Obesity and Outcomes in Older Americans With Severe Sepsis
Obesity and Outcomes in Older Americans With Severe Sepsis
Objectives. Although critical care physicians view obesity as an independent poor prognostic marker, growing evidence suggests that obesity is, instead, associated with improved mortality following ICU admission. However, this prior empirical work may be biased by preferential admission of obese patients to ICUs, and little is known about other patient-centered outcomes following critical illness. We sought to determine whether 1-year mortality, healthcare utilization, and functional outcomes following a severe sepsis hospitalization differ by body mass index.
Design. Observational cohort study.
Setting. U.S. hospitals.
Patients: We analyzed 1,404 severe sepsis hospitalizations (1999–2005) among Medicare beneficiaries enrolled in the nationally representative Health and Retirement Study, of which 597 (42.5%) were normal weight, 473 (33.7%) were overweight, and 334 (23.8%) were obese or severely obese, as assessed at their survey prior to acute illness. Underweight patients were excluded a priori.
Interventions. None.
Measurements and Main Results. Using Medicare claims, we identified severe sepsis hospitalizations and measured inpatient healthcare facility use and calculated total and itemized Medicare spending in the year following hospital discharge. Using the National Death Index, we determined mortality. We ascertained pre- and postmorbid functional status from survey data. Patients with greater body mass indexes experienced lower 1-year mortality compared with nonobese patients, and there was a dose-response relationship such that obese (odds ratio = 0.59; 95% CI, 0.39–0.88) and severely obese patients (odds ratio = 0.46; 95% CI, 0.26–0.80) had the lowest mortality. Total days in a healthcare facility and Medicare expenditures were greater for obese patients (p < 0.01 for both comparisons), but average daily utilization (p = 0.44) and Medicare spending were similar (p = 0.65) among normal, overweight, and obese survivors. Total function limitations following severe sepsis did not differ by body mass index category (p = 0.64).
Conclusions. Obesity is associated with improved mortality among severe sepsis patients. Due to longer survival, obese sepsis survivors use more healthcare and result in higher Medicare spending in the year following hospitalization. Median daily healthcare utilization was similar across body mass index categories.
Given the high prevalence of obesity in the United States and growing costs of hospitalization for critical illness, it is important to understand the effects of obesity on critical illness. Despite population-based studies demonstrating higher general mortality and pathophysiologic variations that would predict worse outcomes, studies examining the impact of obesity on critical illness have yielded mixed results—that is, some studies suggest a possible "obesity paradox" wherein obesity is not harmful and may even be protective once one is ill.
Prior work has been criticized, however, for small sample sizes and use of underweight patients as nonobese comparisons. Furthermore, studies often use weight ascertained at ICU admission—potentially after fluid resuscitation or prior to diuresis for decompensated edema—rather than the patient's true outpatient weight. This practice may misclassify the body mass index (BMI) category in as many as 20% of patients.
Beyond these problems of nonrepresentative samples and misclassification of the key exposure variable, much of the existing research has assessed in-hospital mortality following ICU admission. This study design is susceptible to bias for two reasons. First, discharge practices vary across hospitals and have been shown to alter in-hospital mortality. Second, ICU admission thresholds vary markedly across institutions and may be systematically different in obese patients due to their greater nursing needs.
Because of the limitations of the existing literature on mortality and lack of information on other patient-centered outcomes, we sought to investigate the association of obesity with 1-year mortality, healthcare utilization, and functional limitations in Medicare beneficiaries following a hospitalization for severe sepsis. We selected these additional outcome measures because of the high value patients place on living and functioning independently. We focused on severe sepsis because it is a very common diagnosis that can be treated both within and outside the ICU.
Abstract and Introduction
Abstract
Objectives. Although critical care physicians view obesity as an independent poor prognostic marker, growing evidence suggests that obesity is, instead, associated with improved mortality following ICU admission. However, this prior empirical work may be biased by preferential admission of obese patients to ICUs, and little is known about other patient-centered outcomes following critical illness. We sought to determine whether 1-year mortality, healthcare utilization, and functional outcomes following a severe sepsis hospitalization differ by body mass index.
Design. Observational cohort study.
Setting. U.S. hospitals.
Patients: We analyzed 1,404 severe sepsis hospitalizations (1999–2005) among Medicare beneficiaries enrolled in the nationally representative Health and Retirement Study, of which 597 (42.5%) were normal weight, 473 (33.7%) were overweight, and 334 (23.8%) were obese or severely obese, as assessed at their survey prior to acute illness. Underweight patients were excluded a priori.
Interventions. None.
Measurements and Main Results. Using Medicare claims, we identified severe sepsis hospitalizations and measured inpatient healthcare facility use and calculated total and itemized Medicare spending in the year following hospital discharge. Using the National Death Index, we determined mortality. We ascertained pre- and postmorbid functional status from survey data. Patients with greater body mass indexes experienced lower 1-year mortality compared with nonobese patients, and there was a dose-response relationship such that obese (odds ratio = 0.59; 95% CI, 0.39–0.88) and severely obese patients (odds ratio = 0.46; 95% CI, 0.26–0.80) had the lowest mortality. Total days in a healthcare facility and Medicare expenditures were greater for obese patients (p < 0.01 for both comparisons), but average daily utilization (p = 0.44) and Medicare spending were similar (p = 0.65) among normal, overweight, and obese survivors. Total function limitations following severe sepsis did not differ by body mass index category (p = 0.64).
Conclusions. Obesity is associated with improved mortality among severe sepsis patients. Due to longer survival, obese sepsis survivors use more healthcare and result in higher Medicare spending in the year following hospitalization. Median daily healthcare utilization was similar across body mass index categories.
Introduction
Given the high prevalence of obesity in the United States and growing costs of hospitalization for critical illness, it is important to understand the effects of obesity on critical illness. Despite population-based studies demonstrating higher general mortality and pathophysiologic variations that would predict worse outcomes, studies examining the impact of obesity on critical illness have yielded mixed results—that is, some studies suggest a possible "obesity paradox" wherein obesity is not harmful and may even be protective once one is ill.
Prior work has been criticized, however, for small sample sizes and use of underweight patients as nonobese comparisons. Furthermore, studies often use weight ascertained at ICU admission—potentially after fluid resuscitation or prior to diuresis for decompensated edema—rather than the patient's true outpatient weight. This practice may misclassify the body mass index (BMI) category in as many as 20% of patients.
Beyond these problems of nonrepresentative samples and misclassification of the key exposure variable, much of the existing research has assessed in-hospital mortality following ICU admission. This study design is susceptible to bias for two reasons. First, discharge practices vary across hospitals and have been shown to alter in-hospital mortality. Second, ICU admission thresholds vary markedly across institutions and may be systematically different in obese patients due to their greater nursing needs.
Because of the limitations of the existing literature on mortality and lack of information on other patient-centered outcomes, we sought to investigate the association of obesity with 1-year mortality, healthcare utilization, and functional limitations in Medicare beneficiaries following a hospitalization for severe sepsis. We selected these additional outcome measures because of the high value patients place on living and functioning independently. We focused on severe sepsis because it is a very common diagnosis that can be treated both within and outside the ICU.
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