Disability among elderly survivors of mechanical ventilation

Abstract

Rationale: Studies of long-term functional outcomes of elderly survivors of mechanical ventilation (MV) are limited to local samples and biased retrospective, proxy-reported preadmission functional status.

Objectives: To assess the impact on disability of hospitalization with MV, compared with hospitalization without MV, accounting for prospectively assessed prior functional status.

Methods: Retrospective population-based longitudinal cohort study of Medicare beneficiaries age 65 and older enrolled in the Medicare Current Beneficiary Survey, 1996-2003.

Measurements and main results: Premeasures and postmeasures of disability included mobility difficulty and weighted activities of daily living disability scores ranging from 0 (not disabled) to 100 (completely disabled) based on self-reported health and functional status collected 1 year apart. Among 54,771 person-years (PY) of observation over 7 calendar years of data, 42,890 PY involved no hospitalization, 11,347 PY involved a hospitalization without MV, and 534 PY included a hospitalization with MV. Mortality at 1 year was 8.9%, 23.9%, and 72.5%, respectively. The level of disability at the postassessment was substantially higher for a prototypical patient who survived after hospitalization with MV (adjusted activities of daily living disability score [95% confidence interval] 14.9 [12.2-17.7]; adjusted mobility difficulty score [95% confidence interval] 25.4 [22.4-28.4]) compared with an otherwise identical patient who survived hospitalization without MV (11.5 [11.1-11.9] and 22.3 [21.8-22.9]) or who was not hospitalized (8.0 [7.9-8.1] and 13.4 [13.3-13.6]).

Conclusions: The greater marginal increase in disability among survivors of MV compared with survivors of hospitalization without MV is larger than would be predicted from prior functional status.

Figure 1.

Schematic of the Medicare Current Beneficiary Survey (MCBS) study cohort. The rows represent the MCBS cohort (each cohort participates for 4 yrs) and the columns represent the calendar years, broken down by season. The annual “access to care” survey is administered in the fall of each year. The completion date of this survey became the arbitrary start (and, 1 year later, end) of each beneficiary's person-year (PY) of data. Beneficiaries could contribute up to 3 “pre-post” PY of comparison data over their 4 years of participation in the MCBS. We categorized each PY of data according to the patient's Medicare claims for the year. If the person was hospitalized with mechanical ventilation (MV) one or more times in the year, we categorized them as “hospitalized with MV.” If they were hospitalized one or more times in the year without MV (and never had a hospitalization with MV) we categorized them as “hospitalized without MV.” If they were never hospitalized, we categorized them as “not hospitalized.” If they died during the hospitalization, they were not eligible for this study because they were not “survivors” of MV or hospitalization without MV. If they died before the next autumn, they were censored (missing because of death). If they were alive the next autumn, but did not respond to the survey, they were censored (missing because of nonresponse). As expected, this survivor and nonresponse and survivor bias were greater for the MV group. Assuming these decedents and nonresponders were systematically more disabled, our results underestimate the degree of disability among survivors of MV.

Figure 2.

Person-years of observation. We used 8 years of Medicare Current Beneficiary Survey data, with each participating beneficiary contributing to up to four annual measures of health and physical functioning and inpatient claims before rotating off the panel.

Figure 3.

Unadjusted 1-year change in activities of daily living (ADL) disability (top panel) and mobility difficulty (bottom panel) scores. Nonhospitalized beneficiaries show small increases in disability over the year. Among those who are hospitalized, survivors of mechanical ventilation (MV) experience steeper increases in disability than those who did not receive MV (differences in the unadjusted “post” scores between hospital survivors without MV and with MV for ADL disability [P = 0.0008] and mobility [P = 0.0002]).