The proportion of patients transported was related to the reason for dispatch as well as to whether the emergency location was rather rural or urban. Particularly low transport rates are found for dispatch in association with the fire brigade and in connection with personal, automatic medical emergency response systems, as well as deployments in urban areas. In addition, longer on-scene times were identified for emergencies without patient transport compared to emergencies with subsequent transport.

A study by Infinger, Studnek et al. [19] showed that for an ambulance service with an average annual call volume of about 90,000 calls, for two patients per day, the correct resource would be a nurse consultation and not the dispatch of an ambulance. A retrospective cohort study from Finland by Hoikka, Silfvast et al. [18] concluded that in 13,354 ambulance calls, 41.7% of patients were not transported. However, the comparability with the present study is limited, as Hoikka, Silfvast et al. also included emergency physician deployments and therefore includes physician decisions not to transport. In our approach, we deliberately chose to leave out these medical decision, as our primary aim was to shed light on the dispatching decisions. Khorram-Manesh, Lennquist Montán et al. [21] demonstrated a discrepancy between the dispatch centre assessment and the actual priority, resulting in unnecessary hospital transports. Jensen, Carter et al. present a variety of evaluation methods of dispatching alternatives but conclude that comparability is difficult to establish due to the heterogeneity of the systems [20]. Discussing our findings with experts from a neighbouring dispatch centre, a professional association and quality assurance body revealed that both within Germany and in the neighbouring Austrian state of Tyrol, comparisons of ambulance dispatch without patient transport are complicated by differing legal bases and billing procedures. This indicates that, within Germany, there is a need for a common database for emergency service data (analogous to the German Resuscitation Register [15, 22] or the German Trauma Register DGU® [17, 35]) as a basis for future research. Even though there is a standardized dataset (minimaler Notfalldatensatz MIND), which contains a defined set of characteristics that are required for the documentation of prehospital emergency medical services [13, 25] and is authorised by the Deutsche Interdisziplinäre Vereinigung für Intensiv- und Notfallmedizin [German Interdisciplinary Association for Intensive Care and Emergency Medicine] (DIVI), it is apparently not implemented in a uniform manner.

Some emergencies without transport could essentially be non-emergency deployments. However, other reasons can also be responsible for why a patient is not taken to a treatment facility. Billittier, Moscati et al. already described in 1996 that, in addition to medical reasons for patients, the lack of alternative transport options also plays a role in the use of the emergency medical services [10]. Laukkanen et al. [23] researched that ambulance personnel are usually able to safely assess patients at the scene when there is no patient transport.

Low transport rates could possibly be due to the lack of adequate deployment of resources. In view of the very low transport rates for the reason “fire alarm system”, might be necessary to rethink whether it is appropriate to automatically dispatch ambulances when planning the fire alarm system. Dispatch due to personal emergency response system alarm buttons going off could involve cases where the personal emergency response system call centres do not have enough resources for their own transport service. This circumstance could be improved by the obligatory introduction of an on-call driving service for personal emergency response system call centres, because their own resources could take over these deployments instead of an ambulance.Another factor influencing the transport rate is the community type for the emergency site: in urban areas, the proportion of patients transported is lower than in rural areas, although there are more publicly accessible care services such as on-call practices or day clinics. This partial result of our study corresponds with other studies, such as the analysis of the performance level in the rescue service for the years 2016 and 2017 by the Federal Highway Research Institute (“BAST Study”). In this study, the distribution of false trips in rural regions is 2.2% and in urban regions 8.9% [30]. Possible reasons for this difference may be the different composition of the patient collective, e.g. with regard to socio-economic characteristics or the anonymity of big cities. The differences in the transport rate for the reason intoxication (per 1000 inhabitants: 57.9% without patient transport in the large city vs. 4.9% without patient transport in the rural community) could be indicative of this. Further explanations may be differing patient compliance and better accessibility of specialised clinics in urban areas. The influence of the disposition quality cannot be derived from the available data.

Transport by EMS without medical justification would be counter-intuitive to demand-oriented planning of health care, as outlined in the expert opinion of the expert council (Sachverständigenrates zur Begutachtung der Entwicklung im Gesundheitswesen) [27]. The longer duration of missions without transport might be explained by documentation efforts that are usually included in the on-scene time. This does not only inculde the documentation of the actual mission, which may not even be necessary in the case of incorrect deployments, but also the time spent on filling out transport refusal declarations.

In addition, the on-scene time does not indicate when the ambulance will be available again for further deployments—the transport interval (transport and transfer to a treatment facility) must be added to the PT group. However, very low on-scene times for non-transport missions with the reasons “fire alarm system” (9.02 min on-scene time) and “personal emergency response system active alarm” (10.55 min on-scene time) could indicate incorrect deployments for the ambulance service.

It should be questioned whether adding further low-threshold rescue vehicles to the system would make sense, since some patients may not need the full human and technical resource of an ambulance. In some regions of Germany, additions to the emergency medical services are emerging, such as the pilot project of community emergency paramedics in Oldenburg [2, 32] or rescue response vehicles in Schleswig–Holstein [26] and Bavaria [3], which can be alerted additively or as a substitute. With these response resources, patients who do not require transport capacity can be treated on site. In Rhineland and Hamburg, more than half of the emergency outpatients were treated in hospital in 2018. For 55 per cent of them, only the emergency flat rate was billed—an indication that the patients might have been better off in the statutory emergency service [1, 28].

For the interpretation of reason for deployment it must be considered that the documentation of a reason at dispatch might sometimes differ from the evaluation by the crew at scene. Also, in case a dispatcher made changes to the documentation in the course of the mission (e.g., because a triggered fire alarm system turned out to be a real fire event), the altered reason for deployment is analysed. Dispatchers also have some leeway when it comes to choosing the keyword: For example, when a dispatcher receives a message via a personal emergency response system call centre indicating a fall, he or she can decide whether to select choose “personal emergency response system active alarm” or “fall” as reason for dispatch.

The conclusions of this study are based on the data collection of integrated dispatch centres in Bavaria and thus Bavarian legislation and EMS system. A transfer to other settings with differing legal frameworks, EMS vehicles and documentation is difficult. In Bavaria, there are state-wide standardized user fees controlled by the Zentrale Abrechnungsstelle für den Rettungsdienst Bayern GmbH [Central Billing Office for the Bavarian Ambulance Service GmbH] (ZAST)) [6]. Due to this legal framework, there are no monetary incentives for the provider of EMS to transport patients to a care facility every time. This might be different under other framework conditions—nationally and internationally.

The present study does not give any indication as to why a patient was not transported. For this, further investigations are necessary, such as interviews with the ambulance staff or an analysis of the mission documentation.