Table 2.

Variable importance of out-of-hospital physiologic measures in identifying seriously injured patients in a derivation sample (n = 27,086)

Tree 1		Tree 2		Tree 3
Physiologic measures (7 variables)	Var impta	Physiologic measures and current physiologic triage criteria (11 variables)	Var impta	Physiologic measures and all triage criteria (36 variablesb)	Var impta
GCS	100	GCS	100	GCS	100
Respiratory rate	28.4	Respiratory rate	28.3	Criterion – age > 55 years	64.2
SBP	16.1	Criterion – GCS ≤ 13	19.7	Respiratory rate	28.1
Shock index	10.9	SBP	18.7	Criterion – GCS ≤ 13	19.7
Assisted ventilation	7.1	Shock index	16.5	Shock index	18.1
Intubation	6.7	Heart rate	10.9	Criterion – EMS provider judgment	16.4
Heart rate	6.4	Criterion – SBP	5.7	SBP	16.4
		Criterion – airway	4.2	Criterion – fall	13.6
		Intubation	0	Heart rate	12.7
		Assisted ventilation	0	Criterion – pedestrian vs. auto	10.1
		Criterion – respiratory rate <10 or >29	0	Criterion – respiratory rate <10 or >29	6.0
				Criterion – motor cycle crash	5.3
				Assisted ventilation	2.8
				Criterion – MVC with passenger space intrusion	2.6
				Intubation	2.5
				Criterion – environment	2.0
				Criterion – comorbidities	1.6
ROC values for CART trees
0.68		0.70		0.73

^aEstimates for variable importance (var impt) were calculated using classification and regression tree analysis to develop high-sensitivity (≥95%) decision trees. GCS, Glasgow Coma Scale score; SBP, systolic blood pressure; Criterion, field triage criteria, as determined on-scene by EMS personnel; MVC, motor vehicle crash; ROC, receiver operating characteristic.

^b19 of 36 predictors were not used in decision tree development and therefore given a variable importance score of zero. These predictors are omitted from the table for clarity, but include criterion – paralysis, criterion – SBP < 90, criterion – MVC with rollover, criterion – intoxication, criterion – airway, criterion – flail chest, criterion – MVC with death of occupant, criterion - penetrating torso injury, criterion – CPR, criterion – amputation, criterion – burn, criterion - steering wheel deformity, criterion - skull fracture, criterion – pelvic fracture, criterion – high speed MVC, criterion – long bone fractures, criterion – mangled extremity, criterion –MVC with ejection, and criterion – MVC with extrication.