Effects of hypothermia and hemodilution on oxygen metabolism and hemodynamics in patients recovering from coronary artery bypass operations

The coexistence of hypothermia and hemodilution in patients in the intensive care unit immediately postoperatively after coronary artery bypass graft operations presents concerns regarding the adequacy of hemodynamics and oxygen metabolism. We evaluated the hemodynamic status and oxyten metabolism during the postoperative recovery period in six patients with moderate hemodilution (hematocrit value 34% ± 3%) and in eight patients with marked hemodilution (hematocrit value 23% ± 2%). All patients were well sedated and paralyzed with pancuronium bromide during the study period, during which their body temperature was slowly returning toward normal. In both groups, cardiac index at 34°C was about 40% lower than at 37°C. This was associated with 50% higher systemic vascular resistance and 30% lower oxygen availability to tissue. Oxygen consumption, however, was proportionally lower (45%) and coronary perfusion pressure was higher (28%) at 34°C than at 37°C; thus neither mixed venous nor coronary sinus blood oxygen saturation was compromised under hypothermic conditions. Although the trends in hemodynamic changes were similar in both groups, cardiac indices in patients with marked hemodilution were higher than cardiac indices in those with moderate hemodilution at all temperatures. This observation indicates that the hemodilution-induced rise in cardiac index remains intact even under hypothermic conditions. Under the conditions we studied, hypothermia with or without hemodilution had no significant adverse effects on hemodynamics and oxygen metabolisms of the whole body or of the heart.