In a first-of-its-kind study measuring the incidence of medication errors and adverse drug events during the period immediately before, during and right after a surgical procedure, researchers found the following: “[S]ome sort of mistake or adverse event occurred in every second operation.”
Source: Sue McGreevey, “Medication errors found in 1 out of 2 surgeries,” Harvard Gazette, October 25, 2015, discussing Karen C. Nanji et al., “Evaluation of Perioperative Medication Errors and Adverse Drug Events,” Anesthesiology (October 2015).