Table 1

 Description of characteristics for people with traumatic brain injury in order of relative importance to deriving the clinical decision rule

Variable importance*Subjects not requiring HTI measures† n = 258Subjects requiring HTI measures† n = 246
*The relative importance of each variable ranges from 0–100 (the most important variable in the decision tree derivation process has a score of 100) and represents a quantification of how often a given variable was used as a primary or surrogate splitter in the CART® tree building process. Variables with a score of 0 are listed in no particular order.
†Proportions are calculated based on the total number of subjects in each group, by column. The median and interquartile range (IQR) is presented for continuous variables.
‡Intubation is included in the ED GCS variable (patients intubated in the field or in the first 10 minutes of ED arrival were assigned an ED GCS of 3) and was consequently left out of the analysis as an independent covariate. Analysis with intubation included did not change the results.
ED, emergency department; EMS, ; GCS, Glasgow Coma Score; HTI, high therapeutic intensity; INR, international normalised ratio
Median ED GCS‡10015(14–15)3(3–3)
Median EMS GCS46.014(12–15)6(3–12)
Median ED respiratory rate (breaths/min)14.520(16–22)20(16–26)
Median ED pulse rate (beats/min)11.891(80–104)101(86–116)
Abnormal chest radiograph11.162(24%)127(52%)
Median ED temperature (°C)6.636.2(36.0–36.6)35.9(35.2–36.2)
Median EMS respiratory rate (breaths/min)6.218(16–20)18(14–24)
Median age (years)5.939.5(26–50)36(24–47)
Median EMS pulse rate (beats/min)5.092(80–102)96(80–115)
Median initial INR3.21.0(0.9–1.1)1.0(1.0–1.2)
Median EMS pulse oximetry (%)1.699(98–100)98(95–99)
Median initial haematocrit (%)1.440(37–43)38(34–42)
Median ED pulse oximetry (%)1.398(96–100)99(96–100)
Non-white race037(14%)35(14%)
Comorbid condition021(8%)9(4%)
Median initial serum bicarbonate (mmol/L)023(20–24)20(17–22)
EMS arrest02(1%)6(2%)
EMS systolic blood pressure < 90 mmHg012(5%)36(15%)
ED systolic blood pressure < 90 mmHg06(2%)23(9%)
Dilated unilateral pupil019(7%)39(16%)
Alcohol intoxication0108(42%)102(41%)