Myocardial protective effect of hypothermia during extracorporeal circulation -- by quantitative measurement of myocardial oxygen consumption -.

OBJECTIVE To evaluate the effect of systemic temperature on myocardial protection during extracorporeal circulation, we quantitatively evaluated the relationship between myocardial oxygen consumption and rectal temperature. MATERIALS AND METHODS Myocardial oxygen consumption during cardiac arrest was calculated via blood gas analysis of venous blood samples collected from the coronary sinus. The rectal temperatures of the patients during extracorporeal circulation ranged from 16.0 degrees C to 33.5 degrees C. The patients were classified into three groups according to their rectal temperature: group I (n=10; rectal temperature: 20.3+/-1.80 degrees C), group II (n=24; rectal temperature: 29.4+/-0.97 degrees C), and group III (n=29; rectal temperature: 31.7+/-0.72 degrees C). The myocardial oxygen consumption of each group was then compared. RESULTS The average of the myocardial oxygen consumption of all cases was 62.5+/-64.0 O(2) ml/min/100 mm(3) left ventricle volume, and the averages of the individual groups were 26.9+/-28.8 in group I, 72.2+/-71.8 in group II, and 69.3+/-62.6 in group III. There was a significant difference in the oxygen consumption between group I and the other two groups. There was a positive correlation between the rectal temperature and myocardial oxygen consumption, as reflected in the following formula: Y=-0.3 x X +1.10 x X(2)-0.02 x X(3) (Y, myocardial oxygen consumption; X, rectal temperature; R(2)=0.533; P<0.0001). CONCLUSION This study suggested that rectal temperature below 22.5 degrees C is advantageous due to the resultant myocardial protection such hypothermia affords.