Three-Year Outcomes for Medicare Beneficiaries Who Survive Intensive Care FREE

The success of intensive care, which is designed to mitigate life-threatening critical illness, traditionally has been gauged by the proportion of patients alive at hospital discharge or at day 28.^1- 4 With technological advances, many patients now survive what were previously fatal critical illnesses, in turn generating an enlarging population of intensive care unit (ICU) survivors. There are increasing concerns that these ICU survivors may have ongoing risk for increased mortality and morbidity,^5- 6 raising the question of whether the need for intensive care tends to constitute an acute event, with minimal sequelae, or has the hallmarks of a chronic illness, with increased risk of long-term morbidity and mortality.

Many studies have demonstrated that short-term survivors of conditions classically requiring intensive care, such as acute lung injury or sepsis, often have significant health problems in subsequent months.^6- 7 But studies from Finland and the United Kingdom reported that mortality for ICU survivors was similar to that of the general population after 2 to 4 years,^8- 9 while data from Canada showed that long-term survival was similar to that of patients hospitalized who did not require intensive care.¹⁰ Differences in the provision of intensive care services and patient selection confound international comparisons,¹¹ and there are no nationally representative follow-up studies from the United States.

Intensive care unit services have grown significantly in the United States and are now routinely provided to a broad population.¹² Patients older than 65 years now make up more than half of all ICU admissions.¹³ Information is needed to understand the patterns of mortality, morbidity, and health care resource use in the months and years that follow critical illness to allow for better targeting of follow-up care. This study examines the 3-year outcomes and health care resource use of ICU survivors older than 65 years, and identifies the subgroups and periods in which patients are at highest risk of death.

A matched, retrospective cohort study was conducted using a 5% sample of Medicare beneficiaries older than 65 years. The 2002-2006 data were retrieved from the Centers for Medicare & Medicaid Services Standard Analytic Files. The data set contains all fee-for-service claims, including hospital inpatient, hospital outpatient, skilled nursing facility, and carrier claims, which included all office visits for a random, longitudinal 5% sample of Medicare beneficiaries.

To generate the cohort for this study, the total 5% Medicare cohort (composed of anyone with ≥1 claim from 2003) was randomly split into 2 equal parts. The randomly chosen exposed group was selected from half of the group. The exposed sample for this analysis included all Medicare beneficiaries aged 66 years or older who were discharged alive from their first hospitalization in 2003 in which they received intensive care, and who were not discharged to hospice care. Any person with either intensive care or intermediate intensive care unit charges was categorized as having received intensive care. Anyone who received only coronary care or intermediate coronary care charges was excluded because these patients tend to have lower hospital mortality and constitute a distinct group of patients with cardiac disease.

The control groups were generated from the other half of the cohort. Hospital controls were Medicare beneficiaries who were hospitalized and survived to hospital discharge, but did not receive intensive care during a quarter of 2003 (anyone who received coronary care or intermediate coronary care also were not eligible for inclusion in this group). General population controls were Medicare beneficiaries who had at least 1 claim during the year, did not receive intensive care, but may or may not have been hospitalized. Intensive care unit survivors were individually matched with all controls (hospital and general) based on age (≤5 years), sex, and race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other).

Race and ethnicity are recorded in Medicare's administrative files primarily using data provided to the Social Security Administration by self-report during an application for a Social Security number or for benefits.¹⁴ Sensitivity and specificity for white and black persons is 95% or higher but they are substantially lower for other groups (<60%). Hence, the majority of nonwhite, nonblack categories were collapsed into Hispanic and other.¹⁵ Race was included as a matching factor because it is a strong, independent predictor of mortality for hospitalized patients.^16- 17

Hospital controls also were matched to ICU survivors based on whether they were primarily a medical or surgical patient using diagnosis-related groups. All matches for the intensive care cohort were generated without replacement so that every ICU survivor had a separate hospital match and general match. Patients who were discharged to out-of hospital hospice care (along with their matches) were excluded.

Data from years 2002 through 2006 were linked to allow for use of data from 2003 to generate the inception cohort. Data from all health care encounters from the 4 quarters prior to the index hospitalization were used to provide information on previously existing conditions, which were defined by the Elixhauser comorbidities that were generated from the International Classification of Diseases, Ninth Revision, Clinical Modification codes.¹⁸ All secondary diagnoses from hospital and skilled nursing facility admissions and all diagnoses from outpatient visits were used. Those diagnoses associated with the diagnosis-related group for patients during the index hospitalization were excluded. Use of health care resources in the 4 quarters prior to the index hospitalization were examined, including the number of hospital admissions and skilled nursing facility admissions.

Patient data were then analyzed for the following 12 quarters (3 years) through 2006 or until death. To comply with privacy requirements, the exact dates of hospital discharge were not available in the Standard Analytic Files. The dates for the quarter of the year in which the discharge occurred were used. Therefore, time to death was calculated as the number of quarters (3-month intervals) after the discharge quarter. The discharge destination codes were reduced to home, home with health services, skilled care facility, and other (against medical advice or were discharged to another or the same institution for outpatient services).

Summary statistics were calculated for demographic and clinical characteristics of patients who survived to hospital discharge, using percentages, means (standard deviations), and medians (interquartile ranges [IQRs]). Lengths of stay for the ICU were calculated based on the number of days billed at each level of care. The distributions of Elixhauser comorbidities for each cohort are presented in the eTable). Mortality rates were calculated for those beneficiaries who received intensive care and their respective controls. Three-year mortality was assessed using Kaplan-Meier curves for the whole cohort, and then by whether individuals received mechanical ventilation (International Classification of Diseases, Ninth Revision, codes 96.7x), a common marker of severity of illness in the ICU.

Subsets of the ICU cohort were compared with their own respective subset of matched controls. The log-rank test was used to assess for statistical differences in survival curves. The number of hospitalizations and whether patients were ever admitted to a skilled nursing facility in the 4 quarters prior to their hospital discharge quarter and in the 3 years after discharge were quantified. Risk ratios were calculated using Cox proportional hazards models after demonstrating the proportionality assumption was not violated.

Multivariable models for the entire cohort were generated and then stratified by mechanical ventilation, using the intensive care cohort and hospital controls to assess whether ICU survivors had an increased risk of death after adjustment for other variables (age, source of admission to the hospital, Elixhauser comorbidities, discharge destination after hospitalization, hospitalization in the previous year, and admission to a skilled care facility in the previous year). Also tested was whether the relative risk of mortality changed over time by examining the long-term mortality for only those individuals who survived either 1 or 2 years after discharge from the hospital. Database management and statistical analyses were performed using Excel (Microsoft, Redmond, Washington), and SAS version 9.2 (SAS Institute Inc, Cary, North Carolina).

With an ICU cohort of 35 308 survivors, this study was powered to detect a difference in the hazard ratio (HR) for 3-year mortality of 0.035, assuming an α level of .05 and a power level of 90%. However, due to the large size of the data set, differences for clinical significance also were assessed. There are no data regarding what is considered an appropriate cut-off for clinical significance; therefore, an absolute difference in mortality of 2% or a change in HR of 0.05 was arbitrarily set to be of clinical significance. This research involved secondary analyses of deidentified data and thus was exempt from human subjects review.

There were 35 308 ICU patients who survived to hospital discharge during their index hospitalization in 2003 and were matched with hospital and general population controls, representing 4.6% of the 2.5% random sample of all Medicare beneficiaries, and extrapolating to 1.4 million patients per year in the United States. Of the sample, 45.8% were male and 86.8% were non-Hispanic white (Table 1). Most ICU survivors (84.3%) had at least 1 comorbidity associated with mortality, which was only slightly higher than the matched hospital controls (77.9%; P < .001), but more than the general controls (41.0%; P < .001). (See the eTable for a full data list of comorbidities). A slightly higher proportion of ICU survivors and hospital controls were hospitalized at least once in the year prior to the index hospitalization (36.3% of ICU survivors vs 32.5% of hospital controls; P < .001), while only 16.0% of general controls were hospitalized in the year prior (P < .001). Less than 1% of either ICU survivors or hospital controls were admitted directly from a skilled nursing facility, but 8.8% and 7.9%, respectively, had been in a skilled nursing facility in the year prior to the hospitalization quarter (P < .001). Median hospital length of stay was 5 days (IQR, 3-9 days) for ICU survivors, with longer stays among surgical ICU survivors (median, 7 days; IQR, 4-12 days) vs medical ICU survivors (median, 4 days [IQR, 2-7 days]; P < .001). The median length of stay for hospital controls was 4 days (IQR, 2-6 days), which was a little shorter than for ICU survivors (P < .001).

The ICU survivors who received mechanical ventilation during their hospitalization were more likely to have greater comorbidity compared with ICU survivors who did not receive mechanical ventilation (proportion with ≥3 comorbidities: 57.2% vs 34.2%, respectively; P < .001), were slightly more likely to have been hospitalized in the year prior to the index admission (41.7% vs 36.0%; P < .001), and were more likely to have been in a skilled nursing facility in the year prior (12.9% vs 8.5%; P < .001).

At time of discharge from the hospital, 53.2% of ICU survivors were discharged home without home health support compared with 60.6% of hospital controls (P < .001). A similar percentage were discharged home with home health services (13.2% of ICU survivors vs 12.1% of hospital controls; P < .001). A third of ICU survivors (33.0%) were discharged to a skilled care facility compared with 26.4% of hospital controls (P < .001). Of note, more than half the ICU survivors who received mechanical ventilation (61.7%) were discharged to a skilled care facility.

In the first 2 quarters (6 months) postdischarge, mortality for ICU survivors was 14.1% compared with 10.9% for hospital controls (unadjusted HR, 1.31; 95% confidence interval [CI], 1.25-1.36) and 2.7% for the general controls (unadjusted HR, 5.60 [95% CI, 5.23-6.00]; Table 2 and Figure 1). By 3 years, the differences in mortality were smaller, but still apparent (39.5% for ICU survivors vs 34.5% for hospital controls [unadjusted HR, 1.19; 95% CI, 1.16-1.22] and 14.9% for general controls [unadjusted HR, 3.27; 95% CI, 3.17-3.38]). After adjustment for comorbidities, source of admission, discharge destination, hospitalization in previous year, and admission to a skilled nursing facility in the previous year, the adjusted HRs (AHRs) were markedly attenuated for ICU survivors compared with hospital controls for 6-month mortality (AHR, 1.14; 95% CI, 1.10-1.19) and 3-year mortality (AHR, 1.07 [95% CI, 1.04-1.10]; Table 2).

Stratifying the ICU cohort by whether they received mechanical ventilation, patients admitted to the ICU without mechanical ventilation had slightly higher 3-year mortality compared with hospital controls (38.3% vs 34.6%, respectively [P < .001]; Table 2 and Figure 2). After multivariable adjustment, there was a statistically but not clinically significant difference in 3-year mortality (AHR, 1.04; 95% CI, 1.02-1.07). However, mortality for those who received mechanical ventilation was substantially higher than for the corresponding hospital controls (3-year mortality: 57.6% vs 32.8%, respectively; AHR, 1.56 [95% CI, 1.40-1.73]; Table 2 and Figure 2). This difference was primarily due to mortality during the first 2 quarters following hospital discharge (6-month mortality: 30.1% for ICU survivors vs 9.6% for hospital controls; AHR, 2.26 [95% CI, 1.90-2.69]). Within the ICU cohort, mortality also was consistently higher for medical compared with surgical ICU survivors at both 6 months (16.0% for medical vs 11.1% for surgical; P < .001) and 3 years (44.5% for medical vs 31.8% for surgical; P < .001).

Patients discharged to skilled care facilities (whether or not they received intensive care) also had high postdischarge mortality (Figure 3). Discharge to a skilled care facility remained a strong independent predictor of both 6-month and 3-year mortality for all ICU survivors and hospital controls (6-month mortality: 24.1% for ICU survivors and hospital controls discharged to skilled care vs 7.5% for ICU survivors and hospital controls discharged to home care [AHR, 2.62; 95% CI, 2.50-2.74]; 3-year mortality: 54.6% vs 29.4%, respectively [AHR, 1.77; 95% CI, 1.72-1.82]; Table 3). Only a diagnosis of metastatic cancer was a larger predictor of mortality (6-month: AHR, 3.31 [95% CI, 3.06-3.58]; 3-year: AHR, 3.02 [95% CI, 2.87-3.18]).

Among ICU survivors, one-third (36.1%) were rehospitalized at least once within the next 6 months following the discharge quarter from the hospital (compared with 28.3% of hospital controls [P < .001] and 10.7% of general controls [P < .001]; Table 4). There was a mean (SD) of 0.64 (1.10) hospitalizations for ICU survivors compared with 0.46 (0.92) for hospital controls (P < .001). In the first year, 43.05% of ICU survivors had been rehospitalized at least once with similar rates regardless of whether the ICU stay had included an episode of mechanical ventilation (45.03% with mechanical ventilation vs 42.92% without mechanical ventilation; P = .06). Among those still alive at 1 year, the frequency of rehospitalization was 43.00% among ICU survivors compared with 39.22% for hospital controls (P < .001). Of all ICU survivors, 18.02% were admitted to a skilled nursing facility in the first year after hospital discharge compared with 14.94% of hospital controls (P < .001) and 4.68% of general controls (P < .001). By 3 years, one-third of all ICU survivors (28.96%) had been admitted to a skilled nursing facility, which remained a little higher than for hospital controls (26.10%; P < .001), and more than double the frequency for general controls (13.72%; P < .001).

Approximately 1.4 million elderly Medicare beneficiaries are discharged alive each year from hospitals in the United States after receiving intensive care. Among this elderly cohort, with an average age of 78 years, the need for intensive care confers an increased risk of mortality after discharge from the hospital, mostly attributable to patients who require mechanical ventilation and concentrated in the early postdischarge period. Hospitalization itself is the bigger marker for increased risk compared with the general population, and in particular the need for skilled care after discharge from the hospital is a large predictor of mortality. The risk of death never returns to that of the baseline population, remaining elevated even 3 years later. Despite this elevated risk, almost two-thirds of both ICU survivors and hospital controls were still alive after 3 years. Compared with hospital controls, ICU survivors (whether or not they required mechanical ventilation) had only a small increased risk of rehospitalization or need for admission to a skilled nursing facility in the months and years postdischarge. Whether these patterns suggest appropriate end-of-life planning (avoiding the need for rehospitalization) or poor use of resources (with unnecessary deaths occurring in this early period) remains to be elucidated.

The locations that we designated as skilled care facilities are a heterogeneous group, encompassing subacute nursing facilities, inpatient rehabilitation facilities, and long-term acute care hospitals, among others. The heavy use of these skilled care facilities and the high associated mortality for all hospitalized patients discharged to these facilities adds to the argument against reporting hospital mortality as an accurate or appropriate marker of successful care for elderly individuals. Our findings also are consistent with observations of shifts in place of death for elderly individuals from hospitals to skilled care facilities.^19- 20 Moreover, these data suggest that follow-up clinics that are solely for survivors of intensive care, rather than for more specific groups of hospitalized patients, may not target the true at-risk groups.²¹

Our findings are similar to the Canadian study¹⁰ that found only a small effect of intensive care admission on 3-year mortality compared with hospital controls, but different from the studies in the United Kingdom and Denmark^8- 9 because risk of death never returned to that of the general population. However, these other studies did not distinguish between ICU survivors with regard to mechanical ventilation status, and were not restricted to elderly individuals. Although mechanical ventilation does not define a disease state, it is a substantial marker not only of elevated risk of hospital mortality, but also of longer-term morbidity (required skilled care) and mortality. In a study of Medicare beneficiaries who had been hospitalized for severe community-acquired pneumonia (who may or may not have received intensive care), these individuals had an almost 3-fold increased risk of death over the general population in the first year postdischarge from the hospital.²²

The use of an administrative data set and the retrospective nature of this study are limitations. The use of Medicare data also means that the analysis only includes those older than 65 years, and it is important to note that patterns of postdischarge ICU survival may be different for younger patients. Another limitation of these data is that there is not sufficient detail collected to allow for full assessment of the severity of illness of the patients while hospitalized.

The magnitude of the postdischarge use of skilled care facilities for both ICU survivors and hospital controls and the high long-term mortality for all of these patients call into question whether discharge to skilled care facilities is merely a marker for higher severity of illness with appropriate delivery of care. These patients could have been discharged prematurely from acute care hospitals, and needed a higher level of care than they received. It also is possible that these patients could have had better outcomes if discharged home, but were not able to be sent there due to lack of sufficient support from family or friends to act as caregivers. These findings highlight the need for a much more detailed understanding of the long-term care needs of these patients.