Table 1

Table of papers for HEMS meta-analysis (scene)

Author	Grade of evidence	Study population	Study design	Inclusion criteria	Sample size	Staffing	Intubation rate	Time at scene (min)	Time and/or distance of transfer	Analysis	Adjustments	Outcomes	Findings
TRISS-based analysis of HEMS alone
Bartolacci29	3	Westmead Hospital, Sydney Nurse and paramedic crew	Retrospective	Blunt trauma patients with ISS>14	77 HEMS 4 matched GMT controls per HEMS patient	HEMS — physician GMT— paramedic	HEMS —10% needed intubation on arrival to ED GMT — 37% needed intubation on arrival to ED	HEMS — 33 GMT — NS	HEMS — 18 min GMT— NS	TRISS based analysis of HEMS. (Direct mortality comparison of HEMS vs GMT)	GMT controls matched to ISS within five points	Mortality at 48 h	50% reduction in TRISS predicted mortality (p<0.001). 18 deaths predicted, nine actual deaths Adjusted W statistic of 12.18 (CI 5.3 to 19.1). (M stat=0.52) GMT vs HEMS mortality RR=1.43, CI 0.74 to 2.78
Baxt30	3	Multiple HEMS services (seven centres)	Retrospective	All blunt trauma patients	1273 HEMS	Seven HEMS services — four had physician, three had nurse or paramedic	NS	NS	NS	TRISS based analysis	Done at same time as MTOS collection for TRISS data, so no adjustment made	Mortality predischarge (time period not specified)	21% reduction in overall predicted mortality (p<0.001) OR TRISS vs HEMS=1.32 (CI 1.07 to 1.63)^*
Cameron31	3	Melbourne, Australia	Retrospective	All trauma patients.	254 HEMS	HEMS — paramedic	HEMS — 14% (58% of patients with GCS<8 intubated)	HEMS — 32 min	HEMS — 19 min/28 miles	TRISS based analysis	Only one group, so no need for control	Mortality (time not specified)	Predicted mortality 17%, actual mortality 14% (p>0.05) OR TRISS vs HEMS1.13 (95% CI 0.70 to 1.82)^*
Jacobs32	3	Connecticut, USA	Retrospective	All trauma patients. Scene trauma patients analysed as a subgroup	3620 HEMS	HEMS — nurse or paramedic	NS	NS	NS	TRISS based analysis	Nil	Mortality predischarge (time frame not specified)	13% reduction from predicted mortality with HEMS (p=0.004). If TS between 4 and 13 then 35% reduction in mortality OR TRISS vs HEMS=1.21 (CI 1.09 to 1.34)^*
Younge33	2	London, England	Prospective	Blunt trauma patients	632 HEMS	NS	NS	NS	NS	TRISS based analysis (UK MTOS as control group)	Low M stat (0.61) led authors to calculate an adjusted W stat	Additional survivors (time frame not specified)	W statistic=4.16±2.21 with HEMS (p value not specified)
Comparison of HEMS and GMT using TRISS-based analysis
Baxt34	3	University of California, San Diego	Retrospective	All blunt trauma patients	150 HEMS 150 GMT	HEMS — physician GMT — EMT or paramedic	NS GMT staff only trained to use oesophageal obturator airway	NS	HEMS — 24 min (136 cases in rural setting) GMT — 10 min (16 cases in rural setting)	TRISS based analysis	No further adjustments. Showed age, mechanism of injury and incidence of head injury were not statistically different	Mortality predischarge (time period not specified)	52% reduction in TRISS predicted mortality with HEMS (21 predicted deaths, 10 actual deaths, p<0.001), no change with GMT (15 predicted deaths, 19 actual deaths, p>0.05) OR GMT vs HEMS=3.07 (CI 1.43 to 6.60)^*
Biewener35	3	Dresden, Germany	Retrospective	Blunt trauma (ISS 16–67), alive on arrival to hospital, <75 years of age	140 HEMS 70 GMT	HEMS — physician GMT — physician	HEMS — 91% GMT — 75%	See right	Accident to arrival at ED: HEMS — 90 min GMT — 68 min	TRISS based analysis	Adjustment for time from incident to arrival at ED. Both had physicians onboard	30 day mortality	Adjusted OR GMT vs HEMS=1.06 (CI 0.43 to 2.64)
Buntman36	3	Johannesburg, South Africa	Retrospective	Trauma patients. Not clearly specified, but states it excluded ‘minor injuries’. Patients excluded if dead on arrival to trauma unit.	122 HEMS 306 GMT (BLS)	HEMS — NS GMT — any road transport to hospital, including civilian transport	NS	NS	NS	TRISS based analysis (used USA MTOS data)	Nil — TRISS study	Mortality predischarge (time not specified)	21.4% reduction in mortality with HEMS, p<0.05 (HEMS predicted 38.15 deaths, 39 actual deaths/GMT predicted 38.96 deaths, 51 actual deaths). OR GMT vs HEMS 1.47 (95% CI 0.94 to 2.29)^* (M stat=0.618 HEMS, 0.867 ground)
Phillips37	3	San Antonio, USA (Brookes Army Medical Center)	Retrospective	All trauma patients, paediatric and adult	105 HEMS 687 GMT	HEMS — nurse and paramedic GMT — paramedic	NS. Both intubation capable	NS	HEMS — 24 min GMT — 14 min	TRISS based analysis	Nil	Mortality (time frame not specified)	GMT predicted=39.11, actual=41 deaths HEMS predicted=16.44, actual=15 p value not specified OR GMT vs HEMS 1.14 (CI 0.64 to 2.05)^*
Schwartz38	3	Connecticut, USA	Retrospective	Blunt trauma patients	93 HEMS 33 GMT	HEMS—physician GMT—Paramedic	HEMS—42% GMT—3%	HEMS — 22 min GMT — 19 min	HEMS — 10 min GMT — 11 min	TRISS based analysis	Nil	Mortality (time frame not specified)	HEMS=2.23 SD better than national norm GMT=−2.69 SD worse than national norm Significant difference
Schwartz39	3	Connecticut, USA	Retrospective	Blunt trauma patients	68 HEMS 605 GMT	NS	NS	NS	NS	TRISS based analysis	Insufficient subgroup data to adjust mortality	Mortality predischarge (time frame not specified)	HEMS predicted mortality=19.7%, actual 14.8% GMT predicted mortality=2.7%, actual=3.8% (p value not specified) OR GMT vs HEMS=2.44 (CI 1.22 to 4.88)^*
Adjusted mortality comparison of HEMS and GMT
Braithwaite40	3	Pennsylvania, USA	Retrospective	All trauma patients — split into five categories	15938 HEMS 6473 GMT (ALS capable)	NS	NS	NS	NS	Adjusted mortality comparison	Controlled for age, sex, ISS, RTS hypotension, rural urban status	Survival	Five ISS categories: ISS 1–15 — no significant difference in survival ISS 16–30 — HEMS 2.1 times more likely to survive (p<0.05) ISS 31–45 — HEMS 2.4 times more likely to survive (p<0.05) ISS 46–60 — HEMS 2.6 times more likely to survive (p<0.05) ISS 61–75 — no significant difference in survival
Davis41	3	California, USA	Retrospective	Trauma patients with head AIS≥3	3017 HEMS 7295 GMT	HEMS — nurse + physician, nurse or paramedic GMT — paramedic	HEMS — 41% GMT — 14%	NS	NS	Adjusted mortality comparison	Age, sex, ISS, head AIS, injury mechanism, prehospital GCS, hypotension	Mortality (time frame not specified)	Adjusted OR GMT vs HEMS 1.9 (CI 1.6 to 2.25)
Frankema42	2	Rotterdam, Netherlands	Prospective	All trauma patients with ISS>15. Excluded if dead on arrival at scene, age<15, injuries invariably fatal (AIS-90 code 6)	107 attended by HEMS 239 attended solely by GMT	HEMS — physician GMT — paramedic	NS. Both intubation capable	HEMS — 31 min GMT — 23 min	HEMS — 13 min (by road) GMT — 13 min	Adjusted mortality comparison	Age, trauma mechanism, ISS score, vital scores, time of day	90 day survival	Overall adjusted survival OR HEMS vs GMT=2.2 (CI 0.92 to 5.9) Blunt trauma survival OR=2.8 (CI 1.07 to 7.52)
Oppe43	2	Rotterdam, Netherlands	Prospective	All trauma patients. Excluded patients dead before arrival at hospital	210 attended by HEMS 307 attended solely by GMT	NS	NS	NS	NS	Adjusted mortality comparison	Adjusted for RTS and ISS	Mortality (time-frame not specified)	Maximum mortality reduction of 17% with HEMS (extensive statistical analysis)
Ringburg44	3	Netherlands	Not specified	All trauma patients ≥15years	260 HEMS assistance (no patients transported to hospital by HEMS) 1197 GMT	HEMS — physician GMT — paramedic	NS (GMT team not intubation capable)	HEMS — 35.4 min GMT — 24.6 min	NS	Adjusted mortality comparison	Adjusted for on-scene RTS, ISS, age, mechanism of trauma, day/night time	Mortality within 1 month	Adjusted OR GMT vs HEMS=1.0 (95% CI 0.8 to 1.3)
Thomas45	3	Massachusetts, USA	Retrospective	Blunt trauma patients	1150 HEMS 10106 GMT	HEMS—physician or nurse GMT—Paramedic	NS. All HEMS intubation capable, 90% ground intubation capable	NS	NS	Adjusted mortality comparison	Controlled for age, ISS, prehospital level of care, receiving trauma centre	Mortality predischarge (time frame not specified)	OR GMT vs HEMS =1.61 (CI 2.22 to 1.16)
Direct mortality comparison of HEMS and GMT
Baxt46	3	California	Retrospective	Blunt head injury (GCS≤8)	104 HEMS 128 GMT	HEMS — physician GMT — Paramedic or EMT	HEMS — 100% GMT — oesophageal airway only	HEMS — 17 min GMT — 10 min	HEMS — 15 min GMT — 6 min	Direct mortality comparison	Showed no significant difference in GCS distribution, need for neurosurgery, or pathology	6 month mortality rate	40% GMT mortality 31% HEMS mortality (p<0.001) OR ground vs HEMS=1.49 (CI 0.86 to 2.57) ^*
Celli47	3	Italy	Retrospective	Blunt trauma head injury patients (GCS<8, but not brain dead and in coma for >6 h after admission)	20 HEMS 24 GMT	HEMS — nurse ± physician (distribution not stated) GMT—paramedic, police, firefighter or private	HEMS — 80% GMT — 10%	NS	NS	Direct mortality comparison	Showed no significant difference in age, GCS or associated injuries	6 month mortality	HEMS mortality=20% GMT mortality=54% (p=0.02) OR GMT vs HEMS 4.73 (95% CI 1.22 to 18.39) ^*
Cunningham48	3	North Carolina, USA	Retrospective	All trauma patients.	1346 HEMS 17144 GMT	NS	NS	HEMS — 24 min GMT — 13 min	HEMS — 33 min GMT — 17 min	Direct mortality comparison and adjusted comparison	ISS, trauma score, mortality RR, age, length of transfer	Mortality predischarge (time period not specified)	Overall non-significant improved survival in HEMS group. If ISS 21–30 and TS 5–8 then HEMS mortality 43.4%, GMT mortality 62.6% (p<0.05) If TS 9–12 then HEMS mortality 20%, GMT mortality 37.2% (p<0.05)
Di Bartolomeo49	2	Italy (North East)	Prospective	Blunt trauma cardiac arrest and ISS≥16	56 HEMS 73 GMT	HEMS — physician GMT — nurse	NS	NS	NS	Direct mortality comparison	Showed groups were similar for injury mechanism, gender and time to CPR, but did not allow for age differences, time to hospital and performance of on-scene CPR	Survival to discharge (time frame not specified)	3.6% survival with HEMS, 0% survival with GMT (not significant). Also showed 16% ROSC in HEMS, 1% in GMT
Nardi50	2	Italy (North East)	Prospective	Involuntary blunt trauma, ISS>15	42 HEMS 98 GMT(BLS)	HEMS — physician GMT — EMT, nine had non-intubation capable physician	HEMS – 81% GMT – 0%	NS	Time from dispatch to admission: HEMS — 55 min GMT — no physician 27 mins, physician 34 mins	Direct mortality comparison	Groups were statistically similar with regard to age, sex and mean ISS, so no adjustments made	Mortality to discharge from ICU (time frame not specified)	HEMS mortality= 12% GMT mortality = 32% (p<0.05) OR GMT vs HEMS=3.42 (95% CI 1.23 to 9.56)^*
Schiller51	3	Arizona, USA	Retrospective	Blunt trauma patients with ISS 20–40	347 HEMS 259 GMT	HEMS — paramedic GMT — paramedic	NS	NS	HEMS — 53 min in city, 48 min outside city GMT — 37 min in city, 59 min outside city 92% ground patients from within city, 30% HEMS from within city	Direct mortality comparison	Reported mean TS (HEMS 12.1, GMT 12.7), mean GCS (HEMS 9.6, GMT 10.4), age, days of hospitalisation and gender statistically similar	Mortality (time frame not specified)	18% HEMS mortality 13% GMT mortality (p value not specified) GMT vs HEMS OR=0.68 (95% CI 0.43 to 1.07)^*

↵* Indicates OR calculated by authors of this paper.
AIS, Abbreviated Injury Score; ALS, advanced life support; BLS, basic life support; ED, emergency department; EMT, emergency medical technician; GCS, Glasgow Coma Scale; GMT, ground medical transport; HEMS, helicopter emergency medical service; ISS, Injury Severity Score; NS, not specified; ROSC, return of spontaneous circulation; (R) TS, (Revised) Trauma Score; TRISS, Trauma Score–Injury Severity Score (a score used to predict probability of survival).
W statistic=excess number of survivors per 100 when compared with patients from Major Trauma Outcome Study (MTOS).
M statistic represents the degree of similarity between the sample group and patients from the MTOS (1.00=identical patient group).