Table 2.
Effects of case mix factors on ultimate hospital outcome in admissions with acute kidney injury
| Case mix factor | Deaths (n) | n | % | Adjusted OR (95% CI) | P value | |
| Age (years) | < 45 | 817 | 2,128 | 38.4 | 1.48 (1.44–1.52) per 10 year increase | < 0.001 |
| 45–54 | 846 | 1,776 | 47.6 | |||
| 55–64 | 1,671 | 3,086 | 54.1 | |||
| 65–74 | 2,991 | 4,866 | 61.5 | |||
| 75+ | 2,553 | 3,720 | 68.6 | |||
| Sex | Female | 2,905 | 5,217 | 55.7 | Reference | 0.004 |
| Male | 5,973 | 10,359 | 57.7 | 1.13 (1.04–1.22) | ||
| Past medical history | Absent | 7,355 | 13,298 | 55.3 | Reference | < 0.001 |
| Present | 1,523 | 2,278 | 66.9 | 1.82 (1.63–2.03) | ||
| CPR before admission | No | 7,679 | 14,062 | 54.6 | Reference | < 0.001 |
| Yes | 1,199 | 1,514 | 79.2 | 1.64 (1.41–1.90) | ||
| Mechanical ventilation | No | 2,086 | 5,250 | 39.7 | Reference | < 0.001 |
| Yes | 6,792 | 10,326 | 65.8 | 1.93 (1.76–2.12) | ||
| Surgery within 1 week of admission | No | 6,324 | 10,751 | 58.8 | Reference | < 0.001 |
| Yes | 2,554 | 4,825 | 52.9 | 0.80 (0.73–0.87) | ||
| Sepsis | No | 4,362 | 8,207 | 53.1 | Reference | < 0.001 |
| Yes | 4,516 | 7,369 | 61.3 | 1.14 (1.06–1.21) | ||
| Oliguria | No | 4,766 | 9,660 | 49.3 | Reference | < 0.001 |
| Yes | 3,844 | 5,466 | 70.3 | 1.90 (1.75–2.07) | ||
| Length of stay before unit admission | 0 days | 2,451 | 4,261 | 57.5 | Reference | < 0.001 |
| 1 day | 1,952 | 3,666 | 53.2 | 0.90 (0.81–1.01) | ||
| 2–6 days | 2,269 | 4,133 | 54.9 | 1.00 (0.90–1.12) | ||
| 7+ days | 2,199 | 3,508 | 62.7 | 1.54 (1.38–1.73) | ||
| Temperature (°C)a | < 32 | 68 | 89 | 76.4 | 1.96 (1.12–3.40) | < 0.001 |
| 32–34 | 399 | 557 | 71.6 | 1.32 (1.05–1.65) | ||
| 34–36 | 2,779 | 4,595 | 60.5 | 1.11 (1.01–1.22) | ||
| 36–38.5 | 2,918 | 5,789 | 50.4 | Reference | ||
| 38.5–39 | 882 | 1,680 | 52.5 | 0.96 (0.85–1.10) | ||
| 39–41 | 1,614 | 2,595 | 62.2 | 1.16 (1.03–1.30) | ||
| ≥ 41 | 185 | 217 | 85.3 | 3.35 (2.18–5.15) | ||
| Mean arterial pressure (mmHg)a | < 50 | 2,923 | 3,803 | 76.9 | 2.08 (1.80–2.41) | < 0.001 |
| 50–70 | 4,164 | 7,013 | 59.4 | 1.45 (1.28–1.65) | ||
| 70–110 | 634 | 1,682 | 37.7 | Reference | ||
| 110–130 | 724 | 1,988 | 36.4 | 0.89 (0.77–1.04) | ||
| 130–160 | 366 | 955 | 38.3 | 0.94 (0.78–1.13) | ||
| ≥ 160 | 48 | 96 | 50.0 | 1.33 (0.83–2.12) | ||
| Heart rate (beats/minute)b | < 40 | 134 | 187 | 71.7 | 1.42 (0.97–2.08) | < 0.001 |
| 40–50 | 179 | 324 | 55.2 | 1.14 (0.87–1.50) | ||
| 50–100 | 1,229 | 2,775 | 44.3 | Reference | ||
| 100–110 | 1,044 | 2,085 | 50.1 | 1.18 (1.03–1.35) | ||
| 110–120 | 1,287 | 2,408 | 53.4 | 1.26 (1.11–1.44) | ||
| 120–140 | 2,543 | 4,251 | 59.8 | 1.46 (1.30–1.64) | ||
| 140–155 | 1,262 | 1,878 | 67.2 | 1.66 (1.43–1.93) | ||
| ≥ 155 | 1,173 | 1,623 | 72.3 | 1.94 (1.66–2.28) | ||
| Respiratory rate (breaths/minute)b | < 6 | 403 | 628 | 64.2 | 1.05 (0.85–1.30) | 0.001 |
| 6–12 | 1,836 | 3,509 | 52.3 | 1.00 (0.88–1.13) | ||
| 12–14 | 1,771 | 2,867 | 61.8 | 1.19 (1.05–1.36) | ||
| 14–25 | 1,395 | 2,397 | 58.2 | Reference | ||
| 25–35 | 2,007 | 3,784 | 53.0 | 1.04 (0.92–1.18) | ||
| 35–40 | 689 | 1,109 | 62.1 | 1.33 (1.12–1.58) | ||
| 40–50 | 608 | 1,015 | 59.9 | 1.16 (0.97–1.39) | ||
| ≥ 50 | 135 | 203 | 66.5 | 1.49 (1.05–2.13) | ||
| Oxygenation (mmHg; A-aDO2 [FiO2 ≥0.5])b | A-aDO2 (FIO2 ≥ 0.5) | < 0.001 | ||||
| < 250 | 1,238 | 2,338 | 53.0 | Reference | ||
| 250–350 | 1,576 | 2,540 | 62.0 | 1.25 (1.12–1.40) | ||
| 350–500 | 1,034 | 1,453 | 71.2 | 1.68 (1.45–1.94) | ||
| ≥ 500 | 1,480 | 1,951 | 75.9 | 1.94 (1.69–2.23) | ||
| PaO2 (FIO2 < 0.5) | ||||||
| < 50 | 114 | 206 | 55.3 | 1.10 (0.80–1.53) | ||
| 50–70 | 918 | 1,786 | 51.4 | 1.11 (0.98–1.26) | ||
| 70–80 | 786 | 1,637 | 48.0 | 1.02 (0.90–1.16) | ||
| ≥ 80 | 1,732 | 3,665 | 47.3 | Reference | ||
| Arterial pHa | < 7.15 | 1,380 | 1,676 | 82.3 | 2.13 (1.82–2.49) | < 0.001 |
| 7.15–7.25 | 1,871 | 2,655 | 70.5 | 1.63 (1.46–1.83) | ||
| 7.25–7.33 | 2,177 | 3,744 | 58.1 | 1.20 (1.09–1.32) | ||
| 7.33–7.5 | 3,290 | 7,156 | 46.0 | Reference | ||
| ≥ 7.5 | 160 | 345 | 46.4 | 0.98 (0.76–1.26) | ||
| Serum sodium (mmol/l)a | < 120 | 187 | 326 | 57.4 | 1.49 (1.14–1.94) | < 0.001 |
| 120–130 | 1,506 | 2,654 | 56.7 | 1.19 (1.07–1.32) | ||
| 130–150 | 6,590 | 11,687 | 56.4 | Reference | ||
| 150–155 | 358 | 537 | 66.7 | 1.45 (1.17–1.80) | ||
| 155–160 | 153 | 221 | 69.2 | 1.48 (1.06–2.07) | ||
| ≥ 160 | 84 | 151 | 55.6 | 0.92 (0.63–1.36) | ||
| Serum potassium (mmol/l)a | < 2.5 | 56 | 110 | 50.9 | 0.67 (0.43–1.05) | < 0.001 |
| 2.5–3 | 302 | 535 | 56.4 | 0.93 (0.75–1.14) | ||
| 3–3.5 | 1,106 | 2,008 | 55.1 | 0.91 (0.81–1.02) | ||
| 3.5–5.5 | 4,639 | 8,297 | 55.9 | Reference | ||
| 5.5–6 | 1,137 | 1,858 | 61.2 | 1.17 (1.04–1.32) | ||
| 6–7 | 1,244 | 2,028 | 61.3 | 1.13 (1.00–1.27) | ||
| ≥ 7 | 394 | 740 | 53.2 | 0.79 (0.66–0.95) | ||
| Serum albumin (g/l)b | < 20 | 3,544 | 5,499 | 64.4 | 1.21 (1.11–1.33) | < 0.001 |
| 20–25 | 1,834 | 3,356 | 54.6 | 1.02 (0.93–1.13) | ||
| 25–45 | 3,469 | 6,635 | 52.3 | Reference | ||
| ≥ 45 | 31 | 86 | 36.0 | 0.55 (0.33–0.93) | ||
| Haematocrit (%)a | < 20 | 612 | 1,008 | 60.7 | 0.99 (0.84–1.17) | 0.011 |
| 20–30 | 4,748 | 8,536 | 55.6 | 0.89 (0.82–0.97) | ||
| 30–46 | 3,168 | 5,473 | 57.9 | Reference | ||
| 46–50 | 218 | 335 | 65.1 | 1.28 (0.98–1.68) | ||
| ≥ 50 | 132 | 224 | 58.9 | 0.99 (0.71–1.38) | ||
| White blood count (×1,000/mm3)a | < 1 | 176 | 223 | 78.9 | 2.52 (1.73–3.67) | < 0.001 |
| 1–3 | 506 | 680 | 74.4 | 1.77 (1.44–2.18) | ||
| 3–15 | 3,862 | 7,468 | 51.7 | Reference | ||
| 15–20 | 1,756 | 3,071 | 57.2 | 1.11 (1.00–1.23) | ||
| 20–40 | 2,278 | 3,681 | 61.9 | 1.21 (1.09–1.33) | ||
| ≥ 40 | 300 | 453 | 66.2 | 1.16 (0.91–1.47) | ||
| Glasgow Coma Scale scored | 3–4 | 1,596 | 2,019 | 79.0 | 1.07 (1.06–1.08) per decrease of 1 point | < 0.001 |
| 5–12 | 1,178 | 1,924 | 61.2 | |||
| 13–14 | 1,099 | 1,880 | 58.5 | |||
| 15 | 5,005 | 9,753 | 51.3 | |||
All of the factors emerged as statistically significant (P < 0.005) in the multiple logistic regression analysis. Exclusions were as follows: readmissions within the same hospital stay; admissions with length of ICU stay < 8 hours; admissions of patients aged < 16 years; admissions missing age, sex, surgical status, temperature, mean arterial pressure, heart rate or respiratory rate. Admitted patients with missing values for any other physiology variables are assumed to be normal and are placed in the reference category. aCategories from APACHE II (reference category equivalent to zero APACHE II points) bCategories from APACHE III (reference category equivalent to zero APACHE III points). cPre-sedation values used for admissions sedated or paralyzed during the first 24 hours in ICU. A-aDO2, alveolar-arterial oxygen gradient; APACHE, Acute Physiology and Chronic Health Evaluation; CI, confidence interval; CPR, cardiopulmonary resuscitation; FiO2, fractional inspired oxygen; ICU, intensive care unit; OR, odds ratio.