Myocardial Protective Effect of Hypothermia during Extracorporeal Circulation
-By Quantitative Measurement of Myocardial Oxygen Consumption-

Yukio Kuniyoshi, MD, PhD, Kageharu Koja, MD, PhD, Kazufumi Miyagi, MD, Mituyoshi Shimoji, MD, Tooru Uezu, MD, Satoshi Yamashiro, MD, PhD, Katuya Arakaki, MD, and Katuhito Mabuni, MD

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°C to 33.5°C. The patients were classified into three groups according to their rectal temperature: group I (n=10; rectal temperature: 20.3±1.80°C), group II (n=24; rectal temperature: 29.4±0.97°C), and group III (n=29; rectal temperature: 31.7±0.72°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 O2 ml/min/100 mm3 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+1.10×X2-0.02×X3 (Y, myocardial oxygen consumption; X, rectal temperature; R2=0.533; P<0.0001).
Conclusion: This study suggested that rectal temperature below 22.5°C is advantageous due to the resultant myocardial protection such hypothermia affords. (Ann Thorac Cardiovasc Surg 2003; 9: 155-162)

Key words: myocardial oxygen consumption, hypothermia, rectal temperature

From Second Department of Surgery, Faculty of Medicine, University of the Ryukyus, Okinawa, Japan

Received October 21, 2002; accepted for publication December 10, 2002
Address reprint requests to Yukio Kuniyoshi, MD, PhD: Second Department of Surgery, Faculty of Medicine, University of the Ryukyus, 207 Uehara, Nishihara-cho, Okinawa 903-0215, Japan.