Table 4.
Sensitivity analyses evaluating the association between hospital-level ICU use (modeled as quartiles) and the primary composite outcome,a using alternative definitions of the study cohort, exposure status, and outcome.
| Sensitivity analysis | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | P-valueb | |
|---|---|---|---|---|---|---|
| (1) Restricting cohort to patients with minimal injuries (AIS≤1) other than the SOIs | Events/total | 17/1650 | 18/1535 | 16/1602 | 35/1605 | NA |
| OR (95% CI) | Reference | 1.06 (0.60–1.89) | 0.89 (0.41–1.91) | 1.13 (0.59–2.17) | 0.94 | |
| (2) Including patients admitted to observation status (considered as non-ICU) | Events/total | 5/029 | 53/3824 | 34/3554 | 47/3380 | NA |
| OR (95% CI) | Reference | 1.12 (0.76–1.64) | 0.69 (0.43–1.09) | 0.80 (0.54–1.19) | 0.16 | |
| (3) Expanding the definition of ICU to include admission to telemetry/step-down units | Events/total | 46/3483 | 44/4017 | 34/3132 | 56/3680 | NA |
| OR (95% CI) | Reference | 0.80 (0.51–1.23) | 0.79 (0.50–1.26) | 0.85 (0.56–1.28) | 0.69 | |
| (4) Restricting cohort to those with SOI AIS scores defined by AIS codes | Events/total | 43/3783 | 48/3644 | 35/3448 | 34/3182 | NA |
| OR (95% CI) | Reference | 1.25 (0.83–1.89) | 0.90 (0.59–1.37) | 0.86 (0.55–1.35) | 0.39 | |
| (5) Restricting cohort to SOIs with AIS 3–4 (and expanding the number of hospitals to also include those with 5–9 eligible patients) | Events/total | 16/1280 | 26/1392 | 26/1438 | 9/1120 | NA |
| OR (95% CI) | Reference | 1.53 (0.84–2.79) | 1.44 (0.75–2.77) | 0.58 (0.26–1.26) | 0.037 | |
| (6) Expanding cohort to include SOIs with AIS=5 | Events/total | 47/3815 | 55/3756 | 41/3673 | 51/3381 | NA |
| OR (95% CI) | Reference | 1.26 (0.85–1.86) | 0.81 (0.53–1.24) | 0.94 (0.63–1.41) | 0.28 | |
| (7) Expanding cohort to also include hospitals with 5–9 eligible patients | Events/total | 44/3805 | 57/3940 | 40/3974 | 47/3367 | NA |
| OR (95% CI) | Reference | 1.32 (0.90–1.95) | 0.82 (0.54–1.26) | 0.90 (0.59–1.37) | 0.14 | |
| (8) Expanding definition of the composite outcome to include discharge to hospice | Events/total | 49/3788 | 54/3613 | 42/3595 | 56/3316 | NA |
| OR (95% CI) | Reference | 1.19 (0.82–1.74) | 0.84 (0.56–1.28) | 0.99 (0.65–1.50) | 0.49 | |
Abbreviations: AIS, abbreviated injury scale; ICU, intensive care unit; NA, not applicable; SOI, solid organ injury
a
Adjusted for abdominal AIS score and baseline use of supplemental oxygen as confounders
b
P-value for the null hypothesis that the coefficients of all of the indicator variables representing quartiles of ICU use are 0 (“chunk” test)