This open-label randomized controlled clinical trial (human clinical evidence) investigated whether methylene blue could reduce early postoperative cognitive dysfunction (POCD) in elderly patients undergoing major non-cardiac surgery. The study found that methylene blue treatment reduced the incidence of early POCD in this patient population compared to control. This represents direct clinical evidence from a human trial, though the open-label design (where participants and researchers knew treatment assignment) represents a moderate strength of evidence compared to blinded trials.