Background
Methods
Study setting
Participants and study outcome
Data collection
Candidate predictor variables
Missing data
Model development and predictor effects
Algorithm formation
Assessing the performance
Sensitivity analysis and internal validation
Results
Study population
Alive at 30 days (n=19 758) | Death within 30 days (n=8611) | p-value | Missing data for 30-day mortality (n=1817) | |
---|---|---|---|---|
Age, years | 53.0 [33.4 to 68.4] | 70.2 [60.0 to 79.8] | <0.001 | 50.0 [30.0 to 67.7] |
Missing, n | 0 | 0 | 0 | |
Heart rate, beats per minute | 90 [77 to 108] | 90 [70 to 110] | <0.001 | 90 [77 to 105] |
Missing, n | 2529 (12.8) | 5073 (58.9) | 431 (23.7) | |
Systolic blood pressure, mmHg | 131 [113 to 151] | 134 [103 to 168] | 0.008 | 130 [112 to 148] |
Missing, n | 2843 (14.4) | 5273 (61.2) | 489 (26.9) | |
Respiratory rate, breaths per minute | 16 [14 to 20] | 16 [12 to 22] | <0.001 | 16 [14 to 20] |
Missing, n | 6783 (34.3) | 5880 (68.3) | 867 (47.8) | |
Oxygen saturation, % | 97 [94 to 99] | 95 [89 to 98] | <0.001 | 97 [95 to 99] |
Missing, n | 3078 (15.6) | 5506 (63.9) | 482 (26.5) | |
Time to HEMS arrival, minutes | 19 [14 to 29] | 19 [14 to 28] | 0.14 | 19 [13 to 28] |
Missing, n | 0 | 0 | 0 | |
Time to EMS arrival, minutes | 11 [8 to 16] | 10 [7 to 15] | <0.001 | 11 [8 to 18] |
Missing, n | 13 427 (68.0) | 4885 (56.7) | 1330 (73.2) | |
GCS | 14 [7 to 15] | 3 [3 to 3] | <0.001 | 14 [7 to 15] |
Missing, n | 1284 (6.5) | 763 (8.9) | 151 (8.3) | |
Cardiac rhythm | <0.001 | |||
Sinus rhythm | 14 187 (71.8) | 2287 (26.6) | 1202 (66.2) | |
SVES, VES (mono) | 85 (0.4) | 30 (0.3) | 6 (0.3) | |
AFlut, AFib, AV block (II–III), VES (poly) | 1376 (7.0) | 779 (9.0) | 99 (5.4) | |
VF, VT, asystole, PEA | 832 (4.2) | 4683 (54.4) | 79 (4.3) | |
Not registered | 1620 (8.2) | 132 (1.5) | 198 (10.9) | |
Paced | 94 (0.5) | 79 (0.9) | 5 (0.3) | |
Missing | 1564 (7.9) | 621 (7.2) | 228 (12.5) | |
Medical facility or nursing home | <0.001 | |||
No | 18 727 (94.8) | 7874 (91.4) | 1757 (96.7) | |
Yes | 1035 (5.2) | 737 (8.6) | 60 (3.3) | |
Missing | 0 | 0 | 0 | |
HEMS vehicle | 0.004 | |||
Ground unita | 9908 (50.1) | 4158 (48.3) | 929 (51.1) | |
Helicopterb | 9850 (49.9) | 4453 (51.7) | 888 (48.9) | |
Missing | 0 | 0 | 0 | |
Number of patients | <0.001 | |||
1 | 19 315 (97.8) | 8577 (99.6) | 1765 (97.1) | |
≥ 2 | 443 (2.2) | 34 (0.4) | 52 (2.9) | |
Missing | 0 | 0 | 0 | |
Sex | <0.001 | |||
Female | 7249 (36.7) | 2791 (32.4) | 531 (29.2) | |
Male | 12 509 (63.3) | 5750 (66.8) | 1002 (55.1) | |
Missing | 0 | 70 (0.8) | 284 (15.6) | |
Patient category | <0.001 | |||
Cardiac arrest | 1404 (7.1) | 5461 (63.4) | 135 (7.4) | |
Trauma | 6480 (32.8) | 915 (10.6) | 643 (35.4) | |
Respiratory failure | 1084 (5.5) | 294 (3.4) | 75 (4.1) | |
Chest pain | 810 (4.1) | 75 (0.9) | 48 (2.6) | |
Stroke | 1125 (5.7) | 821 (9.5) | 82 (4.5) | |
Neurologicalc | 2785 (14.1) | 512 (5.9) | 228 (12.5) | |
Psychiatric or intoxication | 2941 (14.9) | 63 (0.7) | 308 (17.0) | |
Gynaecology and obstetrics | 637 (3.2) | 1 (0.0) | 55 (3.0) | |
Infection | 198 (1.0) | 62 (0.7) | 14 (0.8) | |
Other | 2294 (11.6) | 407 (4.7) | 229 (12.6) | |
Missing | 0 | 0 | 0 |
Model development
Variable | Univariate | Multivariate | |||||
---|---|---|---|---|---|---|---|
χ2 | d.f. | P-value | χ2 | d.f. | p-value | ||
Age | 3082.7 | 3 | <0.001 | 814.3 | 3 | <0.001 | |
Heart rate | 122.8 | 3 | <0.001 | 79.4 | 3 | <0.001 | |
Systolic blood pressure | 425.3 | 3 | <0.001 | 107.7 | 3 | <0.001 | |
Oxygen saturation | 3502.1 | 3 | <0.001 | 242.9 | 3 | <0.001 | |
Time to HEMS arrival | 80.5 | 3 | <0.001 | 8.9 | 3 | 0.030 | |
GCS | 6827.7 | 2 | <0.001 | 1759.2 | 2 | <0.001 | |
Cardiac rhythm: VF, VT, asystole, or PEA | 6613.3 | 1 | <0.001 | 350.8 | 1 | <0.001 | |
Mission located in medical facility or nursing home, yes | 108.4 | 1 | <0.001 | 0.7 | 1 | 0.408 | |
HEMS vehicle, ground unita | 11.6 | 1 | <0.001 | 0.6 | 1 | 0.444 | |
Sex, male | 39.7 | 1 | <0.001 | 1.0 | 1 | 0.325 | |
Patient category | Trauma | 21.0 | 1 | <0.001 | 1.5 | 1 | 0.220 |
Cardiac arrest | 871.8 | 1 | <0.001 | 7.4 | 1 | 0.007 | |
Neurologicalb | 38.9 | 1 | <0.001 | 10.9 | 1 | <0.001 | |
Psychiatric or intoxication | 35.7 | 1 | <0.001 | 120.9 | 1 | <0.001 | |
Other | 34.8 | 1 | <0.001 | 1.8 | 1 | 0.185 | |
Stroke | 264.7 | 1 | <0.001 | 13.7 | 1 | <0.001 | |
Respiratory failure | 70.2 | 1 | <0.001 | 0.2 | 1 | 0.664 | |
Chest pain | 1.8 | 1 | 0.186 | 0.0 | 1 | 0.876 |
Variable | Univariate OR (95% CI) | Multivariate OR (95% CI) | |
---|---|---|---|
Cardiac rhythm: VF, VT, asystole, or PEA | 29.33 (27.04 to 31.82) | 3.90 (3.38 to 4.50) | |
Mission located in medical facility or nursing home, yes | 1.68 (1.52 to 1.85) | 1.06 (0.92 to 1.23) | |
HEMS vehicle, ground unita | 0.92 (0.87 to 0.96) | 0.97 (0.88 to 1.06) | |
Sex, male | 1.19 (1.12 to 1.25) | 0.96 (0.88 to 1.04) | |
Patient category | Trauma | 1.83 (1.41 to 2.37) | 1.23 (0.88 to 1.71) |
Cardiac arrest | 46.82 (36.27 to 60.44) | 1.60 (1.14 to 2.24) | |
Neurologicalb | 2.32 (1.78 to 3.03) | 0.57 (0.41 to 0.79) | |
Psychiatric or intoxication | 0.35 (0.25 to 0.49) | 0.10 (0.07 to 0.15) | |
Other | 2.27 (1.73 to 2.98) | 0.79 (0.56 to 1.12) | |
Stroke | 8.97 (6.89 to 11.69) | 1.90 (1.35 to 2.66) | |
Respiratory failure | 3.29 (2.49 to 4.35) | 1.08 (0.76 to 1.54) | |
Chest pain | 1.25 (0.90 to 1.75) | 0.97 (0.65 to 1.45) | |
Infection or Gynaecology and obstetrics | 1.00 (reference) | 1.00 (reference) |
Model performance, sensitivity analysis and internal validation
Metric | Algorithm performance | Validation performance | Sensitivity analysis | ||||||
---|---|---|---|---|---|---|---|---|---|
Estimate | 95% CI | Optimism | 95% CI | Estimate | 95% CI | ||||
Lower | Upper | Lower | Upper | Lower | Upper | ||||
AUROC | 0.932 | 0.929 | 0.935 | 0.011 | 0.008 | 0.015 | 0.887 | 0.881 | 0.893 |
Brier | 0.091 | 0.089 | 0.093 | -0.006 | -0.008 | -0.003 | 0.088 | 0.086 | 0.091 |
Slope | 1.054 | 1.031 | 1.078 | 0.054 | 0.052 | 0.056 | 1.049 | 1.016 | 1.083 |
Intercept | -0.055 | -0.094 | -0.015 | -0.055 | -0.057 | -0.052 | -0.066 | -0.121 | -0.010 |