular coagulation [DIC], hyperadrenocorticism, or those receiving high-dose glucocorticoids), or patients with severe coagulopathies. Fortunately, central vascular access can still be obtained in most patients by using a peripherally inserted central venous catheter (PICC).

Patients should be evaluated for their ability to tolerate the additional fluids that they will receive from the PN admixture. This will not be a problem for most patients; however, animals experiencing heart failure or oliguria will be at risk of volume overload. For patients with reduced fluid tolerance it is especially important to have central venous access to allow the most concentrated nutrient solutions to be used for formulation of the PN admixture. It may be possible to reduce the volume of the other IV fluids that the patient is receiving to accommodate that of the PN. Even so, there will occasionally be patients for whom it will not be possible to meet nutritional goals with parenteral nutritional support due to fluid intolerance.

Metabolic complications of PN are common,^1,2 but most can be minimized, if not avoided, by evaluating each patient for predisposing conditions such as an impaired ability to metabolize a specific nutrient or eliminate its metabolites. Table 14-1 lists some of the more common metabolic complications seen with PN and the conditions that may predispose to them. By anticipating complications, the PN admixture can be formulated in such a way as to reduce the likelihood that they will occur and the magnitude of any problems that do ensue.

Table 14-1 Conditions Predisposing Patients Receiving PN to Metabolic Complications