To be precise, the anaesthesia is part of the masking procedure, the placebo is a saline injection that was administered the same way as the ketamine (in practice the ketamine was simply diluted in a saline dose that is then given to the patient).
Of course, getting all those anaesthesia drugs into you could mess up the body chemistry in all sorts of ways that make the ketamine not work, but it is still very surprising that the net effect of this big cocktail of substances is that you get basically the same outcome regardless of treatment method.
Of course, getting all those anaesthesia drugs into you could mess up the body chemistry in all sorts of ways that make the ketamine not work, but it is still very surprising that the net effect of this big cocktail of substances is that you get basically the same outcome regardless of treatment method.