Awakening following cardiac arrest: Determined by the definitions used or the therapies delivered?

Aims: To investigate patterns of neurologic "awakening" in out-of-hospital cardiac arrest (OHCA) patients using different criteria for prognostication post-arrest. Methods: Data was collected on 194 OHCA survivors to hospital admission. Patients were assigned to one of two groups based on whether they received therapeutic hypothermia (TH). Three separate criteria were used to assess neurologic "awakening": motor-GCS = 6, total-GCS≥9, and CPC = 1 or 2. Demographics, arrest characteristics and intensive care events were compared using unpaired t-test, Chi-square or nonparametric Wilcoxon rank-sum test as appropriate. Primary outcome was the time from arrest to neurologic awakening. Results: Of 194 OHCA survivors, TH was implemented in 94 patients (48%). Compared to conventional care patients, hypothermia treated patients were more likely to be younger (58 vs. 69 years, p < 0.01),), and have a shockable arrest rhythm (27% vs. 10%, p < 0.01). Using the three criteria (m-GCS = 6, t-GCS ≥9 & CPC = 1 or 2), median time to awakening for patients in the hypothermia group versus the conventional therapy group were 6 [4,9] vs. 3 [2,5] days, 3 [3,5] vs. 2 [2,3] days, and 3 [3,6] vs. 2 [2,4] days respectively (all p < 0.01) and prognostication using these criteria on day 3 yielded discordant results about which patients achieved awakening. Conclusions: Patients undergoing therapeutic hypothermia achieve meaningful neurologic "awakening" beyond 72 h post-arrest. Use of different criteria for the assessment of neurologic "awakening" can yield different prognostication predictions which calls for standardization and validation of a single definition of "awakening" by the resuscitation community.