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PEER REVIEWED 68 FLUID THERAPY Colloids Colloid solutions contain large molecules (>10,000 Da) and tend to remain in the intravascular space longer than crystalloids. 3,4 The most commonly used colloid solutions in veterinary medicine contain hydroxyethyl starch (HES). 8 HES solutions are thought to be most effective in treating hypovolemia because the colloid should theoretically remain in the intravascular space, although some extravasation does occur. The half-life of various colloids depends on their molecular properties. As mentioned above, the lack of absorption at the venules means that administration of a colloid does not necessarily "pull" interstitial water into the intravascular space but opposes filtration out of the intravascular space. 2 The use of HES has been under debate—the risk for acute kidney injury (AKI) and increased mortality in humans has resulted in a "black box" warning from the Food and Drug Administration. 8,9 A retrospective study evaluating the occurrence of AKI and death in dogs receiving HES showed an increased risk for both; however, this study evaluated a 10% HES solution, which is thought to be associated with increased risk for AKI compared with 6% solutions. 10 Other potential adverse effects of HES include coagulopathy, pruritus, reticuloendothelial dysfunction, proinflammatory effects, volume overload, hepatopathy, and anaphylaxis. 2,4 The incidence of AKI and increased mortality in humans has been associated with longer infusion times and higher volumes than are used in most veterinary patients, 4 and further research is needed in animal patient populations to determine the risk-to-benefit ratio. HES is still used in our institution, although with somewhat more caution than previously. Other colloids include fresh or fresh frozen plasma, canine albumin, and human serum albumin. Plasma provides albumin and coagulation factors. Because the concentration of albumin present is similar to that in plasma, large volumes must be administered to have an oncotic effect. Approximately 40 to 50 mL/kg must be administered to raise the serum albumin by 1 g/dL. 1,4 Although the administration of an albumin solution would be preferable, species-specific albumin is expensive and is only intermittently available. 1,4 Concentrated human serum albumin can be administered to dogs for the treatment of hypoalbuminemia, but because it is not completely homologous with canine albumin, there is potential for an immediate or delayed hypersensitivity reaction, which can result in death. 1,4 Immediate hypersensitivity reactions are more common in healthy patients. Although immediate hypersensitivity reactions are rare in critically ill patients that receive human serum albumin, delayed hypersensitivity is observed as a serious complication in this population. DETERMINING A FLUID RATE When deciding if fluid therapy is appropriate for a patient, a few basic questions should be asked before determining a fluid therapy plan ( BOX 1 ). These questions can be answered based on assessment of the patient for hypovolemia and dehydration (see Determining Fluid Deficits). Once the patient's volume status and hydration needs have been determined, a fluid therapy plan can be developed. Fluid Therapy for Shock Patients The goal of fluid therapy in patients with hypovolemic and distributive shock is to rapidly restore effective circulating volume and improve BOX 1 Questions to Ask When Formulating a Fluid Plan Is the patient hypovolemic? Does it need a bolus? Is the patient dehydrated? What type of fluid should be given? What route? How much fluid should be given, and over what time period? When can the fluids be discontinued? Signs of overhydration include chemosis, serous nasal discharge, increased skin turgor, peripheral edema, ascites, pleural effusion, and pulmonary edema.