Impact of icing weather conditions on the patients in helicopter emergency medical service: a prospective study from Northern Finland.

Background: A high number of denied or cancelled HEMS missions are caused by poor weather conditions especially during winter season. Furthermore, many helicopter manufacturers have denied their helicopters to be operated in known icing conditions. Icing is a widely known phenomenon in aviation, but there is a lack of evidence about its influence on HEMS operations and patients.

Methods: A prospective observational study of HEMS missions in Northern Finland was conducted over a 1-year period in 2017. A patient was included in the study when the use of helicopter was denied or cancelled due to icing weather conditions. Patients were categorised into two groups based on whether definitive treatment was delayed or not according to previously defined end-points.

Results: During the study period the Finnish northernmost HEMS unit received 1940 missions. A total of 391 missions (20%) could not be operated by helicopter because of poor weather conditions. In 142 of these missions (36%) icing was one of the limiting weather factors. The year-round incidence of icing was 7.3/100 missions. A total of 57 patients were included in the analysis. Icing weather conditions, resulting in denied helicopter flights, caused a delay in definitive treatment for 21 patients (37%). Definitive treatment was more often delayed in trauma and internal medicine patients than in neurological patients. Nevertheless, the patients whose definitive treatment was delayed were located closer to the hospital. The estimated time that would have been saved by helicopter transport was more than 60 min for 10 patients with delayed treatment.

Conclusions: In this study the incidence of icing weather conditions was substantial compared to all HEMS missions in year 2017. The delay in definitive treatment was accentuated among trauma and internal medicine patients. During the 1-year study period many patients whose definitive treatment was delayed would have had a notable (> 60 min) time saved by helicopter transport. A helicopter equipped with an adequate ice protection system for the weather conditions in Northern Finland would have shortened the delay in patients' definitive treatment significantly.