The EU revised Medical Device Directive introduces a major change in the CE marking of medical devices (MD) aiming at improving their safety. Manufacturers must now comply with an "ergonomics" essential requirement to prevent risks of use errors. This requirement is characterized by the integration of a usability engineering process in the MD design cycle to be documented in a usability engineering file. This study focuses on the first step of the usability engineering process, i.e. the analysis of the intended context of use of the MD, and shows the benefits of this analysis when performed early in the MD design cycle. Usability experts have conducted an analysis of the intended contexts of use for the extension of an existing device (analgesia monitor) in order to support manufacturer's design choices. Observations and interviews were carried out in two neonatology units (Maternity and Neonatology Intensive Care units) with a particular focus on pain management activities performed by physicians and nursery nurses. The results highlight irreducible differences between the two environments which led to identify different risks of use errors and specific ergonomics requirements. The results provided the manufacturer enough information to make informed decision about the extension of the device.