We describe formative evaluations of a new software tool which aggregates and displays data about Intensive Care Unit patients. T3TM, which stands for Tracking, Trajectory, and Trigger, not only integrates the data being collected from a variety of devices, but also uses these data to assess the patient’s current state of tissue oxygen perfusion. We performed three different evaluation methods to generate recommendations on ways to improve the usability and utility of this software. First, we organized expert reviews, adapting a proven method of conducting a heuristic evaluation of a medical device so it requires less time for clinical experts to participate, and showed that it produces valuable results. Next we conducted contextual inquiry to help understand how differences among pediatric hospitals’ Cardiac Intensive Care Units including equipment, room layout, staff training, policies, and nursing workflows can impact adoption of physiological data aggregation software. Our approach, which is consistent with user centered design best practices, emphasizes understanding potential interactions between existing equipment and new technology. Finally, we describe how we plan to use simulation both to train nurses who work in different hospitals, with different equipment, different policies and different cultures and to capture additional usability feedback.