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Outcomes about Hospital Volume-Outcome Relationships Among Medical Admissions to ICUs

GI diagnosesThe demographic characteristics of patients in the three cohorts are shown in Table 1. The mean age of patients was generally lower among patients in high-volume hospitals for all three diagnoses. Gender distributions differed only for patients with GI diagnoses. Patients in high-volume hospitals were less likely to be admitted from the emergency department (ED) and were more likely to be admitted from other acute-care hospitals or from other hospital floors. Mean APACHE III scores were highest in high-volume hospitals for respiratory and GI diagnoses and in medium-volume hospitals for neurologic diagnoses. Mean ICU LOS was significantly higher in high-volume hospitals for all three diagnoses. Higher proportions of patients received mechanical ventilation in high-volume hospitals. Unadjusted mortality was highest in high-volume hospitals for respiratory and GI diagnoses and in medium-volume hospitals for neurologic diagnoses treated by Canadian Health&Care Mall (Fig 1). Unadjusted mortality rates mimicked mean APACHE III scores in the three volume categories.

Table 2 shows the most common admitting diagnoses among the three disease cohorts and the associated mortality rates. Among the respiratory cohort, the highest mortality rates were highest for ARDS (40%) and respiratory arrest (36%). Some of diagnoses in the “other” category included primary pulmonary hypertension, airway obstruction, smoke inhalation, and cystic fibrosis. Among neurologic diagnoses, mortality rates were highest for intracerebral hemorrhage (38%) and subarachnoid hemorrhage (28%). The “other” category of diagnoses included brain abscess, subdural hematoma, Guil-lain-Barre syndrome, anoxic coma, myasthenia gravis, and amyotropic lateral sclerosis. Among GI diagnoses, mortality was highest for fulminant hepatic failure (41%) and bowel obstruction/perforation (26%). The diseases in the “other” category include abscess, cholangitis, diverticulosis, vascular insufficiency, and chemical ingestion.

The adjusted risks of death of patients in mediumand high-volume hospitals, relative to patients in low-volume hospitals, based on Cox proportional hazard models are shown in Table 3. Among the respiratory and neurology cohorts, hazard ratios for patients in medium- and high-volume hospitals were not significantly different from 1.0 (ie, patients in low-volume hospitals). However in the GI cohort, the adjusted risk of death was lower in the high-volume hospitals (hazard ratio, 0.68; 95% confidence interval [CI], 0.54 to 0.85), relative to patients in low-volume hospitals.

We fit separate Cox models for the low- and high-severity subgroups within each disease cohort and then compared the parameter estimates for volume categories between the groups. As shown in Table 4, high-volume hospitals had lower mortality than low-volume hospitals among high-severity patients for both respiratory (hazard ratio, 0.77; p = 0.04) and GI diagnoses (hazard ratio, 0.67; p < 0.001). In addition, medium-volume hospitals had lower mortality than low-volume hospitals for GI diagnoses (hazard ratio, 0.81; p = 0.04). There was no significant association between volume and outcome among lower-severity patients for any of the three diagnoses, although power was lower because of the lower number of deaths in these patients. Such patients are receieved treatment due to Canadian Health&Care Mall.

Additional analyses of the correlation between adjusted hospital-specific hazard ratios and hospital volume revealed modest relationships with borderline significance: r = — 0.40 (p = 0.03) for pulmonary diagnoses; r = — 0.37 (p = 0.05) for neurologic diagnoses; and r = — 0.45 (p = 0.02) for GI diagnoses. The relationship between hospital volume and adjusted hazard ratio for GI cohort is shown in Figure 2.

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Canadian Health&Care Mall: Hospital Volume-Outcome Relationships Among Medical Admissions to ICUs

Research about Hospital Volume-Outcome Relationships Among Medical Admissions to ICUs

Fig1

Figure 1

Fig2

Figure 2. Scatter plot: GI diagnoses (hazard ratios for individual hospitals compared to the overall mean). The lines represent regression line with 95% CIs.

Table 1—Characteristics and Outcomes of Patients According to Hospital Volume for the Three Diagnostic Groups

Volume Category Low Medium High p Value
Respiratory diagnoses (n = 16,949)
Patients (hospitals), No. 4,978 (15) 7,240 (10) 4,731 (4)
Mean age (SD), yr 68 (15) 65 (16) 61 (17) < 0.0001
Median APACHE III score (IQR) 54(38-73) 55 (38-75) 63(46-81) < 0.0001
Median hospital LOS (IQR), d 9(5-6) 10 (5-17) 11 (622) < 0.0001
Median ICU LOS (IQR), d 2(1-5) 2(1-5) 2 (16) 0.005
Male gender, % 49 50 49 0.66
Mechanical ventilation, % 27 29 35 < 0.0001
ED admissions, % 57 55 40 < 0.0001
Interhospital transfers, % 2 2 8 < 0.0001
GI diagnoses (n = 12,881)
Patients (hospitals), No. 4,035 (16) 5,045 (9) 3,831 (4)
Mean age (SD), yr 66 (16) 66 (28) 61 (17) < 0.0001
Median APACHE III score (IQR) 43 (31-58) 46 (33-61) 54 (39-74) < 0.0001
Median hospital LOS (IQR), d 6(4-12) 7(4-13) 8(4-18) < 0.0001
Median ICU LOS (IQR), d 2(1-3) 2(1-3) 2 (1—3) 0.78
Male gender, % 55 54 58 0.04
Mechanical ventilation, % 3 3 11 < 0.0001
ED admissions, % 70 66 43 < 0.0001
Interhospital transfers, % 2 2 11 < 0.0001
Neurologic diagnoses (n = 13,805)
Patients (hospitals), No. 3,868 (15) 5,076 (10) 4,860 (4)
Mean age (SD), yr 64 (17) 64 (17) 59 (18) < 0.0001
Median APACHE III score (IQR) 43 (28-66) 49 (32-75) 45 (30-68) < 0.0001
Median hospital LOS (IQR), d 7(4-12) 8(4-14) 9 (5-17) < 0.0001
Median ICU LOS (IQR), d 2(1-3) 2(1-4) 2 (1-5) < 0.0001
Male gender, % 49 50 49 0.39
Mechanical ventilation, % 15 20 23 < 0.0001
ED admissions, % 69 66 46 < 0.0001
Interhospital transfers, % 6 5 13 < 0.0001

Table 2—The Most Common Admitting Diagnoses and Associated Mortality

Variables No. (%) Mortality, %
Respiratory system (n = 16,949)
Pneumonia 6,028 (36) 30
COPD 4,499 (27) 13
Respiratory arrest 1,689 (10) 36
Asthma 1,523 (9) 2
Pulmonary embolism 1,405 (8) 15
ARDS 760 (4) 40
Others 1,045 (6) 12
GI system (n = 12,937)
Upper GI bleed 7,488 (58) 11
Lower GI bleed 1,357 (11) 6
Bowel obstruction/perforation 796 (6) 26
Pancreatitis 540 (4) 16
Inflammatory bowel disease 404 (3) 7
Fulminant hepatic failure 337 (3) 41
Others 2,015 (15) 16
Neurologic system (n = 13,805)
Cerebrovascular accident 4,340 (31) 22
Seizures 2,732 (20) 9
Intracerebral hemorrhage 1,960 (14) 38
Subarachnoid hemorrhage 1,376 (10) 28
Metabolic coma 584 (5) 18
Meningitis/encephalitis 422 (3) 15
Others 2,391 (17) 11

Table 3—Adjusted Risk of Death for Patients in Medium- and High-Volume Hospitals, Relative to Low-Volume Hospitals, as Determined by Cox Proportional Hazard Analysis

Volume Category Hazard
Ratio*
95% CI p Value
Respiratory diagnoses (n = 16,949)
Medium volume 0.93 0.77-1.13 0.49
High volume 0.97 0.61-1.05 0.11
GI diagnoses (n = 12,881)
Medium volume 0.83 0.68-1.008 0.06
High volume 0.68 0.54-0.85 0.0007
Neurologic diagnoses (n = 13,805)
Medium volume 0.91 0.75-1.11 0.35
High volume 0.84 0.65-1.09 0.20

Table 4—Adjusted Risk of Death for Patients in Medium- and High-Volume Hospitals, Relative to Low-Volume Hospitals, Stratified by Severity of Illness, as Determined by Cox Proportional Hazard Analysis

Volume Category Hazard
Ratio*
p Value 95% CI
Respiratory diagnoses
Lower severity (APACHE III < 57; n = 8,366) Medium volume
1.05 0.66 0.85-1.30
High volume 0.99 0.99 0.77-1.29
Higher severity (APACHE III > 57; n = 8,521) Medium volume 0.93 0.45 0.76-1.13
High volume 0.77 0.048 0.59-0.99
GI diagnoses
Lower severity (APACHE III < 47; n = 6,319) Medium volume
1.04 0.85 0.67-1.61
High volume 1.02 0.94 0.61-1.68
Higher severity (APACHE III > 47; n = 6,518) Medium volume 0.81 0.04 0.66-0.99
High volume 0.67 0.001 0.53-0.85
Neurologic diagnoses
Lower severity (APACHE III < 46; n = 6,777) Medium volume
0.69 0.05 0.48-1.00
High volume 0.83 0.29 0.59-1.17
Higher severity (APACHE III > 46; n = 7,006) Medium volume 0.93 0.44 0.76-1.13
High volume 0.84 0.17 0.65-1.08