Influence of the temperature on the moment of awakening in patients treated with therapeutic hypothermia after cardiac arrest

Introduction: Target temperature management (TTM) has shown to reduce brain damage after an out-of-hospital cardiac arrest (CA), but the time to neurological recovery is not defined yet. We sought to determine the time these patients need to regain consciousness, as well as factors associated with a late post-arrest awakening.

Methods: We performed a retrospective analysis of patients cooled to 32-34°C during 24h after CA, who regained neurological responsiveness after rewarming. We measured the time until awakening, defined as obedience to verbal commands.

Results: We included 163 CA survivors (84.7% male, 60.2 years) who regained consciousness after TTM: target temperature was either 32°C (36.2%), 33°C (56.4%) or 34°C (6.7%). Mean time of awakening was 3.8 days. Thirty-four patients (20.9%) regained neurological responsiveness after 5 days after CA. All of them had been cooled to either 32°C (18 patients) or 33°C (16), and no patient cooled to 34°C awakened after day 5. A lower target temperature was associated with a later awakening (p<0.001). The time to advanced cardiopulmonary resuscitation (CPR) was shorter among the early awakers (p=0.04), but we found no other predictors of an earlier awakening.

Conclusions: A high proportion of CA survivors induced to TTM regained consciousness after 5 days, and cooling to a lower target temperature may influence on a late neurological recovery. Therefore, withdrawal of life supporting treatment should be delayed to more than 5 days in patients cooled to 33°C or less. Time to advanced CPR was found to be a predictor of early awakening.