Changes in anticoagulation in dogs assayed by three methods.

As a preliminary to a membrane oxygenator study, a study was made of clotting indices in dogs and their intercorrelation and relationship to human data. The most useful criterion for monitoring coagulation in experimental extracorporeal systems was sought. Linear regression and correlation analysis indicated that activated partial thromboplastin time (APTT) predicted whole blood clotting time with a correlation of 0.77 (p less than 0.01). Changes in the APTT with time after heparinization were similar to those previously reported in man, making the animal model an acceptable one for use in developing extracorporeal systems such as the membrane oxygenator. When blood activated recalcification time (BART), APTT, and whole blood clotting time (WBCT) assays were compared on the basis of applicability to studies of extracorporeal support, the APTT and the BART assays proved superior to the WBCT assay due to their reduced variability and increased speed of determination. The variability of the BART assay was the lowest, and its sensitivity was the same as the APTT assay. The principal drawback to the BART assay was not experienced in this study; that is, its dependence on adequate platelet levels which are unpredictable in extracorporeal systems.