Association between Weather-Related Factors and Cardiac Arrest of Presumed Cardiac Etiology: A Prospective Observational Study Based on Out-of-Hospital Care Data.

Objective: The objective of this study was to determine the association between weather-related factors and out-of-hospital cardiac arrest (OHCA) of presumed cardiac etiology.

Methods: This was a prospective observational study performed in a prehospital setting. Data from the Emergency Medical Service in Hamburg (Germany) and data from the local weather station were evaluated over a 5-year period. Weather data (temperature, humidity, air pressure, wind speed) were obtained every minute and matched with the associated rescue mission data. Lowess-Regression analysis was performed to assess the relationship between the above-mentioned weather-related factors and OHCA of presumed cardiac etiology. Additionally, varying measuring-ranges were defined for each weather-related factor in order to compare them with each other with regard to the probability of occurrence of OHCA.

Results: During the observation period 1,558 OHCA with presumed cardiac etiology were registered (age: 67 ± 19 yrs; 62% male; hospital admission: 37%; survival to hospital discharge: 6.7%). Compared to moderate temperatures (5 - 25°C), probability of OHCA-occurrence increased significantly at temperatures above 25°C (p = 0.028) and below 5°C p = 0.011). Regarding air humidity, probability of OHCA-occurrence increased below a threshold-value of 75% compared to values above this cut-off (p = 0.006). Decreased probability was seen at moderate atmospheric pressure (1000 hPa - 1020 hPa), whereas increased probability was seen above 1020 hPa (p = 0.023) and below 1000 hPa (p = 0.035). Probability of OHCA-occurrence increased continuously with increasing wind speed (p < 0.001).

Conclusions: There are associations between several weather-related factors such as temperature, humidity, air pressure, and wind speed, and occurrence of OHCA of presumed cardiac etiology. Particularly dangerous seem to be cold weather, dry air and strong wind.