Weather information

The weather data were provided by the IDAweb data base of the federal office of Meteorology and Climatology MeteoSwiss (13). We obtained data from a weather station situated approximately 500 m east from our hospital, which is a good representative of our catchment area of the north-eastern part of Switzerland [roughly 12,000 km² (14)]. The required information was the day mean value of atmospheric temperature, humidity and pressure for every day between January 1^st 2006 and December 31^st 2016. Additionally, we calculated temperature humidity and atmospheric pressure difference from one day to another by subtracting the value of the actual from the value of the previous day. This method was chosen by our professional statistician to be statistically appropriate in order to answer our question. All events of AAAD were then analyzed in correlation with the obtained daily weather data including atmospheric temperature, humidity and air pressure (constant, rising and lowering compared to the day before and after) within the entire cohort and in patients with or without hypertension separately. Furthermore, we analyzed if atmospheric temperature, air pressure, humidity had an impact on preoperative neurological impairment and postoperative mortality.