Therapeutic hypothermia (TH) is thought to be due to the downregulation of free 
radical production, although the details of this process remain unclear. Here, 
we investigate changes in oxidative stress and endogenous biological antioxidant 
potential during TH in patients with post-cardiac arrest syndrome (PCAS). 
Nineteen PCAS patients were enrolled in the study. Brain temperature was 
decreased to the target temperature of 33°C, and it was maintained for 24 h. 
Patients were rewarmed slowly (0.1°C/h, <1°C/day). The generation of reactive 
oxygen metabolites (ROMs) was evaluated in plasma samples by d-ROM test. Plasma 
antioxidant capacity was measured by the biological antioxidant potential (BAP) 
test. Levels of d-ROMs and BAP levels during the hypothermic stage (33°C) were 
suppressed significantly compared with pre-TH induction levels (P < 0.05), while 
both d-ROM and BAP levels increased with rewarming (33-36°C) and were correlated 
with brain temperature. Clinical monitoring of oxidative stress and antioxidant 
potential is useful for evaluating the redox state of patients undergoing TH 
after PCAS. Additional therapy to support the antioxidant potential in the 
rewarming stage following TH may reduce some of the observed side effects 
associated with the use of TH.