Synthetic Colloids

In dogs, indications for colloid use include hypovolemic or distributive shock and hypoalbuminemia/decreased oncotic pressure. Tetrastarch is a third-generation hydroxyethyl starch with a smaller molecular weight and lower degree of molar substitution, and, thus, more rapid elimination and lack of accumulation as compared with other hydroxyethyl starches. Reports posit a possible lesser impact of tetrastarch on coagulation as well. 

This randomized, placebo-controlled, blinded study aimed to compare the effects of an isotonic crystalloid and a synthetic colloid on coagulation in healthy dogs and in dogs with systemic inflammation. A secondary goal was to determine the correlation between thromboelastography (TEG) variables and traditional coagulation tests. 

Healthy beagles (n = 16) were randomized into 2 fluid resuscitation groups: 40 mL/kg IV of either 0.9% NaCl or tetrastarch. Each dog was subjected to 2 treatment phases 2 weeks apart: placebo vs lipopolysaccharide to mimic systemic inflammation, followed by fluid resuscitation as assigned. Blood samples at 0, 1, 2, 4, and 24 hours were analyzed for coagulation and TEG variables. All dogs had similar increases in prothrombin time and activated clotting time. Compared with saline administration, tetrastarch resulted in prolonged aPTT, hypocoagulable and hyperfibrinolytic TEG variables, and significantly decreased platelet count and von Willebrand factor antigen in both healthy (placebo) and systemically inflamed dogs; all resolved within 4 hours. The traditional coagulation tests had weak correlations with TEG values. 

Results indicated that tetrastarch induced a transient hypocoagulable and hyperfibrinolytic state. However, most coagulation variables were within reference ranges, which makes the clinical significance uncertain. 

This important study tried to answer the controversial question about using synthetic colloids in critically ill dogs and cats. In 2013, the FDA issued a boxed warning on using synthetic colloids in human patients because consistent data highlighted an increased risk for mortality, acute kidney injury, and excessive bleeding. There has been little evidence evaluating the effects of synthetic colloids in veterinary patients, and thus there are no concrete guidelines for veterinarians. 

Although results indicate that tetrastarch resulted in transient hypocoagulability in dogs, most coagulation parameters remained within normal reference range with no reported evidence of clinical bleeding. However, this study was performed in healthy dogs. It is difficult to extrapolate the results to critically ill dogs, and clinical implications of use of synthetic colloids in critically ill dogs remain uncertain. 

Until more research is published to evaluate the short- and long-term consequences of synthetic colloids in dogs and cats, veterinarians should thoughtfully consider their use, especially in critically ill patients or those with renal disease and coagulopathies.—Adesola Odunayo, DVM, MS, DACVECC