Chapter 48 Fluid Therapy
Pathophysiology
The need for fluid therapy in patients with GI disease arises from a number of pathophysiologic conditions. Because of malaise and anorexia, dogs and cats with GI disease may have fluid intake reduced to a level unable to offset sensible and insensible fluid losses. Patients with GI disease are also susceptible to increased fluid losses as a result of vomiting, diarrhea, and, in some cases, polyuric states. Lastly, some types of GI disease put patients at risk for fluid redistribution into third spaces, such as edema or effusion caused by hypoalbuminemia and peritonitis. These pathophysiologic processes are not mutually exclusive, and all three mechanisms could be operative in a given patient. This chapter is a broad overview of fluid therapy in patients with GI disease. Readers interested in more in-depth information regarding fluid therapy are referred to other references.1,2
Goals of Fluid Therapy
Some important goals of fluid therapy, and the general types of fluids commonly used to meet these goals, include the following:1,2
• Restoration and maintenance of circulating volume for tissue perfusion: crystalloid and colloidal fluids
• Correction of abnormalities of electrolytes, glucose: crystalloids, electrolyte, and glucose supplements
• Provision of oncotic support: synthetic and natural colloids
• Restoration of oxygen-carrying capacity: whole blood and blood products
• Provision of nutritional support: enteral and parenteral nutritional solutions
Drug Classifications
Crystalloids and colloids are the fluid types most commonly used in the treatment of dogs and cats with GI disease. Crystalloids are compositions of fluid and electrolytes in varying proportions that are divided generally into replacement fluids and maintenance fluids. Box 48-1 provides examples of each of these types of fluids. Replacement fluids, as the name suggests, are designed to replace water and electrolytes lost as a consequence of GI (or other) disease, and are characterized by higher concentrations of sodium than maintenance fluids, which have proportionally more water than replacement solutions. Colloids can be synthetic or natural. Box 48-1 also outlines examples of synthetic and natural colloids.
