At what level of unconsciousness is mild therapeutic hypothermia indicated for out-of-hospital cardiac arrest: a retrospective, historical cohort study

BACKGROUND Appropriate patient selection is very important when initiating mild therapeutic hypothermia (MTH) for patients following out-of-hospital cardiac arrest, and the extent of unconsciousness at implementation must be defined in such cases. However, there are no clear standards regarding the level of unconsciousness at which MTH would be beneficial. The effects of MTH in patients with different degrees of unconsciousness according to the motor response score of the Glasgow Coma Scale (GCS) were investigated. METHODS The subjects consisted of witnessed non-traumatic adult out-of-hospital cardiac arrest patients admitted to our institute from April 2002 to August 2011. The patients were divided into six groups according to the GCS motor response score: 1 (GCS M1), 2 (GCS M2), 3 (GCS M3), 4 (GCS M4), 5 (GCS M5), and 6 (GCS M6). The neurological outcome was evaluated at 30 days after hospital admission using the Cerebral Performance Category. Chi-squared Automatic Interaction Detection (CHAID) analysis was performed to estimate the threshold GCS M level where therapeutic hypothermia is indicated. Odds ratios were then calculated by multiple logistic-regression analysis using factors including GCS M5-6 and MTH. RESULTS A total of 289 patients were enrolled in this study. CHAID analysis demonstrated two points of significant increase in percentage of good recovery at 30 days after admission, dividing the GCS M categories into three groups. Patients classified with a GCS motor response score of 5 or higher had the highest percentage of good recovery. The odds ratio for good recovery (CPC1-2) was 2.901 (95 % CI 1.460-5.763, P = 0.002) for MTH, and that for GCS M5-6 was 159.835 (95 % CI 33.592-760.513, P < 0.001). CONCLUSIONS MTH may be unnecessary in patients with a GCS motor response score of 5 or higher. Consequently, because there are post cardiac arrest patients with a GCS motor response score of 4 or lower who benefit from MTH, MTH may be limited to patients with a GCS motor response score of 4 or lower.