Following institutional ethics approvals the Head Injury Retrieval Trial (HIRT) (Clinicaltrials.gov NCT00112398) recruited patients in Sydney, Australia between May 2005 and March 2011. The trial was funded by Insurance Australia Group and the NSW Motor Accidents Authority. The HIRT system was able to rapidly identify trauma patients using web based access to the NSW Ambulance (NSWA) Computer Assisted Dispatch System (CAD). Patients were then randomised via a central computerised randomisation process, to either a standard paramedic Emergency Medical Service (EMS) response or the dispatch of a physician and paramedic team by helicopter; the ‘HIRT HEMS’ response. Details of both the trial methodology [5] and the case identification and dispatch system [6] have been reported elsewhere.

A physician response model existed within the recruiting catchment area prior to commencement of the trial. This system was tasked by the NSWA dispatch system to prehospital trauma cases by road or helicopter. However, historical data indicated that physician response was activated for less than 5% of severe head injuries. In December 2007, two and a half years after commencement of recruitment in HIRT, a proactive tasking system which mimicked components of the trial case identification system was implemented by NSWA to identify severe trauma cases for physician response referred to as the Rapid Launch Trauma Coordinator (RLTC). The adult case identification system for HIRT and the RLTC operated independently without knowledge of the others actions until physician teams were activated and had departed the operations bases. In many cases both systems responded a physician team to the same patient in parallel, producing a unique opportunity to directly compare the physician response models. The HIRT and RLTC dispatch systems worked collaboratively to identify paediatric cases, as age less than 16 years was an exclusion criteria from the trial. A comparison of the two systems in identifying severely injured children and the effect on the paediatric trauma system in Sydney has been previously reported [6].

The dispatch systems are depicted in Figure 1.

When both medical teams responded to a case, the first team to arrive on scene assumed responsibility for the patient. The other team was usually stood down by the central coordination system, although at times both teams arrived on scene particularly where there were multiple patients. The physician bases are seven nautical miles (nm) apart, both located in western Sydney. The HIRT HEMS responded to all cases by helicopter regardless of distance, and all physicians held specialist qualifications in Emergency Medicine, Anaesthesia or Intensive Care. The NSWA physician teams responded by road ambulance or helicopter depending on the distance from their operations base. NSWA physicians were either specialists of the same background as the HIRT physicians or advanced trainees.

Standard care by paramedics only was according to written protocols of the NSWA and included: cannulation and up to 1 Litre intravenous crystalloid infusion; ventilation via supraglottic airways and bag-valve-mask ventilation; intubation without neuromuscular blockade; needle chest decompression; midazolam for seizures or sedation; analgesia with methoxyflurane and morphine; and splinting and spinal immobilization. Interventions additional to standard care by either of the physician teams included: anaesthesia with neuromuscular blockade and induction agents such as Thiopentone or Ketamine; surgical airways; needle cricothyroidotomy; tube or open thoracostomy; administration of 7.5% saline or 20% mannitol; and administration of packed red blood cells. All patients were transported to the nearest Level 1 trauma centre. After arrival in the trauma centre all care was directed by the standard policies of that institution including procedures in the ED and transfer to CT scan.

Times data were collected from the NSWA CAD system, and the case sheets of the responding prehospital units. Time of departure from the ED was obtained from the patient’s hospital medical record, and the time of commencement of the CT scan was obtained from the CT scan film/file. Whether the patient was trapped at the scene and interventions both prehospital and in the receiving hospital ED which may have affected time intervals were abstracted from the prehospital treatment records of the responding teams and the patient’s hospital medical record as per the Human Research Ethics Approval for the HIRT. Seniority of the physician (specialist or trainee) in the two PS-HEMS models was also noted.

The time from FKS to NSWA physician team notified (tasking time) and the time from this notification for the team to depart base (mobilisation time) are also reported as separate items. These discrete time intervals were not available for the HIRT HEMS as the case identification and mobilisation processes partly overlapped.

The response model of the NSWA physician teams evolved over the time the study was recruiting. In May 2007 two previous services were combined into a single service operating from a new base with a new helicopter contractor which became known as the Greater Sydney Area HEMS (GSA HEMS). The RLTC was introduced in December 2007. Data for the NSWA physician response model are reported only after December 2007 when the model had reached its final configuration, the GSA HEMS.

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