Sample Collection and Processing

Serum samples were obtained from indwelling arterial or venous catheters after induction of anesthesia and prior to first surgical incision (“pre-operative”). A portion of the sample was frozen at -20°C and shipped to Mayo Medical Laboratories for assessment of serum AP activity while the remaining serum was stored frozen at -70°C for batch analysis of AMP to adenosine conversion. A second serum sample was obtained from each subject during the rewarming phase of CPB with identical processing (“rewarming”). We limited sampling to the pre-bypass and rewarming periods in order to minimize the risk of post-operative anemia in this critically ill patient population.