Purpose: Previous studies have showed that hypothermia reduces the cerebral metabolic rate of oxygen. If cerebral regional saturation of oxygen (rSO2) accurately reflects the oxygen balance in the cerebrum, the value of rSO2 would decrease during the rewarming process. The objective of this study was to evaluate the change of rSO2 during rewarming in patients with accidental hypothermia.

Material and methods: This study was conducted at a single emergency and critical care center in Japan from October 2017 to March 2018. We included adult hypothermia patients aged ≥ 16 years. Hypothermia was defined as a core temperature of less than 32°C. After hospital arrival, patients were rewarmed at +1 to 2°C per hour, and rSO2 was prospectively monitored throughout rewarming with a TOS-OR device (FUJITA MEDICAL INSTRUMENTS CO., LTD., Tokyo, Japan). We did not use any anesthetics (sedatives or pain-killers) at all.

Result: We could measure serial changes in cerebral rSO2 in five patients with moderate to severe hypothermia. The mean age of the patients was 70.6 years, and the mean initial core temperature was 26.8°C. In all cases, rSO2 remained within almost normal range and did not change according to changes in body temperature. SaO2 and SpO2 did not change at all during rewarming phase.

Conclusion: Contrary to our expectations, body temperature (28–37°C) did not affect cerebral rSO2 during the rewarming process in the patients with hypothermia. Our data suggest that higher temperatures (34-36℃) such as those of mild therapeutic hypothermia may have less of an influence on rSO2.

7 - Cerebral regional oxygen saturation does not change depending on body temperature during the rewarming phase from accidental hypothermia