Differences in one-year health outcomes and resource utilization by definition of prolonged mechanical ventilation: a prospective cohort study

Abstract

Introduction: The outcomes of patients ventilated for longer than average are unclear, in part because of the lack of an accepted definition of prolonged mechanical ventilation (PMV). To better understand the implications of PMV provision, we compared one-year health outcomes between two common definitions of PMV as well as between PMV patients and those ventilated for shorter periods of time.

Methods: We conducted a secondary analysis of prospectively collected data from medical and surgical intensive care units at an academic tertiary care medical center. The study included 817 critically ill patients ventilated for > or = 48 hours, 267 (33%) of whom received PMV based on receipt of a tracheostomy and ventilation for > or = 96 hours. A total of 114 (14%) patients met the alternate definition of PMV by being ventilated for > or = 21 days. Survival, functional status, and costs were measured at baseline and at 2, 6, and 12 months after discharge. Of one-year survivors, 71 (17%) were lost to follow up.

Results: PMV patients ventilated for > or = 21 days had greater costs ($140,409 versus $143,389) and higher one-year mortality (58% versus 48%) than did PMV patients with tracheostomies who were ventilated for > or = 96 hours. The majority of PMV deaths (58%) occurred after hospital discharge whereas 67% of PMV patients aged 65 years or older had died by one year. At one year PMV patients on average had limitations in two basic and five instrumental elements of functional status that exceeded both their pre-admission status and the one-year disability of those ventilated for < 96 hours. Costs per one-year survivor were $423,596, $266,105, and $165,075 for patients ventilated > or = 21 days, > or = 96 hours with a tracheostomy, and < 96 hours, respectively.

Conclusion: Contrasting definitions of PMV capture significantly different patient populations, with > or = 21 days of ventilation specifying the most resource-intensive recipients of critical care. PMV patients, particularly the elderly, suffer from a significant burden of costly, chronic critical illness and are at high risk for death throughout the first year after intensive care.

Figure 1

Flowchart of participants in the study by DRG 541/542 status. Diagram demonstrates enrollment of 817 patients into this prospective study. DRG, diagnosis related group.

Figure 2

Survival by age group among DRG 541/542 patients. Kaplan-Meier plot demonstrating one-year survival stratified by age group among DRG 541/542 patients. Patients aged < 55 years have noticeably better overall survival than do older patients. Those < 55 years old also experience very low mortality rates after two months, whereas other age groups continue to die at relatively constant rates. P < 0.01 for comparisons between 65–74, 75–84, and ≥ 85 year age groups by logistic regression and adjusted for day one APS, preadmission IADLs, admission source, admitting diagnostic group, and preadmission Charlson score; P > 0.05 for comparisons between other age groups. APS, Acute Physiology Score; DRG, diagnosis related group; IADL, instrumental activity of daily living.

Figure 3

Survival among all patients by duration of ventilation and tracheostomy status. Kaplan-Meier plot demonstrating one-year survival by PMV status. The group with the best survival is those who were ventilated for < 21 days and who received a tracheostomy. Persons ventilated for at least 21 days but who did not receive a tracheostomy experienced the worst survival. Other groups had intermediate one-year survival. MV, mechanical ventilation; PMV, prolonged mechanical ventilation.

Figure 4

Hazard ratios for prolonged mechanical ventilation status over one year of follow up. Plot of hazard ratios (solid line) and 95% confidence intervals (dashed lines) for DRG 541/542 patients versus short-term mechanical ventilation patients, determined using a time-varying piecewise-constant nonproportional survival model. The shaded areas represent time periods with statistically significant hazard ratios. The hazard ratios vary over time, predicting an early (< 30 days after intubation) lower risk for death for DRG 541/542 relative to short-term ventilation patients, but a higher risk for mortality between days 60 and 100 as the slope of short-term ventilation mortality levels off (also see Figure 2). Hazard ratios are adjusted by day one APS, pre-admission Charlson score, age, and pre-admission ADLs. APS, Acute Physiology Score; ADL, activity of daily living; DRG, diagnosis related group.

Figure 5

Quality of life and functional status over time for PMV patients. The gray bars represent PMV patients ventilated for ≥ 96 hours with a tracheostomy (DRG 541/542), and the black bars represent PMV patients ventilated for ≥ 21 days. Mean values are shown above the bars corresponding to scores on the SF-36 physical function and physical role scores as well as for limitations in both instrumental (IADLs) and basic (ADLs) activities of daily living. Because of the overlap of 88 persons in these two PMV groups, group-based statistical tests were not performed. ADL, activity of daily living; DRG, diagnosis related group; IADL, instrumental activity of daily living; PMV, prolonged mechanical ventilation; SF-36, Short Form 36-item questionnaire.