Vital sign documentation is an essential part of perioperative workflow. Health information technology can introduce complexity into all facets of documentation and burden clinicians with high cognitive load3-4. The Mayo Clinic enterprise is in the process of documenting current EHR-mediated workflow prior to a system-wide EHR conversion. We compared and evaluated three different vital sign documentation interfaces in pre-operative nursing assessments at three different Mayo Clinic sites. The interfaces differed in their modes of interaction, organization of patient information and cognitive support. Analyses revealed that accessing displays and the organization of interface elements are often unintuitive and inefficient, creating unnecessary complexities when interacting with the system. These differences surface through interface workflow models and interactive behavior measures for accessing, logging and reviewing patient information. Different designs differentially mediate task performance, which can ultimately mitigate errors for complex cognitive tasks, risking patient safety. Identifying barriers to interface usability and bottlenecks in EHR-mediated workflow can lead to system redesigns that minimize cognitive load while improving patient safety and efficiency.