BackgroundThe World Health Organization (WHO) Surgical Safety Checklist is used globally to ensure patient safety during surgery. Two years after its implementation in the University Hospital Basel's operating rooms, adherence to the protocol was evaluated.MethodsThis mixed method observational study took place in the surgical department of the University Hospital of Basel, Switzerland from April to August 2017. Data collection was via individual structured interviews with selected OR team members regarding checklist adherence and on-site non-participant observations of Team Time Out and Team Sign Out sequences in the OR. Data were subjected to thematic analysis and descriptive statistics compiled.ResultsComprehensive local expert interviews indicated that individual, procedural and contextual variables influenced the application of the checklist. Facilitating factors included well-informed specialists who advocated the use of the Checklist, as well as teams focused on the checklist's intended process and on its content. In contrast, factors such as staff insecurity, a generally negative attitude towards the checklist, a lack of teamwork, and hesitance to complete the checklist, hindered its implementation.The checklist's application was evaluated in 104 on-site observations comprising of 72 Team Time Out (TTO) and 32 Team Sign Out (TSO) sections. Adherence to the protocol ranged between 96 and 100% in TTO and 22% in TSO respectively. Lack of implementation of the TSO was mainly due to the absence of one of the key OR team members, who were busy with other tasks or no longer present in the operating room.ConclusionThe study illustrates factors, which foster and hinder consistent application of the WHO surgical safety checklist namely individual, procedural and contextual. It also demonstrates that the TTO was consistently and correctly applied, while the unavailability of key OR team members at sign-out time was the most common reason for omission or incomplete use of the TSO.