Optimum Temperature of Oxygen for Transpulmonary Hypothermia with Cooled Oxygen Inhalation: A Preliminary Study in a Rat Model.

Cooled oxygen inhalation was hypothesized as a novel hypothermia technique in a previous study. In the current study, we aimed to determine the optimal temperature of oxygen for this method. This is a prospective, randomized, controlled, examiner-blinded experimental study conducted with 45 healthy, adult, Wistar Hannover male rats. Rats were randomly divided into five groups; group 1: +4°C intubated group (n = 7), group 2: +4°C nonintubated group (n = 9), group 3: +8°C intubated group (n = 9), group 4: +8°C nonintubated group (n = 9), and group 5: control group (n = 9). The control group received only a standardized anesthesia protocol, and no hypothermia technique was administered. Cooled oxygen was administered in the four study groups until the rectal temperature reached 34°C. The target temperature was maintained between 32°C and 34°C for 2 hours. Then, hypothermia protocols were terminated and rats were rewarmed externally with a blanket. Main outcomes were the speed (°C/minute) of temperature decrease (S) and the time required to reach the target body temperature (T). All study groups had better results than the control group in T and S values (p < 0.001) for both parameters. Group 1 had a better T value than group 4 (p = 0.01), but no difference in S value (p = 0.223). Comparison of group 2 and group 4 showed that group 4 had better results in T and S (p = 0.04 and 0.001, respectively). No pathologic changes in histologic examination were observed in any group. Our study showed that the optimal temperature of oxygen for the cooled oxygen technique was +4°C through an intubation tube.