Cardiopulmonary bypass and oxygen consumption: oxygen delivery and hemodynamics

Background. This study was undertaken to investigate the relations between whole body oxygen consumption (VO2), oxygen delivery (DO2), and hemodynamic variables during cardiopulmonary bypass. Methods. One hundred one patients were studied during cooling, hypothermia, and rewarming. Oxygen consumption, DO2, hemodynamics, and DO2crit were measured at these times. Results. There was a direct linear relation between DO2 and VO2 during all three times. No relation between VO2 and hemodynamics was detected during cooling; during hypothermia, an inverse linear relation with peripheral arterial resistance was found. Finally, during rewarming, there was a direct relation with pump flow rate, and an inverse relation with arterial pressure and arterial resistance. The same relations among the variables were found at delivery levels above or below DO2crit. Conclusions. During cardiopulmonary bypass there is a direct linear relation between DO2 and VO2; the relations with hemodynamic variables depend on the phases of cardiopulmonary bypass. This suggests that increasing delivery levels may recruit and perfuse more vascular beds, and higher delivery levels are advisable during perfusion. During rewarming and hypothermia, lower arterial resistances are also desirable to optimize VO2.