Prolonged veno arterial extracorporeal bypass (50-80% of cardiac output) was evaluated in normal, unanesthetized sheep. The evaluation protocol included serial measurements of hemodynamics, pulmonary and renal function, serum enzymes to detect organ damage, and detailed studies of coagulation and platelets. Blood exposure surfaces were primarily polyvinyl chloride and silicone rubber. Gas interfaces were carefully excluded with the exception of four experiments utilizing bubble oxygenators. Heparin dose was titrated to maintain activated clotting to two to three times baseline. Characteristics of 48 hour uncomplicated extracorporeal circulation in 8 sheep included normal hemodynamics, mild respiratory alkolosis negligable hemolysis, slight gradual increase in heart, liver, and muscle enzymes. The most significant changes occurred in coagulation and platelets characterized by an initial reduction in coagulation factors with a continued reduction in platelet count and return to normal clotting factors during extracorporeal circulation. This is followed by a two times normal increase in platelets and fibrinogen following extracorporeal circulation.
The in vitro stability of porcine factor VIII (PF VIII) was evaluated when it was reconstituted with sterile water (PF VIIISW ) to ≈ 30 U PFVIII mL(-1) , as per the manufacturer's recommendations, and stored in plastic syringes at room temperature, with and without heparin and at four different dilutions. PF VIII was prepared antiseptically without laminar airflow and remained sterile at room temperature for 1 week. PF VIIISW retained at least 88% of baseline activity for 48 h and 74-86% for 72 h. Addition of heparin 1 unit mL(-1) solution resulted in a decrease in the stability of PF VIIISW to 72-74 % of baseline values by 24 h. Reconstituted PF VIIISW , further diluted with normal saline to 10-24 U PF VIII mL(-1) , retained 98% of baseline activity for 48 h and 84% of baseline for 72 h. PF VIII diluted to 6 U mL(-1) , however, retained 100% baseline activity for only 24 h, and declined to 71% and 64 % of baseline by 48 and 72 h, respectively. PF VIII reconstituted with normal saline, instead of sterile water, retained 90% or more of baseline activity for a minimum of 4 days. Once reconstituted, PF VIII appeared to be more stable at room temperature than when stored in the refrigerator. These in vitro stability studies confirm that PF VIII (30 U mL(-1) ) can be given effectively by prolonged continuous infusion, since it retains 88% baseline activity at room temperature in a plastic syringe for a minimum of 48 h, remains sterile and will maintain baseline PF VIII levels when further diluted with saline.
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