The patients were perfused with a pump flow of 3 to 5 L/min and their core temperature was lowered to 24°C (in less than ten minutes) and maintained by cooling this perfusion blood in an ice bath (0 to 15°C). After completion of surgery, the patients were rewarmed in less than 60 minutes by heating the perfused blood to 42°C. Core temperature was measured as esophageal temperature. The temperature was also determined rectally and via the pulmonary artery catheter. All three temperatures were consistently within one degree in all patients.
Blood Sampling
Patients had a preanesthesia arterial blood sample collected 15 to 20 minutes after the placement of indwelling radial artery and pulmonary artery catheters (this sampling time point is labelled “preinduction”). A second sample was obtained 15 minutes after the induction of anesthesia, but before the onset of bypass (induction sample). Blood samples were drawn after the onset of bypass (bypass specimen), but before active cooling, and then during hypothermia, at core temperatures of 32°C, 28°C and 24°C. All intraoperative blood samples were drawn from the afferent pump catheter before the blood reached the oxygenator. Samples were obtained from the afferent bypass pump catheter during the rewarming of the patients at core temperatures of 25°C, 27°C> 29°C, 31°C, 33°C, 35°C, and 37°C. Additionally, arterial blood samples were obtained from the 11 patients three and four hours after surgery when their mean core temperatures (±SE) were 34.5±0.2°C and 35.9±0.1°C, respectively. Here

Blood samples collected for plasma measurements were placed into chilled, heparinized glass test tubes which were immediately-placed on wet ice. The blood was centrifuged within 30 minutes of collection and the plasma stored at — 70°C for subsequent catecholamine analysis. Blood samples collected for serum measurements were allowed to clot, then were centrifuged and the serum samples were stored at — 70°C and later analyzed for T3, FT5, T4, FT,, and ACE activity. Serum samples were also analyzed for albumin concentration before, during, and after bypass. The percentage of hemodilution measured in this manner was then used to calculate a corrected value for T3, Tt, NE, EPI, and ACE. Samples for catecholamine determinations were specially handled as previously reported.