Normothermic versus hypothermic cardiopulmonary bypass: do changes in coagulation differ?

The differences between hypothermic and normothermic cardiopulmonary bypass (CPB) on platelet function and endothelial-related coagulation (eg, the thrombomodulin/protein C/protein S system) should be investigated.

According to a randomized sequence, 30 patients undergoing aortocoronary bypass grafting underwent either hypothermic (rectal temperature, 27 degrees C to 28 degrees C, n = 15) or normothermic CPB (rectal temperature, more than 35 degrees C, n = 15). Arterial blood samples were taken after induction of anesthesia (baseline values), before, during, and immediately after CPB, 5 hours after CPB, and on the morning of the first postoperative day. Circulating thrombomodulin, (free) protein S, protein C, and thrombin/antithrombin III complex were measured from these samples. Platelet function was assessed by aggregometry (turbidometric technique) induced by adenosine diphosphate (2 mumol/L), collagen (4 micrograms/L), and epinephrine (25 mumol/L).

Hypothermic patients showed a significantly higher blood loss and need for homologous blood than the normothermic patients. Thrombomodulin plasma level increased more in the hypothermic (from 28 +/- 5 ng/mL to 60 +/- 10 ng/mL) than in the normothermic group (from 28 +/- 7 ng/mL to 41 ng/mL); p < 0.05). Both protein C and (free) protein S were reduced significantly in the hypothermic (protein C, from 88% +/- 25% to 60% +/- 11%; protein S, from 71% +/- 10% to 40% +/- 8%) than in the normothermic patients. Platelet aggregation was significantly more decreased in the hypothermic (adenosine diphosphate, maximum decrease by -43% relative to baseline) than in the normothermic patients (adenosine diphosphate, maximum decrease by -22% relative to baseline). In the hypothermic CPB group, platelet aggregation had recovered incompletely, whereas in the normothermic patients platelet aggregation even slightly exceeded baseline values.

Hypothermic CPB resulted in more pronounced alterations of platelet aggregation and endothelial-related coagulation than normothermic CPB. Plasma levels of soluble thrombomodulin were more increased in hypothermic than in normothermic CPB indicating more extensive endothelial damage or activation associated with hypothermic CPB.