From 2012 to 2020 DRF helicopters realized 179,003 patient transports. 92,773 (51,8%) were primary rescue missions of which 10,001 (10,8% of primary rescue, 5,6% of all transports) cases the main diagnosis was polytrauma, while 82,772 (89,2% of primary rescue, 46,2% of all transports) were due to other emergencies comprising medical, neurological, or single site traumatic injuries. 86,230 (48,2%) were secondary transfers from one hospital to another. An intermediate transport by ambulance from the landing site to the hospital occurred in 40,459 (22,6% of all transports) cases (Fig. 1).

Number of transports of a HEMS association during a nine-year period

Demographics and severity of illness or injury expressed via the National Advisory Committee for Aeronautics (NACA) score differed between the groups of emergency patients (primary rescue) versus retrieval patients (interhospital transport) and are depicted in Table 2 (Table 2). Two thirds of the patients were male with slightly more male patients among the emergency patients. Compared to patients of primary rescue missions with an average of 48.0 years, retrieval patients were markedly older with an average age of 58.0 years (Table 2).

Among emergency patients, traumatic single injury, intracerebral hemorrhage, other neurological emergencies like stroke and cardiovascular emergencies were the leading diagnoses. With regards to the severity of the emergency, 41% of these patients were assigned to NACA score 3, 25% to NACA 4 and 30% to NACA score of 5. Intubation was required in 16.4% of the emergency patients and ventilation in 17.5%. Catecholamines were applied on 6.8% with syringe infusion pump use in only 1.6%.

In interhospital transfer, main diagnoses included stroke, acute coronary syndrome, vascular emergencies like aortic dissections and neurosurgical pathologies such as intracranial bleeds and acute respiratory distress syndrome and sepsis. 51% of these patients were rated with an NACA score of 5. 23,5% of patients were intubated and 30,0% were dependent on a ventilator. 21,5% received catecholamine therapy and in 32,1% of the cases syringe infusion pumps were utilized (Table 2).

An intermediate ground transport by ambulance occurred in 20.6% of emergency patients and 24.7% of interhospital transfers.

Transfer times from the helicopter landing site to the emergency department were 6.3 and 9.2 min for primary rescue and interhospital transfer and prolonged to 8.78 and 13.5 min respectively when a ground intermediate transport took place (p < 0.001; d = 0.34 and 0.38).

Patient transport time without and with intermediate transport was 14.8 versus 15.8 min (p < 0.001, d = 0.1) in primary rescue and 23.5 versus 26.8 min (p < 0.001, d = 0.16) for interhospital transfer. Details for flight time and patient contact time are listed in Table 3 (Table 3). Linear regression analysis of selected determinants on patient transport time revealed a mean time difference of 3.91 min for mechanical ventilation of a patient (p < 0.001), 7.06 min for the use of SIPs (p < 0.001) and 2.73 min for an intermediate ambulance transfer (p < 0.001); in primary rescue missions, the difference was 1.69 min for ventilation, 4.52 for use of SIPs and 1.03 min for an intermediate transfer.

Mission time – defined from landing at the emergency site or the referring hospital until operational readiness – was 74.2 min versus 78.0 min (p < 0.001, d = 0.13) in primary rescue and 109.6 versus 120.2 min (p < 0.001, d = 0.21) for interhospital transfer cases.

Overall, complications were documented in 1,184 of 138,544 (0,9%) cases in the group without intermediate ambulance transport versus 441 of 40,459 (1,1%) cases in the intermediate transport group (p < 0.001; V = 0.01). Similarly, complication rates were 0.5%, and 0.6% (p = 0.051; V < 0.01) in primary rescue and 1.3% and 1.6% (p = 0.007; V < 0.01) in interhospital transfer. Complications were reported in the categories of medical treatment complication (airway issues, respiratory and hemodynamic complications, iatrogenic injuries), medical equipment failure or organizational issues.

When assessing the impact of ventilation, use of SIPs and intermediate ground transport on complication rates, the need for ventilation was associated with an odds ratio of 3.76 (3.41–4.15) and use of SIP with an OR of 3.20 (2.89–3.53) while intermediate ground transport resulted in an OR of 1.28 (1.15–1.43) (Fig. 2).

Odds ratio for complications over all mission types for mechanical ventilation, use of syringe infusion pumps and intermediate transport: odds ratio and confidence interval

Analysis of variance showed that helicopter model may account for differences in patient transport time (F(3,121859) = 4,287, p < 0.001, R2 = 0.119) but does not alter transfer time at the hospital site (F(3,120151) = 352, p < 0.001, R2 = 0.008) (Appendix 1, Supplementary Material 1). Besides, analysis of variance of neither daytime nor season showed significant results of an influence of intermediate transport on the respective times or complication rates. Similarly, an intermediate transport showed no significant effect on times in transports by means of an incubator or in transports of patients with a percutaneous heart or lung assist device. More detailed results in this regard as well as a subgroup analysis of primary rescue missions for polytraumatized patients versus all other emergencies are presented in the Appendix 2 (Tables 1 and 2, Supplementary Material 2).