INTRODUCTION

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Critical care services account for a large and growing proportion of inpatient services in the United States (1, 2). While intensive care units (ICUs) represent 5 to 10% of all hospital beds, they may consume up to 34% of hospital budgets. This figure extrapolates to over 1% of the gross domestic product (GDP), or over $62 billion (3).

In view of the heightened concern regarding the high cost of health care delivery, increasing attention has been devoted to minimizing costs while maintaining quality. Accordingly, efforts have been devoted to the organizational and managerial aspects of care that promote efficient use of scarce resources. Many ICUs in the United States use the "open" model of ICU organization. In this model, patients are admitted, often without triage and are cared for by their primary care physician. In open units, the level of critical care input is variable. Recently, many ICUs have adopted stricter administrative and triage controls, and utilize a "closed" model of organization. In a closed ICU, patients are transferred to the care of an intensivist. Generally, patients are accepted to the unit only after they have been evaluated (6).

Safar and Grenvik first suggested benefits from an intensivist-led intensive care service in 1977 (7). Since then, several retrospective studies have demonstrated an improvement in the outcome of critically ill patients when geographically dedicated intensivists staff, organize, and direct critical care services and the care of all patients (8, 9). In some studies, the availability of qualified intensivists has been linked to lower mortality and costs (10).

In the studies cited above, data and outcomes were assessed retrospectively. Recently, however, Carson and coworkers prospectively analyzed the impact of a change in ICU organization from "open" to "closed" within their institution. They demonstrated decreased mortality without additional resource utilization (17). We wished to determine whether the conclusions of Carson and coworkers could be extended to apply between institutions. All of these previous studies only investigated an organizational change within a single institution. We conducted a prospective trial of two units, one "open" and one "closed" in two large hospitals serving similar populations in the same geographic area. To control for possible bias and differences related to institutional care policies unrelated to ICU organization, a retrospective analysis was also performed in one of the hospitals comparing the period before closure with that after closure. We tested the hypotheses that unit closure is associated with improved outcome as measured by a decreased mortality, and that unit closure is associated with less resource utilization for similar severity of illness.

	METHODS

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Sites

Long Island Jewish Medical Center (LIJ) and Winthrop-University Hospital (WUH) are nonprofit teaching affiliates of their respective medical schools. Both serve demographically similar populations and are located within 5 miles of each other. WUH is a 581-bed acute care institution in Nassau County, New York, affiliated with the State University of New York at Stony Brook. The critical care area consists of twenty beds which are jointly shared between the medical ICU and the coronary care unit (CCU). Approximately 50% of the beds are allotted for medical ICU patients. Coronary care patients were not included in this study. The ICU and the CCU have their own medical housestaff team. For the ICU service, a senior resident and two interns are continuously present to provide 24-h in-house coverage for all patients. An attending intensivist and a critical care fellow perform teaching rounds with the housestaff on a daily basis. The MICU, however, functions as an "open" unit, as critical care consultation on admitted patients is optional. Intensivists perform no preadmission evaluation.

LIJ is an 800-bed acute care hospital located in suburban New York City affiliated with the Albert Einstein College of Medicine. The critical care area consists of 30 beds equally allocated between the medical (MICU) and the surgical (SICU) service. The MICU and SICU each have their own housestaff and attending intensivist. Patients in the SICU were not included in this study. The MICU service consists of two senior residents and three medical interns. Twenty-four-hour housestaff coverage is provided.

Before July 1992, the MICU at LIJ was an open unit organized similarly to WUH. In July of 1992, the MICU was closed; that is, the attending intensivist became the physician of record for all MICU patients and a mandatory critical care consultation was required to screen all prospective admissions. Nursing and housestaff coverage remained the same. Mandatory critical care consultation was required in the open unit at LIJ for anyone receiving mechanical ventilation.

There were two study designs carried out for this analysis. First, we performed a prospective cohort analysis where data was collected on a daily basis of all consecutive MICU admissions from May 1, 1993 through August 15, 1993, comparing patients at LIJ (closed unit) with patients at WUH (open unit). Second, we performed retrospective analysis comparing outcomes before and after unit closure at LIJ. The retrospective data were gathered via chart review. Each consecutive MICU admission was evaluated from February 1, 1992 through April 30, 1992 (open ICU) and February 1, 1993 through April 30, 1993 (closed ICU). During each of the periods of closure for both retrospective and prospective cohorts, four different intensivists constituted the attending staff. Thus, a total of eight intensivists were represented during the closed periods. There are many differences between institutions that could influence outcome besides unit management. Thus, the retrospective component, carried out at the same institution served as a validation check for conclusions arrived at in the prospective component. Additionally, no changes in institutional practice patterns (care maps, weaning protocols, etc.) were introduced with unit closure in either component of the study.

During the trial period, LIJ had a ventilator unit that could admit and care for chronic ventilatory patients. This unit was not part of the study. However, it could serve as a place to discharge patients from the LIJ ICU. WUH did not have such a unit during the study. Ventilator time included the time on the ventilator in this unit for these patients.

Data Collection

Data were obtained to assess both clinical outcome and resource utilization. These included patients demographics (age, gender, race), primary and secondary diagnoses, insurance status, source of admission (general medical or surgical floor, emergency room, transfer from another institution), calculation of the Mortality Probability Model score upon admission to the MICU (MPM₀) (18), and ultimate outcome (discharge or in-hospital death). The MPM₀ is a logistic model that uses 11 readily accessible clinical variables available to the clinician on admission to the ICU. Resource utilization data included ICU length of stay (LOS), total hospital LOS, and number of days of mechanical ventilation. Days of mechanical ventilation in the chronic ventilator unit were included in the data. We also recorded the number of invasive procedures (pulmonary artery catheters, central venous lines, arterial lines, and mechanical ventilation) that were recorded for each patient.

Statistical Analysis

Categorical variables were analyzed using chi-square. Continuous variables were analyzed using one-way analysis of variance (ANOVA). If assumptions of normality and equal variance were not met, then ANOVA on ranks was used. The null hypothesis was rejected at the 5% level.

Multivariate regression analyses were also performed on pooled data to assess the predictors of hospital LOS, ICU LOS, and days on mechanical ventilation. A multivariate logistic regression model was developed to assess the influence of the same independent variables upon survival.

All analysis was performed using Statistica for Windows (version 4.5; Statsoft, Tulsa, OK), and Excel (version 5.0; Microsoft Corporation, Redmond, WA).

	RESULTS

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A total of 280 patients was evaluated in both units in the prospective investigation: 185 were admitted to the closed ICU at LIJ, and 95 were admitted to the open ICU at WUH. A total of 306 patients was evaluated for the retrospective study at LIJ, 152 while the ICU was "open" and 154 while "closed." There were no significant differences in age, mortality, insurance status, and MPM₀ score obtained upon admission between open and closed units in either the retrospective or the prospective analysis (Table 1). A slight male predominance was noted in the retrospective component analysis (p < 0.04). Two significant differences, however, were noted in patient origin in the prospective cohort. More patients were admitted from the emergency room in the "closed" (i.e., at LIJ) than in the "open" (i.e., at WUH) ICU (p < 0.003) and more Caucasians were admitted in the "open" than the "closed" unit (p < 0.02).

There were no significant differences in primary diagnostic categories between open and closed units in either the retrospective or the prospective analysis (Table 2).

For both the prospective and retrospective cohorts, ICU closure was associated with lower hospital and ICU LOS (Figure 1). There was no difference in the percent of the patients receiving mechanical ventilation, or in their mortality, between closed and open units in either component. However, among patients who received mechanical ventilation, the number of days on mechanical ventilation was lower in the "closed" than the "open" ICU in both cohorts (Table 3).

View larger version (27K): [in this window] [in a new window]   Figure 1.   (A) These graphs represent the ICU (6.1 ± 0.6 versus 9.3 ± 0.9), hospital (22.2 ± 2.2 versus 31.2 ± 3.5), and non-ICU (16.1 ± 1.9 versus 21.8 ± 3.3) lengths of stay in the retrospective component at Long Island Jewish Medical Center. (B) These graphs represent the ICU (6.2 ± 0.5 versus 12.6 ± 2.4), hospital (19.2 ± 1.2 versus 33.2 ± 5.4), and non-ICU (12.9 ± 1.1 versus 21.8 ± 4.4) lengths of stay in the prospective component at Long Island Jewish Medical Center and Winthrop-University Hospital. Values are expressed as mean ± standard error.

Table 4 shows the procedure data. In the prospective cohort, the open MICU had a greater number of arterial lines placed (p < 0.002). In the retrospective cohort, the closed MICU had a greater number of central lines placed (p < 0.001). However, no difference existed between the different units with regard to placing pulmonary artery catheters.

The prospective "closed" cohort at LIJ was also compared with the retrospective "closed" cohort at LIJ. No statistically significant differences were noted in any of the aforementioned outcomes.

Because effects of ICU organization on days of mechanical ventilation, ICU LOS, hospital LOS, and mortality appeared similar in both the retrospective and prospective studies, we pooled the data from all the studies and examined predictors of hospital LOS, ICU LOS, and ventilator days, and predictors of mortality. These included MPM₀, age, gender, mechanical ventilation, the number of days of mechanical ventilation, the use of a pulmonary artery (PA) catheter, arterial and central line placement, and ICU organization type.

Table 5 shows that number of days on a ventilator was the major predictor of hospital and ICU LOS. ICU organization (closed) was a weak, but significant predictor of hospital LOS. Significant predictors of days of mechanical ventilation were ICU organization type and MPM₀ score. However, the regression model accounted for only 7% of the observed variability. The strongest association demonstrated was that between ICU LOS and days of mechanical ventilation, the model accounting for 88% of the observed variability. Table 6 demonstrates that the only significant predictors of mortality were MPM₀ score, mechanical ventilation, and ICU organization type. The use of arterial lines, PA catheters, and central lines, as well as age, gender, and the number of days on a ventilator were not significant predictors of mortality. Overall, however, the model accounted for only 8% of the observed mortality.

The pooled data were then used to compare ICU LOS in patients who received mechanical ventilation and those who did not. 127 patients received mechanical ventilation under the "closed" ICU organization with a mean ICU LOS of 10.2 ± 0.9 d. For those patients who received mechanical ventilation under the "open" ICU organization, the mean ICU LOS was 16.8 ± 2.0 d (p < 0.00001). The 212 patients who did not receive mechanical ventilation under the "closed" ICU organization had an ICU LOS of 3.8 ± 0.2 d. 132 patients did not receive mechanical ventilation under the "open" ICU organization and had an ICU LOS of 4.5 ± 0.3 d (p < 0.002).

The ventilator unit at LIJ could have altered the ICU LOS at LIJ. Ventilator unit data are summarized in Table 7. To account for possible bias effects, we reanalyzed ICU LOS data including all days spent in the ventilator unit as ICU days. The mean ICU LOS for open retrospective component was 11.0 d and 7.3 d as closed (p < 0.05). For the closed prospective component, the mean ICU LOS was 6.73 d and the open prospective component was unchanged from 12.6 d (p < 0.003). The same statistical significance was maintained in both components. Further, there was no difference in the utilization of the chronic ventilator unit between closed and open phases of the retrospective analysis. Of the two patients discharged to rehabilitation hospitals, neither was on the ventilator at the time of discharge.

	DISCUSSION

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This study of ICU organization, resource utilization, and outcome had both a prospective and retrospective component. The diagnostic profile and severity of illness of patients admitted to both types of units in both components were similar. Overall, survival to hospital discharge was not significantly different in either component. However, both components demonstrated that a closed ICU organization was more efficient as measured by a decreased ICU LOS, hospital LOS, and shorter courses of mechanical ventilation. Pooled data from the retrospective and prospective phases demonstrated a slight (odds ratio [or] 1.5) improvement in mortality in the closed ICU organization.

Had there been the introduction of new care policies such as care maps or protocols, along with unit closure, the data could have been confounded. During the retrospective study period, aside from unit closure, no changes in care policy of any sort were introduced at LIJ. Differences in care policies between LIJ and WUH could have influenced data in the prospective component, however, neither unit had at the time of the study introduced care maps, weaning protocols, or other new formal policies. The possibility of confounding variables related to institutional practice patterns between institutions could have confounded the results. These include the greater percentage of patients admitted from the emergency room at LIJ, for instance. However, we believe the influence of unit closure to be robust compared with these factors, because the results of the two components were virtually identical. Because we could find no systematic reason not to assess outcomes predictors between institutions or study components, we felt justified in pooling our data for these purposes.

The prospective component utilized two comparable hospitals, serving similar geographic areas and populations. Aside from unit closure, there were no other alterations in resource allocation relevant to ICU care. The presence of a chronic ventilator unit did not alter the findings. This suggests that unit design has a robust effect on efficiency of care which is demonstrable across institutions as well as within them.

The closed ICU in the prospective component admitted a greater percentage of patients from the emergency department. This may reflect a more efficient method of operation with regard to patient screening, differences of "hospital environments," or differences in the socioeconomic status of the patients. There was no demonstrable difference between institutions in LOS or severity of illness. However, Knaus and colleagues demonstrated that patients admitted from the floor to the ICU have a poorer outcome than those admitted from the emergency department, which may have contributed to the differences in ICU and hospital LOS seen in the prospective component despite similar MPM₀ scores (19).

In both components, increased efficiency in closed ICUs was demonstrated by shorter ICU LOS, shorter hospital LOS, and a decreased number of days on mechanical ventilation. In an open ICU system, there may be a delay in both the weaning and extubation process until there has been input from the outside pulmonary or critical care consultant. Recently, Ely and coworkers demonstrated that daily screening of patients receiving mechanical ventilation followed by a trial of spontaneous breathing and subsequent notification of the patient's primary physician resulted in a reduction in the duration of mechanical ventilation and hence a reduction in ICU costs (20). Similarly, in our study the continued presence of an intensivist could have enhanced the likelihood that care decisions were done in a more timely fashion. Table 5 demonstrates that the strongest predictor of hospital and ICU LOS was the number of ventilator days. Therefore, it is likely that the primary effect on LOS of the continuous presence of intensivists is on the duration of mechanical ventilation.

Data regarding procedures showed an inconsistent effect of ICU type on central and arterial lines, and no effect of PA catheters. This differs from other retrospective studies (8, 9), where the presence of intensivists was correlated with an increased use of invasive monitoring. This may reflect changes in the standard of care with time and increased understanding of strengths and limitations of the procedures, especially PA catheters. Further, unlike a recent multicenter study (21), our data failed to demonstrate an association between mortality and PA catheter placement. This probably represents differences in study design and focus.

Patient mortality was not influenced by ICU organization when each cohort was separately examined. However, when all the data were pooled, mortality was most closely correlated with mechanical ventilation, MPM₀ score, and ICU organization. This suggests that a "closed" ICU may be associated with an overall reduction in mortality, although the effect is small. Although these data are similar to those of Carson and coworkers, our observations of a decrease in hospital and ICU LOS differed, as they found no such significance with regard to length of stay in their study (17). A possible explanation for the difference in LOS was the greater severity of illness seen by Carson and coworkers.

In summary, this study demonstrates advantages to a closed ICU organization. Among patients with similar severity of illness, MICU patients may be treated more efficiently in a closed ICU system, with the same or reduced mortality and a lower LOS. Although it may be difficult to accurately estimate true costs when more than one institution is being studied, our results appear to be applicable even when comparing different hospitals.