Abstract 397: Hydrogen Inhalation in Combination With Hypothermic Temperature Control Improves Survival After Out-of-Hospital Cardiac Arrest

Abstract

Background: In a randomized trial, we demonstrated that hydrogen (H 2 ) inhalation improves the outcomes after cardiac arrest (CA). All patients underwent target temperature management (TTM) in this trial, but the selection of a target temperature between 32 and 36 °C varied per institutional protocol. This study aimed to investigate the interaction of H 2 and hypothermic TTM on survival after CA. Methods: This post-hoc analysis of a randomized controlled trial (HYBRID II Trial; jRCTs031180352) included comatose patients after cardiogenic out-of-hospital CA (OHCA). They received either 2% H 2 mixed oxygen (H 2 group) or oxygen alone (control group) for 18 hours under hypothermic TTM (<35°C) or normothermic TTM (35-36°C). A target temperature was reached quickly, maintained for 24 hours, and rewarmed over 48 hours. The survival rate was compared between the H 2 and control groups under hypothermic or normothermic TTM. Results: The analysis included 72 patients with outcome data (39 and 33 patients in the H 2 and control group, respectively). Hypothermic TTM was implemented in 25 (64%) and 24 (73%) patients in the H 2 and control group, respectively (P=0.46). Under hypothermic TTM, the 90-day survival rate was 88% (22/25) and 46% (11/24) in the H 2 and control group, respectively (P=0.01). In contrast, under normothermic TTM, 78% (7/9) and 79% (11/14) of patients survived 90 days in the H 2 and control group, respectively (P=0.93). The interaction between H 2 and hypothermic TTM was independently associated with 90-day survival in a multivariable logistic regression model (adjusted odds ratio 7.79 [95%CI: 1.46-41.6]), however, it was marginally significant in the Cox proportional hazards model (adjusted hazard ratio 0.33 [95%CI: 0.10-1.17]) after adjusting for confounding factors including age, sex, witness status, bystander CPR implementation, shockable rhythm, CA duration, and time from the return of spontaneous circulation to gas inhalation, respectively. Conclusions: H 2 in combination with hypothermic TTM improved 90-day survival after OHCA but not under normothermic TTM.