The results of our study indicate a year-round demand for HHO-capable helicopters in the three mid-range mountain regions we evaluated. Most HHO missions were conducted in spring and summer in all three regions. Especially in the region of Freiburg, where skiing is a common leisure activity in the winter months, the results might be influenced by the COVID-19 pandemic and the associated protective measures, which included a ban on the public operation of ski lifts in the winter of 2021. The accumulation of HHO missions on weekends reflects a solid connection to recreational activities such as hiking, climbing, mountain biking, and paragliding.

The disparity in the first-on-scene rate and the duration from alert to the arrival of the hoist helicopter must be seen in the context of the specific deployment areas and dispatching practices of each air rescue base. While the Freiburg air rescue base is frequently nearer to the HHO mission locations, the marginal difference in travel distances is insignificant compared to the helicopters' airspeed. It, therefore, does not account for the varying arrival times. Different alerting strategies are more likely to play a role in the hoist helicopter being the first rescue resource to arrive at the scene more frequently in missions around Freiburg. In Freiburg, the alarm for an HHO operation can be raised by the local emergency dispatch center primarily based on the information from the emergency call, such as geographical references matching with predefined regions where HHO is highly likely to be the only or fastest way to conduct a rescue operation. The HHO alarm can be activated without requiring other rescue services, such as the mountain rescue service, to be present on-site to request the HHO helicopter as a secondary measure. This also explains the lower rate of HHO requests fulfilled without HHO being conducted around the Bautzen air rescue base. The operational tactics in cooperation with the RSH of the mountain rescue service are essentially determined by the operational requirements. In most operations in the Freiburg area, which occur in wooded areas with no risk of falling, an emergency doctor can move around safely without being secured by the RSH. In these cases, the EP can be hoisted to the scene as the primary response to shorten the response time. If an RSH is necessary, it can be picked up and brought in secondarily to support the emergency physician. The deployment tactics must be adapted in steep or rocky terrain, where emergency physicians risk falling if improperly belayed. Deploying the RSH on scene, either primarily or together with the emergency physician, to ensure the on-scene safety of the mission has to be preferred in these situations.

For all three observed air rescue bases, HHO missions are rare, representing only 1.6% to 3.9% of the overall mission spectrum. This means crew members may go weeks or months without participating in an HHO mission. Due to this rarity, crew members must undergo continuous training to ensure safety and competence in HHO-related procedures. To supplement real flight training and enhance the frequency of training, indoor high-fidelity simulations are conducted by multiple operators and were also part of the annual training of the crews of this study [9, 10]. How each crew member can achieve the mandatory currency for HHO missions and increase individual proficiency should be part of further discussions.

In addition to the technical HHO-specific skills of all crew members, our results suggest that further requirements and competencies have to be addressed in crew training. It is not a standard task for EPs to provide care for patients, some of whom are seriously injured, without having assistance personnel in challenging environment and without protection from the weather with time being a relevant factor for patients’ outcome. Unlike EPs in ambulance or even helicopter service, who have access to the patient and can intervene any time during transport to the hospital, EPs involved in HHO-mission have to take into account that access to the patient and possibilities to intervene are limited during the hoist process. In addition, the EP must learn to assess the terrain and the corresponding dangers for him and his patient, as well as master rudimentary mountaineering safety techniques. The RSHs usually have no medical education and are unfamiliar with assisting medical interventions. However, in the HHO missions, they not only have to cover their main task of providing safety for patients and EPs on the scene but also of assisting the EP in live-saving interventions ahead of the hoist operation. An additional module of medical education and skill training in medical procedures assistance for the RSH crew members would address this issue.

Our data show that the majority of HHO missions are related to injured patients. While in our analysis, 79% of the HHO missions were trauma-related, the reference data of the physician-staffed ambulance service is only 20% [11]. Our findings are similar to those of a retrospective analysis of the HHO mission spectrum of two alpine-dominated air rescue bases [12]. Whereas air rescue bases in alpine terrain have a relevant amount of HHO-missions caused by uninjured or unharmed people, which ranges from 23% for daytime and 48% for nighttime HHO-missions, these missions were not relevant in our mid-mountain ranges collective [7, 12]. The cumulative proportion of patients with NACA score ≥ 4 in our cohort shows that a relevant part of the patients’ spectrum is severely harmed and needs EP treatment on scene. The number might even be higher as it is well known that EPs frequently underscore their patients, compared to an objective modified scoring system [13]. The frequencies of airway management (5% vs. 2%) and intravenous access (79% vs. 62%) in our cohort were higher compared to the reference data of the SQRBW for overall EP-staffed missions [11]. These findings and the high number of severely injured or otherwise harmed patients in our cohort underline the need for experienced and highly trained emergency physicians in the context of HHO, which has also shown to be beneficial in severe trauma patients [14].

Our study has limitations inherent in a retrospective analysis of routine documentation. As a detailed hoist protocol was not part of the routine documentation during the observation period, interesting aspects of HHO, such as the number of hoist cycles, incidence of airside patient loading, used hoist equipment like rescue bags, etc., have not been documented. To address this issue, the documentation module of HHO missions has been completely revised in 2022 and will undergo further revisions to cover the needs of further chart reviews. The comparability between the three air rescue bases is difficult in some aspects of this analysis. First, the characteristics of the three low mountain ranges and the corresponding mission spectrum do not entirely match. While in Freiburg, there are many operations in wooded and, therefore, difficult-to-access terrain, in Nuremberg and Bautzen, there are many steep rocky formations with injuries related to climbing sports. Secondarily, the Nuremberg air rescue base was limited in its HHO capabilities due to the operation of another type of helicopter, which did not allow airside patient loading. In 2023, the operator of the air rescue base in Nuremberg deployed an Airbus H145 analogous to the bases in Freiburg and Bautzen to lift these operational restrictions.