Intensive Care Unit Outcomes Are Not Adversely Affected by Obesity in Patients with Respiratory Failure
A Joffe, R Mak, K Wood
icu, obesity, outcomes, respiratory failure
A Joffe, R Mak, K Wood. Intensive Care Unit Outcomes Are Not Adversely Affected by Obesity in Patients with Respiratory Failure. The Internet Journal of Anesthesiology. 2009 Volume 24 Number 2.
Introduction and objective
Obesity is a health epidemic of industrialized countries including the United States, United Kingdom, and Eastern Europe and has been associated with substantial morbidity and mortality in the general population. This is not, however, a universal finding among patients within the intensive care unit (ICU). While some investigators have reported increased mortality and resource consumption in the obese compared to the non-obese [1-4], others have not [5-9]. In fact, it has been reported that obese patients who survive of their hospitalization have improved functional status at hospital discharge  and lower odds of death compared with their non-obese counterparts . Furthermore, two non-population based studies of mechanically ventilated obese patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) failed to show worse outcomes [8,10]. A more recent population based study of ALI/ARDS also failed to show an association between body mass index (BMI) and mortality, but did demonstrate the most severely obese patients utilized greater health care resources . In contrast to prior reports, the most obese survivors were more often discharged to a rehabilitation or skilled nursing facility, suggesting impaired functional status at discharge. Actual cost data to support other metrics of health care utilization has rarely been reported.
The objective of the current study was to examine the effect of obesity on mortality and healthcare resource utilization, including cost, in a heterogeneous group of patients with respiratory failure requiring mechanical ventilatory support in the ICU.
The Trauma and Life Support Center (TLC) at the University of Wisconsin Hospital and Clinics (UWHC) is a 24-bed adult ICU, admitting non-cardiac medical and surgical patients. It is a Level 1-Trauma Center and supports one of the largest organ transplant programs in the United States. Admission sources include the emergency department, hospital wards and clinics, and transfers from surrounding community and rural health centers.
During a 12-month period from January 2, 1999 to January 1, 2000, patient weight and height were directly measured by members of the nutrition support service on all patients greater than 16 years-of-age admitted to the TLC Monday through Friday, and BMI was subsequently calculated. Data were collected prospectively in 764 patients using the hospital’s electronic medical records and the patient’s paper charts. Actual cost data was obtained using the UWHC cost-accounting system. Basic demographic information, including age, gender, and chronic health conditions, were recorded at admission. Admission source and other data required to calculate the APACHE III severity of illness scores were gathered within 24 hours of admission to the TLC using APACHE III software (Cerner, McLean, VA.) by an outcomes coordinator trained in data collection. All patients were followed to death or discharge. The protocol was approved by the University of Wisconsin institutional review board. The requirement for informed consent was waived.
From this original prospective cohort, patients with respiratory failure requiring mechanical ventilation were retrospectively identified and stratified into one of 3 groups; underweight (BMI
Measured dependent variables included ICU and hospital length of stay (LOS), ICU and hospital mortality, costs per admission, and discharge disposition. For survivors, discharge locations were as follows: home, home with home health or skilled nursing facility (SNF)[equivalent to nursing home for our analyses], long-term acute care facility (LTACH) [facilities designed for long-term patients who require prolonged ventilator weaning or other high-level care], or hospice. APACHE III scores were used to calculate predicted ICU and hospital mortality, and ICU and hospital LOS. The total cost for each patient was the sum of all direct and indirect costs excluding physician professional fees.
Group comparisons were made by Wilcoxon rank sum test and chi-squares for continuous and categorical variables, respectively. Statistical significance was defined as a two-sided p value
The study population consisted of 201 patients, 150 normal and 51 obese. Comparisons of baseline characteristics are shown in table 1.
Groups were evenly matched for severity of illness, chronic health, and case mix. Commensurate with the severity of illness, both groups had high predicted mortality. Lung injury was significantly worse among obese patients within the first 24 hours of admission as reflected by a lower PaO2:FiO2 ratio (173
Outcomes were similar across study groups as shown in table 2.
Compared to APACHE III predicted outcomes, observed ICU and hospital mortality where lower in both groups while ICU and hospital LOS were longer than predicted.
Multivariate analysis identified several significant associations, but none between obesity and our predefined outcomes of mortality, LOS, cost, or disability. Significant positive relationships were found between total cost and hospital LOS, a respiratory diagnosis, and the PaO2:FiO2 ratio. Every additional hospital day was associated with a 2.6% increase in total cost. Admission for a primary respiratory diagnosis was associated with a 17.5% decrease in total cost compared to other body system related diagnoses, and total cost increased 5.7% for each decrease in PaO2:FiO2 ratio of 100 from 500. The logistic regression analysis added little to the overall results other than confirming the utility of the APACHE III system by showing significant associations between predicted mortality and death.
The main findings of our study are that obese patients (defined as a BMI
Consistent with a several other studies [6-8], no differences in resource consumption between normal weight and obese individuals were found in our study population. This may reflect small numbers of the most severely obese (BMI
Our findings relating to total cost, a measure not previously reported in this population, extends prior observations from general ICU patients . In a single center, prospective study of 2,148 patients admitted to the 9-bed medical ICU of a 650-bed tertiary care hospital, Ray et al. found no differences in total or variable cost among five BMI categories, including obese and severely obese compared with others.
Only one other study has reported the effect of obesity on discharge disposition in a population of ICU patients with respiratory failure . Morris et al. reported the adjusted odds of ALI/ARDS patients being discharged to be a skilled nursing or rehabilitation facility to be 4.3-6 times that of normal controls.
We acknowledge our study has several limitations. First, it is retrospective in nature and includes patients whose data was extracted from a previously prospectively collected data set. As with any study of similar methodology, lack of control over treatments rendered may have influenced the results. This effect is minimized by inclusion of a specific subset of patients who typically receive similar interventions. In addition, our data was collected prior to the widespread use of lower tidal volumes and particular attention to limiting airway pressures in patients suffering ALI/ARDS. An
In sum, we have demonstrated that obese patients are no more likely to die or consume resources during their hospital stay. Additionally, they have similar discharge disposition to normal weight controls indicating similar levels of disability among survivors. Lastly, the total cost is the same among normal and obese patients. Thus, when objectively scrutinized, obese patients with respiratory failure have similar outcomes to their non-obese counterparts. The observations from this study and several others suggest that predicting ICU outcomes in the obese population should be similar to that for the non-obese.