User needs and technology availability drive the introduction of wireless sensing applications in clinical environments. While these applications have the potential to improve efficiency and quality of care, very little is known about their performance during day-to-day use at the hospital. In this work, we use data from a deployment of a 802.15.4-based wireless sensor network at the Emergency Room of the Johns Hopkins hospital to answer these questions. Specifically, over a period of ten days we deployed a system of wireless vital signs monitors that measure the heart rate and blood oxygen levels of Emergency Room patients. During this time we collected statistics about the network's RF links, the performance of its tree routing protocol, and its end-to-end reliability. We find that the hospital environment we tested has considerably higher radio noise levels across multiple frequency channels and more bursty links compared to other indoor environments. Nonetheless, the routing protocol we use finds high quality links and the end-to-end packet reception ratio is above 99.9%. Taken as a whole, these preliminary results suggest that despite the challenges that clinical environments pose, wireless medical sensing applications can perform well in these conditions.