Active_comparator: S-ketamine

S-ketamine is given as a continuous infusion started at a dose of 2.0 mg/kg/hour. The infusion rate will be re-evaluated after 24 hours, where (1) the infusion will be stopped if 24 hours ensue without SDs, (2) maintained at 2.0 mg/kg/hour if the 24-hour incidence of SDs decreases below the rate of the previous 24 hours but SD is not totally abolished, or (3) increased to 3.0 mg/kg/hour if the incidence of SD is at or above the rate of the previous 24 hours. If the infusion rate has been increased to 3.0 mg/kg/hour, the rate will be returned to 2.0 mg/kg/hour if 24 consecutive hours of ECoG show no SD.

Placebo_comparator: Isotonic saline

Isotonic saline is given as placebo. It will be given as a continuous infusion started at a dose corresponding to a dose of S-ketamine of 2.0 mg/kg/hour, and follow the criteria for increasing/decreasing infusion rates as S-ketamine. The infusion rate is read from a table listing different infusion rates (ml/hour) based on participant weight and if the treatment tier corresponds to a S-ketamine dose of 2 or 3 mg/kg/hour.