Table 1.

Prehospital study variables

Dispatch and mission	These describe whether the mission includes search and rescue procedures which are known to increase overall prehospital times; type of dispatch (primary, on-scene crew request or secondary transfer); resources and level of resources on scene (BLS type vs ALS with different configurations); evacuation to hospital (air vs road).
Times	Key times for the prehospital phase: dispatch centre call-connect time (‘injury time’), HEMS team with patient time. Hospital arrival time (emergency department triage) will be used to determine the overall prehospital time.
Mechanism of injury (MOI)	Primary descriptor of the MOI. Road traffic accident (RTA), fall (< or >3 metres), assault (blunt, penetrating knife or gunshot), burns, explosion, crush, electrocution, hanging, animal bite, drowning. If RTA further descriptors are collected: means of transportation, protection (helmet, seat belt, etc), the role of the injured (passenger, pedestrian, etc) and estimated energy (high vs low). Finally, intentionality is recorded (accidental, self-harm, assault, unknown).
HEMS clinical examination	Primary clinical assessment including recording of airway, status, lowest SpO2 and arterial systolic/diastolic blood pressure or radial pulse status. Observed or presumed sites of bleeding (long bones, external compressible haemorrhage, penetrating injury, junctional haemorrhage, (sub)amputation, suspected pelvic fracture, haemothorax, hemoperitoneum. Neurological assessment (first recorded Glasgow Coma Scale, HEMS assessed Glasgow Coma Score and sensorimotor deficits). Ultrasound extended Focused Assessment with Sonography for Trauma (eFAST). If eFAST was performed and findings.
Prehospital cardiac arrest	Whether the patient was at any time in traumatic cardiac arrest and if a return of spontaneous circulation was obtained.
HEMS interventions	Interventions on airways, breathing and circulation including orotracheal intubation or supraglottic device use, use of tourniquets, haemostatic gauzes, pelvic binder, thoracostomies, REBOA or resuscitative thoracotomy and positioning of wide bore vascular access. In case of REBOA a subset of data will be collected (anatomical zone and duration of balloon inflation). Prehospital fluids and blood products. Total volume of prehospital crystalloid, colloid, units of prehospital packed red blood cells, grams of prehospital fibrinogen, volume of prehospital plasma and use of clotting factors (prothrombin complex concentrate). Other drugs. Induction agents, vasopressors, osmotic and hypertonic fluids, electrolytes, tranexamic acid.

ALS, Advanced Life Support; BLS, Basic Life Support; HEMS, Helicopter Emergency Medical Services; REBOA, Rescuscitative Endovascular Balloon Occlusion of the Aorta; SpO2, Peripheral Oxygen Saturation.